Journal of African Earth Sciences xxx (2014) xxx–xxx

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Journal of African Earth Sciences

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Discussion

Comment on ‘‘Assessment of groundwater recharge in a semi-aridgroundwater system using water balance equation, southern Iran’’by Mohammadi et al. [J. Afr. Earth Sci. 95 (2014) 1–8]

http://dx.doi.org/10.1016/j.jafrearsci.2014.07.0061464-343X/� 2014 Elsevier Ltd. All rights reserved.

DOI of original article: http://dx.doi.org/10.1016/j.jafrearsci.2014.02.006⇑ Corresponding author. Fax: +216 71 885 408.

E-mail addresses: chenini_ismail@yahoo.fr (I. Chenini), lamia.kouzana@laposte.net (L. Kouzana).

Please cite this article in press as: Chenini, I., Kouzana, L. Comment on ‘‘Assessment of groundwater recharge in a semi-arid groundwater systemwater balance equation, southern Iran’’ by Mohammadi et al. [J. Afr. Earth Sci. 95 (2014) 1–8]. J. Afr. Earth Sci. (2014), http://dx.doi.org/1j.jafrearsci.2014.07.006

Ismail Chenini a,⇑, Lamia Kouzana b

a UR13ES26, Department of Geology, Faculty of Sciences, Mathematics, Physics and Naturals of Tunis, University of Tunis El Manar, Tunisiab ISSTE Institute, University of Carthage, Tunisia

Mohammadi et al. (2014) presented an estimation of ground-water recharge using a simple water balance equation of an aquiferlocated in southern Iran. The authors have presented a simplemethod to evaluate groundwater recharge for an aquifer systemlimited by a major fault and where hydrodynamic parametersare not well known in space and time. The purpose here is to sug-gest how they might choose the appropriate technique for ground-water recharge assessment based on the available data. Thesuitability of applying the water balance approach to their studyarea was not adequately justified. Two approaches that were usedto estimate the groundwater recharge were based on (1) sum ofthe known inflow components and (2) sum of the known outflowcomponents, which can violate the definition of the water balancewhich is a unique approach. Because of the inadequate definitionof the spatial extent and boundaries of the system, the assump-tions inherent in the water balance approach are violated. The totalinputs and outputs of the defined system boundaries used in thisapplication would be erroneous. The water budget for a basincan be defined as (Bridget et al., 2002):

P þ Q in ¼ ETP þ Q out þ DS;

where P is precipitation, Qin is water flow into the aquifer, Qout iswater flow out of the aquifer, ETP is evapotranspiration and DS isthe change in groundwater storage. This simple definition of thewater budget suggests that the spatial delineation of the hydrogeo-logical system must be done carefully in order to define the spatialextent of the studied aquifer. Several points pertaining to a satisfac-tory application of the water balance method that were omitted ornot clearly presented in the methodology section of Mohammadiet al. (2014) are discussed below.

1. Aquifer hydrodynamics and boundaries conditions

The influence of a fault on groundwater flow is illustrated by thediscontinuities of the groundwater flow patterns shown in a piezo-metric map (Bense et al., 2013). The mapping and interpretation of

groundwater levels on either side of the fault is needed to identifythe influence of the aforementioned major fault in the study area(Bense et al., 2013). Aquifer boundary conditions need to be speci-fied based on the geometry and the hydrodynamic properties of theaquifer. This is necessary to reasonably evaluate flow into or out ofthe studied aquifer. Groundwater recharge is related to severalhydrogeologic properties such as lithology of outcrops and aquiferpermeability variation (Chenini et al., 2010).

2. Choosing appropriate method and parameters evaluation

Many techniques are available for assessing groundwaterrecharge. Choosing an appropriate technique for a particular studyarea is not an easy task. Various factors need to be evaluated beforechoosing the suitable method for quantifying groundwaterrecharge. There are several methods for groundwater rechargeestimation (Bridget et al., 2002; Wendland et al., 2007; Batelaanand DeSmedt, 2007). The choice of method depends in part onthe available data, the hydrogeological system and the expectedaccuracy of the results (Wendland et al., 2007).

Before the water balance assessment, the watershed needs to bedelineated and the aquifer extent defined. The parameters ofthe water budget such as precipitation and evapotranspirationare defined and calculated with respect to the boundaries of thehydrologic basin. This important part is omitted by the authors.For example, in Section 4, aquifer area needs to be evaluated.

3. Water balance applicability

Mohammadi et al. (2014) doesn’t justify the use of the waterbalance method in the case study with a scarcity of available dataneeded to estimate the water balance parameters. The applicabilityof the method is not discussed. The water table fluctuation methodseems to be useful in this case, based on the availability of piezo-metric data and specific yield estimates for the study area. The pie-zometric level fluctuations are the direct results of aquifer rechargeand discharge.

The error in quantifying the groundwater recharge can beexplained by the spatial variability of factors directly influencingthe groundwater recharge process (Batelaan and DeSmedt, 2007).

using0.1016/

2 I. Chenini, L. Kouzana / Journal of African Earth Sciences xxx (2014) xxx–xxx

The authors must consider some other parameters that are spa-tially variable such as topography, soil texture, land use andprecipitation.

The variability of the estimates for groundwater recharge mustbe discussed with regards to

– The spatial variability of runoff, and evapotranspiration(Ketema and Broder, 2009).

– The variation of the vertical permeability of the vadose zone.– The variability in the specific yield estimated from changes in

groundwater levels (Manghi et al., 2009).

These variabilities are needed to explain the error presented inthis case study.

In this case study, the methodology adopted to estimaterecharge is inadequately justified. The water budget evaluationand the error are untenable. Aquifer properties such as the aquifergeometry and the boundaries conditions are not well considered inthe evaluation of the water budget. Factors influencing recharge ofthe aquifer are not discussed and considered in the calculation.

Please cite this article in press as: Chenini, I., Kouzana, L. Comment on ‘‘Asseswater balance equation, southern Iran’’ by Mohammadi et al. [J. Afr. Earthj.jafrearsci.2014.07.006

References

Bridget, R.S., Richard, W.H., Peter, G.C., 2002. Choosing appropriate techniques forquantifying groundwater recharge. Hydrogeol. J. 10, 18–39.

Batelaan, O., DeSmedt, F., 2007. GIS-based recharge estimation by coupling surface–subsurface water balances. J. Hydrol. 337, 337–355.

Bense, V.F., Gleeson, T., Loveless, S.E., Bour, O., Scibek, J., 2013. Fault zonehydrogeology. Earth Sci. Rev. 127, 171–192.

Chenini, I., Ben, Mammou A., El May, M., 2010. Groundwater recharge zone mappingusing GIS-based multi-criteria analysis: a case study in central Tunisia(Maknassy basin). Water Ressour. Manage. 24, 921–939.

Ketema, T., Broder, J.M., 2009. Estimation of groundwater recharge using a GIS-based distributed water balance model in DireDawa, Ethiopia. Hydrogeol. J. 17,1443–1457.

Manghi, F., Mortazavi, B., Crother, C., Hamdi, M.R., 2009. Estimating regionalgroundwater recharge using a hydrological budget method. Water Resour.Manage. 23, 2475–2489.

Mohammadi, Z., Salimi, M., Faghih, A., 2014. Assessment of groundwater rechargein a semi-arid groundwater system using water balance equation, southernIran. J. Afr. Earth Sci. 95, 1–8.

Wendland, E., Barreto, C., Gomes, L.H., 2007. Water balance in the Guarani Aquiferoutcrop zone based on hydrogeologic monitoring. J. Hydrol. 342, 261–269.

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