Modern Dynamic Deposition Research Of Gudong Nearshore In Yellow River Delta

This paper takes Gudong nearshore as study object. On the basic of former people's research, this paper studied systematically of the dynamical character, basic character and transport character of the sediment and erosion and siltation mechanism of profiles.Firstly, the tidal character of Yellow River Delta and wave character of Gudong nearshore are discussed. Because the enflunce of no-tidal point, there are different tide types, tidal depth changes, M₂ no-tidal point moves in EES-trend. No. 5 Pile and Dongying harbour are the especial day-tidal region and the forth day-tidal region of China. There is inequality of tide in littoral region of delta. The wave of Gudong nearshore is mainly the wind-wave transported from Bohai Sea, the frequence of NE, SE and NW are 26.28%, 22.85% and 15.49%, respectively. NE-trending wave is constant wave and strong constant wave.Based on longterm observed profiles data, this paper researches the erosion and siltation character of profiles. The result shows: in the year of no-storm tide, the rate of erosion recession is increase, near dike eroded deeper and deep water depth retreats. CS19 profile eroded entirely after 1985(except 1993-1996), CS20 and CS21 profiles became eroded acutely in deep water, turned to up and down rush, middle silt; The profiles except CS22 became eroding of total erosion quantity after 1998. Strom tide leads to severe erosion, when strom tide happened in 1992 and 1997, re-siltation in the next year is more than the erosion in the first year, it's strong re-siltation in the deep water; The amount of strom tide erosion and re-siltation is different between two times.In the aspect of sediment of nearshore, this paper analysises the sediment parameters of medium diameter, average diameter, sorting coefficient, skewness coefficient and kurtosis coefficient. It's mainly clayey silt, poorly-sorted, forward-bias and narrow tip type. The sediments parallel distributed stripy with the coastline, particles become finner gradually and poorer-sorted form shore to sea. The bulding of groynes changes the sediment distribution nearby. The sediments in mouth bar are coarse and siltey sand; The sediments at the south of sea entrance are fine and clayey silt. Compared to 2002, the sediments at the north of sea entrance shoal are coarser obviously than before, change from sandey silt to siltey sand.From the Fleming ternary diagrams, the sedimentary dynamics of research region is strong generally. It is classified to three regions: near dike, estuary side foreland and shallow sedimentary dynamics, the sediments of first two are relatively coarser. According to Cao-Collins grain size trends model (GSTA model), North Gudong nearshore, sediments transport in NE-trend; East Gudong nearshore, sediments between No.2 drainage station groyne and No.18 bridge groyne transport in N-trend and transport in S-trend in the other region; Xintan water which is at the south of Gudong water and the north of estuary, sediments transport in E-trend.The sediments at the tidalland are mostly silt, poorly-sorted, forward-bias and narrow tip type. The sediments of Profile I which is at north are sandey silt; The sediments of Profiles N which is at the north of No.3 drainage station groyne change from sandey silt to silt from west to east. Because facing the main wave direction and no protection of groyne, the sediments at Profile I and N are more coaser and more sand. The sediments at south are more finner because of the protection of groyne and weak hydrodynamics.Finally, this paper discusses the mechanism of sediment trasnporting: the current cann't stir-up the sediment, 1.0m is constant wave (P(_1/3<1.0m)>54%). The region where water depth is in 5m is the mainly stirring-up region by wave. Current transport the sediments which are stirred-up by wave. When joint action of wave and current, sediments are stirred-up by wave, suspension concentration in bottom get high, it's uniform between surface and middle layer. The velocities of current and residual current increase, sediment transporting flux increase, which lead to coastal erosion. The destruct power of storm tide is stronger than other hydrodynamics. When strom tide appears, strom tide, wave and current effect together. The direct effect is increase-water. Wave in high station keeps long duration and has great destruct power. The sediments are stirred-up and transported, which lead to nearshore erosion.