潮流在长江三角洲形成发育过程中所起作用的探讨

Study on the Role of Tidal Currents in the Process of Formation and Development of the Changjiang River Delta

长江三角洲为巨型潮控三角洲,探讨潮汐、潮流在其形成发育过程中所起的作用可为我国东部地区海陆相互作用过程的研究提供典型实例.数值模拟了冰后期最大海侵时渤、黄、东海的潮汐、潮流;计算了此时古长江河口湾及其周围海区的泥沙输运场,并根据泥沙输运率散度划分了海底冲淤区.得出:冰后期最大海侵时存在大致以古长江河口湾中轴线与其口门处两岸连线的交点为腹点、波腹线向海凸起的独特驻湖波波腹区,在其控制下,外海潮流以古长江河口湾湾口的腹点为顶点作辐聚、辐散运动.在古潮流场作用下,经历一个潮周期后,所有运动着的泥沙都自东、南东方向的外海主要向古长江河口湾内净输运,少量泥沙向古长江河口湾外的北东方向海区净输运.泥沙如此输运导致在古长江河口湾内、古长江河口湾外的北东方向海区以及古长江河口海南岸与钱塘江河口湾北岸之间的岸外海区发生淤积,而在古长江河口湾外的东、南东方向海区发生冲刷.海底的冲淤格局与泥沙输运场中输运率的聚合或发散状况一致.长江三角洲的形成发育是在长江带来大量泥沙,而外海的潮汐、潮流又有利于长江来沙最大限度地沉积在古长江河口海内及其周围海区的情况下实现的,外海的潮汐、潮流为长江三角洲的形成发育提供了必要而又有利的水动力条件.

The Changjiang River Delta is a delta of tremendous scale which is formed under the control of tide and tidal currents. The study on the role of tide and tidal currents in the process of formation and development of the Changjiang River Delta can provide a typical example for the o-ceanic-continental interaction process in the east area of our country. The tide and tidal currents in the Bohai, Huanghai and Donghai seas at the post-glacial marine transgression maximum are simulated, the sediment transport field in the Paleo - Yangtze River Estuary (PYRE) and its peripheral area at that time are calculated, and the seabed erosion-accretion pattern is obtained according to the divergence of sediment transport rate. The results show that a distinctive wave belly of standing tidal wave exists at the post - glacial marine transgression maximum and the wave belly lines protrudes towards sea from the wave belly point in the mouth of the PYRE. Under the wave belly control, tidal currents converge to or diverge from the wave belly point. After a single cycle, sediments moved by tidal currents are mainly netly transported into the PYRE in the southeast and east directions, while there is a small amount of sediment to be netly transported to the northeast - southwest area off the northern Jiangsu coast. The above sediment transport certainly results in deposition in the PYRE, in the northeast area to the PYRE, and in the nearshore area between the southern bank of the PYRE and the northern one of the Qiantangjiang River Estuary, while erosion occurs in the east and southeast area to the PYRE. The seabed erosion - accretion pattern is consistent with the situation of convergence or divergence of sediment transport rate. The Changjiang river delta developed under the condition that the Changjiang River supplies a large amount of sediment, and the tide and tidal currents in the open sea impel this sediment to deposit as much as possible in the PYRE and its peripheral area. The tide and tidal currents in the open sea provide necessary and favorable hydrodynamic conditions for the development of the Changjiang River Delta. When the Changjiang River Delta develops, it is very possible to form small scale sand bodies, which may be the embryonic form of the radial sand ridges in the southern Yellow Sea, in the northeast area to the PYRE. The stretch towards sea of the Changjiang River Delta gradually enlarges the Hangzhou Bay.