*3.5. Topographic Wetness Index (TWI)*

The topographic wetness index (TWI) is a steady-state wetness index used to quantify topographic control on hydrological processes [101]. TWI indicates control over the groundwater processes, such as flow and retention in a specified zone. Several studies have been published explaining the process to calculate the TWI [101,111]. TWI provides detail about the flow of groundwater considering the effect of the slope. TWI can impact groundwater flow and its occurrence in a varied elevation areas such as Islamabad. Numerous studies have linked TWI, slope, and elevation effects to the water recharge potential [65,100,109]. TWI gives an indirect indication of water moisture availability and potential recharge zones. Therefore, this has been used as a key factor in the current study.
