引海水冲刷河口治理黄河下游

Diverting Seawater to Scour the Estuary and to Regulate the Lower Yellow River

提出引海水 5 0 0～ 15 0 0m3 /s在利津注入黄河冲刷河口。冲刷后 ,在利津将产生 3 3～ 7 9m的水面跌差 ,可制止黄河河口延伸的溯源淤积作用上延 ,并诱发其上游产生溯源冲刷。估计可使艾山以下河道得到冲深。因挟沙海水的密度大于渤海环境水体的密度 ,咸浑水进入渤海时可形成异重流 ,将泥沙输去远方 ;而且断流期间河口还可能蚀退 ;因此引海水流量足够时 ,可使河口不外延或外延缓慢。从长远看 ,河口侵蚀基准面得到降低后 ,可以使黄河下游的淤积面均得到降低。这对缓解黄河下游河道持续淤高的局面和减少河口改道的风险都是有利的。黄河下游额定冲沙水占黄河水资源总量很大比例 ,大量抽取淡水会增加下游的淤积。引海水冲刷河口 ,可以增加河口地区从黄河抽取淡水的数量。这样抽取的淡水是冲沙水的一部分 ,不受用水分配额度的限制 ,对河口地区的发展具有重要意义。引海水冲刷口门段 ,可向渤海注入大量咸浑水、有利于改进渤海的环境生态条件。当然 。

The writers propose to divert seawater from Guanli Harbor on the coast of Laizhou Bay with transversal canals and have it discharged into the Lower Yellow River at Lijin, about 110 km upstream of the river mouth (route B, Fig 1). The flow diverted ranges from 500 to 1 500 m 3/s, to be stipulated later in the feasibility study. This flow of “clear' seawater would strongly scour the channel downstream of Lijin and reduce its surface slope so much that for a flood of 3 000 m 3/s an abrupt drop of 3 3 to 7 9m in the water surface would occur at Lijin. This drop would bring about retrogressive erosion of the riverbed upstream of the point of injection of seawater. The extent of this erosion is estimated to be 270 km upstream from Lijin. Thus a total of about 380 km of river channel would be scoured down. The reach downstream of Lijin would be transformed from an above-the-ground river to a down-in-the-ground river and the reach above Lijin would possess a deeper main channel. Safety in the defense against flood would thus be much enhanced. For rational use of the Yellow River water resources, the State Council has allocated definite water right to every riparian province. A runoff of about 20 km 3 is, however, to be reserved for sediment transport, in order to prevent the channel bed from excessive silting. With the facility available for the injection of seawater at Lijin, however, in the region down stream of Lijin one may redeem a portion of fresh water so reserved and restored the channel afterwards by scouring with seawater. Depending on capacities of pumping and reservoir storage available, the amount of fresh water redeemed may well run up to 1 km 3 annually. This would be very valuable to the development of the estuarine region. Since 1972, the Lower Yellow River has experienced a dry spell and has dried up from time to time. This has upset the ecological balance of the Bohai Sea because of interruption in the discharge of nutrient-carrying turbid water from the river. Scouring the estuary by diverting seawater will maintain a year round discharge of turbid water to the sea and help improve the ecological conditions as well as checking the receding of the coastline. Turbid seawater being of greater specific weight than the clear seawater would form density current when discharged to the Bohai Sea. Sediment would then be conveyed to points far from the river mouth, thus delaying or even stopping the extension of the Yellow River delta. Moreover, when the river dries up, the river mouth would most likely recede under the scour of the discharging seawater because of lack of sediment supply from the drainage basin. Taking all the factors into account, one may expect little delta extension when seawater is diverted for scouring. Lijin, where seawater is injected, may then be taken as the effective location of the river mouth where the longitudinal equilibrium profile of the Lower Yellow River would terminate. This equilibrium profile would be lower than the original one by 4～12 m, depending on the estimated values of equilibrium slope for the final reach of the estuary. The hazard of levee breaching is thus much reduced. [