Abstract:Human activities are closely linked to the riverbed evolution and the hydraulic geometry of river, which make the mountains river a series of change in morphology and sediment movement. In recent years, with the rapid increase in the demand for building sand, people mined river sand on a large scale, which changed the original river bed boundary condition of rivers and had considerable impact on riverbed evolution. Studying the influence of sand mining on the riverbed evolution of rivers has important academic and practical significance. Based on the HEC-RAS sediment calculation module, in combination with the practical field investigation, the numerical simulation had several kinds of sandpits in order to study the influence of different longitudinal profile dimensions of sandpit on the riverbed evolution of rivers. According to the data and the practical field investigation, firstly the experiment protocoled HEC-RAS section distribution of numerical model and boundary condition. And then on the condition that the volume and width of sandpit was almost same, five kinds of sandpits with different depth-length ratio was set up. After simulation by HEC-RAS sediment calculation module, the data of the reach longitudinal profile and sediment erosion or deposition of every section were counted and analyzed. The results indicated that erosion of riverbed were promoted by artificial sand mining and negative related to depth-length ratio of sandpit. In addition, with the increase of depth-length ratio, that erosion of upstream declined, while erosion of downstream was different which declined at first and then grown. What’s more, Sandpit would change the channel local slope and the upstream local slope increased, while the downstream local slope decreased. The conclusions can provide certain reference to the protection and design of across river buildings and exploiting plan.