Estimation of Groundwater Recharge under various land ... - RMZ

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192 Purandara B. K., Venkatesh B. & V. K. ChoubeyTable 3. Estimates of Groundwater Recharge using SWIM ModelSl No1ZonesRainfall recordsConsideredLand use typeForestAverage rainfall(mm)Rechargepercentage52–552 Coastal 1986–2000 Degraded land 3090–4192 28–303 Afforested land 60–654Forest30–355 Plateau 1986–1999 Degraded land 941–152118–226 Afforested land 22–257Forest50–558 Up Ghat 1989–2000 Degraded land 2489–2734 28–329 Affores ted land 48–52Simulations using SWIM ModelThe water balance estimated for thecoastal region (using SWIM model)in three plots, namely, natural forest,degraded forest, afforested land, it isfound that with an average rainfall of3663 mm rainfall, the rainfall got apportionedinto 1648 mm as runoff,1200 mm as evapotranspiration, and811 mm as deep drainage. The estimationof evapo–transpiration by theSWIM model is based on the potentialevaporation. The PE values wereavailable for only one station in eachregion. Therefore, no variation wasobserved in the estimated ET amountunder different land use. The variationobserved in the recharge percentageduring the study period (for thedata of 1986 to 2000) was 51–55 % innatural forest, 28–30 % in degradedforest and 60–65 % in areas where theafforestation was done about 10 yearsback. The runoff coefficient observedfor the catchments in coastal area variedbetween 0.17 and 0.85. The minimumwas noted in the forested plotsand maximum is on degraded forests.This shows that there is a wide variationin runoff characteristics due tocontinuous change in land use and climaticconditions. Other important observationmade was that high rechargeand deep drainages are the characteristicfeatures in coastal region due tohigh permeable lateritic rocks. Similarobservations reported for the basinsoriginating from WG of Karnataka(Shetty, 1999).In the plateau area, especially, in black cottonsoils (vertisol), the estimated rechargein natural forest was 30–35 %, degradedforests, 18–22 % and 22–25 % in affor-RMZ-M&G 2010, 57
Estimation of Groundwater Recharge under various land covers in parts of ...193ested lands. SWIM model analysis carriedout for the Barchi nala catchmentshowed that with an average rainfall of1303 mm, 524 mm is evapo–transpirationand 350 mm was estimated runoff.The deep drainage component wasonly 410 mm.Hydrologically, the up lands of the WGare characterized by steep slopes andhigh rainfall. The major part of the WGis covered by lateritic soil underlain bycrystalline rocks. The runoff percentageestimated is 43 %. The averagerainfall in the area is 2361 mm. SWIMmodel results showed that 878 mm asevapotranspiration and 1015 mm runoff.The drainage component estimatedwas 461 mm. This is quite lower thanthat estimated for the coastal region buthigher than that of plateau region.Baseflow indices were estimated fortwo regions (Venkatesh et al., 2002),one dominated by red soils and the otheris black cotton soils. In the black cottonsoil area it is found that, the baseflowindex showed high value (0.51) ascompared to the red soil region (0.36).This variation is attributed to the factthat, in red soil region major part of therainfall infiltrated into deeper zones andincreased the ground water recharge,where as in the black cotton soil area,the deep drainage component is quitelower due to low infiltration rates asobserved in this part of the study area.ConclusionsThe application of SWIM has beendemonstrated for different land use inparts of WG of North Kanara districtof Karnataka, India. The advantage ofthe model is that it can be used both forlaboratory and field studies to simulatethe soil water and solute transport andcan also be used for understanding theimpact of different land use managementhydrologic regime of the area. Inthis study, simulations using the SWIMhas been substantiated by the field experimentsto understand the runoff generationdynamics under different land–use conditions.Following are some of the importantconclusions drawn from the study1. The impact of afforestationshowed a considerable increasein infiltration and hydraulicconductivity and also generatesinfiltration excess overlandflow at higher rainfall intensities.2. The results obtained throughSWIM model indicated thatthere is marked differences inrecharge percentages as theland cover changes (i.e., convertingthe land from degradedhas been brought under Acaciaplantation in the present case).This higher groundwater rechargemay contribute to theRMZ-M&G 2010, 57
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