The application of SWAT-GIS tool to improve the recharge factor in the DRASTIC framework: Case study

The robustness of groundwater vulnerability assessment using the conventional DRASTIC framework is highly dependent on the quality of the input data. The current study investigates the vulnerability of the western part of the coastal aquifer of the Gaza Strip, part of the Palestinian southern-western coastal aquifer. The study intends to re-introduce the recharge factor (R) in DRASTIC framework through the application of SWAT model and investigates its impact on the quality of vulnerability assessment compared with the conventional DRASTIC framework (No SWAT). Not only a higher recharge resolution map was generated when applying the SWAT model, but also an improved vulnerability index by 52% due to the incorporation of the local zonal-operation vulnerability concept was achieved. While the conventional DRASTIC framework (No SWAT) resulted in 74% of the study area has either extreme high or extreme low vulnerability classes, SWAT model was able to smoothen the vulnerability identification by capturing the slight gradual vulnerability variation over the study area with more precise vulnerability assessment. The resulted vulnerability assessment was validated using real field nitratedata(NO₃^-) of water samples collected from the entire study area. The vulnerability assessment using the SWAT model was in good agreement with the nitrate levels in the area compared with the conventional DRASTIC where the residual error encountered in the case of SWAT application (20%) was less than in the conventional DRASTIC;(77%). The results were also validated using receiver operator classification (ROC) and the area under curve (AUC) confirming the improved assessment due to SWAT model application. The current new approach is sought to support the decision-making process and water managers to better manage the proposed aquifer recharge scheme in the study area as well as to better manage the limited water resources.