You can read this paper, please Article Assessment of groundwater recharge in a semi-arid groundwate...

Roosevelt Dieumerci Masumbuko Thanks for sharing the link

Simply put,

P_rain+P_snow+R_irri+R_in-R_out+Q_in-Q_out-ET_veg-E_dir=∆S_soil+∆S_surf+∆S_gw+∆S_snow,

where P_rain, P_snow, R_irri, R_in, R_out, ET_veg and E_dir represent rain, snow, anthropogenic irrigation, inward overland flows, outward overland flow, subsurface influx, subsurface outflux, transpiration, and evaporation from barelands, respectively. Q_in and Q_out denote groundwater flux to deeper reservoirs and downstream. ∆S_soil, ∆S_surf, ∆S_gw and ∆S_snow represent the soil reservoir, surface water ponding, groundwater reservoirs and snow water equivalent, respectively.

Pr Zheng Lu ,

Thank you for the formula. Sometimes, there is an interconnection between the watertable and other deep groundwater. How can I estimate the

watertable flow to deep groundwater and downstream knowing that the pumping effect is permanent? Thanks

Recharge to water table is generally difficult to estimate reliably, particularly in arid regions. If there are monitoring wells available, I can suggest a couple of techniques that will give some indications of mean annual recharge rates, at least in the vicinity of the wells:

(1) Obtain groundwater samples, starting near the water table depth, from several depths below the water table, and measure the groundwater age (using various chemical and isotopic techniques). Slow to very slow recharge rates would usually lead to old to very old groundwater ages; at most sampling locations in recharge areas, age would increase with depth below the water table.

(2) If the water table is deep (>25 meters) or you have some independent indications that the well is located in a recharge (from ground surface) area, then starting about 15 - 20 meters below ground surface (where subsurface temperature T is not measurably affected by seasonal changes in ground surface temperature), measure the temperature - depth profile in the well using a high resolution temperature probe (resolution 0.01C or better; 0.001C resolution best). The curvature of the T-profile is related to the recharge rate; slower recharge rate is associated with straighter T-profile; faster recharge rate with more curved concave-down T-profile (whereas concave-up T-profile indicates upward direction of groundwater flow; e.g. in discharge area). You may need to compensate for decadal or longer scale changes in ground surface T, and for changing subsurface thermal properties (due to changing lithology) with depth.

There are many literature publications describing each of these approaches; I suggest finding and consulting some of these to evaluate applicability of techniques for your area, and for making sure measurements are performed in a meaningful way.

Dr James C. Trask ,

Thank you for the detail concerning the temperature parameter for the recharge estimation. There is the thermal gradient which decreases while ascending. There is also the problem of interconnection between aquifers, which requires a mastery of structural geology. I do not know if it would be correct to use This parameter in deeper groundwater (more than 200 m). I'll try. Thanks

Hafidah--the thermal technique works best for a deep (>25 m) water table, with T-profile measurements extending from at least 5-10 m or more above the water table (and downward to near the water table or even a short distance below the water table) most informative of downward recharge in the unsaturated zone in the vicinity of the well. There must not be any vertical water flow within the wellbore in, above, or near the T-profile depth interval. If lithology changes with depth, then thermal properties (heat capacity and thermal conductivity) will change & these changes will affect the slope of the T-profile.

Dr James C. Trask ,

Thank you.

Hello,

Several of the online tools and models included in the Hydrology Tool Set (HTS; https://portal.hydrotools.tech ) could help with this. All tools and models are free and do not require user registration. None of the tools and models is restricted to specific climate zones or geographical areas and they can be used for any location for which the input data is available.

All tools and models have a streamlined interface, allow for adjusting of the various parameters used, where meant to require minimal input data, and integrate input, visualization (graphs and tables) and export functions.

All HTS tools and models operate with daily datasets and also include test data sets to allow the users to familiarize with them. All the tools come with a Reference Guide and most of the tools are accompanied by peer-review publications.

As of 2024, there are six tools included in HTS as follows:

1) SepHydro (https://sephydro.hydrotools.tech ) for estimating surface runoff and groundwater contributions to streamflow via hydrograph separation. SepHydro is based on 11 previously published algorithms and includes various adaptations;

2) ETCalc (https://etcalc.hydrotools.tech) for the estimation of potential, reference and actual evapotranspiration based on weather data and crop coefficients. ETCalc is based on 8 previously published methods (Penman-Monteith, Thornthwaite, Blaney-Criddle, Turc, Priestley-Taylor, Hargreaves, Jensen-Haise and Abtew) and includes various adaptations;

3) SWIB (Soil Water Stress, Irrigation Requirement and Water Balance; https://swib.hydrotools.tech ) for assessing crop water stress (either as water deficit or excess), soil water balance and irrigation requirements and its impact on aquifer storage, using soil moisture, evapotranspiration and precipitation data. SWIB has been developed using an innovative conceptual model;

4) SNOSWAB (Snow, Soil Water and Water Balance; https://snoswab.hydrotools.tech ) for estimation of soil water content and soil water balance using air temperature, precipitation, rainfall and evapotranspiration data. SNOSWAB has been developed using an innovative conceptual model and is the most complex model in the suite.

5) RECHARGE BUDDY (or Groundwater Recharge Estimation Tool; https://rbuddy.hydrotools.tech ) for the estimation of groundwater recharge, discharge and change in aquifer storage, based on user-provided specific yield and water table elevations;

6) SNOWFALL BUDDY (or Snowfall and Rainfall Estimation Tool; https://sbuddy.hydrotools.tech) for the estimation of the snowfall and rainfall components of total precipitation based on air temperature and total precipitation.

Considering the (limited) elements included in your question, I would say that the water balance could be calculated using the tools included in HTS; https://portal.hydrotools.tech ) as follows:

1. Use weather data with ETCalc (https://etcalc.hydrotools.tech) to calculate actual evapotranspiration;

2. Use actual evapotranspiration, soil water content and total precipitation with SWIB (https://swib.hydrotools.tech ) to calculate soil water balance components. For this purpose use zero for irrigation in SWIB. Groundwater recharge input data is optional in SWIB. If groundwater recharge is not available you can either set it to zero or use RECHARGE BUDDY (https://rbuddy.hydrotools.tech ) to estimate it;

3. If soil water content is not available; you could use SNOSWAB (Snow, Soil Water and Water Balance; https://snoswab.hydrotools.tech) to estimate soil water content. Soil water content can be used directly in SNOSWAB to calculate the water budget terms or can be transferred to SWIB to calculate the water budget with a different methodology.

I hope this helps.

Regards, SD

Mr. Serban Danielescu ,

Thank you for sharing the links.

Regards