Feasibility study on stormwater resource utilization for groundwater recharge in Gadasu small watershed

Abstract

[Objective] The utilization of stormwater resources plays a critical role in enhancing integrated small watershed management and alleviating water shortage in semi-arid regions. The small watershed ecosystems are highly sensitive to groundwater level fluctuations, making the evaluation of stormwater resource utilization for groundwater recharge essential. This also constitutes a key aspect of feasibility studies for underground reservoir construction in semi-arid regions. [Methods] An underground reservoir project in a small watershed within northern semi-arid regions was selected as the study background.Surface runoff generated by rainfall from 1981 to 2023 was analyzed using a modified SCS-CN(curve number) model. The Pearson Type Ⅲ(P-Ⅲ) curve fitting method was employed to determine representative runoff values at 25%, 50%, and 75% rainfall frequencies under different conditions. A coupled surface water-groundwater numerical model was established using the MODFLOW boundary condition method to simulate groundwater flow field variations under different conditions. Furthermore, the potential of groundwater reservoirs to regulate stormwater during flood seasons and balance seasonal water availability was quantified. [Results] The result showed that:(1) utilizing regional analytical rainfall data instead of rain gauge observations effectively addressed issues of data anomalies and high dispersion, with average monthly and seasonal rainfall fitting coefficients of 0. 73.(2) The initial abstraction ratio in the modified SCS-CN model was determined to be 0. 02, and the predicted runoff result closely matched design runoff values derived from the hydrological analogy method.(3) Groundwater recharge through stormwater conservation significantly increased groundwater levels, with a stable rise of 1. 66 m under different rainfall frequency conditions.Additionally, runoff retention in flood detention areas showed exponential growth, accounting for 41. 9%, 73. 2%, and 109. 15%of total runoff, respectively. [Conclusion] The result demonstrate that the modified SCS-CN model accurately predicts rainfallinduced surface runoff in arid and semi-arid regions, especially for small agricultural watersheds where direct measurements are challenging and soil information is limited. The coupled surface water-groundwater model established using the switching boundary condition method effectively captures variations in upstream groundwater flow fields before and after the implementation of stormwater conservation project. Furthermore, stormwater collected in detention areas can be converted into a water supply for the non-flood season, ensuring the rational utilization of stormwater resources. Therefore, the collection potential of surface runoff is crucial for the construction of underground reservoir and largely determines project feasibility. The findings provide theoretical support and technical references for integrated watershed management in northern semi-arid regions and similar mountainous small watersheds.

Keywords

stormwater resource utilization / modified SCS-CN model / rainfall / runoff / coupled surface water-groundwater model / groundwater flow field / underground reservoir