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On the environmental controls of Bangladesh river systems

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... The Jamuna River has developed in a region of significant tectonic activity associated with Himalayan uplift and development of the Bengal foredeep (Alam et al. 1990;Barua 1994;Goodbred, Jr., et al. 2003;Singh 2007;Brammer 2012;Steckler et al. 2016), and the underlying structural control on the location of the major river systems of Bangladesh has long been debated (Morgan and McIntire 1959;Umitsu 1993;Barua 1994;Reitz et al. 2015;Grimaud et al. 2019). Steckler et al. (2016) show how subduction is still active in the region, with c. 13-17 mm yr −1 of plate convergence on an active, shallowly dipping and locked megathrust fault. ...
... The Jamuna River has developed in a region of significant tectonic activity associated with Himalayan uplift and development of the Bengal foredeep (Alam et al. 1990;Barua 1994;Goodbred, Jr., et al. 2003;Singh 2007;Brammer 2012;Steckler et al. 2016), and the underlying structural control on the location of the major river systems of Bangladesh has long been debated (Morgan and McIntire 1959;Umitsu 1993;Barua 1994;Reitz et al. 2015;Grimaud et al. 2019). Steckler et al. (2016) show how subduction is still active in the region, with c. 13-17 mm yr −1 of plate convergence on an active, shallowly dipping and locked megathrust fault. ...
... The control of uplift and subsidence is, however, clear and Allison (1998), in a review of the geologic and environmental framework of the Ganges-Brahmaputra Delta, highlights the uplifted Pleistocene terraces of the Barind and Madhupur tracts (Figure 20.1) as being first-order controls on the courses of the Jamuna and Ganga Rivers. Barua (1994) also presents a synthesis of the major environmental controls on Bangladesh's river systems and, together with the major controlling factors of regional tectonics, geology, climate, sea-level rise and vegetation, highlights the controls by the 'fluvial loading' that is dictated by water and sediment discharge and sediment calibre. Grimaud et al. (2019) contend that Late Quaternary sediment dynamics indicate subsidence and sediment infilling of c. 0.8-2 mm yr −1 in the Teesta River megafan area at the foot of the Himalayas, and uplift and erosion in the Barind Tract region at rates of c. 0.03-0.11 ...
Chapter
Bangladesh is dominated by three great rivers – the Jamuna–Brahmaputra, Ganga, and Meghna – that combine to feed sediment into one of the World's largest deltas in the Bay of Bengal. The Jamuna River has developed in a region of significant tectonic activity associated with Himalayan uplift and development of the Bengal foredeep. The bedload, although only ~10% of the total sediment load, is critical in generating a wide array of bedforms of different scale that drive channel change and migration. Within the Jamuna River, the ubiquitous occurrence of bifurcations and confluences is a key aspect of the river channel pattern and dynamics, and these features form important nodes in the braidbelt. The nature of floodplain sedimentation and inundation is vital in planning annual crop growth and may adopt great significance in the ongoing debate on the sources, causes, and accumulation of arsenic in the groundwaters of Bangladesh.
... The Jamuna River has developed in a region of signifi cant tectonic activity associated with Himalayan uplift and development of the Bengal foredeep (Alam et al., 1990;Barua, 1994;Goodbred et al., 2003), and the underlying structural control on the location of the major river systems of Bangladesh has been hypothesized by several researchers (Morgan and McIntire, 1959;Umitsu, 1993;Barua, 1994). Morgan and McIntire (1959) suggested there is a zone of 'structural weakness' along the present course of the Ganga-Jamuna-Padma Rivers due to either a subsiding trough or a fault at depth. ...
... The Jamuna River has developed in a region of signifi cant tectonic activity associated with Himalayan uplift and development of the Bengal foredeep (Alam et al., 1990;Barua, 1994;Goodbred et al., 2003), and the underlying structural control on the location of the major river systems of Bangladesh has been hypothesized by several researchers (Morgan and McIntire, 1959;Umitsu, 1993;Barua, 1994). Morgan and McIntire (1959) suggested there is a zone of 'structural weakness' along the present course of the Ganga-Jamuna-Padma Rivers due to either a subsiding trough or a fault at depth. ...
... The control of uplift and subsidence is, however, clear and Allison (1998), in a review of the geologic and environmental framework of the Ganga-Brahmaputra Delta, highlights the uplifted Pleistocene terraces of the Barind and Madhupur tracts (Figure 19.1) as being fi rst-order controls on the courses of the Jamuna and Ganga Rivers. Barua (1994) also presents a synthesis of the major environmental controls on Bangladesh's river systems and, together with the major controlling factors of regional tectonics, geology, climate, sea-level rise and vegetation, highlights the controls by the 'fl uvial loading' that is dictated by water and sediment discharge and sediment calibre. The nature of sea-level rise, together with other anthropogenic effects on Bangladesh's rivers such as fl ood control and water usage, will clearly take on great importance in the twenty-fi rst century (Begum and Fleming, 1997a,b;Choudhury et al., 1997;Mirza et al., 2001;Mirza, 2002). ...
Chapter
Full-text available
Background Channel Scale Morphology and Historical Changes in the Course of the Brahmaputra-Jamuna RiverBedform Types and DynamicsBifurcations, Offtakes and ConfluencesFloodplain SedimentationSedimentology of the Jamuna RiverApplied Geomorphology and Engineering in the Jamuna RiverSummaryAcknowledgementsReferences
... The estimated annual sediment yield of the Brahmaputra is 1028 tons km 2 , the highest among the world's largest rivers. On the other hand, the sediment yield from Ganges is only 502 tons km 2 although its basin area is twice that of the Brahmaputra (Barua, 1994). In the recent years the change in course of Ganges and Brahmaputra rivers has significant influence on the morphology of their alluvial flood plains (Rahman, 1993;Brammer, 1996). ...
Article
Abstrac The navigational aspects of marine transport and its manoeuvrability require precise knowledge on tides. Information on time varying water levels, magnitude and direction of tidal currents is quite critical in coastal waterways and estuarine environment. Real-time water levels along with other hydrodynamic parameters are used in almost all major ports for effective operations throughout the year. Also various coastal engineering projects require precise information on site-specific water level elevations. There is a rapid expansion of coastal infrastructure in the recent times, and therefore it is very essential to have reliable water level prediction system that caters the need for coastal engineers, port and harbour activities etc. The Sea Level Processing Package (SLPR2) developed by the University of Hawaii Sea Level Center in collaboration with National Oceanographic Data Center (NODC) provides reliable estimate of location specific sea level information. SLPR2 performs three primary tasks that include tidal analysis and prediction, quality control, and filtering. Harmonic tidal analysis using linear least square produces the relevant tidal constituents of a specific region. High frequency data (preferably one-hour duration) for a minimum duration of one complete year would suffice the tidal analysis phase in SLPR2. The tide prediction algorithm used in the present study uses a maximum of 68 harmonic constituents. The region of interest is the head Bay of Bengal region located along the east coast of India. Preliminary analysis of measured sea level data indicate that tide gauges located along Bangladesh has research quality data, and therefore used in this study. Station data from seven locations viz; Hiron Point, Khepupara, Charchanga, Chittagong, Khal No.10, Cox's Bazaar, and Teknaf all located in Bangladesh were used for tidal analysis, and thereafter the predictive capability of SLPR2 for one-year period was investigated. There are exceptions at two stations, Teknaf (comprising of 87% observed data) and Khal No.10 (99% of observed data), and remaining five stations are free from data gaps. In a hydrographic perspective, the Bangladesh region has complex network of waterways, and bottom topography have several detached shoals. Tides enter the Bangladesh coast through two submarine canyons, reaching Hiron Point and Cox Bazaar at almost the same time. Amongst the principal constituents, dominant modes are exhibited by M 2 and S 2 whose natural oscillation periods are 12 h 25 min, and 12 h respectively. The results from SLPR2 indicate considerable seasonal variation in water level prediction during the monsoon season, attributable to meteorological reasons and excess river discharge, at stations Cox Bazaar and Charchanga. The locations Hiron Point and Khepupara show elevated predicted tides after the onset of monsoon, indicating the presence of seasonal signature resulting from large amplitude of the annual tidal component 'Sa'. Residual time series produce the de-tidal water level variations attributed due to meteorological effects such as wind, atmospheric pressure and river discharge. Inspection of residual can help to quality control measured data such as datum level correction, and replacement of data voids. The effective shallow nature in NorthEastern Bay produces partial reflections thereby increasing the tidal range. In addition, the seasonal * Linta Rose. effects of meteorological forcing along with non-linear shallow water interaction can result in number of higher harmonics. Finally, the correlation of tidal prediction between SLPR2 and measurement show a reasonable good match.
... km, while discharge from the Ganges is about 502 tonnes/ sq. km in spite of the basin area being almost two times large compared to that of the Brahmaputra 6 . The highest tidal range in the east coast of India pertains to the head Bay region, and strong currents with reversing tides play an important role on the suspended sediment concentration and sediment transport mechanisms. ...
Article
The Hooghly estuary located in the head Bay of Ben-gal region is a part of the highly dynamic deltaic environment. Tidal variations are predominant in this estuary, and tides propagate considerable distance through a complex network of various riverine systems , inlets, bays and creeks having vital implications on water mass exchange, reworking of deltaic sediments and the mixing process. The Hooghly River houses two major ports of national importance, viz. Kolkata Dock System and Haldia Dock Complex. Tidal forcing is primarily semi-diurnal in nature and with the presence of complex riverine morphology, the tidal characteristics are substantially modified causing various tidal constituents of compound tides. The present study performs location-specific tidal analysis and prediction utilizing one-hourly tide data with SLPR2 harmonic tidal analysis tool for Gangra situated upstream of the Hooghly River. In a geomorpho-logic perspective, the water-level elevation at Gangra results from natural tidal flow, as well as refracted effects from cross-flow due to the presence of two natural island barriers, namely Sagar Island situated southward off Gangra and Nayachara in the east. The Hooghly channel comprises of complex bathymetric features and tidal analysis at Gangra reveals the presence of Msf (luni-solar synodic fortnightly) tidal constituent. Very few locations in India have reported on the existence of the Msf tides, and Gangra is one among them. This study also performs a comprehensive validation between the computed monthly tidal prediction from SLPR2 and measured water level at Gangra. The skill level of prediction exhibits a good match. This study also investigates the influence of atmospheric effects on sea-level pressure variations and the resultant water-level elevation from extreme weather events such as depressions and severe cyc-lonic storms that occurred during 2013. The study signifies the importance of tidal analysis and prediction for operational needs. Keywords: Estuary, numerical models, tide prediction and analysis, water-level elevation. THE variations in sea-level attributes arise from various factors such as astronomical tides and currents, atmospheric forcing and hydrological aspects of river discharge 1,2. These in turn govern the water-level elevation in estuaries and river channels 3. One can find increasing concerns on the sea-level rise and its variability in the recent literature. The vulnerability aspects due to sea-level rise have implications on livelihood in several coastal areas around the globe. In this context, the Sunderbans situated in the head Bay of Bengal is a low-lying deltaic environment that is highly vulnerable to threat from sea-level rise. In the recent years, one can find several studies on projections for sea-level rise due to global warming and climate change. The subject of sea-level rise and its implications has a direct bearing on socioeconomic aspects. Rapid industrialization with increased emission of greenhouse gases has increased the mean global temperature. Estimates show that global sea-level rise is in the order of about 15 cm over the past century. Several studies have been conducted based on measurements and projections from numerical models that portray increased atmospheric temperature in the near future. This indicates that coastal areas and especially the low-lying regions (such as near-shore areas in the head Bay region) have a direct risk from increased total water-level elevation (TWLE). TWLE is a combined effect due to increased storm-surge activity from high intense cyclones, wave-induced setup , and astronomical tides that happen during landfall of energetic cyclones. In other words, a paradigm shift in climate change during the recent decades has resulted in an increased probability of high-energetic events like cyclones that cause increased storm surge and flooding , as well increased wave setup along near-shore areas. This coupled with a permanent rise in sea level is a subject of major concern, especially for low-lying coastal areas. Tidal variation forms an integral component of TWLE. Therefore, tidal analysis in coastal/near-shore waters is important to understand the residual effects. The present study is confined only to tidal analysis and prediction for a specific location, Gangra, which is a part of the Hooghly riverine system adjoining the head Bay region in the Bay of Bengal (Figure 1). The study demands quality data; in addition, the measured data should be free from data gaps and spurious noise. Therefore, in the present study we develop a tide prediction system specifically for Gangra, with subsequent scope to extend such work to other regions in the head Bay of Bengal.
... e Best et al. (2007); Q is average of lower and upper estimates for bankfull discharge at Bahaduribad (Delft Hydraulics and DHI, 1996; Thorne et al., 1993); S from Delft Hydraulics and DHI (1996). f Barua (1994); Sarker and Thorne (2006). g Carson (1984); values from their Table 1, Rakaia 2. h Smith et al. (2006); Snorrason et al. (1997); estimated peak discharge from 1996 outburst flood. ...
Article
Full-text available
River channels often develop channel belts—wider corridors imprinted by past channel occupation—that record past landscape dynamics and form widespread aquifers. Controls on channel belt width for braided rivers have been inferred through physical experiments that evolve an initially straight channel and yield an interpreted, quasi‐equilibrium form. Yet uncertainties remain regarding the independent effects of discharge, slope, and time on channel belt dimensions and the morphodynamic phenomena that coincide with channel belt development. To address these uncertainties, I conducted four experiments that independently varied discharge and bed slope for flow over a bed of medium sand (D50 = 0.42 mm). The laboratory basin (37 m long, 2.7 m wide) was 200 times longer and nine times wider than the width of the largest initial channel, which reduced boundary effects and provided a baseline to measure downstream variability in channel belt width. Transitions in channel belt growth rate occurred in concert with three phases captured by time‐resolved topography data: (1) meandering; (2) braiding, with logarithmic growth of the channel belt; and (3) maturity, with slowing, localized growth due to decreasing flow depth. A dimensionless framework involving discharge, slope, and sediment grain size collapses the growth trajectories of the channel belts to a common trend. In comparison, for natural cases, discharge is the dominant predictor of channel belt width (wcb ~ Q0.55). The time dependence of channel belt width in the experiments suggests that the widths of isolated, ancient channel sand bodies are wider than their formative channels.
... Amongst these defined four segments, the first three coastline section is a low lying, swampy, rapidly changing alluvial basin with large inputs of sediments deposited by the two vast river systems namely Ganges and Brahmaputra (Snead, 2010). The estimated annual sediment load from Brahmaputra is about 1028 t Km À 2 while the discharge from Ganges is about 502 t Km À 2 although the basin area is almost two times large compared to that of Brahmaputra (Barua, 1994). ...
Article
In a geomorphic sense, the Bangladesh located in the head Bay region comprises of numerous tidal creeks, waterway inlets, and complex coastline geometry. This region encompassing the world׳s largest deltaic system is thickly populated and extremely low-lying, and therefore highly susceptible to coastal flooding and sea level rise. High tidal range existent in this region primarily governs the hydrodynamic behavior and coastal processes. The present study deals on a comprehensive tidal analysis, understanding the variations in tidal behavior over spatial and temporal scales in the near-shore region off Bangladesh. The harmonic tidal analysis using SLPR2 estimates the tidal constituents using linear least squares with respective nodal correction. Tide gauge observations from five different stations viz; Hiron Point, Khepupara, Charchanga, Khal No-10, and Cox׳s Bazaar were used for tidal analysis. The results from SLPR2 signify considerable seasonal variations in water level attributed due to meteorological factors and excess river discharge. Tidal pattern at all these five stations are primarily mixed semi-diurnal with M2 as the dominant constituent. The t-tide toolbox computed the equilibrium tidal amplitude for the study area. Some of the components known to be influenced by meteorological aspects such as Solar Annual component (Sa), Semi-Annual component (Ssa), and Solar Radiational component (S1) have higher amplitudes than expected, in the study area. The shallowness of the delta cause severe deviations in the tidal behavior from equilibrium tides. Interaction of tides with river discharge also dominant in this region indicates the role of hydrological forcing. Interestingly, the study also reveals the existence of compound tidal constituent Msf in this region. Monthly analysis of Msf component, using FFT, revealed peaks corresponding to the monsoon, Kal-Baisakhi months and to the seasonal changes in atmospheric pressure, thereby unfolding the seasonal influence on Msf. The funnel shaped head Bay plays an important role in amplification of tidal constituents, wherein the form factor and maximum tide levels showed an increasing trend. This study also demonstrates how tidal dynamics can be elucidated using location specific water-level observations. Investigations on the annual variations in observed and predicted water levels clearly signify the seasonal patterns. The correlation analysis show a reasonable match with skill level exceeding 93%, and the overall prediction by SLPR2 is highly satisfactory.
... km, while discharge from the Ganges is about 502 tonnes/ sq. km in spite of the basin area being almost two times large compared to that of the Brahmaputra 6 . The highest tidal range in the east coast of India pertains to the head Bay region, and strong currents with reversing tides play an important role on the suspended sediment concentration and sediment transport mechanisms. ...
Article
The Hooghly estuary located in the head Bay of Bengal region is a part of the highly dynamic deltaic environment. Tidal variations are pre-dominant in this estuary, and tides propagate considerable distance through a complex network of various riverine systems, inlets, bays and creeks having vital implications on water mass exchange, reworking of deltaic sediments and the mixing process. The Hooghly River houses two major ports of national importance, viz. Kolkata Dock System and Haldia Dock Complex. Tidal forcing is primarily semi-diurnal in nature and with the presence of complex riverine morphology, the tidal characteristics are substantially modified causing various tidal constituents of compound tides. The present study performs location-specific tidal analysis and prediction utilizing one-hourly tide data with SLPR2 harmonic tidal analysis tool for Gangra situated upstream of the Hooghly River. In a geomorphologic perspective, the water-level elevation at Gangra results from natural tidal flow, as well as refracted effects from cross-flow due to the presence of two natural island barriers, namely Sagar Island situated southward off Gangra and Nayachara in the east. The Hooghly channel comprises of complex bathymetric features and tidal analysis at Gangra reveals the presence of Msf (luni-solar synodic fortnightly) tidal constituent. Very few locations in India have reported on the existence of the Msf tides, and Gangra is one among them. This study also performs a comprehensive validation between the computed monthly tidal prediction from SLPR2 and measured water level at Gangra. The skill level of prediction exhibits a good match. This study also investigates the influence of atmospheric effects on sea-level pressure variations and the resultant water-level elevation from extreme weather events such as depressions and severe cyclonic storms that occurred during 2013. The study signifies the importance of tidal analysis and prediction for operational needs.
... Amongst these defined four segments, the first three coastline section is a low lying, swampy, rapidly changing alluvial basin with large inputs of sediments deposited by the two vast river systems namely Ganges and Brahmaputra (Snead, 2010). The estimated annual sediment load from Brahmaputra is about 1028 t Km À 2 while the discharge from Ganges is about 502 t Km À 2 although the basin area is almost two times large compared to that of Brahmaputra (Barua, 1994). ...
Article
In a geomorphic sense, the Bangladesh located in the head Bay region comprises of numerous tidal creeks, waterway inlets, and complex coastline geometry. This region encompassing the world's largest deltaic system is thickly populated and extremely low-lying, and therefore highly susceptible to coastal flooding and sea level rise. High tidal range existent in this region primarily governs the hydrodynamic behavior and coastal processes. The present study deals on a comprehensive tidal analysis, understanding the variations in tidal behavior over spatial and temporal scales in the near-shore region off Bangladesh. The harmonic tidal analysis using SLPR2 estimates the tidal constituents using linear least squares with respective nodal correction. Tide gauge observations from five different stations viz; Hiron Point, Khepupara, Charchanga, Khal No-10, and Cox's Bazaar were used for tidal analysis. The results from SLPR2 signify considerable seasonal variations in water level attributed due to meteorological factors and excess river discharge. Tidal pattern at all these five stations are primarily mixed semi-diurnal with M 2 as the dominant constituent. The t-tide toolbox computed the equilibrium tidal amplitude for the study area. Some of the components known to be influenced by meteorological aspects such as Solar Annual component (Sa), Semi-Annual component (Ssa), and Solar Radiational component (S 1) have higher amplitudes than expected, in the study area. The shallowness of the delta cause severe deviations in the tidal behavior from equilibrium tides. Interaction of tides with river discharge also dominant in this region indicates the role of hydrological forcing. Interestingly, the study also reveals the existence of compound tidal constituent Msf in this region. Monthly analysis of Msf component, using FFT, revealed peaks corresponding to the monsoon, Kal-Baisakhi months and to the seasonal changes in atmospheric pressure, thereby unfolding the seasonal influence on Msf. The funnel shaped head Bay plays an important role in amplification of tidal constituents, wherein the form factor and maximum tide levels showed an increasing trend. This study also demonstrates how tidal dynamics can be elucidated using location specific water-level observations. Investigations on the annual variations in observed and predicted water levels clearly signify the seasonal patterns. The correlation analysis show a reasonable match with skill level exceeding 93%, and the overall prediction by SLPR2 is highly satisfactory.
... The estimated annual sediment yield of the Brahmaputra is 1028 tons km 2 , the highest among the world's largest rivers. On the other hand, the sediment yield from Ganges is only 502 tons km 2 although its basin area is twice that of the Brahmaputra (Barua, 1994). In the recent years the change in course of Ganges and Brahmaputra rivers has significant influence on the morphology of their alluvial flood plains (Rahman, 1993;Brammer, 1996). ...
Conference Paper
Full-text available
Abstrac The navigational aspects of marine transport and its manoeuvrability require precise knowledge on tides. Information on time varying water levels, magnitude and direction of tidal currents is quite critical in coastal waterways and estuarine environment. Real-time water levels along with other hydrodynamic parameters are used in almost all major ports for effective operations throughout the year. Also various coastal engineering projects require precise information on site-specific water level elevations. There is a rapid expansion of coastal infrastructure in the recent times, and therefore it is very essential to have reliable water level prediction system that caters the need for coastal engineers, port and harbour activities etc. The Sea Level Processing Package (SLPR2) developed by the University of Hawaii Sea Level Center in collaboration with National Oceanographic Data Center (NODC) provides reliable estimate of location specific sea level information. SLPR2 performs three primary tasks that include tidal analysis and prediction, quality control, and filtering. Harmonic tidal analysis using linear least square produces the relevant tidal constituents of a specific region. High frequency data (preferably one-hour duration) for a minimum duration of one complete year would suffice the tidal analysis phase in SLPR2. The tide prediction algorithm used in the present study uses a maximum of 68 harmonic constituents. The region of interest is the head Bay of Bengal region located along the east coast of India. Preliminary analysis of measured sea level data indicate that tide gauges located along Bangladesh has research quality data, and therefore used in this study. Station data from seven locations viz; Hiron Point, Khepupara, Charchanga, Chittagong, Khal No.10, Cox's Bazaar, and Teknaf all located in Bangladesh were used for tidal analysis, and thereafter the predictive capability of SLPR2 for one-year period was investigated. There are exceptions at two stations, Teknaf (comprising of 87% observed data) and Khal No.10 (99% of observed data), and remaining five stations are free from data gaps. In a hydrographic perspective, the Bangladesh region has complex network of waterways, and bottom topography have several detached shoals. Tides enter the Bangladesh coast through two submarine canyons, reaching Hiron Point and Cox Bazaar at almost the same time. Amongst the principal constituents, dominant modes are exhibited by M 2 and S 2 whose natural oscillation periods are 12 h 25 min, and 12 h respectively. The results from SLPR2 indicate considerable seasonal variation in water level prediction during the monsoon season, attributable to meteorological reasons and excess river discharge, at stations Cox Bazaar and Charchanga. The locations Hiron Point and Khepupara show elevated predicted tides after the onset of monsoon, indicating the presence of seasonal signature resulting from large amplitude of the annual tidal component 'Sa'. Residual time series produce the de-tidal water level variations attributed due to meteorological effects such as wind, atmospheric pressure and river discharge. Inspection of residual can help to quality control measured data such as datum level correction, and replacement of data voids. The effective shallow nature in NorthEastern Bay produces partial reflections thereby increasing the tidal range. In addition, the seasonal
... Mean water slope is 0.000076 over the first 130 km and 0.000065 further downstream (Flood Action Plan 24, 1996b). The grain size of the Jamuna is mainly fine sand and silt with less than 1% clay (FAP24, 1996b) and an average grain size of 220 μm (Barua, 1994;Sarker and Thorne, 2006). The fine and abundant sediment supply together with high water discharges results in the one of world's highest sediment yields that is estimated at between 590 and 792 Mt yr − 1 (FAP24, 1996a;Islam et al., 1999) with up to 10% transported as bedload . ...
Article
Big rivers dominate the world's continental surface, yet we are still learning about how they operate and whether they are explicably different, not only from each other, but also from smaller rivers. This paper uses global satellite imagery and ground field-experience to explain and illustrate why and how big rivers are strongly differentiated.At the largest scale, trans-continent sized rivers do not possess unified valley systems created by fluvial erosion but instead involve chains of interlinked domains with contrasted fluvial functions. Alluvial settings are dependent on mainstream and tributary inputs of water and sediment, but big river channel pattern variety is determined by contrasts in sediment feed-rates and differences in the rates and routes of sediment exchange. Four modes of alluvial exchange are recognised: (i) deposition on the floodplain (e.g., levees, infilled palaeochannels and floodbasins), (ii) exchanges involving main channels (e.g., bank erosion and accretion), (iii) deposition within main channels (e.g. bedforms from metres to 10s of kilometres in size), and (iv) material input from tributaries (sediment-rich or sediment-poor). Different combinations of sedimentation activity lead to floodplain morphologies for big rivers that can be classified into four types: (i) lacustrine-dominated, (ii) mainstream-dominated, (iii) tributary or accessory-stream dominated, and (iv) confined or bedrock-dominated.Channel patterning involves a range of main-channel, branch and floodplain styles promoted by variable sediment feeds, complex bed sediment transfers, variable lateral sediment exchanges, plural channel systems and incomplete mineral sedimentation of the hydraulic corridors set by tectonics and prior-valley trenching. In some of the world's largest rivers it is accessory and tributary channels, rather than main-river branches, which determine patterns of floodplain morphology. In some big rivers, but certainly not all, ponded lacustrine environments are common, with water bodies that vary from smaller water-filled swales and palaeochannels, to floodbasins and km-scale linear lakes in sediment-dammed tributaries. Organic sedimentation is significant along relatively sediment-poor and laterally-stable large rivers that fail to fill their alluvial corridors. Three case studies are used to illustrate this variability in big river pattern and process: the Ob, Jamuna and Paraná. These rivers are respectively dominated by meandering, braiding and mixed mainstream and accessory channel morphologies.Big rivers have some processes and patterns that are different from smaller rivers including: (i) no simple down-valley sequence in control variables and channel pattern, (ii) main channels with high width:depth ratios, (iii) few or no channel-wide unit bars migrating through the main thalwegs, (iv) extensive and low-gradient floodplains that provide space for channel shifting and floodplain sedimentation, (v) long distances between significant tributaries to allow full mixing of water and sediment discharges, (vi) in some places, partially-decoupled channels and floodplains, and (vii) significant floodplain water bodies that readily act as sinks for fine-grained sediment where this is supplied, or organic deposition.Although understanding of contemporary big river patterns requires attention to a range of timescales, including inheritance from sediments of Quaternary age, big rivers do have a distinctive character. The variety of patterns on big rivers may usefully be viewed in terms of sediment systems operating at both the catchment and reach scales. Intra-river variability and internal complexity show the need to understand contrasted sediment supply, through-put and alluvial exchange as determinants of big river morphology and pattern.
... Turbid water is delivered to the flood plain by overbank flow and through the offtakes of several distributaries that dissect the study area. Of the major rivers in Bangladesh, the Brahmaputra has the highest downstream gradient, having occupied its present channel only about 200 yr, and is highly sediment charged (Barua, 1994). The Brahmaputra in Bangladesh has an average annual water discharge of 19 600 m 3 /s with a tremendous seasonal range from 2820 m 3 /s in mid-dry season to an estimated 100 000 during the 1988 flood (Environment and Geographic Information Support Project, 1997). ...
Article
Recent authors have suggested that a significant proportion of the worldwide terrigenous sediment budget is trapped landward of the river-ocean boundary in high-load, tectonically active basins. To test this idea, modern flood-plain sediment accumulation rates were determined along a 110 km reach of the Brahmaputra (locally Jamuna) River using 137Cs geochronology of sediment cores and geographic information system (GIS) extrapolation to adjacent areas. 137Cs accumulation rates decrease exponentially away from the channel, from >4 cm/yr on the natural levees to
... population density, mineral stability, terrain topogra- phy and textural properties of the sediments in the Ben- gal basin. However, to attain a 'dynamic metastable equilibrium' (Schumm 1975) the tectonic nature of the drainage basin of the GBM system can be one of the ma- jor factor to consider (Barua 1994). Umitsu (1993) observed that the uppermost sedimentary unit of the Ganges delta and the surrounding region con- sists of silts and clay deposited in poorly drained low- lands. ...
Article
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The Bengal drainage basin is geologically one of the youngest and tectonically most active denudation regimes of the world, and encompasses the total lower reaches of the Ganges–Brahmaputra–Meghna (GBM) drainage basin. The GBM river system contributes around 4.5% of the total annual global freshwater flux to the oceans. The solute load of the GBM river system is dominated by the carbonate weathering products of the transport-limited denudation regime. However, in the Meghna basin, which drains a mountainous region, silicate weathering is slightly more predominant, and the solute load tends to be more influenced by the atmospheric contribution. The river system represents about 5% (152×106 t yr−1) of the annual global chemical flux to the world's oceans. The chemical denudation rate of the GBM system in the Bengal basin, is one of the world's highest (79–114 t km−2 yr−1), suggesting intensive weathering and erosion in the drainage basin both in Bangladesh as well as in the hinterlands of India and China.
... The estimated annual sediment yield of the Brahmaputra is 1028 tons km À2 , the highest among the world's largest rivers. On the other hand, the sediment yield of the Ganges is only 502 tons km À2 although its basin area is two times than that of the Brahmaputra (Barua, 1994). The swinging and avulsion of the courses of the Ganges and Brahmaputra rivers in recent history have significant influence on the morphology of their alluvial flood plains (Rahman, 1993;Brammer, 1996). ...
Article
The Ganges, Brahmaputra and Meghna/Barak rivers are lifelines for millions of people in South Asia in Nepal, India, Bhutan and Bangladesh. They supply water for food and fibre production and for industrial and domestic purposes. They are also sources of disastrous floods that cause substantial damage to agriculture and infrastructure in these countries. There are claims that flood discharges, areal extent, and damage-costs are getting worse in the Ganges, Brahmaputra and Meghna/Barak basins. The validity of these claims was examined by applying four different statistical tests to the peak discharge time series and flooded areas. The results indicate that no conclusive changes have occurred over the last few decades. Reports of increased flood damage may be due to a combination of other factors, such as improved damage assessment techniques, and the expansion and intensification of settlement in flood-prone areas, but this was not tested in this paper and should be top priority for future research.
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