侵蚀基准面对石亭江双盛段河床演变的影响

Impacts of Changed Base Level of Erosion on the Riverbed Evolution in Shuangsheng Section of Shiting River

以四川典型山区河流石亭江双盛段为研究对象,针对该河段有多处涉河建筑物(包括人民渠穿江涵洞、成兰铁路石亭江大桥、成绵复线高速公路石亭江大桥等),在经历2009—2013年间多次洪水后引起桥梁桩基出露高达10 m、涵洞处河床下切20.29 m等影响涉河建筑物运行安全的情况,本文利用HEC-RAS的泥沙计算模块,研究在考虑床沙细化和清水冲刷的条件下,局部侵蚀基准面的改变(包括侵蚀基准面下降、涵洞固床工程和桥位处的硬化工程的存在与否)对石亭江双盛段河床演变的影响。结果表明,下游侵蚀基准面的下降、涵洞固床工程的存在和桥位处的硬化工程均会不同程度地加剧该河段的局部河床变形幅度。其中,下游侵蚀基准面的下降会引起溯源冲刷、改变局部河段纵比降;涵洞固床工程与河床交界处易形成局部冲刷坑并加剧河床下切,由此建议将涵洞下移;桥位硬化工程会加剧冲刷和淤积,并在两桥之间产生淤积。针对清水冲刷下的研究成果可对山区河道内涉河建筑物对河床演变的影响进行预测,为河流的综合开发与管理提供科学依据。本文可进一步研究该河段人工采砂等人类因素干扰下河床粗化表层的破坏对河床演变的影响,以对涉河建筑物的设计与防护提供参考;或结合震后河流水沙变化研究河道横向与纵向演变趋势,对震后河道治理提供依据。

This paper is based on the Shuangsheng section of Shiting River,a typical mountain river in Sichuan. The study mainly focused on those river constructions distributed around this section. These sections include 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 10 m due to the flood during 2009—2013; the culvert increased the incision degree of riverbed and it declined 20. 29 m. Based on the HEC-RAS sediment calculation module,thwas 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 was suggested to lower the evolution of the culvert. 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 affected by river construction projects in mountain rivers. This study 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 provide reference to channel management after earthquake,the study can further combine the fluvial process both on cross section and profile to analyze the change of hydrodynamic and sediment.