A Study of Sediment Sink between Longmen and Sanmenxia on the Yellow River

The Longmen-Sanmenxia reach of the middle Yellow River is one of the three major sediment sinks along the the mianstream of the Yellow River. Based on the concept of sediment budget and using the hydrometric data in the past 87 years, a study has been made on sediment storage, release and transport in this sediment sink. At the timescale of 80 years, the variation in sediment storage can be divided into four stages: (1) from 1920 to 1959, the Longmen-Sanmenxia sediment sink was in "quasi-natural" state, and sediment storage increased slowly; (2) from 1960 to 1967, due to sediment trapping of the Sanmenxia Reservoir, sedimentt storage increased rapidly; (3) from 1968 to 1985, the operational mode of the Sanmenxia reservoir was changed successively to "flood retention and sediment releasing afterwards" and "releasing sediment during high flow season and storing clear water during low flow season", sediment storage and release were nearly balanced each other; (3) from 1986 to 2006, water diversion increased rapidly, leading to an increase in sediment storage, although sediment input decreased. Within a year, sediment storage occurred during July and August, and sediment release occurred from September to the next May. During the 1800 years from 155 AD to 2006, the variation of sedimentation rate in the Longmen-Tongguan sink underwent a cycle from increase to decrease, which can be explained by the changed manner and intensity of human activities. During the "quasi-natural" stage from 1920 to 1959, the sediment storage and sediment delivery ratio in the Longmen-Sanmenxia sink were closely related with sediment and flow input to the sink.