强降雨条件下城市回填土草坪径流系数的影响因子分析

Factor Analysis of Runoff Coefficient Subjected to Heavy Rainfall on Urban Lawns with Backfill Soils

城市建设产生的大量建筑垃圾被无序堆放,显著改变了下垫面条件,在暴雨条件下形成了城市草坪特殊的产流模式。为了充分利用雨水,防止过度浇灌草坪,必须明确其物理性质和蓄水能力。基于人工降雨模拟方法模拟了多种暴雨条件,测定了紫花苜蓿、早熟禾和冬青在不同地形和降雨条件下的径流系数。通过测定回填土壤的粒径组成,探讨小区尺度下降雨、坡长、坡度等因素对径流系数的影响。结果表明:(1)只要建设方法和填土来源相同,同一草坪的保水能力基本一致。(2)径流系数和蓄水能力随着降雨量的增加而增加,当降雨达到一定量级,植被倒伏将导致蓄水能力的下降。(3)恒定降雨强度下,降雨历时延长导致降雨阈值的下降,但径流系数的增长率也因此降低。(4)坡长变化对降雨阈值的影响较小,但单位面积的径流量随坡长的增大呈先增大后减小的变化趋势。(5)10°坡面上的降雨阈值最低,同等降雨条件下径流系数最高,径流系数和坡度的关系在10°附近存在拐点。

Amount of construction and demolition waste was generated in urban area,which changed the underlying surface of urban catchment significantly.This caused a distinct mode of runoff generation in urban lawn,especially under the condition of torrential rains.In order to mitigate the waste of freshwater caused by over irrigation,it was necessary to identify the storage capacity of underlying surface in an urban lawn area.Aimed to evaluate the runoff coefficients of alfalfa,bluegrass and holly Cr,the percentage of rainfall that appeared as runoff,based on reproducing torrential rains using a designed rainfall simulator.The influences of rainfall,slope lengths and slope gradients on runoff generation were discussed through analyzing the soil physical properties at the site scale.The experimental results showed that：（1）Variability of water retention varied slightly within a single lawn if lawns were built in the same way.（2）Cr and Ws,water storage capacity per second,increased with the increasing rainfall,but declined due to vegetation lodging when the rainfall arrived at a certain value.（3）With constant rainfall intensity,the extension of rainfall duration caused the declines of rainfall threshold and growth rate of Cr.（4）The effect of slope length on rainfall threshold was insignificant,but runoff efficiency increased with decreasing slope length first and then declined.（5）On the 10 degree slope,rainfall threshold was the lowest and rainfall coefficient was the highest under the same conditions of rainfall.An inflection point exists around 10 degree to the relationship of runoff coefficient and slope gradient.