| The operation of Xiaolangdi reservoir has changed the relationship between water and sediment by water storage and silt detention for preparation of the water-sediment regulation scheme. The water-sediment regulation scheme (WSRS) implementing in 2002 affects channel erosion by altering duration of the high flow, the sediment grain size and concentration. We find that the varitation of runoff, sediment load, the sediment grain size, and the river channel of the lower Yellow River is obvious after the implementation of the water-sediment regulation scheme. During the water-sediment modulation period the runoff and sediment into the sea accounted for a third of the annual, the runoff and sediment gather into the sea will surely have the significant impact on the Yellow River Delta. Therefore, studying the influence of WSRS on the sediment distribution, deposition process and the morphological evolution is helpful to grasp the variations of the Yellow River Delta.Based on Water and sediment data from 2000 to 2013, this paper analyzes the variation processes of water discharge and sediment load in the lower Yellow River. This article based on data of bed material, suspended load, bathymetry data and the remote sensing image in the Yellow River delta. By means of statistics and software of Surfer and ArcGIS, this paper discusses the evolution of sedimentary environment of the Yellow River Delta. The results are shown as follows:The WSRS by Xiaolangdi and other upper reservoirs changed the relationship between water and sediment. Incoming sediment coefficient reduced which benefit of erosion in lower Yellow River. Basing on erosion efficiency, this article divide 2000-2013 into three stages:preparation period of WSRS, the efficient phase of WSRS, the inefficiency phase of WSRS. During preparation period of water-sediment regulation (2000-2002):the reservoir was deposited rapid, the erosion efficiency was lower, the river cross-section was stable. During the efficient phase of water-sediment regulation, the grain size of suspended sediment and bed material, the erosion efficiency, the river cross-section, the bank-full discharge changed dramatically, However which is stable during inefficiency phase of water-sediment regulation. Although the influence of WSRS to water and sediment into lower Yellow River increased, the reduction of erosion efficiency is larger as the sediment grain size and concentration increase.The grain size of bed materials in the littoral area of Yellow River Delta in 2007 was coarser overall than that in 2000 due to the decrease of river sediment supply and the increase of the grain size of sediment. During 2008 to 2013, the bed materials which the sediment discharged into sea can influenced was fine and the skewness, kurtosis, skewness increase as the sediment discharged into sea became fine. By way of grain size analysis we found that:surface sediments carry abundant information (e.g., material sources, erosion and deposition of beach, seasonal changes of the erosion-sedimentation and storm surge disasters), and the information is mainly stored in the grain size frequency curve which can be extracted from the curve. Comparison of sedimentary types in current estuary and old Yellow River estuary showed that sand, silty sand and sandy silt are considered as erosion sedimentary, and sand-silt-clay, silt, clayey silt are sedimentation sedimentary.The evolution of dynamic morphology of the Yellow River delta is influenced by the sediment into sea, river channel avulsion changed, ocean dynamic and human activities. In the northern of Yellow River Delta, the evolution of subaqueous delta is mainly shaped by wave and tide current. The resuspension sediment was transported by tide current towards sea, causing the silitation in the depth water, therefor the coastline retreated. As the human activities including the enclosing tideland for cultivation and building shrimp and fish ponds during 2007-2013, the coastline in these area change slowly. In the eastern of Yellow River Delta, the coastline keep stable as it was protected by the sea wall. During 1996-2000, the subaqueous delta was eroded. After 2000, these area was siltation in all, as the area of sediment into sea enlarged due to WSRS.In the abandoned old estuary, the subaqueous delta is eroded by wave dynamic. The resuspension sediment was transported by tide current towards to the nearshore of LaiZhou Bay, causing the silitation in these area, therefore the coastline extend towards sea. In the present estuary, because the barrier effects of tidal shear front in the present estuary, the sediment delivered into the sea is mainly deposited in the nearshore area above 10m isobaths, some suspended sediment diffuses northwestern and southeastern under influence of residual current and the coastline extend towards sea, the area of estuary increase. As the WSRS implemented, the area of sediment delivered into the sea and the deposition range enlarge, nevertheless the siltation in nearshore slowly. Due to the direction of river channel avulsion shifted, the present estuary was strong silitation in the subaqueous delta especially in the front slope and the coastline extend towards sea,while the original estuary was erosion drastic. |
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