Suspended Sediment Dispersal Off The Huanghe (Yellow River) River Mouth And Its Morphological Effects Under Impact Of The Water-sediment Regulation Scheme

In this paper, based on the data obtained from the25-hour continuousobservations of hydrologic and sediment with three boats surveying simultaneouslyon four sections during the Huanghe Water and Sediment Regulation Scheme (WSRS)period (July6to13) in2013, the dispersal characteristics and deposition range of thesuspended sediment that flow into the Huanghe river mouth were studied. Themorphological effects of the suspended sediment dispersal were discussed based onthe grain-size data of surface sediments collected before the WSRS in May, during theWSRS in July and after the WSRS in September in2010combined with theLANDSAT satellite remote sensing data during1996-2008. The major results arepresented as follows.(1) During the WSRS, the river plume (the Huanghe diluted water with hightemperature and low salinity) is dispersed offshore rather than along the coast. Coarseparticles of the sediment that emptied into the sea rapidly deposited near the rivermouth with the dispersal extent of only approximately11km from the river mouth,resulting a mismatching of the water and sediment dispersal range. Thermocline andhalocline of water column are evident at each station during the WSRS. In the shallowarea, the surface and bottom layer mix strongly. But in the deep area, the suspendedsediment mainly transport below the thermocline.(2) During the Huanghe River water and sediment regulation the sedimentfluxes along the four transects show that the river mouth is mainly affected by therunoff of the Huanghe River, the sediment flux reaches a maximum value along thedirection of the river channel, with the peak of85×103g/m/s, but sharply decrease atapproximately10km away from the river mouth. The suspended sediment dispersal in the Qingshuigou estuary is slightly lower. It becomes lower in other regions whichis consistent with the distribution of sediment concentration.(3) Before the Huanghe River water and sediment regulation in2010, the grainsize of the sediment that deposited near the mouth was relatively coarse (with sandand silt as the main fractions), with good sorting; during the early period of the waterand sediment regulation, the sediment with coarser particles deposited rapidly near theriver mouth; after the water and sediment regulation, the surface sediment particlebecame finer with the increase of clay content and worse sorting, indicating that finersediment were deposited and overlaid the earlier deposited coarse sediment during thelate period of the water and sediment regulation. After winter storm erosion, theoverlying fine sediment was re-suspended into the water column, leaving thepreviously deposited coarse sediment exposed on the seabed, which are morepersistent to erosion. As the water and sediment regulation project carried out everyyear, the amount of coarse sediment deposited at the mouth increased, making agreater contribution to the land accretion of the river mouth.(4) Before the implementation of water and sediment regulation (1996-2002),the shoreline of river mouth propagated at an average maximum rate of about1.7km/a, while the shoreline of the abandoned river mouth retreated at an averagemaximum rate of0.4km/a. The Gudong area mainly experienced erosion, with anerosion rate of0.277km/a, while the northwest of the Laizhou Bay show slightlydeposition. After the water and sediment regulation, shoreline of the river mouthpropagated substantially with the maximum rate of about0.777km/a. Although theaccretion rate is less than that before the implementation of water and sedimentregulation, the total accumulation area is much larger than those during the period in1996-2002. The subaqueous part of the active delta lobe is mainly characterized byerosion with a total erosion amount of0.39Gt (Giga tons,109t) during the period in1996-2002, with the maximum accumulation thickness of about4m in the rivermouth area. However, the subaqueous part of the active delta lobe was shifted to anaccumulation phase with a total accumulation amount of0.28Gt after2002, with amaximum accumulation thickness of about6m. These indicate that after the implementation of water and sediment regulation, sediment that delivered by theHuanghe to the sea was mainly deposited in the vicinity of the river mouth due to thecoarse particle size, resulting that the land area increased and the subaqueous partshifted from an erosion phase to an accumulation phase.