Influencing factors of the shrinkage of the braided reach of the lower Yellow River
黄河下游游荡段河床萎缩的影响因素分析

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".