A time-varying distributed unit hydrograph method considering soil moisture

[摘要] The distributed unit hydrograph (DUH) method has been widely usedfor flow routing in a watershed because it adequately characterizes theunderlying surface characteristics and varying rainfall intensity.Fundamental to the calculation of DUH is flow velocity. However, thecurrently used velocity formula assumes a global equilibrium of thewatershed and ignores the impact of time-varying soil moisture content onflow velocity, which thus leads to a larger flow velocity. The objective ofthis study was to identify a soil moisture content factor, which, based onthe tension water storage capacity curve, was derived to investigate theresponse of DUH to soil moisture content in unsaturated areas. Thus, animproved distributed unit hydrograph, based on time-varying soil moisturecontent, was obtained. The proposed DUH considered the impact of bothtime-varying rainfall intensity and soil moisture content on flow velocity,assuming the watershed to be not in equilibrium but varying with soilmoisture. The Qin River basin and Longhu River basin were selected as twocase studies, and the synthetic unit hydrograph (SUH), the time-varyingdistributed unit hydrograph (TDUH) and the current DUH methods werecompared with the proposed method. Then, the influence of time-varying soilmoisture content on flow velocity and flow routing was evaluated, and resultsshowed that the proposed method performed the best among the four methods.The shape and duration of the unit hydrograph (UH) were mainly related tothe soil moisture content at the initial stage of a rainstorm, and when thewatershed was approximately saturated, the grid flow velocity was mainlydominated by excess rainfall. The proposed method can be used for thewatersheds with sparse gauging stations and limited observed rainfall andrunoff data.

[学科分类] 妇产科学