Assessment of Recharge in Shallow Groundwater Aquifers Using Soil and Water Assessment Tool: A Case Study of the Thuthapuzha Subbasin

Aim: To study the spatial and temporal variability of shallow groundwater recharge using the Soil-Water Assessment Tool (SWAT) model on a watershed scale.

Place of Study: Thuthapuzha subbasin.

Methodology: Groundwater recharge is a significant factor in groundwater simulations, which may aid in realistic groundwater resource management and decision-making. The study assessed the spatial and temporal variability of shallow groundwater recharge in the Thuthapuzha subbasin using a semi-distributed hydrological model called SWAT. Land use map, soil map, topographic data (Digital Elevation Model [DEM]), and basic meteorological data are the general input data necessary to run the SWAT model.

Results: Results from the study show that the average annual groundwater recharge in the Thuthapuzha subbasin estimated using the SWAT model is 201.26 mm/year (from 1992 to 2019). According to the long-term water balance of the whole watershed, runoff accounts for 60% of the average annual precipitation. Evapotranspiration accounts for 27% of the average yearly precipitation in the research region. Meanwhile, groundwater recharge is barely 8% of the average annual rainfall. The topography and land use in the study region were found to influence the spatial variability of groundwater recharge. The groundwater recharge also showed monthly and annual fluctuations. While the major rainy season (South-West monsoon) lasts from June to September, July to September period shows the highest recharge. The comparison of recharge obtained from the SWAT model with the recharge estimated using the rainfall infiltration factor (RIF) method shows a good correlation (R2 = 0.68).

Conclusion: SWAT modeling is a feasible option over field-scale approaches for assessing groundwater recharge and its response to various influences on a catchment scale.