Abstract:This paper based on the Shuangsheng section of Shiting River

a typical mountain river in Sichuan. The study mainly focused on those river construction distributed around this section.(This section contains the Culvert of the People’s Canal

the Shiting River Bridges of Chengdu-Lanzhou Railway and Chengdu-Mianyang Double-Track Highway

etc.) The bridge pile foundation in Shuangsheng section of Shiting River has been exposed up to 10m due to the flood during 2009-2013; the culvert increased the incision degree of riverbed and it declined 20.29m. Based on the HEC-RAS sediment calculation module

this paper studied changes of local base level of erosion on the riverbed and the impacts to evolution of riverbed under the condition of sediment refining and the clear water scouring. The numerical simulation showed that the changed local base level of erosion caused headward erosion and changed the gradient of a part of riverbed. The hardening projects of culvert intensified the fluvial process

and the junction with riverbed caused scour pit

in order to balance the erosion it is suggested to lower the evolution of the culvert. And the hardening project of bridges both intensified erosion and deposition

and accumulated the deposition between two bridges. According to the clear water scouring

the results were adequate as a prediction of fluvial process effected by river construction projects in mountain rivers. This project provided a reference for comprehensive development for river and the management. This analysis can be further develop to the study of the impacts of the destruction of armor layer under human factors such as sand mining

and it can be the reference for the design and protection of river construction. To reference the channel management after earthquake the study can combine the fluvial process both on cross section and profile to analysis the change of hydrodynamic and sediment after earthquake.