应用流体运动最小阻力原理导出了分流角发育的理论计算公式，并在弓形断面假定条件下，对不同宽度比时的分流角作了计算，得出了与实测值相一致的结果；同时还定量地证明了长江南北港、南北槽分流角发育由小到大，直至极限而消亡的规律。分汊水槽试验表明推移质大多偏向支汊，原因是在分流口支汊一侧由于边界层脱离而“搓”出一个个旋涡以吸引底沙。分析得知，从南港主槽下泄的落潮流，在扩散角增大处，也会产生旋涡并吸引底沙经南槽输移入海。

The circumfluence around the Jiuduan Sandbank is thoroughly studied by means of the princi-ple of least resistance in fluid dynamics. The diversion ratio of the North Channel for 1998 is calculated, which is almost the same as the field survey data. The normal and minimum diversion ratios of the North Channel after stages I, [I and I]I regulation works as well as the future phase are obtained. The numerical results and predicted value are accurate.

Based upon the long-term observation of field data, a two-dimensional numerical model is applied to simulating the tidal flow covering from the neap tide to spring nde m the radial sandbank area m the southern Yellow Sea. From the development of tidal current ridges under the hydrodynamic action, multi-purpose analysis and study are carried out, which include the propagation process of tidal wave, the distributions of ndal wave energy rate and tidal range, the tidal ellipses and traces. It is shown that the tidal current is the major dynamm factor for the formation and development of the radial sandbanks, and the differences of tidal wave energy rate and current strength determine the distract plane shapes of ridges and troughs in this region.

本文根据流体运动的最小阻力原理，研究了长江口九段沙的分流，导出了它发育长度的理论公式，这一公式的建立加深了对该河段河床演变规律的认识。文中计算了1998年南、北槽的分流比，预测了长江口深水航道整治工程一、二、三期及远景规划实施后，北槽在正常条件下的分流比，以及当丁坝间淤满时的最小分流比，这些计算值和预测值均有一定的精度。对深水航道治理的研究来说，本文又提供了一个新的方法。

In order to study the tidal current ridges, a three-dimensional numerical model is, for the first time, applied to studying the hydrodynamic circumstance with Houbolt's spiral assumption in the rachal sandbank area. It successfully reveals that the radial sandbanks are molded by to-and-fro tidal current as well as the subtransverse circulation current, and that both contribute to maintaining the interior dynamic balance of the sandbanks. It is also found that the subtransverse circulation current would not always appear in pair within the ridges. These discoveries enrich the theoretical results m hydrodynamics of tidal current ridges.