Estimating recharge is a ...

Estimating recharge is a topic of intense research. I would suggest a simplistic approach: the Net Recharge would be Rainfall - Runoff - ET. Rainfall - runoff, that is, the captured volume can be calculated from the topographic details of the catchment using GIS tools. ET can be estimated using meteorological data such as solar radiation, temperature, wind speed etc using Penman-Monteith equation (https://en.wikipedia.org/wiki/Penman%E2%80%93Monteith_equation). Another way (and perhaps this can be used in case of an artificial recharge site) is to establish a monitoring system by measuring the water levels (and thereby the volume) in the pond over a period of time to provide potential recharge volume and also putting a pan evaporation station (https://en.wikipedia.org/wiki/Pan_evaporation) on site to provide the potential evaporation rate. Assuming there is low to no vegetation around the pond, recharge would be volume in storage - (potential evaporation rate * surface area of pond * correction factor). Correction factor of 0.75 is generally used. Note: the pan evaporation rate and surface area would vary over time so this requires a little bit of calculations. Depending on the conditions, you could also put a few tensiometers in the pond at various depths to check the movement of the infiltration front - this would provide an idea of recharge too. Conducting infiltrometer or permeameter tests would also help in developing an idea of recharge conditions of the pond site. Hope this helps and good luck!