Erosion And Sedimentation In Sanmenxia Reservoir In Recent Years

Since the impoundment of water of Sanmenxia reservoir commenced inSeptember 1960, serious sedimentation occurred in the reservoir area.Tongguan is 113.5km upstream of the reservoir, which is situated at a gorgesection downstream of the confluence of the Yellow, Wei and Luo River,forming a naturally constricted river reach which acts as a hydraulic controlsection that influences the river's stage. The Tongguan elevation is animportant guide line reflecting the sedimentation in the reservoir area.To alleviate the negative effect caused by the operation of Sanmenxiadam on the lower Wei River, the dam was reconstructed twice and theoperation mode was adjusted twice. Since 1986, sediment deposition inbackwater zone of the reservoir has aggravated, causing the channel bed atTongguan gradually rising due to the significant decrease in annual runoff.In recent years, the characteristic of water runoff and sediment loadchanged in a certain extent, a prototype experiment by limiting the maximumpool level not exceeding 318 m in the non-flood season has been conductedsince 2003, and an artificial cutoff was actualized in the reach between sectionno. 30 and 27 in June, 2003.Aiming at the new conditions, this paper gathers the latest data on waterrunoff, sediment load, water level and section, studies the features of waterrunoff and operation mode, distribution of sediment deposition and variationof longitudinal bed profile, and dominating factors affect sediment deposition.In this paper, the sedimentation processes in the reservoir area, the variationof Tongguan's elevation during the prototype experiment and the effect ofartificial cutoff were analyzed.In recent years, sedimentation in Sanmenxia reservoir area continued thecharacter before. It was found that the decrease of the elevation of Tongguanin 2003 was mainly caused by the flood flows in the flood season, while theinterim scheme of limiting the pool level not exceeding 318 m had littleeffect.This paper gives some advice on operation mode. That is, the operationof Sanmenxia reservoir in the non-flood season should not only limit themaximum pool level, but also consider the average pool level and their overalleffect. The ideal operation mode is decreasing the average pool level innon-flood season, the maximum pool level in flood season, and increasing thenumber of days for releasing sediment. Besides, as centain water runoff andoperation mode the meandering pattern rests with, artificial cutoff can onlyact as assistant measure.