On the Connections Between Surficial Processes and Stratigraphy in River Deltas
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Abstract:
We explore connections between surficial deltaic processes (e.g. avulsion, deposition) and the stratigraphic record using a simple numerical model of delta-plain evolution, with the aim of constraining these connections and thus improving prediction of subsurface features. The model represents channel dynamics using a simple but flexible cellular approach, and is unique in that it explicitly includes backwater effects that are known to be important in low-gradient channel networks. The patterns of channel deposits in the stratigraphic record vary spatially due to variation in avulsion statistics with radial distance from the delta's source of water and sediment. We introduce channel residence time as an important statistical measure of the surface channel kinematics. The model suggests that the mean channel residence time anywhere within the delta is nicely described by a power law distribution showing a cutoff that depends on radial distance. Thicknesses of channel deposits are not uniquely determined by the residence time of channelization. The channel residence time distributions at given radial distances from the source are found to be approximately lognormally distributed, a finding consistent with the scale-dependent radial structure of channel deposits in the stratigraphic record.Keywords:
River delta
Deposition
During the twentieth century about 25% of the wetlands of the Mississippi delta was lost, partially a result of isolation of the river from the delta. River diversions are being implemented to reintroduce river water to the delta plain. We synthesize here the results of extensive studies on a river diversion at Caernarvon, Louisiana, one of the largest diversions in the delta.
River delta
Mississippi delta
Coastal plain
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River delta
River mouth
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Previous studies mostly focus on an individual delta, or deltas at a global scale, to explore dam effects on deltaic hydrological alteration and morphological evolution, while comparative studies on selected similar deltas remain scarce. In this study, we compare the alteration of river discharge and sediment load, as well as the associated deltaic area and shoreline, of two deltas, namely, the Volta River Delta in Ghana and the Yellow River Delta in China, which are subject to similar forcings and mainstem dam influences. The results show that the sediment loads of the Volta River Delta and Yellow River Delta have decreased abruptly and gradually, respectively, to ~10% of the pre-dam level, presumably due to differences in reservoir capacity and upstream dam location. Sediment decline has led to a decrease of the fluvial dominance ratio, which has also been affected by the river mouth location and shoreline orientation. As a consequence, the area of the Volta River Delta has shifted to a new quasi-equilibrium, whereas the Yellow River Delta has kept prograding. This comparative study provides references for understanding the future evolution of similar deltas around the world.
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Dominance (genetics)
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Deltas are essential for studying the nature and behaviour of a large river. They are part subaerial and part subaqueous accumulation of sediment at the mouth of a river draining into a sea or a lake. A delta is divided primarily into a subaerial delta and a subaqueous delta. The subaerial delta may be further divided into a tidal delta and a non-tidal delta. Morphologically deltas can be divided into three parts: delta plain, delta front, and prodelta. Deltas of large rivers can be complex. Such a delta may extend over a large area and display varied morphology, multiple delta-forming processes, and the contribution of water and sediment discharges of the large river. The Ganga-Brahmaputra Delta demonstrates the complex nature of major deltas. The evolution of the delta is related to changes in the river system, climate, and sea level during the Late Pleistocene and Holocene.
Subaerial
River delta
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Area changes of plain reservoirs and aquafarms in the Yellow River Delta with remote sensing(RS) data and geographic information system(GIS)are presented in this paper.Results indicate that the areas of reservoirs and aquafarms in the Yellow River Delta are very small in 1976,and they increased very slowly until the year of 1981.From the year of 1986,they increased very quickly.According to the regression analysis between areas and years,areas of plain reservoirs and aquafarms in the Yellow River Delta in the year of 2005 and 2010 will be 352 km~2 and 418 km~2 respectively.These results can help to give decision-makers some evidence for management of the Yellow River Delta.
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Coastal plain
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