The delta is formed mainly by the large, sediment-laden waters of the Ganges and Brahmaputra rivers.
The river bed of the Ganges can be seen in the left of the image, while Brahmaputra can be seen to the right. The snow-covered Himalayas can be seen at the top of the image. The Ganges river carries fertile soil and nutrients, which it deposits across its vast delta floodplain.
It is here where the murky coloured waters mix with the darker coloured waters of the Indian Ocean. The water-quality data of four monitoring stations of the Dong- gang River for the period of are selected for trend analysis. These four water-quality parameters are integrated into an index called river pollution index RPI to indicate the pollution level of rivers.
Although widely used non-parametric Mann-Kendall test and linear regression exhibit computational efficiency to identify trends of water-quality indices, limitations of such approaches include sensitive to outliers and estimations of conditional mean only. Quantile regression, capable of identifying changes over time of any percentile values, is employed in this study to detect long-term trend of water-quality indices for the Dong- gang River located in southern Taiwan.
The results show that Dong- gang River 4 stations from to monthly long-term trends in water quality. To analyze s Dong- gang River long-term water quality trends and pollution characteristics. The results form Chau-Jhou station also ahowed simialar trends. Construction and maintenance of the Ganges -Brahmaputra-Meghna delta : linking process, morphology, and stratigraphy.
We present a review of the processes, morphology, and stratigraphy of the Ganges -Brahmaputra-Meghna delta GBMD , including insights gained from detailed elevation data. The review shows that the GBMD is best characterized as a composite system, with different regions having morphologic and stratigraphic attributes of an upland fluvial fan delta ; a lowland, backwater-reach delta ; a downdrift tidal delta plain; and an offshore subaqueous- delta clinoform.
These distinct areas of upland and lowland fluvial reaches and tidal dominance vary in time and space, and we distinguish late-Holocene phases of delta construction, maintenance, and decline similar to delta -lobe cycling in other systems.
The overall stability of the GBMD landform, relative to many deltas , reflects the efficient, widespread dispersal of sediment by the large monsoon discharge and high-energy tides that affect this region. However, we do identify portions of the delta that are in decline and losing elevation relative to sea level owing to insufficient sediment delivery.
These areas, some of which are well inland of the coast, represent those most at risk to the continued effect of sea-level rise.
Clicking in shallow rivers : short-range echolocation of Irrawaddy and Ganges River dolphins in a shallow, acoustically complex habitat. Toothed whales Cetacea, odontoceti use biosonar to navigate their environment and to find and catch prey.
All studied toothed whale species have evolved highly directional, high-amplitude ultrasonic clicks suited for long-range echolocation of prey in open water. Little is known about the biosonar signals of toothed whale species inhabiting freshwater habitats such as endangered river dolphins. To address the evolutionary pressures shaping the echolocation signal parameters of non-marine toothed whales, we investigated the biosonar source parameters of Ganges river dolphins Platanista gangetica gangetica and Irrawaddy dolphins Orcaella brevirostris within the river systems of the Sundarban mangrove forest.
Both Ganges and Irrawaddy dolphins produced echolocation clicks with a high repetition rate and low source level compared to marine species. These source levels are orders of magnitude lower than those of similar sized marine delphinids and may reflect an adaptation to a shallow, acoustically complex freshwater habitat with high reverberation and acoustic clutter.
The centroid frequency of Ganges river dolphin clicks are an octave lower than predicted from scaling, but with an estimated beamwidth comparable to that of porpoises. The unique bony maxillary crests found in the Platanista forehead may help achieve a higher directionality than expected using clicks nearly an octave lower than similar sized odontocetes.
Jensen, Frants H. These source levels are 1—2 orders of magnitude lower than those of similar sized marine delphinids and may reflect an adaptation to a shallow, acoustically complex freshwater habitat with high reverberation and acoustic clutter.
Bioaccumulation profiles of polychlorinated biphenyl congeners and organochlorine pesticides in Ganges River dolphins.
Isomer-specific concentrations of polychlorinated biphenyls PCBs including non-, mono-, and di-ortho-substituted congeners, DDT and its metabolites, hexachlorocyclohexane HCH isomers, chlordane compounds, and hexachlorobenzene HCB were determined in river dolphin blubber and prey fishes collected during through from the River Ganges in India.
Concentrations of organochlorines were also measured in the milk and liver of dolphins, benthic invertebrates, and sediments. The DDTs and PCBs were the predominant compounds found in dolphin tissues and fish that comprise the diet of dolphins.
Hexachlorobiphenyl congener 2. The mean 2,3,7,8-tetrachlorodibenzo-p-dioxin equivalents TEQs estimated in river dolphin blubber was greater than those that can cause adverse effects in mink. Comparison of organochlorine concentrations in river dolphins with those of the values reported for samples analyzed during through suggested that the contamination by these compounds has increased in the River Ganges.
Nile River Delta , Egypt. The Nile River Delta of Egypt The capital city of Cairo is at the apex of the delta. Just across the river from Cairo can be seen the ancient three big pyramids and sphinx at Giza and the Suez Canal is just to the right of the delta. The Gangetic plain of eastern India has been long known as the "bread basket" of the Indian subcontinent. However, indiscriminate use of pesticides in the agricultural fields is to increase crop production.
These resulted to increased vulnerability of pesticide pollution of the hydrological systems of the area, potentially exposing to significant human health consequences. Our present study delineate pesticides occurrence in lower Ganges in West Bengal. The major organic contaminants regularly detected in the studied reaches of the Ganges belong to wide range of herbicides and insecticides, which especially include organochlorides and organophosphates such as Aldrin, Alachlor, Lindane, Malathion, Chlorpyrifos and Methyl parathion.
Results show Alachlor and Malathion were the most abundant organic contaminant in the river. Among the other pesticides, one of the most venomous substances, Malathion has been noticed from the last year insecticide screening study. The mean concentration of river water Malathion was found to be 5 times higher than the maximum concentration limit MCL. Presence of Malathion or its derivative Malaoxon in river water is suspected to be caused by agricultural run-off and it showed a good correlation with river water chlorine concentrations.
River deltas are one of the environmental ecosystems most threatened by climate change and anthropogenic activity. While their low elevation gradients and fertile soil have made them optimal for human inhabitation and diverse ecologic growth, it also makes them susceptible to adverse effects of sea level rise, flooding, subsidence, and manmade structures such as dams, levees, and dikes. In this study we analyze the GBMD channel network, identify areas of maximum change of the network, and use this information to predict how the network will respond under future scenarios.
Landsat images of the delta from to are analyzed using new tools for the automatic extraction of channel networks from remotely sensed imagery [Isikdogan et al. The tools return channel width and channel centerline location at the resolution of the input imagery 30 m. Channel location variance over time is computed using the combined data from to and, based on this information, zones of highest change in the system are identified Figure 1. Network metrics measuring characteristics of the delta 's channels and islands are calculated for each year of the study and compared to the variance results in order to identify what metrics capture this change.
These results provide both a method to identify zones of the GBMD that are currently experiencing the most change, as well as a means to predict what areas of the delta will experience network changes in the future.
This information will be useful for informing coastal sustainability decisions about what areas of such a large and complex network should be the focus of remediation and mitigation efforts. Isikdogan, F. Bovik, P. Zambezi River Delta. It drains a watershed that spans eight countries and nearly 1. The Zambezi also Zambeze is the fourth largest river in Africa, and the largest east-flowing waterway.
Sandbars and barrier spits stretch across the mouths of the delta , and suspended sediment extends tens of kilometers out into the sea. The sandy outflow turns the coastal waters to a milky blue-green compared to the deep blue of open water in the Indian Ocean. The Zambezi Delta includes kilometers of coastline fronting 18, square kilometers 7,00 square miles of swamps, floodplains, and even savannahs inland.
The area has long been prized by subsistence fishermen and farmers, who find fertile ground for crops like sugar and fertile waters for prawns and fish. Two species of endangered cranes and one of the largest concentration of buffalo in Africa -- among many other species of wildlife -- have found a haven in this internationally recognized wetland.
However, the past six decades have brought great changes to the Zambezi Delta , which used to pour more water and sediment off of the continent. Hydropower dams upstream-most prominently, the Kariba and the Cahora Bassa-greatly reduce river flows during the wet season; they also trap sediments that would otherwise flow downstream.
The result has been less water reaching the delta and the floodplains, which rely on pulses of nutrients and sediments from annual and mostly benign natural flooding. The change in the flow of the river affects freshwater availability and quality in the delta. Strong flows push fresh water further out into the sea and naturally keep most of a delta full of fresh or mostly fresh water.
When that fresh flow eases, the wetlands become drier and more prone to fire. Salt water from the Indian Ocean also can penetrate further into the marsh. The prevalence of Clonorchis sinensis metacercariae Cs Mc was examined in freshwater fish from the water systems of Seomjin- gang River , the Republic of Korea.
Total 1, fish from 7 local sites of Seomjin- gang were examined by artificial digestion methods. The metacercariae of C. Their average density was 9. They were also found in Their average density was Cs Mc were detected in 77 The metacercariae of Metorchis orientalis were also detected in 6 fish species from 4 sites of Seomjin- gang. Conclusively, it has been confirmed that Cs Mc are more or less prevalent in fish from some water systems of Seomjin- gang in Korea.
The prevalence of Clonorchis sinensis metacercariae CsMc was examined in freshwater fish from the water systems of Seomjin- gang River , the Republic of Korea. CsMc were detected in 77 Conclusively, it has been confirmed that CsMc are more or less prevalent in fish from some water systems of Seomjin- gang in Korea. Impacts of climate change and socio-economic scenarios on flow and water quality of the Ganges , Brahmaputra and Meghna GBM river systems: low flow and flood statistics.
The potential impacts of climate change and socio-economic change on flow and water quality in rivers worldwide is a key area of interest. The Ganges -Brahmaputra-Meghna GBM is one of the largest river basins in the world serving a population of over million, and is of vital concern to India and Bangladesh as it provides fresh water for people, agriculture, industry, conservation and for the delta system downstream.
This paper seeks to assess future changes in flow and water quality utilising a modelling approach as a means of assessment in a very complex system. The INCA-N model has been applied to the Ganges , Brahmaputra and Meghna river systems to simulate flow and water quality along the rivers under a range of future climate conditions.
Three model realisations of the Met Office Hadley Centre global and regional climate models were selected from 17 perturbed model runs to evaluate a range of potential futures in climate.
In addition, the models have also been evaluated using socio-economic scenarios, comprising 1 a business as usual future, 2 a more sustainable future, and 3 a less sustainable future.
Model results for the s and the s indicate a significant increase in monsoon flows under the future climates, with enhanced flood potential. Low flows are predicted to fall with extended drought periods, which could have impacts on water and sediment supply, irrigated agriculture and saline intrusion.
In contrast, the socio-economic changes had relatively little impact on flows, except under the low flow regimes where increased irrigation could further reduce water availability. However, should large scale water transfers upstream of Bangladesh be constructed, these have the potential to reduce flows and divert water away from the delta region depending on the volume and timing of the transfers.
This could have significant implications for the delta in terms of saline intrusion, water supply, agriculture and maintaining crucial ecosystems such. Subsidence driving forces in large Delta Plain. Recent studies show large variability in subsidence rates among large delta plains that directly impact coastal management of these highly vulnerable environments. Observations show both significant spatial variation in subsidence across each delta , as well as large differences in magnitude between different deltas.
This variability raises the question of what are the driving forces that control subsidence in large delta plains that this study aims to address. Subsidence and sediment compaction is studied in 4 end-member large Delta Plains: the Ganges -Brahmaputra, the Mekong, the Mississippi and the Nile. The volume of sediment deposited in each delta plain during the Holocene is estimated and the compaction of the underlying sedimentary column is computed by using a backstripping approach.
Sediment compaction behaviors are defined accordingly to the observed clay, silt and organic contents, and the rate of subsidence associated with compaction is determined. The compaction appears to be significantly higher in delta plains characterized by a high sediment input and a high organic matter and clay content. Thus, the observed subsidence rates in the muddy Mekong delta appear to be one order of magnitude higher than other delta plains.
In contrast, subsidence rates are modest in the Ganges -Brahmaputra, the Mississippi and the Nile delta plains, except away from the major rivers where deposits are muddier.
Tidal controls on river delta morphology. River delta degradation has been caused by extraction of natural resources, sediment retention by reservoirs, and sea-level rise. Harbour development, construction of flood defences, sand mining and land reclamation emerge as key contemporary factors that exert an impact on delta morphology. Tides interacting with river discharge can play a crucial role in the morphodynamic development of deltas under pressure.
Emerging insights into tidal controls on river delta morphology suggest that--despite the active morphodynamics in tidal channels and mouth bar regions--tidal motion acts to stabilize delta morphology at the landscape scale under the condition that sediment import during low flows largely balances sediment export during high flows.
Distributary channels subject to tides show lower migration rates and are less easily flooded by the river because of opposing non-linear interactions between river discharge and the tide.
These interactions lead to flow changes within channels, and a more uniform distribution of discharge across channels. Sediment depletion and rigorous human interventions in deltas , including storm surge defence works, disrupt the dynamic morphological equilibrium and can lead to erosion and severe scour at the channel bed, even decades after an intervention.
Assessing regional climate simulations of the last 30 years over Ganges -Brahmaputra-Meghna River Basin. The Ganges -Brahmaputra-Meghna GBM River Basin presents a spatially diverse hydrological regime due to it's complex topography and escalating demand for freshwater resources.
This presents a big challenge in applying the current state-of-the-art regional climate models RCMs for climate change impact studies in the GBM River Basin. The results indicate that in general, RegCM4. On average, the RegCM4. Both RegCM4. Despite large spatial variations in onset and withdrawal periods across the GBM River Basin, the basin-averaged results agree reasonably well with the observed periods.
Although global climate model GCM driven simulations are generally poor in representing the interannual variability of precipitation and winter temperature variations, they tend to agree well with observed precipitation anomalies when driven by. Determining river discharge is of critical importance to many societies as they struggle with fresh water supply and risk of flooding. In Bangladesh, floods occur almost every year but with sufficient irregularity to have adverse social and economical consequences.
Important goals are to predict the discharge to be used for the optimization of agricultural practices, disaster mitigation and water resource management. The aim of this study is to determine the predictability of river discharge in a number of major rivers on time scale varying from weeks to a century.
We investigated predictability considering relationship between SST and discharge. Next, we consider IPCC model projections of river discharge while the models are statistically adjusted against observed discharges. On seasonal time scales, statistically significant correlations are found between mean monthly equatorial Pacific sea surface temperature SST and the summer Ganges discharge with lead times of months due to oscillations of the El Nino-Southern Oscillation ENSO phenomena.
In addition, there are strong correlations in the southwest and northeast Pacific. These, too, appear to be tied to the ENSO cycle. The Brahmaputra discharge, on the other hand, shows somewhat weaker relationships with tropical SST. Strong lagged correlations relationships are found with SST in the Bay of Bengal but these are the result of very warm SSTs and exceptional Brahmaputra discharge during the summer of When this year is removed from the time series, relationships weaken everywhere except in the northwestern Pacific for the June discharge and in areas of the central Pacific straddling the equator for the July discharge.
The relationships are relative strong, but they are persistent from month to month and suggest that two different and sequential factors influence Brahmaputra. Mississippi River Delta.
As the Mississippi River enters the Gulf of Mexico, it loses energy and dumps its load of sediment that it has carried on its journey through the mid continent. This pile of sediment, or mud, accumulates over the years building up the delta front. As one part of the delta becomes clogged with sediment, the delta front will migrate in search of new areas to grow.
The area shown on this image is the currently active delta front of the Mississippi. The migratory nature of the delta forms natural traps for oil. Most of the land in the image consists of mud flats and marsh lands. There is little human settlement in this area due to the instability of the sediments. The main shipping channel of the Mississippi River is the broad stripe running northwest to southeast.
With its 14 spectral bands from the visible to the thermal infrared wavelength region, and its high spatial resolution of 15 to 90 meters about 50 to feet , ASTER will image Earth for the next 6 years to map and monitor the changing surface of our planet.
Projections of historical and 21st century fluvial sediment delivery to the Ganges -Brahmaputra-Meghna, Mahanadi, and Volta deltas. Regular sediment inputs are required for deltas to maintain their surface elevation relative to sea level, which is important for avoiding salinization, erosion, and flooding.
However, fluvial sediment inputs to deltas are being threatened by changes in upstream catchments due to climate and land use change and, particularly, reservoir construction.
In this research, the global hydrogeomorphic model WBMsed is used to project and contrast 'pristine' no anthropogenic impacts and 'recent' historical fluvial sediment delivery to the Ganges -Brahmaputra-Meghna, Mahanadi, and Volta deltas. Additionally, 12 potential future scenarios of environmental change comprising combinations of four climate and three socioeconomic pathways, combined with a single construction timeline for future reservoirs, were simulated and analysed.
The Volta delta shows a large decrease in sediment delivery historically, from 8 to 0. For the Volta delta , catchment management short of removing or re-engineering the Volta dam would have little effect, however without careful management of the upstream catchments these deltas may be unable to maintain their current elevation relative to sea level, suggesting increasing salinization, erosion, flood hazards, and adaptation demands.
Growth laws for sub- delta crevasses in the Mississippi River Delta. River deltas are threatened by environmental change, including subsidence, global sea level rise, reduced sediment inputs and other local factors. In the Mississippi River Delta MRD these impacts are exemplified, and have led to proposed solutions to build land that include sediment diversions to reinitiate the delta cycle. Deltas were studied extensively using numerical models, theoretical and conceptual frameworks, empirical scaling relationships, laboratory models and field observations.
But predicting the future of deltas relies on field observations where for most deltas data are still lacking. Moreover, empirical and theoretical scaling laws may be influenced by the data used to develop them, while laboratory deltas may be influenced by scaling issues. Anthropogenic crevasses in the MRD are large enough to overcome limitations of laboratory deltas , and small enough to allow for rapid channel and wetland development, providing an ideal setting to investigate delta development mechanics.
Here we assessed growth laws of sub- delta crevasses SDC in the MRD, in two experimental laboratory deltas LD - weakly and strongly cohesive and compared them to river dominated deltas worldwide.
Channel and delta geometry metrics for each system were obtained using geospatial tools, bathymetric datasets, sediment size, and hydrodynamic observations. Results show that SDC follow growth laws similar to large river dominated deltas , with the exception of some that exhibit anomalous behavior with respect to the frequency and distance to a bifurcation and the fraction of wetted delta shoreline allometry metrics.
Most SDC exhibit a systematic decrease of non-dimensional channel geometries with increased bifurcation order, indicating that channels are adjusting to decreased flow after bifurcations occur, and exhibit linear trends for land allometry and width-depth ratio, although geometries decrease more rapidly per bifurcation order.
Measured distance to bifurcations in SDC. Deltas form where riverborne sediment accumulates at the interface of river mouths and their receiving water bodies. Their areal extent is determined by the net effect of processes that increase their extent, such as sediment accumulation, and processes that decrease their extent, such as erosion and subsidence.
Through sequential mapping and construction of river discharge and sediment histories, this study examined changes in the subaerial extents of the Cree Creek and Athabasca River Deltas both on the Athabasca River system and the Birch River Delta in northern Canada over the period The purpose of the study was to determine how, when, and why the deltas changed in areal extent.
Temporal growth patterns were similar across the Athabasca and Birch River systems indicative of a climatic signal. Little or no areal growth occurred from to ; moderate growth occurred between and the early to mids; and rapid growth occurred between and Factors that affected delta progradation included dredging, sediment supply, isostatic drowning, delta front bathymetry, sediment capture efficiency, and storms.
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