三峡工程蓄水以来宜昌–城陵矶河段洪水河槽阻力变化规律研究

Study on Flood Bed Resistance Variation Law of the Yichang to Chenlingji Reach after Impoundment of the Three Gorges Project

摘要: 三峡工程蓄水以来，长江干流宜昌–城陵矶河段发生了明显冲刷，河道下切、断面扩大，但洪水位却没有发生趋势性的变化，导致这种现象的原因可能是冲刷过程中河道综合阻力有所增加，目前综合阻力随时间的变化规律尚不清楚。本文基于宜昌–城陵矶河段的实测地形资料研究了河道坡降J、过水面积A、河道湿周χ等的变化规律，并以此为基础反向研究了河道综合糙率系数n随冲刷时间的变化规律。结果表明三峡工程蓄水运用以来，随着宜昌–城陵矶河段的冲刷发展，河道纵坡降J调平，洪水河槽过水面积A明显增大，湿周χ在蓄水初期略有增大、而后基本保持不变；在此过程中，宜昌–城陵矶河段洪水河槽综合糙率n是增大的，而且随着冲刷的发展、n呈逐渐增大的趋势，2016年相比于2002年综合糙率n平均增大了约16.7%。

Abstract: After the impoundment of the Three Gorges Project, the riverbed from Yichang to Chenglingji was eroded severely and the corresponded area of cross-section was enlarged substantially. Nevertheless, the flood water level remained unchanged all the time. This phenomenon could be due to the increase of bed resistance during erosion. Based on the measured topographic data from Yichang to Chenglingji, the variation of longitudinal slope J, cross-section area A and wetted perimeter χ were studied in this research, and then the roughness coefficient n of flood channel was inferred. After impoundment of the Three Gorges Project, the reach longitudinal slope J from Yichang to Chenglingji decreased and the cross-section area A increased continuously. However, the wetted perimeter χ increased slightly at the seedling stage, and then kept unchanged. During this process, the roughness coefficient n increased gradually with erosion of riverbed from Yichang to Chenglingji, the roughness n in the year of 2016 increased by 16.7% compared with that in 2002.