REGULATION OF WATER AND SEDIMENT BY RESERVOIRS THE CAUSE OF 'SECONDARY PERCHED RIVER' IN THE LOWER YELLOW RIVER

摘要

Serious deposition in the Lower Yellow River was resulted from the diminishing runoff and 'excessive sediment load, together with disadvantageous combination of water and sediment. This has accelerated the building up of the well-known "perched river". In recent years, with the operation of Longyangxia, Liujiaxia and Sanmenxia Reservoirs, the incoming water and sediment of the lower reaches become more incompatible than before, and regulation is becoming more and more intensive. The reservoirs release clear water in non-flood seasons and the flood water volume, the frequency of floods and the peak discharge have all been reduced in flood seasons. The deposition in the main channel aggravated in the Lower Yellow River and the "Secondary Perched River" with the rising of floodplain-berm and low-lying near dyke has been formed gradually. The elevation difference of the "Secondary Suspended River" between Dongbatou and Taochengpu is up to 3 m- 4 m and the transverse slope on the floodplain is 0.5%- 1per thousand where the situation of "Secondary Perched River" is most serious. Through analysing the variety of water-sediment characters in different periods and analyzing the distribution of sediment deposition and the variety of cross-sectional shape between Dongbatou and Taochengpu, we can conclude that regulation of water-sediment is a main reason of formation of the "Secondary Perched River" in the Lower Yellow River.