常流河向季节河转变过程中河床适应性调整及对行洪影响--以黄河和滹沱河为例

研究黄河和滹沱河对季节河化的适应性调整，发现季节化程度较高的滹沱河下游河床断面和平面形态调整幅度不大，而河床的糙率成倍增加造成下游的小水大灾现象；黄河下游近年流量减小，不断断流，主槽淤积，虽然河槽断面形态在游荡段变得更窄深，但主槽明显变小、变窄、变高，构成下游近年出现的小水大灾现象的主要原因。

Channel Adjustment to River Transformation from Permanent to Seasonal and Effects on Flood Control--The Case of the Yellow River and the Hutuo River

The Hutuo River has been strongly regulated after two large reservoirs were built on the river in 1959.The annual runoff and mean sediment concentration in the lower reaches of the river in the period from 1969 to1988 were decreased by 13.7 and 9.2 times respectively than those in the period before 1960. In the recent overtwo decades, there were only small water flows down the reservoirs in flood season, and the river kept dry in therest time of the year. The discharge of the lower Yellow River decreased by over 1/3 in the period 1986- 1996comparing with that in the 1950' s and the 1960' s, but the mean sediment concentration changed inconsider-ably. The phenomenon of flow breaking occurred as early as 1972 in the river, and the time and coverage of flowbreaking had increased steadily thenceforth. Therefore, two of them have become essentially seasonal rivers. The paper discusses the adaptive adjustment of channels of the Yellow River and the Hutuo River to thechange from a permanent to a seasonal river. The analyses show that the channel was eroded upstream and silteddownstream along the lower reaches of the Hutuo River and was cut in the lower part and uplifted in the upperpart cross-sectionally. Since the river has been nearly cut off the flow and sediment load, the natural heavy sedi-ment accumulation before 1959 has disappeared, and the changes in channel geometry and sinuosity were notsignificant. However, the hydraulic coarseness of the channel has been nearly doubled as a result of the invasionof vegetation into the channel and other reasons, resulting in the frequent occurrence of large disasters caused bysmall discharges which were harmless before. In the case of the Yellow River, the concentrated sediment accu-mulation in main channel has taken place in recent years since the discharge of the river was lowered conspicu-ously. Although the channel was deepened in the braided reach, it was seriously uplifted and narrowed, with ob-vious decrease in capacity, in the overall lower reaches. The result of the channel adjustment was the obvious ris-ing of water level of a certain discharge and the huge disasters occasioned by small floods in recent years. Withthe enhancement of regulation, the possibility of increase in hydraulic roughness of the channel of the YellowRiver due to the invasion of vegetation as the case of the Hutuo River should be paid more attentio