A coupled soil water balance model for simulating depression-focused groundwater recharge

In arid and semi-arid environments focussed infiltration of rain and snowmelt water under topographic depressions is an important mechanism of groundwater recharge. Quantifying the aggregated recharge from numerous small depressions is a major challenge in water resource management. Building on field-based investigations into the surface water-groundwater interaction of individual depressions and their catchments (i.e. uplands) in the Canadian Prairies, we have developed a simple water balance model to simulate groundwater recharge considering the hydrological coupling of a depression-upland system. The model is based on the Versatile Soil Moisture Budget (VSMB), which has been widely used in the Canadian Prairies to simulate soil moisture conditions. We evaluated the new model, VSMB Depression-Upland System (VSMB-DUS) using field data consisting of an artificial flooding experiment and long-term monitoring of a depression in Alberta, Canada. The model captured surface water level, soil moisture, and groundwater responses to the artificial flooding with a reasonable accuracy, and also represented the inter-annual variability of recharge fluxes during a five year period (2007-2011) including dry and wet years. Simulated annual recharge varied between 12 and 45 mm, whereas annual precipitation varied between 453 and 597 mm during the five-year period. The VSMB-DUS tends to over- or under-estimate snowmelt runoff in individual years, however, simulated recharge was only slightly impacted by the errors in snowmelt runoff estimation. Due to its computational efficiency and robust algorithms, the VSMB-DUS will provide a useful tool for estimating aggregated recharge in a large-scale model grid cell containing hundreds of depression-upland systems.

在干旱与半干旱环境中，地形洼地下方的降雨与融雪水优先入渗，是地下水补给的重要机制。量化众多小型洼地产生的总补给量，是水资源管理领域的一大挑战。
本研究基于加拿大草原区单个洼地及其集水区（即高地）的地表水-地下水相互作用野外调查，开发了一款考虑洼地-高地系统水文耦合作用的简易水平衡模型，用于模拟地下水补给过程。
该模型以通用土壤水分收支模型（Versatile Soil Moisture Budget, VSMB）为基础，该模型已在加拿大草原区广泛用于土壤水分状况模拟。
本研究利用加拿大阿尔伯塔省某洼地的人工洪水试验与长期监测野外数据，对新模型——洼地-高地系统通用土壤水分收支模型（VSMB Depression-Upland System, VSMB-DUS）进行了评估。
该模型能够以合理精度复现人工洪水事件下的地表水水位、土壤水分与地下水响应特征，同时也能反映2007-2011年五年间（包含枯水年与丰水年）补给通量的年际变化特征。
五年模拟期内，估算的年补给量介于12至45毫米之间，而同期年降水量介于453至597毫米之间。
尽管VSMB-DUS模型在部分年份会高估或低估融雪径流，但融雪径流估算误差对模拟补给量的影响极小。
由于该模型计算效率高且算法稳健，VSMB-DUS将成为估算包含数百个洼地-高地系统的大型模型网格单元总补给量的有效工具。