24 May 2022
24 May 2022
Status: a revised version of this preprint is currently under review for the journal HESS.

A Time-Varying Distributed Unit Hydrograph method considering soil moisture content

Bin Yi1,2, Lu Chen1,2, Hansong Zhang3, Vijay P. Singh4, Ping Jiang5, Yizhuo Liu1,2, and Hongya Qiu1,2 Bin Yi et al.
  • 1School of Civil and Hydraulic Engineering, Huazhong University of Science and Technology, Wuhan, 430074, China
  • 2Hubei Key Laboratory of Digital Valley Science and Technology, Wuhan 430074, China
  • 3PowerChina Huadong Engineering Corporation Limited ,Hangzhou 310014, China
  • 4Department of Biological & Agricultural Engineering, and Zachry Department of Civil & Environmental Engineering, Texas A&M University, College Station, Texas 77843-2117, USA; National Water and Energy Center, UAE University, Al Ain, UAE
  • 5Meizhou Hydrological Bureau, Guangdong Province, Meizhou 514000, China

Abstract. The distributed unit hydrograph (DUH) method has been widely used for flow routing in a watershed, because it adequately characterizes the underlying surface characteristics and varying rainfall intensity. Fundamental to the calculation of DUH is flow velocity. However, the currently used velocity formula assumes a global equilibrium of the watershed and ignores the impact of time-varying soil moisture content on flow velocity, which thus leads to a larger flow velocity. The objective of this study is to identify a soil moisture content factor, which, based on the tension water storage capacity curve, was derived to investigate the response of DUH to soil moisture content in unsaturated areas. Thus, an improved distributed unit hydrograph, based on time-varying soil moisture content, was developed. The proposed DUH considered the impact of both the time-varying rainfall intensity and soil moisture content on flow velocity, assuming the watershed to be not in equilibrium but varying with soil moisture. The Qin River basin and Longhu River basin were selected as two case studies, and the synthetic unit hydrograph (SUH), time-varying distributed unit hydrograph (TDUH) and the current DUH methods were compared with the proposed method. The influence of time-varying soil moisture content on the flow velocity and flow routing was evaluated. Results showed that the proposed method performed the best among the four methods. The shape and duration of the unit hydrograph can be mainly related to the soil moisture content at the initial stage of a rainstorm. When the watershed is approximately saturated, the grid flow velocity is mainly dominated by excess rainfall.

Bin Yi et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on hess-2022-112', Anonymous Referee #1, 23 Jun 2022
    • AC2: 'Reply on RC1', Bin Yi, 10 Aug 2022
  • RC2: 'Comment on hess-2022-112', Anonymous Referee #2, 29 Jun 2022
    • AC1: 'Reply on RC2', Bin Yi, 10 Aug 2022

Bin Yi et al.

Bin Yi et al.


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Short summary
An improved Gis-derived distributed unit hydrograph routing method considering time-varying soil moisture content was proposed for flow routing. The proposed method considered the changes of time-varying soil moisture content and rainfall intensity. The response of underlying surface to the soil moisture content was considered as an important factor in this study. The SUH, DUH, TDUH and proposed routing methods were used for flood forecasts, and the simulated results were compared and discussed.