城市屋顶降雨径流过程单位线模型研究

Study on unit hydrograph model for rainfall-runoff simulation of urban roofs

城市屋顶按透水性质可分为不透水与绿色(渗透)屋顶。对于绿色屋顶,基于土壤水饱和下渗理论,考虑基质土壤层厚度有限性及表面积水深影响,推导建立了降雨径流过程的单位线模型,再联合不透水屋顶降雨径流过程单位线模型,共同构成城市屋顶降雨径流过程的单位线模型,并建立了统一的数学方程表达形式,参数包括响应速率与径流(产流)起始时间。其中,对于不透水与绿色屋顶,模型响应速率参数分别为坡面汇流时间的倒数与基质土壤层稳渗时间的倒数。根据不透水与绿色屋顶降雨径流过程实际监测数据,分别采用单位线模型进行了模拟,取得了良好的模拟效果。模型参数比较分析表明,绿色屋顶降雨径流削减效应主要依赖于基质土壤层的雨水蓄存作用,增大基质土壤层厚度可以增大雨水渗蓄量,并有效削减径流前期峰值,但对后期峰值的削减效应有所减弱,并会延长表面积水的排水时间。

According to the permeability characteristics,urban roofs can be divided into two types,impermeable roof and green roof.For the rainfall-runoff process on green roof,a unit hydrograph model was proposed based on the saturated infiltration theory,where the thickness limitation of substrate material layer and the influence of accumulated surface-water are considered.Meanwhile,Nash unit hydrograph model for rainfall-runoff process on impermeable roof is introduced.Then,a unified unit hydrograph model for rainfall-runoff simulation on different urban roof types was developed,in which there are two parameters,response rate and runoff generating time.For impermeable roof,model response rate is the reciprocal of concentration flow time.For green roof,model response rate is the reciprocal of stable infiltration time.Using the proposed unit hydrograph model,rainfall-runoff processes on impermeable roof and green roof are simulated.The results show that the estimated and measured values are consistent well.Comparison and analysis on model parameters for different urban roof types show that the rainwater storage capacity of substrate material layer plays an important role for the rainfall-runoff reduction effects of green roof.With the increase of substrate material layer thickness,both the rainwater storage capacity and the first peak-flow reduction effect will increase,but later the peak-flow reduction effect will decrease,and the drainage time of accumulated surface-water will be extended.