深水航道的河势控制和航道回淤问题

Study on River Regime Control and Siltiation in Deepwater Channel

长江口深水航道的整治为检验和深化潮汐河口汊道整治理论及方法提供了依据。河势的宏观控制要求北槽维持落潮流输沙优势。分析表明,工程后北槽分流比下降,已接近河槽性质转变的阈值。一、二期整治工程使河槽断面由宽浅向相对窄深转变,形成了覆盖航槽的连续深泓,为航道维护提供了重要保证,但三期减淤工程使-8 m以下河槽断面向相对宽浅逆转,加上北槽中段过高的流速造成该河段的高含沙量和高输沙率以及该河段近底净输沙方向指向航槽内,使回淤量进一步增大。通过现场观测进一步揭示了近底高含沙量及浮泥形成的机制。进一步的减淤措施应注意恢复合理的导治线放宽率以使输沙率的沿程分布较为均匀。

The deep waterway regulation project in the Yangtze Estuary provides bases to verify and deepen the theories and methods for regulation of tidal and estuarial channels. In macroscopic view, the river regime requires the North Passage （NP） to keep the status that the sediment transport should be dominated during ebb. The analysis shows that the rate of freshwater through the NP decreases after the project, which is close to the critical value of the transformation of the river regime. The shape of transect changes after the I, II phase of the regulating project, from broad-shallow to narrow-deep, forming continuous thalweg covering the navigation channel, which provides the important guarantee to maintain the channel. The opposite change occurs in transects （below -8 m） after the third phase of the siltation-reduction project and the velocity of flow in the middle of North Passage becomes extremely high. The sediment concentration and sediment transport in this zone are both very high and the direction of the net sediment transport may point to the main channel, which would enlarge the back-siltation amount. The field data reveal the mechanism of the formation of the high sediment concentration and fluid mud near bottom. To make further efforts to reduce siltation, it is important to recovery the reasonable widening rate of regulation line so that the sediment transport rate will be uniform along the waterway.