The Study Of Sediment Movement Of Sandbar Profile And Recovery Profile

In shallow water areas of coastal, wave is the main driving force to cause sediment movement, when the waves enter shallow water, the movement of water begin to affect the sediment of seabed, when the shear stress of wave flow on the bed reaches a critical value, sediment begin to move, sediment trajectory velocity increases with the water depth decreases, the movement became increasingly evident, form ripples outside the surf zone, the existence of ripples make the movement of sediment more complicated.Inside the surf zone, the turbulence caused by wave breaking activates sediment movement substantially, sediment scoured by waves accumulation in an offshore zone and form a sandbar,the formation of sandbar make waves broken in distant places, finally,sanbar tends to adapt to the wave conditions to achieve a balance, due to wave breaking,the affect of broken waves weaken,therefor to protect the coast.Through the establishment of the sandbar coast physical model and analyze the experimental datas,aim to research the law of motion of the sandbar and the associated sediment movement phenomenon in different slopes (1:10and1:20slope) under storm wave conditions and often wave conditions.They are:(1)The sediment transport characteristics of sandbar under storm wave conditions. Include the vertical distribution of suspended sediment concentration, suspended sediment mass flux and spectral analysis, and the changment of net sediment transport rate and bed load transport rate in the the movement process of sandbar. The results showed that:the time series of the suspended sediment concentration related to wave conditions, the regular wave base frequency play a major role in the movement of sediment. The movement of suspended sediment concentration mainly rely on the wave group frequency and the base frequency as the increase of wave group modulation coefficient8, the frequency of the wave group make the greater contribution to the movement of sediment.Sediment transport is also depended on the spatial position of sandbar, the distribution of sediment concentration befor the sandbar along the depth approximately equal to wich behind and above the sandbar crest, the sediment concentration decreases with the distance from the bottom. The wave average water flow rate before and above the sandbar is different to which behind the sandbar crest,average velocity in the front and above the crest decrease with the depth of water,which behind the sandbar increase with water depth.. The onshore and offshore movement of the sanbar has little effect on average velocity distribution. In the same wave condition, the mean average velocity of the1:10slope is greater than which of1:20slope. In the similar exercise intensity, the net sediment and bed load transport of1:10slop is much larger than which of1:20slope (close to1times). the magnitude of net load transport proportional to the movement of sandbar,they have the same directions. Bed load transport suspended to net sediment transport and suspende sediment transport, the magnitude of bed load transport proportional to the movement of sandbar,if the movent of sandbar is relatively strong.they have the same directions(2) Sediment transport characteristics under the normal wave conditions. The sandbar which formed by storm wave conditions disappear gradually in the role of normal wave conditions, water depth bove the crest gradually increase, bed load transport, suspended sediment transport rate and the total sediment transport rate gradually decreases,when the terrain stability, the total sediment load close to0. Vertical distribution of sediment concentration is similar to storm wave conditions,the concentration blow water is larger than which on the surface. Bed load transport and net sediment transport move toward to the shore, the suspended load is offshore. The net sediment transport to shore form normal wave profile which has a berm.(3) Sediment transport rate include average flow, short wave and long wave contribution under storm and normal wave conditions, the average flow and long-wave conveyor sediment offshore,and the shortwave conveyor sediment to the shore, the average water velocity take the most important role in sediment transport.