弯道推移质同异岸输移的时空演变模拟

野外及室内实验观测均表明,弯道内的推移质泥沙运动同时存在着沿河道同岸和异岸的输移,然而对于同异岸输移的比例以往文献中还存在着很大的分歧。本文采用平面二维水沙数学模型CCHE2D模拟固定河岸大曲率弯道(中心线为110°正弦派生曲线)内的水沙运动,定量地描述了床面变化过程中泥沙同异岸输移的时空演变规律。计算结果表明,大曲率弯道在平床到冲淤平衡的发展过程中存在两个高强度冲刷区,即凸岸边滩上游区和凹岸区。凸岸边滩上游冲起的泥沙绝大部分都沿河道同岸输移到同一边滩下游;凹岸冲起的泥沙则先以同岸输移为主,待河床变形稳定后,受主流贴近凹岸的影响,异岸输移逐渐占优,绝大部分推移质颗粒都集中在"凹岸—过渡段浅滩—凹岸"这条输沙带内运动。

Modeling bedload transport along river meanders

Field observation and flume experiments indicate that bedload sediment in meanders takes two simultaneous motions, one part along the same bank, and the other part to the opposite bank. However, few quantitative studies can be found in the literature. The authors have simulated the flow and bedload transport in a 110° sine-generated meandering laboratorial flume by applying a two-dimensional depth-averaged model of unsteady flow and sediment transport, viz. CCHE2D. The calculations indicate two erosion zones of distinctively high scour intensity created in the process of bed deformation, one in the foreside of point bars at convex bank and the other near concave bank. In the early stage of bed deformation, nearly all the sediment eroded from these two zones are transported along the same banks, neither crossing the channel centerline nor moving to the opposite bank. After the equilibrium topography is reached, however, the main flow will gradually converge to the concave bank. Meanwhile, the moving paths of all particles are constrained to a concave bank-crossing bars-concave bank belt.