黄土高原关中地区植草沟径流水力学特性

Hydrodynamic characteristics of grass swale runoff in Guanzhong area of Loess Plateau,Northwest China

植草沟被广泛应用于海绵城市建设中,可有效改善城市生态环境。为探究植草沟径流调控作用的机理,通过放水模拟试验,研究了5个坡度(1%、2%、3%、4%、5%)、5个放水流量(20、30、40、50、60 L·min^(-1))组合条件下植草沟径流的水力学特性与断面流速分布变化规律。结果表明:植草沟径流水力学特性主要表现为,随流量和坡度的增加,流速、雷诺数和佛汝德数均逐渐增加,曼宁糙率系数与Darcy-Weisbach阻力系数逐渐减小。流速(V)可以用流量(Q)与坡度(S)的幂函数V=0.3387Q^(0.555)S^(0.6601)来表示。雷诺数和佛汝德数变化范围分别为1160.95~6596.82和0.17~1.21,径流流态均为紊流,流型受坡度影响较大。流量和坡度较小时,两者对阻力系数的影响较大,试验条件下水流阻力系数与雷诺数呈负相关关系。植草沟径流断面流速分布表现出关于中心两侧对称分布,最大流速点位于中心水面处,断面流速等值线随流量和坡度的增加而逐渐变密,流速变化梯度增大。本研究可为黄土区海绵城市建设中植草沟的设计应用与水力计算提供理论基础,也可以通过分析植草沟径流水力学特性以探索其径流调控机理。

Grass swale has been widely used in sponge city construction,which can effectively improve the urban ecological environment.To explore the regulation mechanism of runoff in grass swale,runoff scouring experiment was carried out to study the hydrodynamic characteristics of runoff and the distribution of cross-section velocity under the combined conditions of five slopes(1%,2%,3%,4%,5%)and five scour flows(20,30,40,50,60 L·min).With the increases of flow rate and slope,flow velocity,Reynolds number and Froude number all increased gradually,while the Manning roughness coefficient and Darcy-Weisbach friction coefficient decreased gradually.The velocity(V)could be expressed as a power function V=0.3387Q^(0.555)S^(0.6601) of flow rate(Q)and slope(S).The variation ranges of Reynolds number and Froude number were 1160.95-6596.82 and 0.17-1.21,respectively.The runoff flow patterns were all turbulent.The flow pattern was greatly affected by the slope.When flow rate and slope were small,they had great influence on friction coefficient.Under the experimental conditions,the Darcy-Weisbach friction coefficient was negatively correlated with Reynolds number.The velocity distribution of cross-section showed symmetrical distribution on both sides of the center.The maximum velocity point was located at the center of water surface.With the increases of flow rate and slope,the velocity contours of cross section gradually became dense and the gradient of the velocity change increased.Our results provide a theoretical basis for the design,application and hydraulic calculation of grass swale in the construction of sponge cities in loess areas,and reveal the runoff regulation mechanism by analyzing the hydraulic characteristics of grass swale runoff.