黄河下游游荡段河床萎缩的影响因素分析

黄河下游河床萎缩典型地表现为平滩水位下河床断面面积的趋势性减小,本文根据黄河下游实测断面和水沙资料采用相关分析方法研究了游荡段河床萎缩的主要影响因素。1960~1997年游荡段河床平滩水位下断面面积经历了1960~1964年和1974~1985年的扩张时期及1965~1973年和1986~1997年的萎缩时期,这种变化是多种因素共同作用的结果。在来水来沙中,年径流量是主要因素,洪峰流量和年平均含沙量是较次要的因素;本文所讨论的其它4个因素中,花园口以上引水量影响最大,降雨量影响次之,兰州以上水库的调节作用对河床断面面积的变化也有较明显的影响;三门峡水库三种不同的使用方式对下游河床有不同的影响,采取"蓄清排浊"方式后对下游河床的影响较小。

Influencing factors of the shrinkage of the braided reach of the lower Yellow River

The Yellow River has a vast expanse of drainage basin,but most of which is in arid and semi-arid areas.The influencing factors,such as increasing water demand,flow regulations by reservoirs,water diversion,and climate change impose intense effect on the channel.Based on field data in 1960-1997,the relations of several influencing factors with the wet area at full-bank stage of the wandering reach in the lower Yellow River are discussed,and linear multiple regression functions have been found. The bankfull cross-section area of the lower Yellow River experienced four alternating periods with expansion and shrinkage from 1960 to 1997,i.e.1960-1964 expansion,1965-1973 shrinkage,1974-1985 expansion and 1986-1997 shrinkage.The variation was caused by many factors.Among them annual runoff was most important and annual sediment load was minor important.The peak discharge in flood season and annual average sediment concentration have also influence.Moreover,water diversion is an important factor affecting the bankfull wet area.Flow regulation by the reservoirs upstream of Lanzhou station exerted a remarkable influence on bankfull wet area.Different operation modes of the Sanmenxia reservoir had a direct effect on the channel of the lower Yellow River,but the influence became limited after 1973 when the reservoir began the operation mode of "storing clear water and releasing flood".