Sedimentary Features of Liaohe Estuary and the Evolution of Dynamics of the Tidal Banks

Sea area around Liaohe Estuary refer the region between Liaohe Estuary to the east and Xiaolinghe Estuary to the west,which's water depth is defined as 10m shallower. Drainages where enter into the sea are liaohe.Shuangtaihe, Dalinghe and Xiaolinghe rivers, characterized by 9.14×109m³/a of total water discharge and 4. 892×10⁷t/a of sediment input. Broad tidal flats and submerged deltas were formed attributed to the large capicity of sediment input. Based on the datd obtained from the seacoast survey in 1983 and the comprehensive investigation of Liaohe Esturay in 1988,the following two aspects are discussed in the present paper. 1. Sedimentary features and grain sige parameters are shown by figures and tables that concerning the sedimental units of different water dinmics in the the sea area around Liaohe estuary, such as tidal flat complexes, submarine delttas, barriers, tidal inlets and tidal furrows. Wheras the tidal flat complexes were mainly effected by tidal currents. From the lower,to middle and higher tidal flat as well as to the submarine delta,the grain size of sediments decrease from silt to muddy silt and sorting become worse,the oblique beddings gradally replaced by horizontal ones,meanwhile organism disturbance strenghened. The formation of the barriers were mainly controlled by wave and tide as well as topograph. The sediments, which's grain size decreasing from outer barrier (coarse sand) to inner barrier (sandy silt, silt),are structured by beddings and small-scaled cross-beddings,featured by ripples on the surface and weak organism disturbance. Tidal inlets distribute as finger gullys on both sides of barries and their V-shaped cross-sections deeper than 5m,that filled with fine sands structured by cross-beddings, shell buildings can be found but no organism disturbance. Tidal burrowes distributed mainly on tidal flats as snaking gullys of U-shaped cross-section obvious mud and sand interlayered structures were formed attributed to the swing of the burrows. 2. Prospecting of tidal flat dynamics. The estimate of tidal flats progression is based on the equilibrium equation of sediment discharge and the sedimentation rates that determined by 210Pb. Take the present height of high and low tidal lines as basis,the duration time needed for reaching the mean height of the supreme is estimated too. For the tidal flats west to Shangtaihe estuary, the duration time and progression rate estimated by the above two methods are 62 and 72 years, 127m/a and 114 m/a respectively,and for those locate between Shangtaihe estuary and Liaohe estuary,the datd are 182 and 193 years,22m/a and 20m/a respectively.