北江红壤河岸坡面侵蚀水动力特征

受自然和人为干扰的交互影响,北江河岸带水土保持功能退化严重.本研究基于野外原位模拟径流冲刷试验,分析不同坡度(7°、9°、11°和15°)和放水强度(15、12和9 L/min)条件下红壤河岸坡面侵蚀水动力学参数变化特征及其与侵蚀产沙的关系.结果表明:1)平均流速随放水量增加而增加,在相同放水量下与坡度呈极显著线性正相关关系(P＜0.01);雷诺数随着放水时间增加总体上呈增大趋势,但增幅较小,坡度对雷诺数的影响较复杂,无明显规律;弗劳德数随放水历时增加呈先减小后趋于稳定,各处理的平均弗劳德数均＞1,说明坡面流均处于急流状态,且与坡度呈线性极显著正相关关系(P＜0.01);阻力系数随着放水时间增加总体呈增大趋势,且随坡度增加呈先增大后减小的趋势,说明阻力系数与坡度可能存在非线性关系.2)径流系数随放水历时增加呈先增大后趋于平稳趋势,相同放水量下随坡度增大而增大,同时坡度之间存在显著的幂函数关系(P＜0.05);侵蚀产沙量随着放水历时的增加呈先减小后稳定的趋势,且随坡度的增大而增大,二者之间存在显著的线性关系(P＜0.05).3)侵蚀产沙量随水流剪切力和水流功率的增大而增大,且与二者之间均存在线性显著正相关关系(P＜0.01).鉴于河岸带作为阻滞坡地泥沙进入河流的最后一道屏障,本研究的结果可为红壤河岸带坡面水土保持提供科学依据.

Hydrodynamic characteristics of surface runoff on red soil slope in the riparian zone of the Beijiang River

[Background] Influenced by interaction effects of human activities and natural factors,soil and water conservation function of the riparian zone in Beijiang River is facing serious degradation.[Methods] Based on the field runoff scouring experiment on the red soil slope in the riparian zone of the Beijiang River,this study analyzed the changes in hydrodynamic parameters and their relationship with erosion and sediment yields under different slope gradients (7°,9°,11°,and 15°) and runoff inflow rates (15 L/min,12 L/min,and 9 L/rin).[Results] 1) The average flow velocity increased with runoff inflow rates and presented significantly positive linear correlation with slope gradient (P ＜ 0.01) under the same runoff inflow condition.Reynolds number increased slightly with the increase of runoff inflow time,while it was irregular and complex with increasing slope gradients.The Froude number decreased firstly and then tended to be stable with the increase of the runoff inflow time,and the average Froude number was greater than 1 in all treatments,demonstrating that overland flow was in a state of torrent and presented significantly positive linear correlation with slope gradient (P ＜ 0.01).The resistance coefficient increased with runoff inflow time,and increased initially and then decreased with increasing slope gradients,inferring nonlinear relationship existed between resistance coefficient and slope gradient.2) Runoff coefficient increased first and then maintained stable with the increasing runoff inflow time,and showed significant power function relation with slope gradient (P ＜ 0.05).The relationship between sediment yield and discharge duration presented the same variation tendency as Reynolds number,while there was a significant linear relationship between sediment yield and slope (P ＜ 0.05).3) The sediment yield had significantly positive linear correlation with the flow shear stress and stream power (P ＜ 0.01).[Conclusions] As the last barrier,the riparian zone is of great significance for retarding surface runoff and trapping sediment from upland into river,thus above results can provide scientific evidence for water and soil conservation of riparian slope in red soil area.