Hi Pooja, If surface runoff ...

Hi Pooja,

If surface runoff is low at the site, you could use hydrochemical information to estimate groundwater recharge. In principle, the concentration of a conservative ion (does not react with/leach from soil minerals or participates in biogeochemical processes) is concentrated due to evaporation while the water percolates through the ecosystem. Chloride can often be considered conservative. You can make a Cl mass balance to see how much water was lost by evaporation and determine recharge. This would not work in areas where the soil still has marine water from past sea transgressions, where the soil releases Cl from minerals, or where the groundwater is mixed with lateral inflow.

If you have long-term chloride concentrations in rainfall, you can compare these with those in groundwater to come up with a recharge rate:

Qr = P * [Clp]/[Clgw]

Where:

Qr = average recharge [mm y-1]

P = average precipitation [mm y-1]

[Clp] = volume-weighted average Cl concentration in precipitation [mg l-1]

[Clgw] = average Cl concentration in groundwater [mg l-1]

Regards,

Maarten