Study On Powder Sand Movement Laws In Coastal Dynamic Condition

The construction of harbors and other coastal engineering have been developing very fast in our country, with our country opening to outside and the economic development, and because our country shares a long sea shoal line. There are many sea shoal areas along the line which are covered by fine sand. The harbor and other coastal engineering are facing some disasters, such as sand accumulation and erosion, caused by fine sand. The sand moment laws over silt sea bed and sand sea bed have been studied by many scholars both domestic and oversea, in the meantime ,there are many success examples of harbor engineering and other coastal engineering, so we can understand it more clearly. The sand moment laws of fine sand are seldom studied, and not many engineering can be drawn as examples, some of the examples are success, but some are not success. Based on amount of conferences, fine sand moment laws under waves and current coexist condition are studied systematically by the means of theoretical analysis, water tank tests, analyses of site data and experiences summing-up of relative engineering. The main contents and conclusions are as follows:Sand moment is faint over fine sand beach when waves are small, water is clear. There is intense sand movement when winds and waves are strong enough. The main subjects about fine sand movement are the fine sand movement laws under bad climate condition.The movement patterns of fine sand are different from silt sand and sand. Under tide current and waves co-exist condition, fine sand movement patterns can be considered as in three layers, that are suspended load in upper water body, high concentration layer near bottom and bed load.Fine sand start movement laws are studied under current and waves co-exist condition, the results shows that the criterion can be described by modified Shields curve.The height, concentration and transport velocity of the high concentration layer near bottom are derived, so the sand transport rate in this layer can be calculated, and the formula is given. The deposition of suspended sand previous and ripe in upper water body and bed sand transport rate should be calculated by formula. The formula derived in this paper are checked and verified by site data. The results show that near bottom sand movement (high concentration layer near bottom and bed sand movement) is the main cause of deposition, deposition amount caused by suspended sand in upper water body is small. In the main cause, high concentration layer near bottom is the more important aspect. In nearshore zone, the stranger the waves are, the more important the bed sand would be in the main cause.Some harbor engineering features on fine sand seabed are summarized in this paper, and sand protection and deposition reducing manners are giaven also.