ESTIMATION OF GROUNDWATER RECHARGE USING SWAT HYDROLOGIC MODEL A CASE STUDY OF LOWER CHENAB CANAL AREA

Abstract

Estimation of groundwater recharge is important for the better management of this precious commodity. The objectives of the study were to determine and map groundwater recharge at Hydrologic Response Units (HRUs) and Canal Command Area (CCA) for the better management of this resource. For this purpose, Soil and Water Assessment Tool (SWAT) hydrologic model and conceptual modeling based on empirical approach of water balance were used. Actual Evapotranspiration (ETa) is a main component of hydrologic cycle, and for its estimation, land cover data of area is very important. SWAT uses elevation, climate, soil and land cover data as input to estimate parameters of water balance. Land cover mapping was done based on crops growth phenology using MODIS NDVI product and the results showed an overall accuracy of 78.84 per cent. SWAT model was calibrated and validated on ETa, derived from Surface Energy Balance Algorithm for Land (SEBAL) model. For calibration and validation, NSE (Nash-Sutcliffe Efficiency) and R2 were 0.89 and 0.90, and 0.76 and 0.80, respectively. Recharge in any CCA can be attributed to rainfall, irrigation practices and canal water losses. The analysis shows that Sagar CCA received highest average annual recharge of about 650 mm, whereas Mian Ali CCA with least recharge of 368 mm per year. In HRU, groundwater recharge depends on land cover and soil properties. At HRUs level, maximum annual recharge of about 570 mm is received by the areas under rice and sugarcane cultivation, whereas built-up areas and barren soil received least recharge. Water balance approach revealed that groundwater in Jhang CCA has gone down at the rate of 19 mm per year from 2005-2011. While in Upper and Lower Gugeera CCA, water table has improved during these years.