基于原型观测与DEM的强风化花岗岩小流域水文过程模拟

Hydrological model of weathered granite watershed based on prototype monitoring and DEM

为了解华南花岗岩小流域特殊的产流机制,以土壤为砂壤土、基岩为强风化花岗岩的中山大学珠海校区滨海小流域作为研究对象,观测了2个分别代表森林、灌丛覆盖的5m×10m的径流试验场的产流过程和土壤含水率变化过程。观测结果表明超渗产流、优先流是试验场的重要产流方式,壤中流(尤其是在土壤-基岩界面上产生的壤中流)对试验场的总产流量也有较大贡献。在径流试验场原型观测基础上,建立了一个基于数字高程模型(DEM)的、包括地表径流、壤中流和基岩裂隙出流的三水源小流域水文模型。利用9次降雨径流过程对模型参数进行率定,利用4次降雨径流过程进行验证,模型的率定、验证均取得了良好的拟合效果。根据模型的模拟结果,在径流的起涨阶段地表产流贡献最大,而基岩裂隙出流对退水过程贡献明显。综合试验场原型观测结果与模型模拟结果得出结论:明显的壤中流和基岩裂隙出流是华南花岗岩小流域显著的产流特点。

The aim of the research is to investigate the particular runoff generation mechanisms of granite watersheds.The small coastal basin within Zhuhai campus of Sun Yat-sen University was selected for runoff generation study.With dominant sandy loam soil to a depth of 2 m and weathered granite bedrock in the basin,two plots of 5 m×10 m slope with bush and tree cover respectively were built to monitor the runoff processes of varied layers from surface,subsurface to the bedrock.Moisture profiles by time domain reflectometry（TDR） indicated that preferential flow and excess infiltration flow usually occurred,and subsurface flow,including runoff from the interface of soil and bedrock could contribute a large component to the hydrograph,especially during a heavy rainfall event.Based on these observations and flow discharge at two weirs,a hydrological model with three sources from overland flow,interflow and bedrock fissure flow was developed.The whole basin was separated into 2 736 cells（20 m×20 m） based on a digital elevation map（DEM） with runoff generation calculated for each cell.The linear reservoir concept was used to derive runoff components and route runoff to the next cell with the steepest slope among eight flow directions,while water was routed in the channel by solving one dimensional Saint-Venant equation.Nine rainfall events were used to calibrate the parameters by the trial-and-error method,and the other four were used to verify the model;hydrographs of both calibrated and verified events were reproduced relatively well using the model.According to the simulated result,the overland flow,particularly from the zone next to the channel was found to be the main contribution to the rising hydrograph,while the fissure flow to the recession processes.The monitoring and modeling results illustrated that obvious subsurface flow and bedrock fissure flow were the runoff generation characteristics of granite watersheds in southern China.