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Air photo interpretation and field survey were used to examine rates and patterns of planform change over the last 40 years on an 80 km reach of the Luangwa River, Zambia. The river, a tributary of the Zambezi, is a 100–200 m wide, medium sinuosity sand-bed river (sinuosity index 1·84). High rates of channel migration (<33 m a−1) and cutoffs on mea...
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Context 1
... of the flow record at Great East Road Bridge shows a modest increase in magnitude of flood peaks over the last 50 years and particularly since 1989 ( Figure 2). A regression analysis of annual peak flow against time is significant (p ` 0Á05). This is consistent with trends in rainfall and flow elsewhere in eastern Zambia (Sichingabula, ...
Context 2
... response to increasing flood magnitudes and frequency Figure 2 shows that the last 10 years have experienced a greater frequency of high magnitude events than the preceding 40 years, with four of the largest six floods occurring. This phenomenon may or may not be part of a trend but the response of the channel planform to these events by comparison of up-to-date aerial photography with that in 1983 and 1988 would shed light on the relationship between channel planform change and flood magnitudes. Palaeomeander evidence and the channel dynamics over the last 40 years possibly suggest that the Luangwa River, like so many rivers, is sensitive to environmental change. Based on bankfull channel width measurements on successive aerial photographs, a mean increase in channel width of over 20 per cent has been observed. This may be a response to the trend towards increasing flood magnitudes and presumably sediment loads. This suggests that the Luangwa and other similar rivers are sensitive to changes in hydrological regime in short to medium timescales. Analysis of the morphology of palaeomeanders on the floodplain suggests, although more evidence is needed to confirm the fact, that the Luangwa River was once more sinuous, further highlighting the sensitivity of the channel morphology to hydrological change. Recent increases in flood magnitudes induced by increased precipitation, together with effects of future land-use change, could therefore alter future bank erosion and modes of channel planform change. Earth Surf. Process. Landforms 25, 421±436 (2000) ...
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Citations
... Previous studies were based on field data and aerial photographs in most of the cases. However, advances in computation and computer powers are extensively used to identify river planform dynamics (Ashworth et al., 2000;Gilvear et al., 2000). Therefore, recent studies have used remotely sensed satellite data along with tools and programming languages such as QGIS and MATLAB, and Python (Mosselman, 1995). ...
The development of hydraulic structures has impacted the river discharge and sediment transportation, thus highlighting the river planform changes. Among 103 river catchments in Sri Lanka, the Mahaweli River is the longest river with the largest basin. Many development projects over the years diversely impacted the changes in river masks. However, no study has been conducted to quantify the planform changes in the lower Mahaweli River. Therefore, a comprehensive study was conducted to analyse the river planform changes over 30 years (1991-2021) from Damanewewa to Trincomalee. Freely available remotely sensed satellite data with 30 m resolution were used in the analysis. These images were processed using the QGIS mapping tool and RivMAP toolbox in MATLAB. Major changes were identified at the downstream part of the river and an oxbow lake formation was also observed. The average width for the entire reach (Wra) was identified as 14.83 m and channel width average (Wavg) was noted as 18.09 m. In addition, erosion and accretion rates were calculated, and the cumulative sequence of these rates was increased over the years affecting the change in channel width. Furthermore, the migration rates were also computed with generated river centerline. Highest migration rate reached about 400 m/yr, in the downstream which finally leads to severe meandering. Results revealed that this methodology can be applied to similar river planform analysis. Further, these results showcase the potential importance of analyzing channel stability as well as for water resource management.
... Heavier rains and longer dry periods can lead to more extreme flows [1]. However, while some rivers have experienced more frequent low flows and disappearing floods [9], in others, the magnitude and frequency of floods have increased [20,21]. Researchers differ in their opinions on which characteristic discharge plays the most important role in transforming channels and floodplains. ...
... Researchers differ in their opinions on which characteristic discharge plays the most important role in transforming channels and floodplains. Gilvear et al. [20] stressed the role of increasingly frequent extreme floods; others considered the changes in bankfull discharge as the key factor [22,23]. However, the role of increasingly frequent and persistent low stages in shaping the channel morphology is also not negligible [24]. ...
... The consequences of altered hydrology may differ between rivers [33] as the fluvial response to change may vary in space and time, even within the same river, depending on the current state of the system [20,33]. The main difficulties in analysing the effects of environmental change are the uncertainties of the initial state and the non-linearity of the processes involved [34,35]. ...
In the 21st century, climate change and its consequences are getting more serious. The changes in temperature and precipitation alter the run-off conditions, subsequently influencing the channel processes of rivers. The study aims to analyse the hydrological changes in a small, sub-alpine river (Rába/Raab River, Central Europe) and the bank erosional processes (1951–2024). The bank erosion was determined based on topographical maps, aerial photographs, and field (RTK–GPS) surveys. Short (2–3 days) floods were common between 1950 and 1980, and low stages occurred in 65–81% of a year. However, extreme regimes developed in the 21st century, as record-high, flash floods altered with long low stages (91–96% of a year). The bank erosion shows a cyclic temporal pattern, gradually increasing until it reaches a high value (4.1–4.9 m/y), followed by a limited erosional rate (2.2–2.8 m/y). However, the magnitude of the bank erosion is decreasing. This could be explained by (1) the lower transport capacity of the more common low stages and (2) the seasonal shift of the flood waves, which appear in the growing season when the riparian vegetation can more effectively protect the banks from erosion.
... Especially vulnerable to elephant depredation were drought-prone areas where crop raiding elephants threatened food security (Osborn & Rasmussen, 1996). Due to geomorphological characteristics of the Luangwa Valley, the river action also played a role in the regular changes of the Luangwa River course in particular (Gilvear, Winterbottom & Sichingabula, 2000). Such phenomena might have been locally influencing the seasonal distribution of the wild fauna. ...
... One such underexplored possible corridor is the Luangwa Valley in eastern Zambia. The Luangwa River, a tributary of the Zambezi, is one the last undammed large rivers in Africa (Gilvear et al., 2000). For more than 700 km, the Luangwa flows unimpeded through a northeast/southwest-oriented valley that is a southern extension of the Eastern African Rift System (Fig. 1). ...
... Chute cutoffs tend to occur in bends with low and intermediate curvatures [Howard, 1996], though they could happen in highly convoluted bends as well [Camporeale et al., 2008;Ghinassi, 2011;Grenfell et al., 2014]. They are often caused by high flows, coupled with appropriate combinations of channel and floodplain geomorphology [Ghinassi, 2011;Gilvear et al., 2000;Hooke, 2004;Howard and Knutson, 1984;Kleinhans and van den Berg, 2011]. ...
... In some models, the effect of bank erosion on migration is represented by a simple constant [Ferguson, 1981;Gilvear et al., 2000;Hooke, 2003]. In others, it is incorporated into h(s) that has complex, nonlinear functions as one of many parameters [Guneralp and Rhoads, 2009;Sylvester et al., 2019]. ...
... After the initiation of neck cutoff, the abandoned channel bend is removed and the remaining segment is smoothed for subsequent simulation [Bogoni et al., 2017;Frascati and Lanzoni, 2009] ( Fig. 4). Many of these models, simpler or more complex, have successfully reproduced the planform shapes of the simulated river reaches or bends that are statistically (or visually) similar to those of the real meandering rivers [Gilvear et al., 2000;Guneralp and Rhoads, 2009;Motta et al., 2012;Schwendel et al., 2015;Schwenk et al., 2015;Sylvester et al., 2021]. The apparent success implies that ...
Cutoffs, which include neck and chute cutoffs, are the results of the fluvial processes that fundamentally influence evolution of meandering rivers. Neck cutoff happens when the two limbs of a highly sinuous bend touch, whereas chute cutoff refers to the formation of a shortcut channel passing through a meander bend. In this review, we begin by distinguishing the morphological and hydrological conditions of the two cutoff types. Mechanisms driving the development of neck cutoff are embodied in a variety of kinematical and hydrodynamic models simulating processes governing the long-term evolution of meandering rivers. These models adopt a morphological threshold for judging the occurrence of neck cutoff, b = αw where α is a constant ranging between 0 and 1, b is the bend neck width, and w is the mean channel width. The potential underestimation of the evolutionary period during the late-stage of bend evolution toward neck cutoff by using this morphological threshold and uncertainties in quantifying the migration-curvature relationship limit the abilities of the existing models in predicting the occurrence of neck cutoffs. We then suggest three possible directions for future research on meander neck cutoffs. Mechanisms controlling chute cutoffs are relevant to six key factors representing meander hydrological regime, planform morphology, bed topography, and floodplain characteristics. The combination of these factors gives rise to four distinguishable triggering mechanisms: headward-erosion, embayment, mid-channel bar, and scroll-slough chute cutoffs, though initiation of chute cutoff may be caused by some of their combinations. However, the hydraulic and morphological characteristics of meander bends under these triggering mechanisms are so complex that they are often site-specific, making it extremely challenging to generalize the known morphodynamic and hydrodynamic processes driving the formation of chute cutoffs in individual meander bends. We close the review by recommending three possible research directions on chute cutoffs for tackling the existing challenges in the future.
... This could not only damage the riverbank stability, also created wide conduits through which sediment would cascade into the riverbed and hence, the observed heavy laden of sediments on the riverbed [21]. Studies in and outside Africa also confirm similar patterns, which show the geospatially distributed nature of the impact of anthropogenic activities on river system [22,23,24,25,26]. The findings are also in tandem [27] who found that landuse change affected channel morphology in the Northern Puerto Rico. ...
Aims: This study sought to investigate the role of humans in modification and creation of landforms in river channels with specific focus on the Magoye River. The objectives of this study were to: document geomorphic characteristics of Magoye River, assess anthropogenic activities and landuse/cover change in the buffer zone and, examine key anthropogenic river landforms. Study Design: This study was inspired by analytic eclecticism research philosophy and adopted mixed methods, particularly concurrent research design. Methodology: The landcover images were analysed using image processing tools in ArcGIS 10.4 for the periods 1990, 2005 and 2020. Descriptive statistics were used to quantitatively visualize the changes in land cover/use. The data was collected using field observation, photography, GPS and a Likert scale tool and, analysed using descriptive statistics, specifically frequency graphs showing mean and standard deviation. 2 Results: The results showed that sand mining and brick moulding accounted for almost 68% of human activities in the 11.48 km 2 delineated buffer zone by 2020, compared to 35% in 1990. These punctuated creation of sand conical heaps, stone bunds, pot holes and pools, shallow wells on the river bed, gullies induced by water accessed points, which weakened river banks. Generally, sand mining and brick moulding were the most severe in the buffer zone and they created wide range of deformations riverbanks and beds. The findings further revealed that Magoye River had geomorphologically evolved into Reservoir River covering 80% on the upstream (139.4km) and Sand Bank River accounting 20% on downstream (27.6 km). Conclusion: The study concludes that, the catchment and buffer zone have undergone degradation propelled by anthropogenic activities, which have punctuated channel morphological degradation. Although the Magoye River channel was highly damaged, it was not beyond regeneration if restoration measures, were collaboratively identified and implemented with the local communities.
... As such, one of the primary natural factors that influence oxbow lake formation and persistence is the dynamic nature of river systems. Rivers in Africa are subject to frequent changes in flow regime, which can lead to the formation of meanders and the subsequent detachment of meander bends to form oxbow lakes (Gilvear et al., 2000;Rodnight et al., 2005). Since the existence and functionality of oxbow lakes are dependant on intermittent flooding events or rainfall patterns within an area, they could gradually transit into a different habitat type i.e., from wetlands, into non-inundated terrestrial landscape depending on the intensity of sedimentation processes (Piégay et al., 2000). ...
... It is the most feasible method to estimate and evaluates the basins that retaliate to climate, drainage, and flash flood probability [4,27,39,45,46,51,64,74,75,78]. Remote sensing is an efficient tool used for interpreting structural impacts [2,18,49,67,96] and channel sifting [1,25,29,68] beside the tectonic controls in river sinuosity [26,30,37,38]. ...
The Reth River is a ground water fed river of Central Ganga Plain, ~107 km long and drains ~391.71 km2. It flows through an incised valley until confluences with the Gomati River. Incision of the river valley has been investigated by using a longitudinal profile, escarpment height and morphology of the valley. The study was executed using Toposheet of scale 1 : 50 000 of Survey of India (SOI) and decadal satellite imageries, with GIS techniques to estimate the properties of basins. The mean bifurcation ratio of the basin is 5.49, but variation between the successive stream orders suggests that the study area is tectonically controlled. The drainage density (0.66), stream frequency (0.46), constant of channel maintenance (1.51) and length of overland flows (0.80) indicate of the high surface rock permeability, low surface runoff, high infiltration rate, and least erodible properties respectively. The drainage texture (0.30) suggests a very coarse texture and smooth topography. RHO coefficient value (0.13) indicates the low capacity of water. The elongation ratio (0.45), circulatory ratio (0.28) and form factor (0.16) indicate that the basin is highly elongated due to shallow relief. The downstream variation of escarpment heights indicates an increasing downstream trend of escarpment heights. According to aerial views of 46 years, oxbow lakes are formed through several processes, such as (i) a flow separation zone at the entrance of the channel creating a sediment plug, (ii) sediment sorting by flow gradients and decantation in the ponded areas. The drainage basin shape (3.02) indicates the basin is tectonically active. River longitudinal profile ranges are from 124 to 102 m amsl. This indicates the 4th-order river with dendritic pattern.
... Archaeological research in the region was not pursued further at the time, due to a lack of chronostratigraphic information and access difficulties [6,7]. In the late 20 th Century hydrocarbon exploration, advances in satellite imagery and the development of wetland management schemes contributed to renewed scientific interest in the hydrology and sedimentary history of the Luangwa Basin, e.g., [8][9][10][11]. New archaeological and Ocean off the coast of Mozambique [15,16]. The valley is drained by the Luangwa River, which flows 850 km in a southwesterly direction from its headwaters in the Mafinga Hills to its' confluence with the Zambezi. ...
... Regional vegetation cover is dominated by grassland and deciduous miombo woodland (Fig 2B). The dynamic floodplain widens in the central portion of the basin where the Luangwa River's main channel forms a network of meanders that actively reshape the landscape [11]. ...
... The "post-Karoo" sediment burden is considerably lighter in the northern sub-basin. Overlying the Luangwa formation is a succession of poorly differentiated Neogene deposits capped by Quaternary sediments, composed of colluvium and alluvium, which have been substantially reworked in places by climate-driven changes to the hydrological system [11]. ...
The Luangwa Basin, Zambia, which forms part of the Zambezi drainage, is strategically located between the Central African plateau and the East African Rift system. The Luangwa River and major tributaries, such as the Luwumbu River, are perennial water sources supporting essential resources that sustain human communities and a rich and diverse fauna and flora. The archaeological record of Luangwa is relatively unknown, despite early archaeological exploration hinting at its potential. Recent research in the southern Luangwa valley, however, suggests that it preserves a long record of hominin occupation spanning the Early to Late Stone Age. The research described here details fieldwork carried out in northeastern Luangwa, in the Luwumbu Basin, that confirms that a relatively deep package of Quaternary deposits, containing evidence of the Stone Age occupation of the region persists in the upper piedmont zone.
... Therefore, the total error can be calculated by summing the squares of all individual errors and taking the square root of the sum, resulting in a value of 5.99 m. This error is acceptable, as measurement displacement of channel boundaries with a magnitude of >5 m likely represents true channel adjustments in aerial photographs , an absolute value criterion adopted in multiple previous studies (e.g., Gilvear et al., 2000;Nicoll & Hickin, 2010;Winterbottom, 2000). ...
The understanding of fluvial processes controlling morphological adjustments and stability of anabranching rivers remains incomplete. Focusing on a complex anabranching system in the Upper Yellow River, this study quantifies the morphological characteristics and lateral dynamics of islands and channels in four reaches over a 56‐km river course from 1986 to 2017. Using five heuristic anabranching structures derived from the studied anabranching system, we estimate sediment transport capacities and assess their implications for the morphodynamics of anabranching rivers. These results show that the system exhibited a highly complex pattern featuring high channel multiplicity and dominance of islands. Over the study periods, the system exhibited an accreting disequilibrium state, which was highlighted by spatiotemporally diverse and dynamic patterns of islands. Morphological changes in islands were dominated by expansion and shrinkage, which caused more areal changes than other modes of change, including coalescence, cleavage, new island formation, and elimination. These processes controlled the creation and elimination of small anabranches, whereas the size and morphology of large channels remained comparatively stable, which maintained the stability of this anabranching pattern. The stability of the anabranching pattern is further supported by estimations of transport capacity in that the main channels transport most sediments and in that excess development of small anabranches promotes sediment deposition within the system. Overall, this study provides new insight into the morphodynamic properties of anabranching rivers, demonstrating that, instead of channel numbers, island dynamics and interactions with channels are controls of the evolutionary processes and stability of anabranching rivers.
