Author(s): Changzhi Li; Zhaoyin Wang; Baosheng Wu
Keywords: Tongguan’s elevation; Retrogressive erosion; The lower Weihe River; Flood defense
Abstract: The Weihe River is the largest tributary of the Yellow River and empties itself into the Yellow River at Tongguan. The lower Weihe River is in the backwater region of Sanmenxia Reservoir. Severe sedimentation has occurred in this river since the impoundment of water at Sammenxia Reservoir began in1960. Tongguan elevation is defined as the stage of a flood discharge 1,000 m 3 ·s -1 at Tongguan hydrologic station, which is essentially the datum of the Weihe River. Floods as small as 2-or 3-years floods have caused great economic losses because of severe sedimentation and extremely high flood stages. To mitigate flood disasters and control sedimentation, scientists and engineers have urgently appealed for Tongguan’s elevation to be controlled. This paper presents a study of whether and how the flood stage will be reduced if Tongguan’s elevation is reduced by 2 m. Tongguan’s high elevation is one of the main reasons for the sedimentation in the lower Weihe River. Sedimentation volume in the river has been increasing and fluctuating as a result of the variation of Tongguan’s elevation. Retrogressive erosion occurred in the stream channel as a consequence of a fall in Tongguan’s elevation in the 1970s. But sedimentation has been continuing on the floodplain. Computations show that if the Tongguan’s elevation decreases by 2 m, the flood discharge capacity of the channel will increase and the risks of small-or mid-scale floods will diminish. However, the risk of a large flood is still high because the stage will be higher if an over-bank flood occurs.