How to calculate groundwater recharge rate?

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How to estimate groundwater recharge rate.

Your advice much appreciated.

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7 Answers

  1. 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

  2. Groundwater recharge rate - best method is to use a deep soil moisture probe. Several manufacturers sell probes up to 400 feet long. Measuring a) the volume / quantity of water in the catchment/reservoir using property geometry and water depth; and, b) the water saturation (corrected for soil type) at each interval, one may infer the water recharge. To be even more accurate, include evapotranspiration (Et), rainfall and measured water flowing into the catchment.  Most owners of groundwater reservoirs assume a 1:1 relationship between water in surface storage and water percolating into underground reservoirs.  It is more likely that some water moves horizontally.  Good luck with your project. 

  3. Hello Pooja, following Mr Nithin's very brief description, may I expand slightly on his suggestion:

    the surface area of the catchment will normally be approximately the surface area of the surface runoff catchment.  This means estimating the catchment boundaries based on the contours.  You may need to modify this when you look at a geological map and identify dykes and faults which may either reduce or expand the size of your catchment, as well as stream flows passing through the catchment from neighboring sub-catchments.

    also try to identify boundary issues of the catchment - e.g. which boundaries are confined and which are unconfined (allowing leakage out of the aquifer).

    secondly determining the percolation coefficient is a major challenge as it is likely to vary across the catchment, and will also be different depending on the antecedent moisture content of the catchment.  This means that you may need to sub-divide your catchment into areas for which the percolation coefficient is more or less uniform (e.g. rocky areas, grassland, natural vegetation of trees and shrubs, cultivated land, urban land, etc.  In dry years the percolation will only initiate once sufficient rainfall has occurred to moisten the underlying soil layers, and hence use of only the average annual rainfall will give you an average infiltration, but not a probability distribution to determine your acceptable pumping rate.

    Note that pumping tests evaluate the permeability of the aquifer, but not the recharge rate.  

  4. Nice question.

    The point is what is the purpose for this. Storage or recovery of  one over pumping?

    I am more familiar with the second case. If for example you recharge to face a problem of Saline Water Intrusion (SWI) it would be very helpful to monitor with electrochemical sensors (especially electrical conductivity sensors) the progress of decrease of the water Electrical Conductivity (EC) vs time. If you have already EC historical values you will be able to decide and define the correct amount of infiltrated water and to control the recharge process. The hydraulic gradient plays also a significant role. In areas with very low hydraulic gradient (flat plains) the recharged water stays into one specific volume area and it is possible to recover it after long periods. In contrary, you may loss large amounts of recharged water in areas with higher hydraulic gradients. I think that specific hydraulic tests in the recharge area are very useful to give to you one quantitative image on the amounts of water to be stored, prior to proceed.

     

  5. It is difficult to quantify such since certain related processes such as

    reverberation, transpiration and infiltration processes must be measured or estimated to determine the balance. However, the physical method uses the principal of soil physics to estimate the groundwater recharge rate by measuring the volume of water that passes below the region. In addition, an indirect physical method rely on measurement of soil physical parameters along soil physical principles can be used to measure the potential recharge rate of aquifers/water bearing formation. Such is calculated using numerical method. Using such code in Richards equation to estimate the recharging rate of water bearing formation

     

  6. Factually, if a RWH pit or an open dug-well is available, then a flow is diverted to the pit / well and the rate of flow can be recored. 

    Before this data- check, the pit is cleaned and maintained.

    We have observed that on the initial flow it appeared low, but as time passed the discharge rate increased. This may be that sub-soil pores in soil, with air pockets facilitated the needed flows into the aquifer- regime.

    well wishes

    Prof Ajit Seshadri. India .