Article

Dynamics of 30 large channel bars in the Lower Mississippi River in response to river engineering from 1985 to 2015

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Channel bars are a major depositional feature in alluvial rivers and their morphodynamics has been investigated intensively in the past several decades. However, relatively less is known about how channel bars in alluvial rivers respond to river engineering and regulations. In this study, we assessed 30-yr morphologic changes of 30 large emerged bars located in a 223 km reach of the highly regulated Lower Mississippi River from Vicksburg, Mississippi, to the Mississippi-Atchafalaya River diversion. Landsat imagery and river stage data between 1985 and 2015 were utilized to characterize bar morphologic features and quantify decadal changes. Based on bar surface areas estimated with the satellite images at different river stages, a rating curve was developed for each of the 30 bars to determine their volumes. Results from this study show that the highly regulated river reach favored the growth of mid-channel and attached bars, while more than half of the point bars showed degradation. Currently, the mid-channel and attached bars accounted for 38% and 34% of the total volume of the 30 bars. The average volume of a single mid-channel bar is over two times that of an attached bar and over four times that of a point bar. Overall, in the past three decades, the total volume of the studied 30 bars increased by 110,118,000 m3 (41%). Total dike length in a dike field was found mostly contributing to the bar volume increase. Currently, the emerged volume of the 30 bars was estimated approximately 378,183,000 m3. The total bar volume is equivalent to ~ 530 million metric tons of coarse sand, based on an average measured bulk density of 1.4 t/m3 for the bar sediment. The findings show that these bars are large sediment reservoirs. [See full text at http://www.sciencedirect.com/science/article/pii/S0169555X17304142]
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... In their work, bar volume changes were estimated through the integral of a surface area-river stage rating curve. With this method, the total volume of 30 bars in the Lowermost Mississippi River was found to increase by 110,118,000 m 3 in the past three decades [15]. Unlike direct measurements, a remote sensing approach offers an alternative, cost-efficient way to monitor bar features over broader spatial extents and in quick succession, and hence, can be used to investigate the geomorphic processes that shape channel bars. ...
... The method assumes that the bar is of uniform geometry, which means the sediment is evenly distributed, such that it can be integrated. This approach has been successfully applied to estimate the volume changes of bars in response to either a flood event or long-term river engineering in the Lowermost Mississippi River [14,15], and hence, is employed in this study. According to this method, the volume of each bar between the lowest stage and the highest stage was calculated by integrating the surface area-river stage rating curves, which is given as follows [14]: ...
... In general, the four bars lost a total volume of 5.89 × 10 6 m 3 in the river stages between 20.81 m and 25.75 m, accounting for 6.10% of the total volume. This value was equivalent to 8.25 million metric tons (Mt), assuming a bulk density of sediment of 1.4 metric tons per cubic meter [15]. The estimated amount of sediment loss from these four bars made up 3.65% of the total suspended sediment load in 2002 recorded by the Luoshan gauging station, which is quite significant. ...
Article
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Channel bars are a major depositional feature in channels, and are considered as an important part of the morphodynamics of an alluvial river. The long-term morphodynamics of bars have been intensively investigated. However, relatively little is known about the response of channel bars to a major river flood, which is considered to be the predominant force in shaping bar morphology. This is especially the case for the monsoon-affected Yangtze River, where fluvial geomorphic work is largely carried out during monsoon floods. In this study, multi-temporal satellite images and river stage data were used to examine the morphodynamics of four large channel bars in the middle Yangtze River in response to a major monsoon flood in 2002. Based on bar surface areas estimated with Landsat images at different river stages, a rating curve was developed for each of the four bars, which was used to estimate bar volume through an integral process. Our study shows that two of the bars tended to be stable, while the other two experienced severe erosion during the flood. The results reveal that the flood caused a total bar surface area decrease of 1,655,100 m2 (or 8.30%), and a total bar volume decline of 5.89 × 106 m3 (or 6.10%) between the river stages of 20.81 m and 25.75 m. The volume decrease is equivalent to a sediment loss of approximately 8.25 × 106 metric tons, based on an average bulk density of 1.4 metric tons per cubic meter. The results imply that channel bars in the middle Yangtze River can also be large sediment sources rather than depositional areas during the flood. The decrease of sediment load in the middle of Yangtze River was found to be responsible for the dramatic morphodynamics of channel bars, which could last for a long period of time, depending on the operation of the Three Gorges Dam, which opened in 2003. Hence, we suggest making management efforts to protect the bars from further erosion.
... There has been little research concerning the dynamics of island formation and adjustment in the lower Mississippi River (Moore et al., 2011; Wang and Xu, 2018). Along the lower Mississippi River, the presence and growth of channel bars and islands has been linked to engineering works, such as meander bend cutoffs and the construction of dikes (Smith and Winkley, 1996;Wang and Xu, 2018). ...
... There has been little research concerning the dynamics of island formation and adjustment in the lower Mississippi River (Moore et al., 2011; Wang and Xu, 2018). Along the lower Mississippi River, the presence and growth of channel bars and islands has been linked to engineering works, such as meander bend cutoffs and the construction of dikes (Smith and Winkley, 1996;Wang and Xu, 2018). Dike fields result in lower flow velocity levels, which causes deposition of coarse bed material during larger discharge events, resulting in the formation of channel bars. ...
... The development of modern islands along the lower Mississippi can be viewed as unintentionally enhancing a degraded riparian habitat. While other scholars have examined the development and sedimentary processes associated with channel bars (e.g., Wang and Xu, 2018), no prior research has systematically inventoried the development of channel islands over time or considered their formation from the perspective of the evolution of the overall riparian corridor. In view of discussion concerning restoration of the great alluvial valley (LMRCC, 2015), as well as the identification of sources of coarse sediment to restore coastal environments (e.g., Nittouer and Viparelli, 2014a;, mapping islands over different time periods provides insights into human interactions important to understanding both fluvial geomorphology and riparian ecology. ...
Article
The development and evolution of islands along the lower Mississippi River were examined over a 50 year period, between 1965 and 2015. Fluvial islands were historically a fundamental component of the riparian corridor, serving as important ecological habitat for aquatic and terrestrial species. Their degradation was associated with channel engineering, leading to a pronounced single thread channel. Continued channel engineering in the latter twentieth century, however, is associated with a rapid increase in channel islands along the lower Mississippi River. The study utilizes a GIS framework to examine and analyze a range of geospatial data sets, including (i) lidar DEMs, (ii) historic aerial photos, (iii) historic and recent satellite imagery, (iv) historic topographic maps, and (vi) hydrologic data from gauging stations along the lower Mississippi River. Islands were digitized in Google Earth Pro and ArcGIS by identification of vegetation lines. Spatial data (polygons) were used to extract (clip) the LiDAR DEM data for subsequent analysis. The island data was statistically analyzed using a MANOVA and two-way t-test to examine the association of dikes with the morphologic characteristics of islands. The number of islands (>1 ha) significantly increased over the five decade study period, from 105 in 1965, 206 in 1995, to 295 in 2015. The average size of islands decreased from 101 ha (hectare) to 63 ha, because so many new (small) islands formed within the dike fields. The total area of islands (within the river channel) increased from 103 km² in 1965, 169 km² in 1995, to 206 km² in 2015. The total sediment storage within fluvial islands above the average low water surface is 1.81 billion m³. The lower Mississippi has sufficient coarse sediment to construct new riparian lands, despite the large historic decline in sediment load and overall channel bed degradation that occurred in response to large-scale engineering projects over much of the twentieth century. The new rapid growth and development of fluvial lands within the riparian corridor of the lower Mississippi is a positive outcome of an unintended geomorphic consequence, but one that requires additional management considerations.
... Dikes were built in many reaches along the river to constrain flow to the river's navigation channel. These engineering projects have influenced riverine sediment transport and distribution, resulting in load reduction (Meade & Moody, 2010) and channel sedimentation (Munoz et al., 2018;Wang & Xu, 2018a With the hydrological alterations, we found considerable sediment trapping on channel bars in the middle reach of the Lower Mississippi River from river kilometer (RK) 515 to RK 737 (Wang and Xu, 2018a). There were 30 large emerged channel bars in the 223-km river reach with a total emerged bar volume of 268,065 x 10 3 m 3 in the year of 1985. ...
... Dikes were built in many reaches along the river to constrain flow to the river's navigation channel. These engineering projects have influenced riverine sediment transport and distribution, resulting in load reduction (Meade & Moody, 2010) and channel sedimentation (Munoz et al., 2018;Wang & Xu, 2018a With the hydrological alterations, we found considerable sediment trapping on channel bars in the middle reach of the Lower Mississippi River from river kilometer (RK) 515 to RK 737 (Wang and Xu, 2018a). There were 30 large emerged channel bars in the 223-km river reach with a total emerged bar volume of 268,065 x 10 3 m 3 in the year of 1985. ...
... Sediment trapping by channel bars in the 223-km middle reach of the Lower Mississippi River (Data sources fromWang & Xu, 2018a). ...
Conference Paper
Full-text available
Sediment transport and channel dynamics of large alluvial rivers in their lower reaches can strongly influence physical, chemical and biological conditions in their deltaic regions. In this paper, we report the latest assessment on sediment transport and riverbed dynamics of the last 500-km reach of the Mississippi River before entering the Gulf of Mexico. This river reach is also termed as the Lowermost Mississippi River (LmMR), which begins downstream of its division node to the Atchafalaya River. Our assessment shows that in the past 2-3 decades, suspended sediment and bed material loads in the LmMR were significantly higher at the upstream location than those at the downstream locations. Nearly 70% of the riverine sand is trapped within the LmMR. Continuous riverbed aggradation (up to 10 m) occurred below the Mississippi-Atchafalaya diversion, presenting favorable backwater conditions for an avulsion. Backwater effects have mainly controlled riverbed deformation in the LmMR, while flow reduction may have also contributed to channel aggradation in the lowermost reach. Our assessment reveals the considerable complexity of morphodynamical responses of a large alluvial river to human interventions, strongly suggesting that future river engineering and management of the world large alluvial rivers need to look for effective strategies that will improve sediment transport.
... Dikes were built in many reaches along the river to constrain flow to the river's navigation channel. These engineering projects have influenced riverine sediment transport and distribution, resulting in load reduction (Meade & Moody, 2010) and channel sedimentation (Munoz et al., 2018;Wang & Xu, 2018a With the hydrological alterations, we found considerable sediment trapping on channel bars in the middle reach of the Lower Mississippi River from river kilometer (RK) 515 to RK 737 (Wang and Xu, 2018a). There were 30 large emerged channel bars in the 223-km river reach with a total emerged bar volume of 268,065 x 10 3 m 3 in the year of 1985. ...
... Dikes were built in many reaches along the river to constrain flow to the river's navigation channel. These engineering projects have influenced riverine sediment transport and distribution, resulting in load reduction (Meade & Moody, 2010) and channel sedimentation (Munoz et al., 2018;Wang & Xu, 2018a With the hydrological alterations, we found considerable sediment trapping on channel bars in the middle reach of the Lower Mississippi River from river kilometer (RK) 515 to RK 737 (Wang and Xu, 2018a). There were 30 large emerged channel bars in the 223-km river reach with a total emerged bar volume of 268,065 x 10 3 m 3 in the year of 1985. ...
... Sediment trapping by channel bars in the 223-km middle reach of the Lower Mississippi River (Data sources fromWang & Xu, 2018a). ...
Presentation
Full-text available
Sediment transport and channel dynamics of large alluvial rivers in their lower reaches can strongly influence physical, chemical and biological conditions in their deltaic regions. In this paper, we report the latest assessment on sediment transport and riverbed dynamics of the last 500-km reach of the Mississippi River before entering the Gulf of Mexico. This river reach is also termed as the Lowermost Mississippi River (LmMR), which begins downstream of its division node to the Atchafalaya River. Our assessment shows that in the past 2-3 decades, suspended sediment and bed material loads in the LmMR were significantly higher at the upstream location than those at the downstream locations. Nearly 70% of the riverine sand is trapped within the LmMR. Continuous riverbed aggradation (up to 10 m) occurred below the Mississippi-Atchafalaya diversion, presenting favorable backwater conditions for an avulsion. Backwater effects have mainly controlled riverbed deformation in the LmMR, while flow reduction may have also contributed to channel aggradation in the lowermost reach. Our assessment reveals the considerable complexity of morphodynamical responses of a large alluvial river to human interventions, strongly suggesting that future river engineering and management of the world large alluvial rivers need to look for effective strategies that will improve sediment transport.
... Additionally, traditional dam-release schedules in the Missouri River often include higher releases in the late summer to support navigation, causing sandbar inundation during the tern nesting season (Schwalbach 1988). By contrast, the abundance and volume of natural and dike field sandbars in the lower Mississippi River have increased as the channel has steepened and widened, and the USACE has constructed additional wing dikes (Kesel 2003, Wang andXu 2018). The relatively natural flood regime and a dike-notching program have also kept sandbars in the lower Mississippi naturally barren and disconnected from banks (Killgore et al. 2014). ...
... Second, there is evidence that changes in the extent and methods of tern nesting surveys under-represented tern nesting populations at the time of listing relative to surveys after listing (USFWS 2013). Finally, the lower Mississippi River mainstem has been the locus of tern nesting population recovery, and recent work has indicated that sandbar volumes in reaches there have increased by nearly twofold over the last 30 yr (Wang and Xu 2018). It is possible that the lower Mississippi mainstem was undergoing early stages of adjustment to the meander cutoff program, and was not providing adequate sandbar nesting habitat at the time of listing. ...
Article
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The world's large river systems are under increasing stress to support growing populations and economies. Balancing inevitable fluvial alteration with protections of river ecosystems will require awareness of lessons learned in big river systems where system‐scale alterations have already occurred. In 1985, the Interior Least Tern (Sternula antillarum; terns) was listed as endangered, citing “alteration of natural river dynamics” as cause for population declines. We refer to this as the “fluvial alteration hypothesis” and examine it by attempting to answer two primary questions: [Q1] What are the first‐order physical and hydrologic metrics associated with tern nesting reach selection at the regional scale? [Q2] Did human‐induced changes in these metrics differ between regions where tern breeding populations have recovered and where it has been stable or declined? We compiled metrics of sandbar nesting habitat across the nesting region for modern conditions and used regression modeling to assess the relative effects of each metric on nesting reach selection. At the scale of a nesting region, terns selected for nesting reaches that are wider have greater potential to braid, and are less likely to flood during nesting season. A comparison between subregions indicates that modern tern nesting conditions are substantially better in the lower Mississippi River and tributaries (LMRT) systems than the Missouri River and tributaries (MORT) system. However, both subregions had nearly equivalent sandbar nesting habitat quality prior to major human modifications. The fluvial alteration hypothesis was consistent with geomorphic assessments for the MORT system, but overlooked potential for human alterations to have differing, even beneficial effects to tern nesting habitat in the LMRT system.
... The upstream reach between LJ and HK7 has a river length of~48 km, whereas the length of the downstream reach varied in different time periods due to a lack of surveys at some downstream cross-sections (Fig. 2). For example, the river length of the downstream reach was~17 km between HK7 and Q3 in 1976,~22 km between HK7 and Q4 from 1977to 1980,~29 km between HK7 and Q6 from 1980to 1985 km between HK7 and Q7 from 1985 to 2015. ...
... In addition, farm dikes or levees near Q1 or Q2 may contribute to channel aggradation. Recent studies have recognized sediment deposition within the void space of in-channel dikes and aggradation of point bars due to the construction of dikes (Alexander et al., 2012;Wang and Xu, 2018b). As shown in Figs. ...
Article
As rivers approach base level, their water and sediment dynamics are affected by a transitional reach known as the backwater zone. At low flows, backwater zones cause flow deceleration and in-channel sedimentation, but at high flows, they cause flow acceleration and erosion. Over many floods, the dynamics of deposition and erosion in the backwater zone are thought to control the locations of avulsions on some large deltaic channels. However, in various studies, the role of the backwater is often inferred or modeled, and directly observed evidence of how backwater affects channel dynamics at avulsion sites remains scarce. In this study, we show how the backwater zone impacts the evolution and avulsion of the Qingshuigou channel, a recent lobe on the Yellow River Delta, using four decades (1976–2015) of data from systematic surveys of water discharge, sediment load, cross-sectional profiles and water surface elevation. The results show that the channel was commonly eroded during flood seasons and aggraded during nonflood seasons. Erosion rates generally decreased in the downstream direction along the lower channel reach during flood seasons, primarily due to downstream channel widening and the subsequent decrease in sediment transport capacity. The erosion rate reached zero at the cross-sections farthest downstream, which is contrary to expectations under hydrodynamic backwater effects, where drawdown causes erosion to increase downstream during high flows. During nonflood seasons, maximum sedimentation occurred upstream of the backwater zone, possibly due to impacts of local topography of meandering bends or constriction from dikes. Morphodynamic backwater accompanied by the deposition and gradual progradation of a mouth bar resulted in downstream increasing sedimentation, superelevation, and lateral migration rates along the lower channel reach from 1985 to 1996. The predicted avulsion location was near cross-sections Q6 or Q7 with an avulsion length of ~20–30 km upstream of the shoreline, which was consistent with those for historical avulsions. We emphasize the close interplay between backwater effects and channel geometry and argue that morphodynamic backwater may play a more important role than hydrodynamic backwater in setting up and triggering avulsions on the Yellow River Delta.
... Field observations and numerical simulations show that bar evolution involve not only bar migration but also include bar lateral variation and bar elongation (Best et al., 2003;Khan and Islam, 2003;Akhtar et al., 2011;An et al., 2013;Kleinhans et al., 2013;Nicholas, 2013;Schuurman et al., 2016;Vesipa et al., 2017;Wang and Xu, 2018;Castelltort, 2018). ...
... Through satellite imagery, mid-channel bars have been found to be elongated and laterally changed in the Lower Mississippi River, and these mechanisms are substantially related to surface area variations (Wang and Xu, 2018). Karmaker and Dutta (2016) proposed that thalweg shift of braided channel results in the erosion of island bank. ...
Article
Bar dynamics in sandy braided rivers are keys to better understand the morphological processes of braided rivers and sediment distributions. Limited by insufficient quantitative information and satellite images that only show the larger-scale morphology and do not reveal the sand bars in the deeper channels, most previous studies have qualitatively assessed bar dynamics, but the ways in which the hydraulic parameters of sandy braided rivers control bar dynamics remains poorly understood. Here, we present sediment numerical simulations on sandy braided rivers to investigate the quantitative controls of river parameters on bar dynamics. Three bar dynamic forms (downstream migration, lateral variations and bar tail elongation) are observed. Unit bars are prone to downstream migration following formation, and the migration rate shows a deceasing trend during braided river evolution. This gradually decreasing migration rate is proven to be strongly connected to the decreasing flow velocity of braided channels that confine bar growth. The lateral variation in bar dynamics exhibits narrowing, migration and widening of sectional morphologies. We suggest that braided channel curvature dominantly controls lateral sediment transportation around the bar and thus results in several lateral variation forms of bars. The bar tail elongation difference between the two sides of the bar is associated with bar asymmetry. Strong bar asymmetry can make apparent differences in bar tail elongation.
... [7][8][9][10] Over the past several decades, sediment transportation and regular deposition of many alluvial large rivers in the world in lower regions especially coastal areas has continuously shown a decrease. [11][12][13][14][15][16] The Mississippi River (Mississippi to Gulf of Mexico, 400 MT before 1900 to 172 MT during last 3 decades) and Yangtze River (Yangtze to East China Sea, 40% decrease in 2000s) are examples for decreasing annual suspended sediment. [17][18][19][20] So, the scenario of aggradation and degradation is rapidly changing. ...
... Some of the bars are seasonally destroyed, some get migrated, and some new ones need to be accommodated. Channel bars 5,9,11,13,14,16,17,33,38,43,45, and 46 continuously show their dynamic nature which is basically under the lower and middle area of piedmont region (Figure 7). It is seen that in the upper zone of the piedmont area, since the 2000s, 58% to 72% channel bar area are stable. ...
Article
Full-text available
Channel bars are common, striking fluvio-geomorphic depositional features of alluvial rivers. The study of this article has aimed to investigate the formation, migration, and morphodynamic alteration of channel bars (n = 50) in gravel braided alluvial rivers in Darjeeling Himalayan Piedmont zone. Dynamics of micro to meso bar deposition is mainly accomplished by the channel gradient, huge upstream landslide, and variation of discharge. Multi-criteria analysis method has been used to explain the variation of principal component analysis (PCA1, PCA2, and PCA3), both monsoon to post-monsoon. Bridge scouring, empirical aggradation, and degradation values are 0.1 to 1.05 m and [Formula: see text]. Migration, re-generation, and degradation of the micro bars with their optimum morphology show changes during the rainy season. In the upper ([Formula: see text]), middle ([Formula: see text]), and lower ([Formula: see text]) piedmont region, the bar dynamic area are 0.12 to 0.71, 0.12 to 2.83, and 0.10 to 5.43 km ² , respectively. In total, 58% to 72% stability of the channel bars is observed in the upper piedmont region. The coefficient of determination ( R²) of channel bar area and width shows positive (0.63) relation.
... To address this issue, have proposed an approach for estimation of bar volume through the integral of a rating curve of bar surface areas with river stages. This method has been used to calculate volumetric changes of channel bars responded to both natural and anthropogenic interferences (Wang et al., 2018b;Wang and Xu, 2018). Furthermore, most of previous works only examined changes in bar morphology, however bar migration was barely addressed, which was also closely associated with bar morphodynamics (Evans et al., 2007). ...
... The bar growth as a consequence of river engineering work was widely reported in the rivers around the world. For example, Wang and Xu (2018) found that total dike length in a dike field mostly contributed to the gain of mid-channel bars' volume in the Lower Mississippi River, with an increase of 41% in the past three decades. It may be concluded that the stabilization and accretion of the bar in this period was a direct result of the river engineering works designed to protect the channel bar after 2009. ...
Article
The study focused on the question of how the natural and human forcing has affected the morphodynamic evolution of bars in the middle Yangtze River. A large channel bar was investigated using satellite remote sensing data during 1986-2017. A novel algorithm was proposed to select images acquired at the similar river stage. The bar was delineated from selected images and surface area, volume and centroid were quantified to examine bar morphodynamics. The results indicated a four-stage evolution process, including a steady extension (1986-1998), a quick shrinkage (1998-2002), a fluctuated shrinkage (2002-2012), and a fluctuated extension (2012-2017). The first stage was characterized by the steady growth at a rate of 0.087 km 2 /a, and a centroid translation towards the inner bend by 400 m. The second stage was the most dynamic episode, with the bar degradation at a rate of 0.71 km 2 /a, and a downstream migration by 850 m. In the third stage, the bar was eroded at a rate of 0.05 km 2 /a, and migrated towards the inner bend by about 80 m. In the fourth stage, the bar was deposited at a rate of 0.12 km 2 /a, and traveled upstream by around 400 m. The bar volume exhibited the similar trend. The analysis showed that the four stages were separated by the consecutive floods, the closure of Three Gorges Dam and the installation of two river engineering works. The results suggested that the bar evolved much more dynamic under the natural flow (1985-2003) than that of the regulated (2003-2012). The findings revealed that the evolution was largely governed by the flow and sediment supply while the human forcing can affect the process by altering these regimes. This study also demonstrated the great usefulness of combining multi-temporal imagery and river stage records in the assessment of bar morphodynamics.
... As John Barry notes, "the biggest danger is pressure, constant unrelenting pressure" ( [28], p. 191). The Low-Sill Structure is now one of four structures that convey Mississippi River flow into the Atchafalaya Basin Floodway, but it almost failed during the 1973 flood and remains a weak link in the MR&T control system [47][48][49][50]. But prolonged high discharges can threaten earthen levees as well as concrete floodwalls and control structures [51]. ...
... Most of the flaws are not visible until failure is in progress. MR&T levees may fail in the future due to a reduction of the conveyance of the river channel downstream because of sedimentation and increased pressure due to prolonged high water during very large floods [50][51][52][53][54]. The nightmare scenario on the Mississippi River is when stage drops very quickly after a prolonged high water period. ...
Article
Full-text available
Climate change forcings are having significant impacts in coastal Louisiana today and increasingly affect the future of New Orleans, a deltaic city mostly below sea level, which depends on levee and pumps to protect from a host of water-related threats. Precipitation has increased in the Mississippi River basin generally, increasing runoff, so that in recent years the Mississippi River has been above flood stage for longer periods of time both earlier and later in the year, increasing the likelihood that hurricane surge, traditionally confined to summer and fall, may compound effects of prolonged high water on river levees. The Bonnet Carré Spillway, just upstream of New Orleans has been operated more often and for longer periods of time in recent years than ever before in its nearly 100-year history. Because all rain that falls within the city must be pumped out, residents have been exposed to interior flooding more frequently as high-intensity precipitation events can occur in any season. A sustainable path for New Orleans should involve elevating people and sensitive infrastructure above flood levels, raising some land levels, and creating water storage areas within the city. Management of the lower Mississippi River in the future must include consideration that the river will exceed its design capacity on a regular basis. The river must also be used to restore coastal wetlands through the use of diversions, which will also relieve pressure on levees.
... Under current strict flow management, the uppermost Atchafalaya riverbed might become stable in the future if there were no substantial changes in suspended sand input and water discharge. However, sand loads in the river may decrease because a large amount of sand is trapped in the upper reach of the lower Mississippi River due to the construction of spur dikes (Wang and Xu, 2018b). River discharge of the Mississippi has been projected to increase by 10.7%-59.8% ...
... A plausible physical explanation for this may be the following. From a study on sand stores in the Lower Mississippi River, Wang and Xu (2018b) report a tremendous accumulation of sands in the river channel bars (530 MT) upstream of the Old River Control Complex during 1985-2015. In a subsequent work on the 500-km lowermost Mississippi River (Wang and Xu, 2018a), the same authors find a channel bed aggradation downstream of the Old River Control Complex during 1992-2004. ...
Article
Full-text available
Previous studies have established that under natural conditions, alluvial river confluence zones experience channel scour followed by mid-channel bar development. Less attention is given to bed evolution downstream of large alluvial river confluences under engineered conditions, such as discharge regulation and levee confinement. Here we present four decades of morphologic changes along the 69-km uppermost Atchafalaya River, a downstream distributary of the confluence of the Mississippi River Outflow channel and the Red River. We aim to find the answer to one critical question: how does the channel bed downstream of an engineering-controlled confluence respond to regulated flow? We utilize single-beam bathymetry data collected in 1967, 1977, 1989, 1998, and 2006 to quantify riverbed deformation of the reach after the flow regulation began in 1963. Suspended sediment load and stream power during the four periods are calculated. Results show that between 1967 and 2006, extensive bed degradation occurred and the average bed elevation reduced by 3.8 m. A total volume of 105 ± 26 × 10⁶ m³ sediment was scoured from the uppermost Atchafalaya riverbed over this 40-year period, implying that channel erosion in this river reach has contributed to downstream coarse sediment delivery and associated deltaic growth in the Atchafalaya Bay. Bed aggradation only occurred during 1989–1998 in response to excess sediment input from the Mississippi River, likely attributable to the 1993 long-lasting Mississippi River flood. But the same amount of riverbed deposit eroded in the following eight years, demonstrating how quickly a large regulated river can diminish a perturbation owing to excess sediment input. These findings not only reveal the complexity of morphologic adjustments of a river channel in response to intensive engineering disturbances but also provide useful information for future modeling studies and management plans for the Atchafalaya and other large, engineered alluvial river confluences.
... Alluvial rivers have been a widely studied subject of recent researches in geomorphology (Knox and Latrubesse, 2016;Wang and Xu, 2018), as their morphological changes affect their human use, and also the risks and hazards. Key points in the morphological evolution of meandering lowland rivers are the bank erosion and the formation of bars, as they could indicate channel processes and equilibrium conditions of a reach. ...
... Key points in the morphological evolution of meandering lowland rivers are the bank erosion and the formation of bars, as they could indicate channel processes and equilibrium conditions of a reach. In recent years, several researches focused both on bank erosion (Piégay et al., 2005;Schuurman et al., 2016) and on the development of point-bars (Wang and Xu, 2016;Wang and Xu, 2018). According to Schuurman et al. (2016), spatially alternating bank erosion and point-bar growth are crucial in the development of meanders in rivers. ...
Conference Paper
Alluvial rivers have been a widely studied subject of recent researches in geomorphology (Knox and Latrubesse, 2016; Wang and Xu, 2018), as their morphological changes affect their human use, and also the risks and hazards. Key points in the morphological evolution of meandering lowland rivers are the bank erosion and the formation of bars, as they could indicate channel processes and equilibrium conditions of a reach. In recent years, several researches focused both on bank erosion (Piégay et al., 2005; Schuurman et al., 2016) and on the development of point-bars (Wang and Xu, 2016; Wang and Xu, 2018). According to Schuurman et al. (2016), spatially alternating bank erosion and point-bar growth are crucial in the development of meanders in rivers. While bars serve as sinks for sediments in alluvial rivers, bank erosion on the other hand is often the dominant source of sediments especially in modified watersheds (Shields et al, 2009). Bank erosion resulting from mass failure of steep banks is one of the most serious forms. The state of bars on the other hand, are representative of the equilibrium of channels (Church and Rice, 2009). The Tisza River in Hungary has been altered by various human interventions since the 19th century. It began with construction of embanked levees to control floods, artificial meander cutoffs and channelization to improve shipping and shorten the flood waves, as well as recovering land for agricultural purposes. Later works included the construction of revetments and groins to control the lateral erosion of the river. In the last fifty years, dams have also been constructed to support irrigation and to generate electrical power. As a result of these intensive human impacts, the channel processes seem to change. In a natural state (pre-19th c.), the Tisza had a meandering pattern with alternating point-bars. However, only some point-bars remain nowadays, the channel incises and bank erosional processes alter. The aim of the present research is to reveal the driving factors of recent point-bar formation and bank erosion, to determine the rate of these processes, and finally to give an evaluation on the channel evolution of the studied reach. Our study was performed on the 89-km-long section of the Lower Tisza River (between Csongrád and the Hungarian-Serbian border). Here, the regulation works doubled the slope (2-4 cm/km) and reduced floodplain (from 10-20 km wide floodplain to just 1-5 km; Kiss et al., 2008). To understand the role of point-bars and bank erosion in the morphological evolution of the Lower Tisza River, two approaches were applied. Firstly, to evaluate the long-term morphological changes of the river, military maps (since late 18th c.), hydrological surveys (1891-1999) including the planform and vertical cross-sectional parameters were applied. Based on this series of maps, the sinuosity, the width, the number and the length of point-bars were determined. Secondly, in selected study sites, the recent evolution of point-bars (at Csongrád and Ányás), and the rate of bank erosion (Csanytelek 1-2, and Ányás) were measured and analyzed between 2013
... River bars, as basic units in large rivers, impact the geomorphologic evolution of rivers. Changes in sediment supply determining the dynamics of individual depositional bars can reverberate and amplify to elicit large-scale changes in main channel morphology and flow distribution (Lou et al., 2018;Wang and Xu, 2018). With intense sediment movement, river bars are likely to experience a geomorphologic life cycle (Church and Rice, 2009;Hooke and Yorke, 2011;Van Denderen et al., 2018). ...
... Long et al. (2021) demonstrated that the lower-reach bar was more dynamic under naturally imposed flow conditions than under anthropogenic interferences such as channelization, riverbed dredging and bank reinforcement. Wang and Xu (2018) reported that without the effect of upstream dams, regulation measures such as dikes in the Lower Mississippi River promoted the growth of river bars, leading to a 41% increase in overall bar area in the past three decades. However, river engineering works may lose their functions of bankline protection and reducing erosion under the huge pressure of extreme floods (Vuik et al., 2018;Ohtsuka et al., 2021), weakening their roles in stabilizing riverine geomorphological boundaries. ...
Article
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Mid-river bars are important agents that impact the flow and sediment dynamics of rivers and are commonly used for the development of human society. This study focused on the geomorphologic change (riverbed and bar morphology) around a large-scale river bar system in the lower Yangtze River (namely, Heishazhou) that was possibly impacted by the Three Gorges Dam (TGD) and other river engineering works. Relevant data sources including field surveys, hydrological station records, satellite images and historical practice reports were gathered for the investigation. The Heishazhou bar system previously consisted of two major subbars and recently merged as an entirety. Rapid bar growth occurred after the construction and operation of the TGD, leading to the closure of the Middle Channel and the South Channel dominating water conveyance at the reach. With the examination of another three bar systems in the lower Yangtze River, the lower-reach bar systems generally grew due to sediment deposition around bars, which differred from those in the middle reach that generally shrunk. The underlying cause may be that the middle-reach riverbed still supplies sediment to the lower reach. The riverbed at the Heishazhou reach, however, experienced apparent erosion after the construction of the TGD. Combining historical investigations and satellite images, a conceptual description was created to understand the geomorphologic cycle of river bar systems at a meandering reach and found that the formation of an inner-bank bar shall be a major force driving the geomorphologic cycle. Sediment deficits caused by the TGD and human activities such as dikes, bank revetments and riverbed dredging are highly likely to cause a slow-down of the geomorphologic cycle of these river bar systems with distinct mechanisms.
... River islands are also characterized by a certain cyclical period of erosion and deposition; some studies have suggested that the full cycle of incipient mid-channel bars becoming attached to the riverbank is approximately 5e15 years (Hooke, 1986;Hooke & Yorke, 2011). Furthermore, sandbar and island development are related to divergence and confluence (Gilvear, 2004), dam operation (Gu et al., 2020;Ra ska et al., 2017;Wang & Xu, 2018), and revetment engineering (Yang et al., 2021). Vegetation also plays a vital role in island development (Liu et al., 2016;Tooth & Nanson, 2000). ...
... The river island equilibrium and channel stability reflects a long-term quasi-dynamic equilibrium rather than a short-term instantaneous stable status (Huang et al., 2014;Liu et al., 2016;Pan, 2001;Xu et al., 2011). Island stability is related to the hydrologic regime, riverbank stability and human activities (Baubinien _ e et al., 2015;Kl€ osch et al., 2015;Meshkova & Carling, 2012;Nicholas et al., 2013;Ra ska et al., 2017;Wang & Xu, 2018;Xu, 1997). Therefore, the result obtained at a specific moment may be far from reality and cannot indicate whether equilibrium is present. ...
Article
River islands are vital geomorphic units in alluvial rivers, and the variation of their morphology and position plays a significant role in regulating flow-sediment transport and channel stability. Based on the theories of minimum energy dissipation theory of fluid movement and river morphodynamics, this study uses the river islands in anabranching channels to analyze the relationship between the shape coefficient of river island and the flow-sediment dynamics under stable equilibrium conditions. Results indicate that the river islands could adjust their lengths and widths to reach an appropriate allocation of flow diversion ratio and sediment separation ratio in the two anabranching channels to ensure flow-sediment being smoothly transported downstream and achieve the minimum energy dissipation. Under the minimum energy dissipation condition of flow-sediment transport balance, the ratio of “sediment separation ratio” to “flow diversion ratio” in short and straight branching channels is between 1 and 1.1. When the proportion of flow-sediment transport reaches its maximum, the steady island morphology coefficient is approximately 0.2; that is, the island length is five times the width. We verify the steady island morphology coefficients using two typical islands in the middle and lower reaches of the Yangtze River and find the relative error is within ± 3%.
... Les études sur la dynamique des canaux fluviaux permettent de bien comprendre les raisons et 3 l'ampleur des résultats après les épisodes d'érosion et/ou d'accumulation pour la gestion et la planification du comportement des rivières (Alam, 2007). Ces dernières années, les outils et techniques géospatiaux et les systèmes d'informations géographiques (SIG) sont devenus stratégiques par leurs capacités à couvrir les aspects spatio-temporels à l'aide de données synoptiques (Cunningham, 2009) (Wang, 2016) (Batalla, 2018) (Wang, 2018). ...
Conference Paper
Full-text available
The flow is strongly dependent on the bed which conveys it. On the other hand, this same flow can modify this bed by the phenomenon of erosion or deposition according to the variation of the speed of the flow. This complex and dynamic phenomenon is manifested especially during a flood. A technique using a Geographic Information System (GIS) and a simple remote sensing (RS) are used to characterize the bed change of the Sambirano River (Madagascar) near its mouth towards the Mozambique Channel. The method is applied on a test section to compare the sequential change of its bed during two periods:. The results are maps in which we can clearly see the dynamics. This sequential comparison shows a considerable change after each passage of an intense cyclone, ie a five-year and / or ten-year return period flood. This article shows the results of the passage of two remarkable cyclones: GAFILO (2004) and ELIACKIM (2018). These results illustrate the last modifications of this bed during the last two decades, which are used for different management approaches and / or measures against the risks of floods.
... For measuring, mapping, representing, and monitoring the geomorphodynamic features, effective tools, and techniques are very important. At present, remote sensing (RS) and geographical information systems (GIS) have enormous importance for change detection and mapping in rivers and their buffer zone dynamics at a different strategic scale (Wang and Mei 2016;Wang and Xu 2018). RS and GIS tools and techniques with field verification can accurately and quickly map and investigate river morphological changes (Rinaldi et al. 2013;Langat et al. 2018). ...
Chapter
Dynamicity of the channel is the main characteristic of the Kaljani River in the Himalayan foothill. The present work intends to document the historical changes in the land use and land cover (LULC) pattern driven by channel migration during 1987–2020 at the Kaljani River adjacent village area. In this study, the sinuosity index, the radius of curvature, meander wavelength, amplitude, meander width, channel width, arc angle, direction angle, rate of channel migration, and direction of migration have been calculated for the years of 1987, 2004, and 2020. The historical positions of both bankline and dynamic channel width and meander width indicate that a large portion of the floodplain area depicts an erosion-accretion sequence with time. This work also investigated LULC changes in the Kaljani River adjacent village area using supervised image classification with an overall accuracy ranging between 85 and 89%. This research has demonstrated the application and capability of RS and GIS technology and generated a detailed evaluation of temporal and spatial changes in river channel processes and adjustment of LULC types. The LULC result revealed that their water bodies and dense forest are decreased and sandy area and built-up areas are increased. The LULC changes by the direct effect of bankline migration have a bad impact on the dwellers of the floodplain adjacent village area of the Kaljani River. The results of this study can represent an important indicator of the vulnerability of the Kaljani River adjacent village area and also provide information about geomorphological instabilities of the study area.
... Efficient and cost-effective scientific tools and techniques for geomorphodynamic mapping and monitoring, as a modern-day prerequisite for river development planning and projects evaluation, are of enormous importance. Geospatial tools and techniques (remote sensing-RS and geographical information systems-GIS) have, in recent years, become geomorphology tools for change detection in rivers and their floodplain dynamics at the strategic scale because of their capability to cover spatiotemporal aspects using synoptic data (Cunningham et al., 2009;Arthun et al., 2013;Wang and Mei, 2016;Batalla et al., 2018;Wang and Xu, 2018) and analytical power and integration of data (Walsh et al., 1998). Unlike traditional geomorphology investigation methods that require intensive data collection through field surveys and processing, they provide excellent tools for river channel spatial data extraction, processing, storage, visualization, and analysis. ...
Article
River channel dynamics are natural autogenic occurrences for fluvial rivers with influences from human modifications and climatic factors. Remote sensing and geographic information system tools and techniques, aerial photographs, and satellite imagery have been used to determine epochal channel erosion, accretion, and unchanged locations along Tana River, Kenya's longest river. Six reaches within a 142-km Saka-Mnazini stretch were studied by comparing sequential changes in the position of the channel in 1975–1986, 1986–2000, 2000–2017, and 1975–2017 epochs. Manual and automatic digital processing procedures and GIS tools were applied to visualize and quantify the reach-wise spatial and temporal morphological changes. The erosion and accretion channel changes over the study period were observed and quantified at all reaches. Meandering and switching off or abandoning the main active channel was also illustrated. The potential driving forces of morphological changes included varying hydrological regime, upstream land use practices, nature of channel gradient, and riparian vegetation occurrence changes. We found no clear evidence to link river regulation with the river channel dynamics. Results deliver the latest evidence on the dynamics of Tana River. This information is crucial for understanding river evolution characteristics and aid in planning and management at the lower reaches which has remained poorly understood. Use of remote sensing data in concert with GIS provides efficient and economical quantitative spatial and temporal analysis of river channel changes.
... La validation de ces résultats pourrait être importante en termes d'actions de restauration à mener afin de favoriser les espèces riveraines pionnières. Celle-ci conforterait l'idée qu'une largeur de lit réduite dégrade les flux latéraux de matière et d'énergie ainsi que la présence et la dynamique des bancs (Duro et al. 2016;Wang & Xu 2018). Le recul et l'effacement des digues seraient ainsi des leviers majeurs de la restauration de la fonctionnalité des cours d'eau et de la dynamique de la végétation riveraine. ...
Thesis
La dynamique de la végétation riveraine est étroitement liée aux régimes de perturbation du cours d’eau, notamment les crues, ainsi qu’aux processus physiques et biologiques qui en découlent. L’impact des activités humaines sur les rivières comme l’endiguement, la chenalisation ou l’exploitation hydroélectrique et sédimentaire, a fortement modifié ces régimes. Cela se traduit, entre autre, par une stabilisation du milieu et une régression des stades pionniers de l’habitat riverain due au manque de rajeunissement de celui-ci par les crues. A l’échelle de l’arc alpin, Typha minima Hoppe (la petite massette) est une espèce herbacée clonale qui colonise les habitats pionniers des cours d’eau de piémont. Cette espèce a vu ses populations fortement décroître au cours du siècle dernier, lui valant le statut d’espèce protégée dans plusieurs pays européens. En France, de nombreuses menaces pesant sur cette espèce persistent tel que la chenalisation, la modification du régime de crue et la destruction de son habitat par des travaux menés dans le lit et sur les berges des cours d’eau. C’est notamment le cas des travaux menés depuis 2004 par le Symbhi (Syndicat Mixte des Bassins Hydrauliques de l'Isère) dans le cadre du projet « Isère Amont » qui ont impacté des stations de T. minima sur l’Isère. Des mesures de compensations en ont résulté et ont accompagné la mise en place d’un projet de restauration de l’espèce dans la zone d’emprise des travaux.L’objectif de ce travail de thèse est de produire des connaissances sur la niche écologique et la dynamique spatiotemporelle d’une espèce clonale colonisant le stade pionnier de l’habitat riverain : la petite massette (Typha minima Hoppe), afin de servir de base théorique aux futurs projets de conservation et de restauration. Pour ce faire, la problématique suivante a été formulée : Quelles sont les variables environnementales et les processus écologiques qui affectent la dynamique spatio-temporelle de T. minima et en quoi ces connaissances peuvent-elles être appliquées à sa restauration et sa conservation?i) La première étape est de déterminer quels sont les facteurs biotiques et abiotiques liés aux processus sédimentaires et de succession écologique qui affectent la dynamique locale des taches de T. minima. Les résultats montrent que la progression des taches de T. minima est liée au caractère pionnier des bancs (sédiments fins, faible altitude et couvert végétal). Le maintien et la régression des taches sont au contraire liés à la maturité de l’habitat, induits par un processus de succession écologique plus avancé, avec un développement de la végétation et une amplification du phénomène d’accrétion.ii) Dans une seconde partie nous avons testé les effets de la compétition interspécifique avec des saules (Salix alba) et de l’ensevelissement par les sédiments sur la compétitivité et l’investissement dans la reproduction de T. minima. Bien que souvent mentionnée comme la principale cause de régression de l’espèce, la compétition interspécifique avec les saules n’affecte que peu T. minima alors que l’effet de l’ensevelissement par les sédiments est important.iii) Enfin, dans le but d’améliorer les protocoles de restauration de T. minima, plusieurs expérimentations visant à tester l’effet de différentes biomasses initiales transplantées, hauteurs par rapport à l’eau, types de berge, formes des placettes et associations avec d’autres espèces pionnières ont été réalisées entre 2013 et 2016. Les résultats montrent que transplanter T. minima avec une biomasse initiale importante sous forme de placette linéaire parallèle au cours d’eau à des hauteurs comprises entre +1.00m et +1.55m est optimal.Ces travaux caractérisent d’une part les facteurs environnementaux et les processus en jeu dans la dynamique de T. minima et d’autre part, optimisent les protocoles de restauration, contribuant ainsi à alimenter les futurs projets de restauration et de conservation de l’espèce.
... The dynamic development of remote sensing techniques based on airborne and satellite imagery in spectres reaching beyond the visible bandwidth, as well as measurement techniques based on laser scanning (ALS), enable the acquisition of high resolution data involving, for example, the morphology and dynamics of processes shaping the images of floodplains (e.g., [22][23][24]). Combined with the capabilities of the GIS software [25] and tools for mathematical modelling of groundwater filtration processes, these techniques enable the performance of advanced analyses of the spatial distribution of specific parameters characterising the hydrogeological environment and the very dynamics of the water filtration process in alluvial aquiferous strata [26]. ...
Article
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We aim to answer a question: how does the evolution of fluvial environment affect to risk of embankments failure in lowland rivers and how can we identify and describe places at risk of levees failure using the remote sensing data? The study was carried out in the Vistula River valley near Magnuszew (middle Vistula course, central Poland). 24 geological boreholes were drilled to a depth of 2.0–8.5 m and groundwater table observations were conducted in a monitoring network consisting of 22 wells, 5 piezometers (screened within the Holocene alluvial aquifer) and 2 temporary water gauges. Identification of the diversity of the geological structure of the floodplain was supported by airborne laser scanning imaging, as well as high resolution satellite images and aerial photos. This remote sensing study allowed the creation of a conceptual model of hydrogeological conditions. Study takes into account the effects of the land forming activity of flood waters resulting from the evolution of the fluvial environment in the Holocene. Created conceptual model subsequently fed into the construction and calibration of a mathematical groundwater flow model using MODFLOW software. The study allowed the identification and characterisation of intensified groundwater flow zones. Concentrated flow in the substrate of flood protection levees constitutes a threat to their stability. Documented in many publications climate change will induce in future climate scenarios an increase in rainfall and prolongation of dry periods. The implementation of the methodology of identifying the geological forms with the use of presented techniques allows the identification of sections of flood embankments potentially at risk of failure.
... River morphological and sediment depositional changes can be caused by human activities, i.e., in-channel sand mining, dredging, deforestation, and construction of manmade structures such as weirs, barrages, and dams in a very short time, i.e. in a few decades [1][2][3][4][5][6][7][8][9][10][11][12]. Normally, sediment load is significantly trapped above a regulating structure and reduced downstream of it. ...
Article
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The Chao Phraya River flows in the largest river basin of Thailand and represents one of the important agricultural and industrial areas in Southeast Asia. The Ping River is one major upstream branch flowing down slope southwardly, joining the Chao Phraya River in the low-lying central plain and ending its course at the Gulf of Thailand. Surprisingly, the overflow occurs frequently and rapidly at the Lower Ping River where channel slope is high, and in particular area, sand-choked is extensively observed, even in normal rainfall condition. In contrary, at the downstream part, the erosion of river bank and shoreline around the mouth of Chao Phraya River has been spatially increasing in place where there should be a massive sediment supply to form a delta. Here we use Landsat imageries taken in 1987, 1997, 2007 and 2017 to analyze geomorphological changes of rivers. Results show that both rivers have undergone the rapid decreasing of water storage capacity and increasing of sand bar areas in river embayment. The total emerged sand bar area in the Lower Ping River increases from 1987 to 2017 up to 28.8 km ² . The excessive trapped bed sediments deposition along the upper reaches is responsible for the shallower of river embankment leading to rapid overflow during flooding. At the Chao Phraya River mouth, a total of 18.8 km ² of the coastal area has been eroded from 1987 to 2017.This is caused by the reducing of sediment supply leading to non-equilibrium in the deltaic zone of the upper Gulf of Thailand. There are several possibility implications from this study involving construction of weir, in-channel sand mining, reservoir sedimentation and coastal erosion management.
... Relating to the cases of the Congo and the Mississippi rivers, the 0-D model outcomes clearly show that both rivers are not able to attain a quasi-equilibrium state given the present hydrological and sedimentological conditions, which is indicative of potential problems when managing such watercourses at the basin scale. In fact, as pointed out, among many others, by Harmar and Clifford (2007) and Wang and Xu (2018), the Mississippi River behaviour is clearly affected by the human presence, both in the upper alluvial valley, where the slight convexity of the longitudinal profile can be attributed to high rates of localised aggradation in the late Wisconsinan and early Holocene periods, and in the middle zone, where the linear profile reflects the dramatic shortening of the river by the programme of artificial channel cut-offs between 1932 and 1942 and the subsequent bank stabilisation. In summary, these authors pointed out that the profile concavity of this river can be considered, at least partially, as a feature inherited from past geomorphological conditions which are maintained by engineering modifications to the planform and channel length, and thus highly impacted by human drivers (Harmar and Clifford, 2007). ...
Article
To date, many numerical approaches are available in studying water flow and sediment dynamics along rivers from the reach to the watershed scale, based on various simplifications. The aim of the present research is to demonstrate how the so-called “morphodynamic quasi-equilibrium hypothesis” is effective in modelling riverine landscape morphodynamics evolution at the watershed scale, focussing on the long-term changes of longitudinal profile and bed grainsize composition of large alluvial rivers. A lumped 0-D, two-reach, two-grainsize model based on the Local Uniform Flow hypothesis and originally developed for reproducing fluvial changes at the historical time-scale, has been applied to three large watercourses to reproduce their long-term evolution, performing a sensitivity analysis based on the present conditions. Three morphometric parameters were analysed, aiming to describe the evolution of the longitudinal profile (concavity and aggrading) and the grainsize composition of the river bed (fining). Though the 0-D approach does not allow for a spatial distribution of the input parameters, namely the liquid and solid discharge, the modelling outcomes show reasonably good qualitative trends. At the scale of analysis (centuries to millennia) and for the chosen large sedimentary systems (thousands of kilometres long), which show high inertia to geomorphological changes likely owing to their longitudinal scale, the model can be helpful in detecting where the present conditions reflect a big disturbance to the “natural” trend. This initial detection method can provide additional insights in evaluating the capability of actual rivers to respond to the present external forcing, eventually reaching a quasi-stable configuration.
... They reported that sand has been a stable resource for nourishing the MRDP, but Blum and Roberts (2014) argued that the sand resource is not sustainable. Wang and Xu (2018a) studied 30-yr morphologic changes of 30 large emerged sand bars located in a 223-km reach from Vicksburg, Mississippi, to the Mississippi-Atchafalaya River diversion and identified a total of 530 Mt of coarse sand reservoirs, but the actual amount that can be used for coastal restoration need to be further studied. ...
Article
One of the proposed methods for restoring the disappearing Mississippi Delta is sediment diversion which uses channels and structures to divert water and sediment from the Mississippi and Atchafalaya Rivers into adjacent basins. This study presents a comprehensive review of geological and physical aspects of sediment dynamics in the Mississippi River Deltaic Plain (MRDP), with special reference to diversion studies over the past two decades. We synthesize these studies, present the current understanding of sediment diversions in the context of sediment dynamics, identify multiple key knowledge gaps, and make recommendations for future studies. To maximize net land building in the MRDP, management strategies should be focused on (a) enhancing river sediment delivery (both mud and sand), (b) increasing sediment retention in receiving basins and (c) minimizing erosion in bays and estuaries. Compared with extensive studies of land building, there have been relatively fewer studies of erosional processes. A heterogeneous coastal geological framework, cohesive sediment erodibility and subsidence together play complicated yet critical roles in future sediment dynamics in bays and estuaries of the MRDP. Sediment retention rates are highly sensitive to spatial and temporal scales, types of sediments and delivery season. Sediment diversions to seaward receiving basins provide more surge protection but tend to have lower sediment retention due to active coastal processes. Structures and devices that improve sediment retention, trap sediments, dissipate waves, and build living shorelines should be explored and cost-to-benefit analysis is needed. Long-term planning should consider more landward diversions, strategic community relocation, and nonlinear response of the complex sedimentary system of the MRDP.
... Furthermore, higher channel erosion Gurnell & Petts 2002), and upper Missouri River (Graf 2006;Skalak et al., 2013), have shown that erosion of the mid-channel bars was closely related to sediment deficit due to upstream damming and river engineering. In the lower Mississippi River, Wang & Xu (2018) also observed the growth of mid-channel bars from 1985 to 2015 caused by river regulation (i.e., dike fields). However, until now there has not been a study that has quantitatively linked mid-channel bar geometry with variations in sediment regime. ...
... (Thakur et al. 2012;Hasanuzzaman et al. 2021). At present, earth observatory tools like remote sensing (RS) and geographic information systems (GIS) have played an important role in various fields of geography (Wang and Mei 2016;Wang and Xu 2018). But, in the morphological field, the use of various GIS tools is limited, especially for the study of riverbank shifting and future prediction. ...
Article
Full-text available
Channel dynamics is an inherent characteristic of river in the floodplain region. It has some significant impacts on the ecosystem and human life. GIS-based, DSAS and CA-Markov models are efficient techniques to measure historical and predictive changes following channel shifting and LULC change. In this study, forty-eight years (1972-2020) of earth observatory data were taken to demarcate and detect the channel bank position and LULC change along the Kaljani River, located at the eastern Himalayan foothill. During 1998-2008, a very high rate of erosion has been taken place on both the bankline, which are about −4.48 m/y (left bank) and −3.48 m/y (right bank), respectively. The overall result of the predicted bankline represents that the bulky expansion will occur along the left bank, and sediment accretion will take place at the right bank. Among the three zones, both banks of zone 'A' (lower part of the river) are worst affected in the past and present and will follow the same trends in future. The LULC change of all six classes from 1972 to 1998 is very high compared with the changes between 1998 and 2020. Moreover, long profile, hypsometric curve value, and the Soil Conservation Service Curve Number (SCS-CN) value have a significant help in understanding and identifying consequences reasons. The accuracy level is validated by the actual bankline positions (2020) with predicted bankline (2020) and actual LULC (2020) to predicted LULC (2020) empirically with RMSE and statistical test. The accuracy level of this study is conducted with the Kappa statistics for LULC map of 2020, and the result is 87.57%, and bankline shifting RMSE varies from 0.007 to 0.176. Therefore, the prediction output serves as the spatial guidelines for monitoring future trends of channel shift and land use planning management.
... La validation de ces résultats pourrait être importante en termes d'actions de restauration à mener afin de favoriser les espèces riveraines pionnières. Celle-ci conforterait l'idée qu'une largeur de lit réduite dégrade les flux latéraux de matière et d'énergie ainsi que la présence et la dynamique des bancs (Duro et al. 2016;Wang & Xu 2018). Le recul et l'effacement des digues seraient ainsi des leviers majeurs de la restauration de la fonctionnalité des cours d'eau et de la dynamique de la végétation riveraine. ...
Thesis
Full-text available
La dynamique de la végétation riveraine est étroitement liée aux régimes de perturbation du cours d’eau, notamment les crues, ainsi qu’aux processus physiques et biologiques qui en découlent. L ’impact des activités humaines sur les rivières comme l’endiguement, la chenalisation ou l’exploitation hydroélectrique et sédimentaire, a fortement modifié ces régimes. Cela se traduit, entre autre, par une stabilisation du milieu et une régression des stades pionniers de l’habitat riverain due au manque de rajeunissement de celui-ci par les crues . A l’échelle de l’arc alpin, Typha minima Hoppe (la petite massette) est une espèce herbacée clonale qui colonise les habitats pionniers des cours d’eau de piémont. Cette espèce a vu ses populations fortement décroître au cours du siècle dernier, lui valant le statut d’espèce protégée dans plusieurs pays européens. En France, de nombreuses menaces pesant sur cette espèce persistent tel que la chenalisation, la modification du régime de crue et la destruction de son habitat par des travaux menés dans le lit et sur les berges des cours d’eau. C’est notamment le cas des travaux menés depuis 2004 par le Symbhi (Syndicat Mixte des Bassins Hydrauliques de l'Isère) dans le cadre du projet « Isère Amont » qui ont impacté des stations de T. minima sur l’Isère .Des mesures de compensations en ont résulté et ont accompagné la mise en place d’un projet de restauration de l’espèce dans la zone d’emprise des travaux. L’objectif de ce travail de thèse est de produire des connaissances sur la niche écologique et la dynamique spatiotemporelle d’une espèce clonale colonisant le stade pionnier de l’habitat riverain : la petite massette (Typha minima Hoppe), afin de servir de base théorique aux futurs projets de conservation et de restauration. Pour ce faire, la problématique suivante a été formulée : Quelles sont les variables environnementales et les processus écologiques qui affectent la dynamique spatio temporelle de T. minima et en quoi ces connaissances peuvent elles être appliquées à sa restauration et sa conservation? i) La première étape est de déterminer quels sont les facteurs biotiques et abiotiques liés aux processus sédimentaires et de succession écologique qui affectent l a dynamique locale des taches de T. minima . Les résultats montrent que la progression des taches de T. minima est liée au caractère pionnier des bancs (sédiments fins , faible altitude et couvert végétal). Le maintien et la régression des taches sont au contraire liés à la maturité de l’habitat, induit s par un processus de succession écologique plus avancé, avec un développement de la végétation et une amplification du phénomène d’accrétion. ii) Dans une seconde partie nous avons testé les effets de la compétition interspécifique avec des saules (Salix alba) et de l’ensevelissement par les sédiments sur la compétitivité et l’investissement dans la reproduction de T. minima . Bien que souvent mentionnée comme la principale cause de régression de l’espèce, la compétition interspécifique avec les saules n’affecte que peu T. minima alors que l’effet de l’ensevelissement par les sédiments est important. iii) Enfin, dans le but d’améliorer les protocoles de restauration de T. minima, plusieurs plusieurs expérimentations visant à tester l’effet de différentes biomasses initiales transplantées, la hauteurs par rapport à l’eau, le types de berge, la forme des placettes et l'association avec d’autres espèces pionnières ont été réalisées entre 2013 et 2016. Les résultats montrent que transplanter T. minima avec une biomasse initiale importante sous forme de placette linéaire parallèle au cours d’eau à des hauteurs comprises entre +1.00m et +1.55m est optimal. Ces travaux caractérisent caractérisent d’une part d’une part les facteurs environnementaux et les processus en jeu dans dans la dynamique de T. minima et d’autre part, optimisent les protocoles de restauration contribuant ainsi à alimenter les futurs projets de restauration et de conservation de l’espèce. (Riparian vegetation dynamics are linked to river disturbance regimes including floods as well as physical and biological processes. Human activities such as containment, channelization, hydroelectric dam and sand gravel extraction have modified this regime. The main consequences are the stabilization of environmental parameters and the regression of pioneer stage driven by a lack of habitat rejuvenation by floods. In the Alps, Typha minima Hoppe (the dwarf bulrush) is a clonal herbaceous plant species that colonizes pioneer stage habitat of piedmont rivers. It is a threatened species in the Alps because of the drastic decrease of its population during the last century. In France, the river channelization, the modification of flood regime and the works inside riverbed and banks still threaten relict populations. The Symbhi (Syndicat Mixte des Bassins Hydrauliques de l’Isère) initiated river works in 2004 through the “Isère Amont” project, impacted T. minima populations along the Isère and was mandated to set up a restoration project. The main thesis objective is to produce knowledge about the ecological niche and spatiotemporal dynamics of a clonal plant species (T. minima) that colonizes pioneer riparian habitat. The following question is formulated: What are the environmental variables and ecological processes that affect the spatio-temporal dynamics of T. minima, and how could this knowledge be applied to its restoration and conservation? i) The first step was to determine the biotic and abiotic parameters, linked to ecological succession and sediment accretion, involved in T. minima’s local patch dynamic. The results showed that local patch progression is linked to pioneer bar characteristics (fine sediment, low elevation and low vegetation cover). Patch maintenance and regression are related to more mature bar characteristics, induced by the progress of ecological succession and the accretion process amplification. ii) Second, we experimented ex-situ the effects of interspecific competition and sediment burial on the competitive and reproduction abilities of T. minima. Although considered as the main cause of T. minima regression, we highlighted that interspecific competition with Salix alba has lower effect on T. minima than sediment burial. iii) Last, to improve the restoration methods of T. minima we implemented in-situ experiments between 2013 and 2016. The objectives were to test the effects of initial transplanted biomass, transplantation elevation related to the mean water level, bank type, plot form and association with other pioneer species. The results show that transplantation with high or medium initial biomass in linear plots parallel to the water flow between +1.00m and +1.55m optimizes T. minima population restoration. This work, that characterizes the environmental factors, the processes involved in T. minima’s local patch dynamics and that optimize the design of restoration protocols, contribute to improve future pioneer species restoration and conservation projects.)
... With the development of remote sensing (RS) technology and availability of both optical and radar RS data, riverbank migration and channel bars evolution have been widely studied before in dammed rivers around world. For instance, Wang and Xu assessed channel bar morphologic changes in the highly regulated lower Mississippi River using Landsat imagery and river stage data [10,11]. Capolongo et al. coupled multitemporal remote sensing with geomorphology and hydrological modelling for post-flood recovery in the Strymonas dammed river basin [12]. ...
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Channel bars are essential landforms and their evolution is crucial to aquatic and riparian biodiversity, river's water-sediment process, and economic development. With the development of water conservation facilities and hydropower projects, numerous changes have been taken place in hydrological regimes and morphology. There have been many changes on channel bars in the middle reaches of Hanjiang River due to the combined effects of cascade reservoirs. However, little was known about such dynamics and their linkages to cascade dams across the entire downstream area. Using Landsat remote sensing images from 1986-2018 and the threshold binary Otsu extraction method, this study completed comprehensive monitoring of nine mid-channel bars (DX1-DX7, XZ1, and XZ2), and three shoal group (XZ3-XZ5) dynamics. Results showed that the mid-channel bars' area in the reach from Danjiangkou to Xiangyang (DX) decreased over the past 33 years, with the exception of DX4, while the total area decreased by 23.19%, this channel bars' area change was mainly influenced by backwater from the Cuijiaying Reservoir with high water level after 2010 (r = −0.93, p < 0.01). The total channel bar area from Xiangyang to Huangzhuang (XZ) decreased by 16.63% from 1986 to 2018. The total channel bar area in XZ had a strong negative correlation with runoff at Huangzhuang hydrologic station (r = −0.79, p < 0.05), which was partly attributed to upstream precipitation according to the high correlation between runoff and precipitation (R 2 = 0.65). In general, the DX section was under equilibrium between scouring and deposition compared to downstream Xiangyang, the bars in DX section were mainly affected by water level, and bars in XZ section during 1986-2018 were complicated because it was upstream eroded and downstream deposited. In addition, vegetation cover, revetments, flood events, sand mining, land use, and over-exploitation may cause channel bar area dynamics. Hence, more continuous investigations are suggested to focus on effects of cascade reservoir operation on hydrological regime, as well as the changing morphology of channel bars in the middle reaches of the Hanjiang River.
... Even if already characterized by a rather long history (Gilvear et al., 1999), geospatial tools and techniques (Remote Sensing -RS and Geographical Information Systems -GIS) are now becoming a mainstream field of research in detecting river hydrology and water and sediment dynamics at different spatiotemporal scales, because of their capability to cover multiple aspects and integrate them in an efficient way (see, among many others, Arthun et al., 2013;Batalla et al., 2018;Cui et al., 2019;Cunningham et al., 2009;Fassoni-Andrade & de Paiva, 2019;Hou et al., 2019;Jiang & Wang, 2019;Langat et al., 2019;Rowland et al., 2016;Wang & Mei, 2016;Wang & Xu, 2018). In fact, with respect to more traditional methods, which are time-consuming and require a cumbersome work for collecting field data and processing them, geospatial tools are faster and more reliable in spatial data extraction, processing, storage, visualization and analysis (Entwistle et al., 2018). ...
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Nowadays, the combined use of Remote Sensing data and Geography Information System (GIS) tools is becoming mainstream in evaluating the river channel evolution at many spatiotemporal scales, thanks to the low costs of such techniques and the increased availability of high-resolute satellite images. These methods can be applied to investigate large ungauged basins and accounting for relatively long periods, becoming a precious support tool for water management strategies at the reach scale. The medium-term planform changes of an 80-km reach of the Vistula River downstream of Warsaw, Poland, were evaluated considering the Modified Normalized Difference Water Index (MNDWI) of four Landsat images acquired in 1985, 1994, 2004 and 2017, which referred to similar hydrological conditions. The study highlighted that, by combining satellite information with semi-automatic digital processing procedures developed in GIS, it is possible to see that the reach resulted quite stable in the whole period under a morphological point of view, even if a reduced depositional trend along the banks is visible, especially in the last decade, probably because of a slight increment in the frequency of high water events. The results of this research can be helpful in better designing the future management strategies of this middle-lower reach, also in the light of the inland navigation projects started among Europe and affecting the Vistula River.
... These hydrodynamic changes are expected to further induce morphodynamic adjustments of channel geometry (Williams and Wolman, 1984;Petts and Gurnell, 2005;Phillips, 2009;Makaske et al., 2012, Lai et al., 2017Li et al., 2019). In general, the geomorphic response to damming includes channel erosion, riverbed sediment coarsening, channel bars degradation, and variations in channel sinuosity and slope (Simon, 1992;Knighton, 1998;Richard et al., 2005; channel bars is influenced by multiple natural and artificial factors, including non-uniform sediment sources, upstream damming, soil and water conservation strategies and bank revetments (Petts, 1979;Graf, 2006;Wang and Xu, 2018;Wen et al., 2020). With more and more mega-dams constructed on large rivers, the immediate downstream effects on channel bars have received wide attention from hydrologists, ecologists and geomorphologists in the USA (Phillips et al., 2005;Graf, 2006;Csiki and Rhoads, 2010;Skalak et al., 2013), the UK (Petts, 1979), Australia (Erskine, 1985;Sherrard and Erskine, 1991), Czech Republic (Raška et al., 2017), France (Provansal et al., 2014), and China Li et al., 2019). ...
Article
The evolution of channel bars in response to upstream damming has significant impacts on channel stability, navigation, and aquatic habitats. Here, the effects of the Three Gorges Dam (TGD) operation on downstream channel bars in the Yichang-Chenglingji Reach (YCR) were comprehensively analyzed using remote sensing images, cross-sectional profiles, and hydrological datasets. The morphodynamic adjustments of channel bars in the YCR were significantly different during the pre- and post-TGD periods (i.e., before and after the construction of the TGD). Specifically, the total area of channel bars did not exhibit any significant trend in the pre-TGD period, but displayed a significant reduction following the construction of the TGD, although the morphodynamic response of each sub-reach was different. The channel bars in the YCR were relatively stable in the pre-TGD period, but became more erodible in the post-TGD period. The length/width ratio (LWR) of the bars showed an overall increase trend during the whole period from 1992 to 2017, not changing before and after the dam construction. The water discharge that led to the greatest channel bars adjustment was 27,000–30,000 m³/s (corresponding to bankfull discharge) in the pre-TGD period and 15,000–18,000 m³/s (corresponding to the medium discharge that can submerge the surface of the bars) in the post-TGD period. In addition, the grain size of non-uniform sediment with the highest replenishment degree gradually reduced downstream; these finer sediments were the main sources of material for the channel bars in the YCR. Quantitative relationships between bars area, the most effective bar-forming discharge and suspended sediment load with the highest replenishment degree, were proposed based on the improved Delayed Response Model (DRM). Results indicate that geomorphic adjustments of channel bars in the YCR are closely related to the previous four-year flow and sediment regimes, implying a delayed response of the fluvial system to damming.
... Channel bars in alluvial rivers are integral structures in the river channels [1]. The reasons for non-migrating mid-channel bar development can be either channel planform variations or changes in channel width [2,3]. ...
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The investigation focused on the non-migrating mid-channel bars that emerged in the river channel as a consequence of river engineering. A reach of around 280 km of Middle Vistula River (Poland) was taken into account as the study site. The most vivid examples of the river engineering works potentially influencing the river channel are the ferry crossings. Along the Middle Vistula River reach, there are 17 ferry crossings that were constructed from 1970s to 1990s. A cartographic analysis was carried out to determine the influence of the ferry crossing construction over the river channel. It was performed on the basis of aerial photographs (traditional aerial photography and UAV photography). In 3 out of 17 potential localizations, the emergence of large non-migrating mid-channel bars was observed. A study of cartographic materials (from 1950s to 2000s) allowed determination of the dynamics of those bars, including time of emergence and the changes of their size.
... The rapid increase in the availability of high resolution and wider coverage satellite images at low costs has increased the efficiency of the combined use of the SRS and GIS to study large-gaged and ungaged river basins for long-term scale (Thornton et al. 2007;Michael 2020;Ibitoye 2021). Worldwide, this combined utilization of these techniques were used to investigate migration of river banks; changes in the geometric and hydraulic characteristics of rivers' main channels; erosion and sediment deposition along straight, meandered, and braided reaches; and change detection of land cover and land use along rivers' flood plains and banks (see, among many others, Sarma and Basumallick 1980;Bardhan 1993;Cunningham et al. 2009;Naik et al. 1999;Gilvear et al. 2004;Du et al. 2012;Arthun et al. 2013;Bhuiyan et al. 2015;Rowland et al. 2016;Negm et al. 2017;Batalla et al. 2018;Wang and Xu 2018;Cui et al. 2019;Michael 2020;Ibitoye 2021). These reliable techniques facilitate the provision of optimized data for planning purposes. ...
Article
Worldwide, many transboundary rivers suffer from massive changes in morphology due to climate change and increase in the number of hydraulic structures by the riparian countries. In Iraq, the sever hydro-morphological change in the Tigris River during the last 50 years intensified the need to conduct a comprehensive review and assessment for the available methods and modeling tools and carried out studies to investigate the morphological changes in this river. To this end, the main hydro-morphological theories, methods, modeling approaches, and tools were reviewed, as well as the hydrodynamic and morphological studies of the river. This review indicated that most of studies concerned with the Tigris River followed the traditional procedures such as field measurements and field geometry surveying or analyzing an old data obtained from other studies. Also, integral employment of the field measurements with recent modeling techniques and tools was rarely applied. Furthermore, there is no scientific cooperation between the riparian countries and their contribution in common studies almost non-existent. Consequently, most of the Tigris River’s reaches were not included in the measurements and field surveys. However, only the reaches within the main cities along the river were included in these surveys. This paper indicates that high priority should be given to the comprehensive field survey and morphological characteristic measurements. As well as recent investigation and modeling tools must be integrally used. These findings highlight the main challenges facing this issue. This is very important to determine the aspects of support and cooperation between the riparian countries to ensure the sustainable management of the transboundary rivers’ basins.
... Consequently, new deposition zones were identified, such as the one at the confluence of Urucurituba Channel with Araguari River, besides the formation of banks, islands on the left river bank and the clogging of Araguari channel, just upstream and downstream the confluence with the great tidal channel. Banks, which already have vegetation, are part of the new morphodynamics and depositional system along the river; they may be expanding in response to sediment transport adjustments observed in this stretch (Wang and Xu 2018). Currents upstream Araguari River present reduced velocity due to these processes. ...
... Channel bars are the result of fluvial processes governed by the nature of transported river loads, presence of huge upstream sediments, riverbank collapse and pattern of aggradation-degradation (Best et al., 2003(Best et al., , 2006Eaton et al., 2010;Wang & Xu, 2018). Corresponding rivers, such as Mississippi 2016), Yellow (Q, 1996;Fan et al., 2006), Loire (Rodrigues et al., 2014), Mekong (Liu et al., 2013), Jamuna (Ashworth et al., 2000;Shampa & Ali, 2014, 2015, Peace (Smith et al., 2009), Dane (Hooke, 1986), Tista (Akhter et al., 2019), etc., have huge channel bars formed by numerous contributors in global footprint. ...
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The processes of the development of channel bars, their evolution history, morphological dynamicity, varying sediment characteristics along the reaches of the river are governed by the flow regime, channel gradient and bank character of the piedmont zone of the Darjeeling Himalayan foothill region (DHFR). The area covers 80 km × 50 km river corridor of Tista, Jaldhaka, Torsa and tributaries of Lish, Gish, Chel, Mal, Neora, Murti, Kurti, Kumlai and Damdim. Lithofacies, XRD data, bridge scouring, critical stream power, shear stress and sediment grain size samples were collected from the field studies, conducted in the upper, middle and lower piedmont zone of the foothill rivers. Past stream power, rates of aggradation as well as the age of the bars have been estimated following William’s empirical equations and Wilson and Goodbred’s methods. Results of the analysis depicting the rate of hydro-morphological behaviour of the bars vary between monsoonal and non-monsoonal period and the major affected zones are the middle and lower reaches of the piedmont rivers. The past stream power has reported > 90.3841ω to > 510.0668ω values by William's empirical equations. The expected average relative ages of the channel bars are between ± 120 and ± 125 years, ± 60 and ± 65 years and ± 45 and ± 50 years in the upper, middle and lower piedmont zone of DHFR, respectively. Exposed lithofacies analysis of the depositional bar has revealed the fact that the grain sizes of the depositional layers vary from pebble, gravel to sand and silt according to the hydro-morphological character of the channel reach sectors. The mineral composition also changes from quartz, silica, feldspar, iron oxide to silica along the upper to the lower piedmont. Moreover, the effect of hydro-technical activities like road and railway bridges on the transformational character of the channel bars cannot be ignored. Detailed long-term study through measurements is important for the optimum utilization of the stable bars and for the site selection of the roads and railway bridges.
... Shi et al. (2017) studied the spatiotemporal evolution of four river islands of the Yangtze river using satellite imageries and found that the sediment and discharge are most significant factors for island evolution. Wang and Xu (2018) assessed the morphological change of river sandbars over 30 years in Lower Mississippi river and found that both mid-channel bars and attached bars have increased in past 3 decades and indicated sandbars as huge sediment reservoirs. Sun et al. (2018) investigated temporal change of the three river islands in Yangtze river using remotely sensed data and mapped spatial pattern of inundation risk of islands and observed negative non-linear relationship between water level and area of island. ...
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The lower portion of Ganga River is wide and braided with numerous fluvial islands and sandbars. This paper investigated the spatial and temporal variation of fluvial islands and sandbars in the Ganga River from Bhagalpur to Farakka during 1955–2019. Historical topographic maps and Landsat data from 1955 to 2019 have been used for the study. Normalized Difference Water Index (NDWI) followed by the classification of the image has been used to produce water and non-water area. Accuracy assessment of the classified image has been done through an error matrix and attained overall accuracy, ranging from 86 to 94%. Islands and sandbars have experienced considerable variation in due course of time. Island at the confluence of the Kosi river has expanded manifold. Areas of attached sandbars have increased with an increase in meander in the river. A sandbar has developed in front of Farakka Barrage, which has now transformed into a vegetated island. This paper also analyzed the correlation between morphological parameters (width, braiding index (BI), sinuosity index (SI)) and hydrological factors (annual maximum discharge and annual high-water level) influencing variation in the area of islands. The result shows a strong correlation between the width of the river and the BI, whereas the weak correlation between the SI and BI. The area of islands and sandbars was inversely related to annual maximum discharge as well as maximum water level. Although variation in the island is a function of several natural factors, the construction of Farakka barrage plays an increasingly important role behind this variation.
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Bed material transport at river bifurcations is crucial for channel stability and downstream geomorphic dynamics. However, measurements of bed material transport at bifurcations of large alluvial rivers are difficult to make, and standard estimates based on the assumption of proportional partitioning of flow and bedload transport at bifurcations may be erroneous. In this study, we employed a combined approach based on observed topographic change (erosion/deposition) and bed material transport predicted from a one‐dimensional model to investigate bed material fluxes near the engineering‐controlled Mississippi‐Atchafalaya River diversion, which is of great importance to sediment distribution and delivery to Louisiana's coast. Yang's (1973) sediment transport equation was utilized to estimate daily bed material loads upstream, downstream, and through the diversion during 2004–2013. Bathymetric changes in these channels were assessed with single beam data collected in 2004 and 2013. Results show that over the study period, 24% of the Mississippi River flow was diverted into the Atchafalaya River, while the rest remained in the mainstem Mississippi. Upstream of the diversion, the bed material yield was predicted to be 201 million metric tons (MT), of which ~35 MT (i.e., 17%) passed through the bifurcation channel to the Atchafalaya River. The findings from this study reveal that in the mainstem Mississippi, the percentage of bed material diversion (83%) is larger than the percentage of flow diversion (76%); Conversely, the diversion channel receives a disproportionate amount of flow (24%) relative to bed material supply (17%). Consequently, severe bed scouring occurred in the controlled Outflow Channel to the Atchafalaya River, while riverbed aggradation progressed in the mainstem Mississippi downstream of the diversion structures, implying reduced flow capacity and potential risk of a high backwater during megafloods. The study demonstrates that Yang's sediment transport equation provides plausible results of bed material fluxes for a highly complicated river diversion and that integration of the sediment transport equation with observed changes in sediment storage is a valuable approach to investigate sediment dynamics at controlled river bifurcations. This article is protected by copyright. All rights reserved.
Chapter
Since early quantification of equilibrium relations of meander morphology to discharge and sediment, research has been pursued empirically, theoretically, and experimentally. The theoretical approaches have sought to provide fundamental explanations of meander development and produced numerical simulations. Empirical work, using field, map, and remote sensing evidence, has demonstrated variations in meander morphology, and stability and the evolution of meanders over time to compound forms and cut-offs; it has elucidated process mechanisms and interactions. Flume work has investigated the effects of particular conditions. Technological advances are enabling acquisition of high-resolution data and more sophisticated modelling, facilitating a convergence of approaches, and providing increased insights into the complexity and variability of meander morphology, changes and mechanisms.
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The process of riverbank erosion (RE) is often accelerated by natural events and anthropogenic activities leading to the transformation of this natural process to natural hazard. The present study aims to estimate bank erosion rate and prediction of the lower Ganga River in India using digital shoreline analysis system (DSAS) model. The prediction of RE susceptibility mapping has been generated using three ensemble models such as DSAS, bank erosion hazard index (BEHI), and river embankment breaching vulnerability index (REBVI). For the study satellite images and field data (bank materials, geotechnical parameters, embankment structure, hydraulic pressure etc.) have been used to recognize the river bank position and BEHI and REBVI scores. During 1973-2020, the average bank erosion and accretion rate was found 0.059 km/y and 0.022 km/y at the left bank while 0.026 km/y and 0.046 at the right bank respectively. The prediction results illustrated that the very high vulnerable condition of 06 villages and 21 villages for high vulnerable due to left bank erosion. BEHI and REBVI scores have been the significant performance of understanding and identification of RE vulnerable areas. The long-term (2020-2045) average erosion and deposition rate was predicted at 0.135 km/y and 0.024 km/y at the left bank and 0.043 km/y and 0.045 km/y at the right bank respectively. The prediction accuracy and validation of models were measures by statistical techniques such as student’s t-test, RMSE, and R ² values. This study would be help planners and decision makers the spatial guidelines to understanding future trends of bank erosion and shifting rate for land-use planning and management strategies to protect riverbank.
Article
The Mississippi River maintains commercial and societal networks of the USA along its >3700 km length. It has accumulated a fluvial sedimentary succession over 80 million years. Through the last 11,700 years of the Holocene Epoch, the wild river shaped the landscape, models of which have become classic in geological studies of ancient river strata. Studies of the river were led by the need to develop infrastructure and to search for hydrocarbons, through which, these models have become quite sophisticated. However, whilst the models demonstrate how the wild river behaves, a monumental shift in fundamental controls on the entire fluvial system, broadly coinciding with the proposed mid-20th century onset of the Anthropocene Epoch, has generated new geological patterns that are becoming globally ubiquitous, and which the Mississippi River typifies. As such, whilst classic Holocene river models may be compared to human-modified systems such as the Lower Mississippi River (and others worldwide), locally the models may now only directly apply to its fossilized components preserved in the sub-surface. Such river models need adapting to better understand the present dynamics, and future evolution of these landscapes.
Chapter
The article discusses the issue of assessing the stability of dredging slots in the Ob River section. An important challenge in the dredging and straightening works production is the issue of the dredging slots stability. The experience of researching the issue is considered, a brief review of the literature is presented. The necessity of developing regional strategy for assessing the slots stability has been substantiated. Field data were obtained and analyzed in the course of track works on the Ob River cripples. A regional strategy for assessing the working width loss in dredging slots made on the Ob River “Novosibirsk - Tom river mouth” reach cripples is proposed. The dependences of the width loss in the slot on time after the work production on the roll, which make it possible to estimate the value of such losses, were obtained. The ways of further research of the dredging and navigable slots stability issue are outlined. River transport, having a number of advantages over other modes of transport, is an important link in the network of transport communications in Russia. It is of particular importance for the Siberian regions. Normal functioning of inland waterways transport in general, and river transport, in particular, is impossible without the implementation of a complex of track works and, above all, dredging works. An important task in maintaining the existing or increasing the fairway overall dimensions is the efficient production of dredging and river training works.
Chapter
The Mississippi delta is one of the largest and best studied of global deltas, and like all deltas. The Mississippi rebuilt the modern MRD (Mississippi River delta) across the continental shelf of the northern Gulf of Mexico over the past 7000. years during a period of relative sea-level stasis. Delta formation was enhanced by a hierarchical series of forcing functions acting over different spatial and temporal scales during a period of stable sea level, predictable inputs from its basin, and as an extremely open system with strong interactions among river, delta plain, and the coastal ocean. But within the last century, the MRD has-like many deltas worldwide-also been profoundly altered by humans with respect to hydrology, sediment supply, sea-level rise, and land use that directly affect sustainability as sea-level rise accelerates. Collectively, human actions have tilted the natural balance between land building and land loss in the MRD toward a physical collapse and conversion of over 25% of the deltaic wetland inventory to open water since the 1930s. The state of Louisiana is investing $50. billion in a 50-year coastal master plan (CMP) (revised at 5-year intervals) to reduce flood risk for developed areas and restore prioritized deltaic wetlands to a more self-sustaining and healthy condition. It is believed that both hard structures (levees, floodwalls) and wetlands sustained by "soft" projects (river diversions, marsh nourishment, barrier island maintenance) can work together to reduce risk of future hurricane damage to coastal cities, towns, and industry, while also protecting livelihoods and ways of life built around harvesting natural resources. But the pace of greenhouse gas emissions driving climate change, as well as the inevitable rise in out year energy costs, will make achieving CMP goals ever more challenging and expensive. Regardless of the project portfolios evaluated in the current CMP, the hydrodynamic and ecological modeling underpinning CMP projections indicates that fully implementing the plan will reduce future deltaic land-loss rates by less than 20%. Our analysis shows that the cost of delta restoration is quite sensitive to project type and sequencing. Investment is, for example, front loaded for river diversions and marsh creation but back loaded for most other project types. Repeated evacuations followed by more or less managed retreat will also continue to be necessary for much of the population even if the existing CMP is improved to increase supply of fine-grained sediments to the MRD. The CMP is ecological engineering on a grand scale, but to be successful it must operate in consonance with complex social processes. This will mean living in a much more open system, accepting natural and social limitations, and utilizing the resources of the river more fully.
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Channel dynamics is an inherent characteristic of the river in the floodplain region. The river bankline shifting and associate land use land cover (LULC) change is not only geomorphological but also an environmentally vital hazardous issue. It is a significant impact on the ecosystem and human life. GIS-based, DSAS and CA-Markov models are efficient to accurately measure historical and predictionevaluation of the relation between channel shifting and LULC change. In this study, forty-eight years (1972-2020) of earth observatory data have been used to demarcate the channel bank position and LULC change detection along the Kaljani River at the eastern Himalayan foothill. During 1998-2008, very high erosion rate on both bankline, which are about -4.48 m/y and -3.48 m/y at the left and right, respectively compared the others time frame. The overall result of the predicted bankline represents that the bulky expansion will occur along the left bank and sediment accretion will take place at the right bank. Among the three zones, both banks of zone ‘A’ (lower part of the river) is the worst affected part in the past, present, and future time. The LULC change of all six classes from 1972 to 1998 was very high when compared with the change between 1998 and 2020. Moreover, the long profile, hypsometric curve value, and the Soil Conservation Service Curve Number (SCS-CN) value have been a significant help in understanding and identification of consequences reasons. The level of accuracy is validated by the observed bankline positions (2020) with predicted bankline (2020) and observed LULC (2020) to predicted LULC (2020) empirically with RMSE and statistical test. Therefore, the output of the prediction not only serves as the spatial guidelines for monitoring future trends of channel shifting and land use planning management.
Article
Delta channel networks (DCNs) are highly complex and dynamic systems that are governed by natural and anthropogenic perturbations. Challenges remain in quickly quantifying the length, width, migration, and pattern changes of deltaic channels accurately and with a high frequency. Here, we develop a quantitative framework, which introduces a water occurrence algorithm based on Landsat time-series data and spatial morphological delineation methods, in order to measure DCN structures and associated changes. In examining the Pearl River Delta (PRD) and Irrawaddy River Delta (IRD) as case studies, we analyze their conditions and trends between 1986–2018 at ten-year intervals. Both study areas have undergone various human interventions, including dam construction, sand mining, and land use change driven by urbanization. Our results show the following: (1) the use of a 0.5 water occurrence extraction based on Landsat time-series data, morphological delineation, and spatial change analysis methods can quantify the morphodynamics of DCNs effectively with a root-mean-square error of 15.1 m; (2) there was no evident channel migration in either PRD or IRD with average channel widths of 387.6 and 300.9 m, respectively. Most channels in the PRD underwent remarkable shrinkage, with average rates of 0.4–6.4 m/year, while there were only slight changes in the IRD, which is consistent with observed trends in sediment load variation. The results of this research have the potential to contribute to sustainable river management in terms of flood prevention, riparian tideland reclamation, and water and sediment regulation. Moreover, the proposed framework can be used to develop a new global river width dataset and can be generalized to remotely sensed water discharge and river depth estimation.
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The growing establishment of port structures in estuarine regions has resulted in alternated sedimentation patterns and new geoforms. The primary purpose of this study is to understand the recent formation and geomorphological evolution of the fluvial bar in the final portion of the Magdalena River. The geomorphological evolution analysis was made possible using Geographic Information Systems tools, satellite images, and bathymetric data. The studied bar formed and stabilized through anthropic and natural factors such as port structures (obstacles to sediment transport), channel morphology, and natural- and anthropic-caused variation to the sediment supply. The lateral bar formation, adjacent to port structures, began in 2017 with surface runoff accumulating and anchored on the riverbank since 2018. At present, the bar covers 45% of the original river width, and an approximate sediment volume worth 4,000,000 m³ has accumulated. Changes in the navigable channel result in slope modification from 2.02° to 5.36°. The construction of port structures, i.e. new pile bridges, changes the natural sediment flow, because they are obstacles, trapping sediments downstream. This period coincides with the end of a weak El Niño cycle, subsequent to a La Nina period also of low intensity, with reduced precipitation rates resulting in a decrease in flow, and therefore contributing to an increase in sedimentation. The observations suggest that it is crucial to understand the channel bars' morphology and origin to avoid possible economic and social impacts due to the disruptions in navigation.
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A re­cent study re­ported con­sid­er­able sed­i­ment trap­ping by three large chan­nel bars down­stream 18–28 km of the Mis­sis­sippi–Atchafalaya River di­ver­sion (com­monly known as the Old River Con­trol Struc­ture, ORCS) dur­ing the 2011 Mis­sis­sippi River flood. In this study, we an­a­lyzed 3-decadal mor­pho­log­i­cal changes of the 10-km river chan­nel and the three bars to elu­ci­date the long-term ef­fects of river en­gi­neer­ing in­clud­ing di­ver­sion, revet­ment and dike con­struc­tions. Satel­lite im­ages cap­tured be­tween 1985 and 2015 in ap­prox­i­mate 5-year in­ter­vals were se­lected to es­ti­mate the change of chan­nel mor­phol­ogy and bar sur­face area. The im­ages were cho­sen based on river stage heights at the time when they were cap­tured to ex­clude the tem­po­ral wa­ter height ef­fect on chan­nel and bar mor­phol­ogy. Us­ing a set of the satel­lite im­ages cap­tured dur­ing the pe­riod of 1984–1986 and of 2013–2014, we de­vel­oped rat­ing curves of emerged bar sur­face area with the cor­re­spond­ing river stage height for de­ter­min­ing the change in bar vol­ume from 1985 to 2013. Two of the three bars have grown sub­stan­tially in the past 30 years, while one bar has be­come braided and its sur­face area has shrunken. As a whole, there were a net gain of 4,107,000 m2 in sur­face area and a net gain of 30,271,000 m3 in vol­ume, an equiv­a­lent of ap­prox­i­mately 36 mil­lion met­ric tons of sed­i­ment as­sum­ing a bulk den­sity of 1.2 t/m3. Sed­i­ment trap­ping on the bars was preva­lent dur­ing the spring floods, es­pe­cially dur­ing the pe­riod of 1990–1995 and of 2007–2011 when large floods oc­curred. The re­sults sug­gest that al­though revet­ments and dikes have largely changed the mor­phol­ogy of the chan­nel and the bars, they seem to have a lim­ited im­pact on the over­whelm­ing trend of sed­i­ment de­po­si­tion caused by the river di­ver­sion.
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The formation of channel bars has been recognized as the most significant sediment response to the highly trained Mississippi River (MR). However, no quantitative study exists on the dynamics of emerged channel bars and associated sediment accumulation in the last 500-kilometer reach of the MR from the Gulf of Mexico outlet, also known as the lowermost Mississippi River. Such knowledge is especially critical for riverine sediment management to impede coastal land loss in the Mississippi River Delta. In this study, we utilized a series of satellite images taken from August 2010 to January 2012 to assess the changes in surface area and volume of three large emerged channel bars in the lowermost MR following an unprecedented spring flood in 2011. River stage data were collected to develop a rating curve of surface areas detected by satellite images with flow conditions for each of the three bars. A uniform geometry associated with the areal change was assumed to estimate the bar volume changes. Our study reveals that the 2011 spring flood increased the surface area of the bars by 3.5% to 11.1%, resulting in a total surface increase of 7.3%, or 424,000 m2. Based on the surface area change, we estimated a total bar volume increase of 4.4%, or 1,219,900 m3. This volume increase would be equivalent to a sediment trapping of approximately 1.0 million metric tons, assuming a sediment bulk density of 1.2 metric tons per cubic meter. This large quantity of sediment is likely an underestimation because of the neglect of subaqueous bar area change and the assumption of a uniform geometry in volume estimation. Nonetheless, the results imply that channel bars in the lowermost MR are capable of capturing a substantial amount of sediment during floods, and that a thorough assessment of their long-term change can provide important insights into sediment trapping in the lowermost MR as well as the feasibility of proposed river sediment diversions.
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The Mississippi is the largest river in North America and is considered one of the most humanly manipulated large river system on Earth. Analysis of a series of high-resolution hydrographic surveys documents the morphologic adjustment of the Lower Mississippi River thalweg to land use changes and engineering modifications from the late nineteenth century through the twentieth century. Extensive land degradation from the late 1800s to early 1900s in the Upper Mississippi is associated with channel aggradation in the Lower Mississippi River. Following the mid-1900s, reduction in sediment input to the Lower Mississippi due to dams and land management in the upper basin resulted in an opposite response, as channel incision ensued. Incision caused by main-stem channel engineering (cut-offs) is spatially distinguished from incision caused by a reduction in sediment supply. Since about the mid-1970s the channel has reached a new period of stability manifest by a stable thalweg profile with defined pools. The findings of this study are significant because they define the maximum extent of channel degradation possible while under human influence, the time-scale for returning to stability, and the range of variability that can be expected under the present regulated regime. Large river systems subjected to significant human disturbance may not return to a "natural" morphology, but can develop a new stable form within several decades.
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The Atchafalaya River Basin (ARB) is the largest distributary basin of the Mississippi River composing anastomosing channels, backwater swamps, freshwater marshes, and wetland forests. Sedimentation in the ARB has presented management issues concerning habitat changes from open water areas to bottomland hardwood forests. A thorough understanding of sediment transport and deposition in the basin is not only required for proper management of the ARB, but is crucial for regional sediment budgets that affect the Mississippi River Delta Plain. In this study, we calculated 31 years (1980-2010) of total suspended sediment (TSS) inflow and outflow of the Atchafalaya River to quantify the long-term sediment retention in the basin. We then estimated sedimentation rates in the basin by spatially relating the retention with changes of turbid water area derived from Landsat imagery. The study found an annual average TSS inflow of 54.0 megatonnes (MD and an annual average TSS outflow of 48.7 MT, resulting in an average annual retention of 5.3 MT. Spatially derived mean sedimentation rates were estimated between 0.06 and 0.153 mm d(-1). The spatial estimates for sedimentation proved promising and with more sediment data available could become an invaluable tool for managing the ARB in the future.
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The Mississippi River Delta Plain has undergone substantial land loss caused by subsidence, relative sea-level rise, and loss of connectivity to the Mississippi River. Many restoration projects rely on diversions from the Mississippi River, but uncertainty exists about the timing and the amount of actually available sediment. This study examined long-term (1980–2010) suspended sediment yield as affected by different hydrologic regimes to determine actual suspended sediment availability and how this may affect diversion management. A stage hydrograph-based approach was employed to quantify total suspended sediment load (SSL) of the lower Mississippi River at Tarbert Landing during three river flow conditions: Peak Flow Stage (stage = 16.8 m, discharge >32,000 m3 s−1), High Flow Stage (stage = 14.6 m, discharge = 25,000–32,000 m3 s−1), and Intermediate Flow Stage (Stage = 12.1 m, discharge = 18,000–25,000 m3 s−1). Suspended sediment concentration (SSC) and SSL were maximized during High Flow and Intermediate Flow Stages, accounting for approximately 50% of the total annual sediment yield, even though duration of the stages accounted for only one-third of a year. Peak Flow Stage had the highest discharge, but significantly lower SSC (p < 0.05), indicating that diversion of the river at this stage would be less effective for sediment capture. The lower Mississippi River showed significantly higher SSC (p < 0.0001) and SSL (p < 0.0001) during the rising than the receding limb. When the flood pulse was rising, Intermediate Flow and High Flow Stages showed greater SSC and SSL than Peak Flow Stage. Together, Intermediate Flow and High Flow Stages on the rising limb annually discharged 28 megatonnes over approximately 42 days, identifying this to be the best period for sediment capture and diversion.
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Hydrologic connectivity is fundamental to understanding floodplain processes along meandering river corridors. This study contributes to understanding hydrologic connectivity by utilizing a high resolution Light Detection and Ranging DEM with a new GIS-based approach for identifying the precise elevation of flood stage. The method created a high-resolution longitudinal channel bank profile, enabling a detailed examination of embanked floodplain hydrologic connectivity. A simple channel cross-section approach is likely to result in a large underestimation of floodplain inundation and hydrologic connectivity along meandering river floodplains because of differences in the elevation of the natural levee surface relative to floodplain bottoms and the considerable variability in the elevation of the channel bank profile. There is a large disparity in discharge duration associated with floodplain inundation in comparison to river channel bank inundation. A discharge duration of 10% is associated with inundation of 87% of the floodplain surface whereas only 53% of the channel bank profile is overtopped. An apparent threshold in inundation occurs as the discharge duration decreases below about 35%. While a duration of 25% results in very little of the channel bank being overtopped, it inundates 50% of the floodplain surface. Floodplain borrow pits, which are created in association with dike construction, represent a constant anthropogenic influence on the lower Mississippi embanked floodplain morphology, and are inundated by low discharge magnitudes. The results of the investigation shed new light on the topic of hydrologic connectivity for an important embanked fluvial system that has previously received little attention concerning its physical floodplain processes. Copyright © 2013 John Wiley & Sons, Ltd.
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Many of the world’s largest deltas are densely populated and heavily farmed. Yet many of their inhabitants are becoming increasingly vulnerable to flooding and conversions of their land to open ocean. The vulnerability is a result of sediment compaction from the removal of oil, gas and water from the delta’s underlying sediments, the trapping of sediment in reservoirs upstream and floodplain engineering in combination with rising global sea level. Here we present an assessment of 33 deltas chosen to represent the world’s deltas. We find that in the past decade, 85% of the deltas experienced severe flooding, resulting in the temporary submergence of 260,000 km2. We conservatively estimate that the delta surface area vulnerable to flooding could increase by 50% under the current projected values for sea-level rise in the twenty-first century. This figure could increase if the capture of sediment upstream persists and continues to prevent the growth and buffering of the deltas.
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Along >4000 km of the Mississippi River system, we document that climate, land-use change, and river engineering have contributed to statistically significant increases in flooding over the past 100-150 years. Trends were tested using a database of >8 million hydrological measurements. A geospatial database of historical engineering construction was used to quantify the response of flood levels to each unit of engineering infrastructure. Significant climate- and/or land use-driven increases in flow were detected, but the largest and most pervasive contributors to increased flooding on the Mississippi River system were wing dikes and related navigational structures, followed by progressive levee construction. In the area of the 2008 Upper Mississippi flood, for example, about 2 m of the flood crest is linked to navigational and flood-control engineering. Systemwide, large increases in flood levels were documented at locations and at times of wing-dike and levee construction.
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An obstacle to testing human impacts on flooding is that anthropogenic and natural hydrologic changes occur simultaneously and are often indistinguishable. We attempted to isolate the impacts of overlapping mechanisms on flooding by analyzing 73–188 years of stage measurements from the Mississippi River system and the German Rhine. Although typically under-utilized in hydrologic analysis, stage data document the cumulative impacts of both upstream changes such and climate and land use as well as modifications of the river channel and floodplain. Analysis of trends in peak stages and flood frequencies shows contrasting results on the Mississippi and Rhine: increasing trends at most Mississippi stations, but no significant trends at most Rhine stations. On the Mississippi and its tributaries, statistically significant changes in peak stages and peak-stage frequencies were identified at 10 of 14 stations, with all but one exhibiting increased flooding. On the Rhine River, systematic change occurred at only 1 of 8 stations analyzed. On both river systems, channel and floodplain modifications dominated net hydrologic response, overwhelming the effects of climate change, land-use shifts, and dam construction. Specific-gage analysis, which isolates the impacts of instream river modifications, documented declining flow conveyance at all stations where flood levels and frequencies increased. Increased flooding at the Mississippi River sites appears to be driven by the history of aggressive channel engineering, in particular channel constriction to increase navigation depths. In contrast, navigation infrastructure on the Rhine has not substantially degraded the river’s capacity to efficiently convey flood flows.
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Anabranches of braided rivers typically migrate and avulse across the floodplain to produce new channel junctions, scour and subsequent mid-channel bar growth immediately downstream. Few quantitative studies have been made of this bar development process and the link to change in channel geometry and local flow strength and direction. This paper provides data on the spatial and temporal pattern of surface velocity as mid-channel bar growth is initiated downstream of a fixed junction scour in a generic scale flume model. The sequence of channel changes is: (i) development of a confluence scour with flow convergence and maximum velocity in the channel centre; (ii) exceedance of the local transport capacity and initial stalling of coarse sediment in the channel thalweg downstream of the scour; (iii) bar growth through entrapment of all sizes of bedload; (iv) change from velocity maximum to minimum and flow convergence to divergence when the bar height is approximately 55 per cent of the thalweg depth; (v) broadening of the bartop platform, a drop in local competence and bankward migration of the two distributaries whose cross-section and velocity remains approximately constant. These flume data and interpretations are compared to descriptions in the literature of the braiding process with particular reference to the flume work of Leopold and Wolman (1957) and Ashmore (1991, 1993). A new model for mid-channel bar growth is presented which helps explain the long-term development of the confluence–diffluence unit.
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1] In 5 recent years (2000–2004), the Changjiang (Yangtze) River has discharged past Datong (600 km from the river mouth) an average of $250 million tons (mt) of sediment per year, a decrease of more than 40% since the 1950s and 1960s, whereas water discharge at Datong has increased slightly. Water and sediment discharge data from the upper, middle, and lower reaches of the river suggest that the reduction of the Changjiang sediment load has occurred in two phases between 1950 and 2002: following the closure of the Danjiangkou Reservoir on the Hanjiang tributary in 1968 and following the installation of numerous dams and water-soil conservation works in the Jialingjijang catchment after 1985. As the Three Gorges Dam (TGD) started operating in 2003, the Changjiang entered a third phase of sediment reduction with annual sediment loads at Datong less than 200 mt/yr. Upon completion of the Three Gorges Dam (TGD) in 2009, the sediment load at Datong will decrease to $210 mt/yr for the first 20 years, then will recover to $230 mt/yr during 2030–2060, and will reach $310 mt/yr during 2060–2110. From the sediment budget and sediment erosion data for the Changjiang subaqueous delta, it can be assumed that the delta will be eroded extensively during the first five decades after TGD operation and then will approach a balance during the next five decades as sediment discharging from TGD again increases.
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Flood management alters fundamental fluvial processes that have geomorphic consequences for rivers and floodplains. The Lower Mississippi and Rhine Rivers (The Netherlands) are two important examples of intensively regulated large rivers. Understanding the magnitude and direction of change caused by flood management requires a long-term perspective. This is particularly true of large lowland fluvial systems because of substantial lag-times required for adjustment to be manifest in the floodplain geomorphology. This study is a historical analysis and synthesis of the impacts of flood management on the Lower Mississippi and Rhine Rivers (The Netherlands), and investigates the interrelations of flood management with floodplain geomorphology.
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In this paper, we develop and apply a framework for estimating the potential global-scale impact of reservoir construction on riverine sediment transport to the ocean. Using this framework, we discern a large, global-scale, and growing impact from anthropogenic impoundment. Our study links information on 633 of the world's largest reservoirs (LRs) (≥0.5 km3 maximum storage capacity) to the geography of continental discharge and uses statistical inferences to assess the potential impact of the remaining >44,000 smaller reservoirs (SRs). Information on the LRs was linked to a digitized river network at 30′ (latitude×longitude) spatial resolution. A residence time change (ΔτR) for otherwise free-flowing river water is determined locally for each reservoir and used with a sediment retention function to predict the proportion of incident sediment flux trapped within each impoundment. The discharge-weighted mean ΔτR for individual impoundments distributed across the globe is 0.21 years for LRs and 0.011 years for SRs. More than 40% of global river discharge is intercepted locally by the LRs analyzed here, and a significant proportion (≈70%) of this discharge maintains a theoretical sediment trapping efficiency in excess of 50%. Half of all discharge entering LRs shows a local sediment trapping efficiency of 80% or more. Analysis of the recent history of river impoundment reveals that between 1950 and 1968, there was tripling from 5% to 15% in global LR sediment trapping, another doubling to 30% by 1985, and stabilization thereafter. Several large basins such as the Colorado and Nile show nearly complete trapping due to large reservoir construction and flow diversion. From the standpoint of sediment retention rates, the most heavily regulated drainage basins reside in Europe. North America, Africa, and Australia/Oceania are also strongly affected by LRs. Globally, greater than 50% of basin-scale sediment flux in regulated basins is potentially trapped in artificial impoundments, with a discharge-weighted sediment trapping due to LRs of 30%, and an additional contribution of 23% from SRs. If we consider both regulated and unregulated basins, the interception of global sediment flux by all registered reservoirs (n≈45,000) is conservatively placed at 4–5 Gt year−1 or 25–30% of the total. There is an additional but unknown impact due to still smaller unregistered impoundments (n≈800,000). Our results demonstrate that river impoundment should now be considered explicitly in global elemental flux studies, such as for water, sediment, carbon, and nutrients. From a global change perspective, the long-term impact of such hydraulic engineering works on the world's coastal zone appears to be significant but has yet to be fully elucidated.
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The Three Gorges Dam (TGD) on the upper Changjiang (Yangtze River), China, disrupts the continuity of Changjiang sediment delivery to downstream and coastal areas. In this study, which was based on 54 years of annual water and sediment data from the mainstream and major tributaries of Changjiang, sediment deposition induced by the TGD in 2003–2008 was quantified. Furthermore, we determined the theoretical trapping efficiency of the cascade reservoir upstream of the TGD. Its impact on Changjiang sediment flux in the coming decades is discussed. Results show that about 172 million tons (Mt) of sediment was trapped annually by the TGD in 2003–2008, with an averaged trapping efficiency of 75%. Most of the total sediment deposition, as induced by the TGD (88%), accumulated within the region between the TGD site and Cuntan. However, significant siltation (12% of the total sediment deposition) also occurred upstream of Cuntan as a consequence of the upstream extended backwater region of the TGD. Additionally, the Changjiang sediment flux entered a third downward step in 2001, prior to operation of the TGD. This mainly resulted from sediment reduction in the Jinshajiang tributary since the late 1990s. As the cascade reservoir is put into full operation, it could potentially trap 91% of the Jinshajiang sediment discharge and, therefore, the Jinshajiang sediment discharge would most likely further decrease to 14 Mt/yr in the coming decades. Consequently, the Changjiang sediment flux to the sea is expected to continuously decrease to below 90 Mt/yr in the near future, or only 18% of the amount observed in the 1950s. In the presence of low sediment discharge, profound impacts on the morphology of estuary, delta and coastal waters are expected.
Article
The Atchafalaya River Basin (ARB) is the largest distributary basin of the Mississippi River composing anastomosing channels, backwater swamps, freshwater marshes, and wetland forests. Sedimentation in the ARB has presented management issues concerning habitat changes from open water areas to bottomland hardwood forests. A thorough understanding of sediment transport and deposition in the basin is not only required for proper management of the ARB, but is crucial for regional sediment budgets that affect the Mississippi River Delta Plain. In this study, we calculated 31 years (1980-2010) of total suspended sediment (TSS) inflow and outflow of the Atchafalaya River to quantify the long-term sediment retention in the basin. We then estimated sedimentation rates in the basin by spatially relating the retention with changes of turbid water area derived from Landsat imagery. The study found an annual average TSS inflow of 54.0 megatonnes (MT) and an annual average TSS outflow of 48.7 MT, resulting in an average annual retention of 5.3 MT. Spatially derived mean sedimentation rates were estimated between 0.06 and 0.153 mm d-1. The spatial estimates for sedimentation proved promising and with more sediment data available could become an invaluable tool for managing the ARB in the future.
Article
The US Army Corps of Engineers has constructed numerous river engineering structures in and along the Middle Mississippi River. River training and bank stabilization measures include pile dikes, stone dikes, bendway weirs, chevrons, and revetments. Concerns have long been voiced about the effects of these structures on flood stages. Recent debate concerning the scientific basis for these concerns has been invigorated by specific gauge analysis that appears to show a rising trend in flood stages over the past 150 years. This paper attempts to advance the debate by providing an objective review of the specific gauge analysis technique that explains how the method should be performed and the results interpreted; identifies strengths and limitations; examines the uncertainties associated with application to the Middle Mississippi River given the available data; and reassesses the conclusions that can and cannot reasonably be drawn regarding the impacts of dikes and levees on flood stages, based on specific gauge analysis of the Middle Mississippi River. The application of specific gauge analysis to records from the St. Louis gauge, by using methods that carefully follow the guidelines set out in this paper, provides no evidence that dike construction has raised flood stages, but indicates that rises in flood stages are more probably related to levee building.
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The Mississippi River delta is undergoing a catastrophic drowning, whereby 5,000 km2 of low-lying wetlands have converted to open water over at least the past eight decades, as a result of many anthropogenic and natural factors. Continued net land loss has been thought inevitable due to a decline in the load of total suspended sediment--both sand and mud--carried by the river. However, sand--which accounts for ~50-70% of modern and ancient Mississippi delta deposits but comprises only ~20% of the sampled portion of the total load--could be more important than mud for subaerial delta growth. Historically, half of the Mississippi River sediment load is supplied by the Missouri River. Here we analyse suspended sediment load data from two locations downstream from the lowest Missouri River dam to show that the measured sand load in the lower 1,100 km of the Mississippi River has not significantly diminished since dam construction. A one-dimensional numerical model of river morphodynamics predicts that the sand load feeding the delta will decrease only gradually over the next several centuries, with an estimated decline from current values of no more than about 17% within the coming six centuries. We conclude that the lower Mississippi River channel holds a significant reservoir of sand that is available to replenish diminished loads via bed scour and substantially mitigate land loss.
Article
Land loss mapping and rate curve development for 62 quadrangles in the Mississippi River deltaic and chenier plains shows that land loss rates and trends vary significantly throughout coastal Louisiana. Land loss rates were defined for each quadrangle for four time periods (1930's to 1956-1958, 1956-1958 to 1974, 1974 to 1983, and 1983 to 1990). Differences in land loss rates among the individual quadrangles are a function of the geologic and hydrologic setting and the factors which contribute to land loss such as subsidence, storm induced erosion, channelization of streams and rivers, and canal dredging. On a regional scale, the land loss rate for the entire Louisiana Coastal Plain has decreased from an average yearly rate of 41.83 square miles in the 1956-1958 to 1974 period to 25.34 square miles during the 1983 to 1990 period. The regional land loss rate will probably continue to decrease slowly until a background rate is reached. -from Authors
Article
The Mississippi delta region of south Louisiana houses a wealth of resources within a dynamic, subsiding landscape. Foundations for the delta region reflect Neogene evolution of the depocenter, whereas details of the modern landscape reflect late Pleistocene to Holocene evolution of the alluvial-deltaic plain. The Holocene delta plain was constructed by cyclical growth of deltaic headlands, followed by avulsion and relocation of the fluvial sediment source. Abandoned headlands were then submerged and reworked while a new headland was created at the site of active fluvial sediment input. Historic-period levees have decoupled the delta plain from its fluvial sediment source at the same time global sea-level rise was accelerating, which has accelerated delta-plain submergence. Diversions of Mississippi River water and sediment are necessary to achieve delta plain sustainability, but upstream dams trap ∼50% of the total sediment load, and there is not enough supply to keep pace with subsidence and accelerated...
Article
Over the past few centuries, 25% of the deltaic wetlands associated with the Mississippi Delta have been lost to the ocean1. Plans to protect and restore the coast call for diversions of the Mississippi River, and its associated sediment, to sustain and build new land2, 3. However, the sediment load of the Mississippi River has been reduced by 50% through dam construction in the Mississippi Basin, which could affect the effectiveness of diversion plans4, 5, 6. Here we calculate the amount of sediment stored on the delta plain for the past 12,000 years, and find that mean storage rates necessary to construct the flood plain and delta over this period exceed modern Mississippi River sediment loads. We estimate that, in the absence of sediment input, an additional 10,000–13,500 km2 will be submerged by the year 2100 owing to subsidence and sea-level rise. Sustaining existing delta surface area would require 18–24 billion tons of sediment, which is significantly more than can be drawn from the Mississippi River in its current state. We conclude that significant drowning is inevitable, even if sediment loads are restored, because sea level is now rising at least three times faster than during delta-plain construction.
Article
Occurrence and development of channel bars are major components of the morphodynamics of rivers and their relation to river meandering has been much explored through theory and experimentation. However, field and documentary data of characteristics and evolution over timescales from years to several decades are lacking. Four sets of aerial photographs in the period 1984–2007 were used to map and quantify bar numbers and areas in GIS on an active meandering reach. Bar types were classified. Additional temporal resolution was provided by annual ground photography and mapping for 1981–2010. Analysis was extended backward by use of large scale Ordnance Survey maps from 1873 onwards. As expected, point bars are the most common type but ‘free’ bars of several types are major components of bar deposition. Point bars and attached bars are significantly larger in size than mid-channel and side bars. Spatial distribution of bars varies down the reach and over time but is related to channel sinuosity, gradient and mobility and to bend evolution. Different types of bar occur in distinctive channel locations, with point and concave-bend bars in zones of high curvature. Bar activity shows a relation with discharge events and phases and possibly with changing riparian conditions, but superimposed on this is a common sequence of bar evolution from incipient gravel mid-channel bars to full floodplain integration. This life-cycle is identified as 7–9 years on average. No evidence for mobility of free bars within the course is found. The results are compared with bar and bend theory; the bars are forced and conform in general to bend theory but detailed variation relates to geomorphic factors and to autogenic sequences of bends and bars. Mid-channel bars are width induced. Variability of bar occurrence needs to be taken into account in river management and ecological evaluation, including for the EU WFD. Copyright © 2011 John Wiley & Sons, Ltd.
Article
An analytical modelling framework is proposed to reproduce the frequently observed but poorly studied occurrence of mid-channel bars in meandering channels. Mid-channel bars occur in meanders and may characterize transitional morphologies between pure meandering and braided rivers. Based on existing field and experimental observations, we propose that two different mechanisms can generate central topographical patterns in meanders. A former mechanism (‘width-forced’) is related to spatial width oscillations which determine a laterally symmetrical bed shear stress pattern that promotes mid-channel bars. A second mechanism (‘curvature-forced’) can take place also in curvilinear equiwidth streams since also longitudinal variations of channel curvature can produce laterally symmetrical alterations of the sediment transport capacity. A perturbation approach is employed to model both mechanisms within a common framework, allowing reproduction, at least qualitatively, of several observed features. While width-forced mid-channel bars are a symmetric linear altimetric response, to reproduce curvature-forced mid-channel bars requires modelling nonlinear flow-bed topography interactions at the second order of the perturbation expansion. Hypotheses on how these mechanisms operate are further discussed through an application to field cases. The amplitude of the nonlinear response can be relevant compared to that of the point bar in equiwidth meanders and the location of mid-channel bars seldom coincides with bend apexes, mainly depending upon the intrinsic meander wavelength. Central bars tend to symmetrically divert the flow against the two banks, a process which is proposed as a possible cause of cross-sectional overwidening, along with the asymmetry between the rates of bank erosion and of the opposite bank accretion. The outcomes of this first modelling step on the subject allow discussion of the mutual feedback processes that characterize interactions between mid-channel bars and width variations in river meanders. Copyright © 2010 John Wiley & Sons, Ltd.
Article
During the twentieth century, the planform and profile of the Lower Mississippi River from Cairo, Illinois, to New Orleans, Louisiana, have been transformed by a series of engineering modifications. These include steepening of the long profile by removal of the most sinuous bends, extensive bank stabilization, and regulating sediment movement by dyke field construction. Prior to these modifications, the Lower Mississippi River adjusted its morphology in the planform, long profile and cross-section. Planform adjustment has, however, effectively been negated and other adjustments are now constrained. Nevertheless, analysis of hydrographic surveys between 1949 and 1989 demonstrates that geomorphological response during the post-cutoff period remained complex. Morphological adjustments involved phased patterns of aggradation and degradation, together with changes in cross-sectional form, and in the number, size, location and shape of pools and crossings. Greatest changes occurred in the early post-cutoff period (1949–64) upstream from Vicksburg, Mississippi, but were accompanied by complementary changes elsewhere which propagated downstream. The combined set of responses may be interpreted with respect to a dynamic equilibrium in which the river responded to additional energy created by the cutoffs by increasing and adapting flow resistance over various scales and time periods. This study helps resolve paradoxes from previous analyses, and has significance for interpreting past engineering impacts and for suggesting future management strategies for the Lower Mississippi River. Copyright © 2005 John Wiley & Sons, Ltd.
Article
The Mississippi River is one of the most regulated rivers in the world. Human modifications constructed mainly after 1920 include dams and reservoirs, artificial levees, dikes, concrete revetments and a series of channel cutoffs. This paper examines some of the effects of these modifications on the channel and sediment budget of the river. In particular, the changes to the thalweg profile and the size of channel bars are examined in detail. It is concluded, that prior to the 1930s, when major modifications were introduced, the Lower Mississippi River was an aggrading meandering river. The role of the flood plain has also changed. Prior to modifications, the flood plain was the major sediment source as the result of bank caving. Today the flood plain provides only a minor amount of sediment. It can be shown that major degradation to the channel including the growth of channel bars has occurred as a result of these engineered modifications. The data also indicates that the different geomorphic regions respond to modifications in different ways. D 2003 Elsevier Science B.V. All rights reserved.
Article
Using 50 years of hydrologic and bathymetric data, we show that construction of ~ 50,000 dams throughout the Yangtze River watershed, particularly the 2003 closing of the Three Gorges Dam (TGD), has resulted in downstream channel erosion and coarsening of bottom sediment, and erosion of the Yangtze's subaqueous delta. The downstream channel from TGD reverted from an accretion rate of ~ 90 Mt (1Mt = 1000 000 t)/yr between the mid-1950 s and mid-1980 s to an erosion rate of ~ 60 Mt/yr after closing of the TGD. The delta front has devolved from ~ 125 Mm 3 (1 Mm 3 = 1000 000 m 3)/yr of sediment accumulation in the 1960 s and 1970 s, when river sediment load exceeded 450 Mt/yr, to perhaps 100 Mm 3 /yr of erosion in recent years. As of 2007 erosion seemed to have been primarily centered at 5–8 m water depths; shallower areas remained relatively stable, perhaps in part due to sediment input from eroding deltaic islands. In the coming decades the Yangtze's sediment load will probably continue to decrease, and its middle-lower river channel and delta will continue to erode as new dams are built, and the South-to-North Water Diversion is begun.
Article
A sediment budget is constructed for the Lower Mississippi River prior to the introduction of most human modifications. Components of the budget are derived from historical data including Mississippi River Commission hydrographic survey maps for the period from 1877 to 1924. A quantitative estimate of major sediment sources, sinks and storage locations in the Lower Mississippi Valley suggest that the most important sediment source was from bank caving and that at least 50 per cent more sediment was deposited in short-term channel storage than in longer-term overbank storage. The budget indicates that the proportion of sediment transported as bedload was significantly greater than previously estimated. The magnitude and variability of these sediment budget components are discussed. The results of the study suggest that prior to modifications the river was aggrading over much of its length.
Article
Before 1900, the Missouri–Mississippi River system transported an estimated 400 million metric tons per year of sediment from the interior of the United States to coastal Louisiana. During the last two decades (1987–2006), this transport has averaged 145 million metric tons per year. The cause for this substantial decrease in sediment has been attributed to the trapping characteristics of dams constructed on the muddy part of the Missouri River during the 1950s. However, reexamination of more than 60 years of water- and sediment-discharge data indicates that the dams alone are not the sole cause. These dams trap about 100–150 million metric tons per year, which represent about half the decrease in sediment discharge near the mouth of the Mississippi. Changes in relations between water discharge and suspended-sediment concentration suggest that the Missouri–Mississippi has been transformed from a transport-limited to a supply-limited system. Thus, other engineering activities such as meander cutoffs, river-training structures, and bank revetments as well as soil erosion controls have trapped sediment, eliminated sediment sources, or protected sediment that was once available for transport episodically throughout the year. Removing major engineering structures such as dams probably would not restore sediment discharges to pre-1900 state, mainly because of the numerous smaller engineering structures and other soil-retention works throughout the Missouri–Mississippi system. Published in 2009 by John Wiley & Sons, Ltd.
Article
The transport of sediment by rivers to the oceans represents an important pathway in the global geochemical cycle, a key component of the global denudation system, and an important measure of land degradation and the associated reduction in the global soil resource. With the growth of interest in global environmental change, it is important to consider the extent to which this important index of the functioning of the earth system is changing. Evidence from longer-term sediment load records indicates that river sediment fluxes are sensitive to many influences, including reservoir construction, land clearance and land use change, other forms of land disturbance, including mining activity, soil and water conservation measures and sediment control programmes, and climate change. Some of these influences cause sediment loads to increase, whilst others, namely, soil and water conservation and sediment control programmes, and reservoir construction cause decreased sediment fluxes. In many cases, it is difficult to disentangle the influence of climate change from that of other changes in catchment condition. Although there is clear evidence that the sediment loads of some rivers are changing, others show little evidence of any significant temporal trend. This could reflect either lack of change in the controlling factors or the buffering of any change by the river basin. To provide a preliminary assessment of current trends in the sediment loads of the world's rivers, longer-term records of annual sediment load and runoff were assembled for 145 major rivers. Simple trend analysis of these data indicated that ca. 50% of the sediment load records showed evidence of statistically significant upward or downward trends, with the majority evidencing declining loads. In the case of the annual runoff series, far fewer rivers (i.e. ca. 30%) showed evidence of statistically significant trends. The evidence afforded by the sample of the world's rivers indicates that reservoir construction is probably the most important influence on land–ocean sediment fluxes, but the influence of other controls resulting in increasing sediment loads could also be detected. A larger database, however, is required to provide a more definitive assessment of current trends in land–ocean sediment transfer by the world's rivers.
Article
Land–ocean transfer of sediment by rivers is a key pathway for material transfer on Earth. Contemporary data on the sediment loads of rivers provide clear evidence of significant recent changes in the sediment fluxes of several rivers in response to human impact. The key drivers of increased sediment loads include land clearance for agriculture and other facets of land surface disturbance, including logging activity and mining. Although, programmes for soil conservation and sediment control can result in reduced sediment loads, the trapping of sediment by dams represents the dominant cause of reduced loads. This influence is currently assuming increasing importance at the global scale. Any attempt to link these drivers to changes in the global land–ocean sediment flux must take account of the aggregation and buffering effects that operate in larger basins, which can cause damping and even removal of signals of increasing flux within the upstream basin, and complicate the link between upstream and downstream response to human impact. Further work is required to provide a precise quantitative assessment of the human impact on global land–ocean sediment fluxes and the net effect of increasing and decreasing fluxes. Particular attention must be paid to the temporal perspective and the variation of impact trajectories in different areas of the globe and for river basins of different sizes.
Article
An examination of the response of the Lower Mississippi River (LMR) to a variety of engineering activities is presented through the discussion of: (a) a brief history of engineering investigations and activities on the LMR; (b) the impact of artificial cutoffs on the channel geometry and water surface profiles of adjacent reaches; (c) the impact of channel alignment activities on channel morphology; and (d) the apparent impact of all of the LMR engineering activities on sediment dynamics in the channel.
Article
Concavity in the long profile of rivers has traditionally been explained through the concept of grade, in which the slope declines downstream as a response to changing discharge, bed material size and sediment transport. Applying this concept to particular river systems has, however, proved problematic. The long profile reflects spatially-distributed form–process feedbacks between all aspects of channel morphology operating at a range of poorly defined time- and space-scales, and in the presence of natural controls. In many river systems, process–form dynamics are further complicated by engineering interventions which add additional extrinsic controls and constrain the range of intrinsic dynamics. In this paper, the 1974–75 long profile of the Lower Mississippi River is examined at three scales: the regional; the reach; and the sub-reach (pool–crossing) scales. A combination of curve-fitting, zonation algorithms, and empirical classification techniques are used to show that, although the long profile of the Lower Mississippi River is concave at the largest scale, the profile is characterised by discontinuities, shorter trends and zonal variations in the amplitude and wavelength of pool–crossing morphology. These characteristics are a response to morphological and bed material changes relating to a range of physical (geological, tectonic, tributary input) and engineering controls. Despite its apparent simplicity and correspondence to a ‘graded’ condition, the long profile of the Lower Mississippi River is actually a complex and scale-dependent morphological property. At best, the concave river profile is, therefore, a property which emerges from several scales of process–form interaction; at worst, it is no more than an artefact arising from the application of over-simplified curve-fitting techniques. Disclosure of the nature of the long profile thus requires the application of a variety of analytical techniques, as well as geomorphological explanations which are themselves scale-dependent and which consider the interaction of natural processes and the history of engineering intervention.
A brief history and summary of the effects of river engineering and dams on the Mississippi River system and delta. 1067084X
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The significance of mid-channel bars in an active meandering river
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Syvitski, J.P.M., Kettner, A.J., Overeem, I., Hutton, E.W.H., Hannon, M.T., Brakenridge, G.R., Day, J., Vorosmarty, C., Saito, Y., Giosan, L., Nicholls, R.J., 2009. Sinking deltas due to human activities. Nat. Geosci. 2 (10), 681-686.
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USACE (U.S. Army Corps of Engineers), 2013. 2013 Vicksburg District Navigation Bulletin. U.S. Army Corps of Engineers, Vicksburg, Mississippi.