长江河口涨、落潮槽内的沙波地貌和输移特征

GEOMORPHOLOGIC FEATURES AND TRANSPORT OF SANDWAVES IN THE FLOOD AND EBB CHANNELS OF THE CHANGJIANG ESTUARY

涨、落潮槽是河口区的重要地貌单元,槽内由于不同的优势流作用而表现出不同的泥沙运移特征。沙波是底沙输移的表现,因此研究槽内的沙波特征对于涨、落潮槽的水动力和沉积地貌研究有重要的意义。本文依据现场声纳观测、测深仪测深、表层取样和现场水动力观测等方法获得河槽床面沙波和水动力资料,对沙波的几何形态、波高和全潮周期的迁移距离进行了分析和计算。结果显示,涨潮槽沙波的波长和波高都小于落潮槽内的沙波,波型指数大于落潮槽。涨潮槽内有部分沙波倾向上游,落潮槽沙波一般倾向下游。除了涨潮槽新桥水道在大潮时沙波净向上游输移,涨潮槽南小泓和落潮槽的底沙无论大、小潮都净向下游输移,大、小潮全潮周期内涨潮槽净输移距离约为1—10m,落潮槽内的沙波净输移距离约为涨潮槽的3倍。涨、落潮槽内的沙波特征和迁移距离的差异主要反映了河槽内不同水动力与河床地形的相互作用关系,这种差异导致了两种河槽中的底形不稳定。

Flood and ebb channels are important geomorphological units. Different deposits and hydrodynamic properties exist in these channels. Sandwave is an important way for bedload transport. Sandwave data obtained from sonar, geometric features, sedimentary composition and migratory distance during one tide cycle are analyzed and calculated. The results show the length and height of the sandwave in the flood channel are smaller than that in the ebb channel, but the L/H ratio of complex sandwave in the flood channel is higher. Sandwave in the ebb channel inclined to move downstream while sandwave in the flood channel inclined to move upstream. The sandwave in the ebb channel moves downstream during both spring and neap tides while sandwave in one flood channel moves upstream during spring tide. The features of sandwave are correlated to channel geomorphological properties, surrounding sand ridge and hydrodynamic environment.