Study on Medium and Small Design Floods in the Middle and Lower Reaches of The Yellow River Under the Current Underlying Surface

Influenced by both climate change and human activities, the measured flood of the Yellow River has decreased obviously in recent years, and the results of design flood of frequent magnitude in the middle and lower reaches are quite different from the actual situation. The measured flood in the middle and lower reaches is greatly affected by the large reservoirs in the upper reaches and the hydraulic and water conservancy projects in the middle reaches, and consistency processing of restoration and forward restoration shall be conducted for the influences. In this paper, the main influencing factors affecting the consistency are analyzed and determined, the operation modes of Longyangxia and Liujiaxia Reservoirs are studied, and the influences of large reservoirs in the upper reaches are restored and forward restored. The influence of the existing hydraulic and water conservancy projects in the middle reaches is analyzed, the rain-flood relationship of typical river basins and regional floods in different periods is presented, and the rain-flood relationship under the current underlying surface is used to restore/forward restore the influence of hydraulic and water conservancy projects in the middle reaches. The annual year analysis and the typical year analysis are performed to calculate the 5-year and smaller design floods at the main stream control stations under the current underlying surface. The results show that the 5-year design flood at Huayuankou station under the current underlying surface is about 20.6% ~ 26.1% less than the natural design flood results currently adopted.