Ground water recharge zonation mapping and modeling using Geomatics techniques

Availability of groundwater varies spatially and temporally depending upon the terrain. The scarcity of water affects the environmental and developmental activities of an area. Continuous failure of monsoon, increasing demand and over exploitation leads to depletion of ground-water level. This problem could be sorted out to certain extent by artificially recharging the potential aquifers. Construction of small water harvesting structures across streams/watersheds is gaining momentum in recent years. In the present study, potential sites for construction of rainwater harvesting structures in the Lower Sanjai Watershed of Kolhan Division of Jharkhand have been identified using remote sensing and GIS techniques. Since the study area comprises of hard rocky basement of Precambrians/Archaeans, the intersection zones of lineaments provides potential avenues for ground water accumulation and ground water recharge. Occurrence of groundwater in such rocks is essentially confined to fractured and weathered horizons. Use of remote sensing data along with GIS, topographical maps, collateral information and limited field checks, has opened new avenues and made it easier to establish the base line information on groundwater prospective zones. Delineation of potential sites for artificial recharge is governed by several factors such as geology, geomorphology, lineaments, landuse/landcover, permeability, soil depth, drainage intensity, soil texture, water holding capacity and physiography. Various thematic maps such as LanduselLandcover, geomorphology and lineaments, etc. were prepared by on screen visual interpretation techniques. These layers along with geology and drainage were integrated using GIS techniques to derive suitable zones for construction of ground water harvesting/recharge sites. Each theme was assigned a weightage depending on its influence on ground water recharge. Each class or unit in the map was assigned a knowledge based ranking depending on its significance in storage and transmittance of groundwater, and these values were multiplied with layer weightage. The next step deals with classification of all these parameters into ‘suitable’ classes and assignment of ‘suitable’ ranks to these classes, and finally integration of all the ranked and weighed parameters in a GIS environment. Subsequently, the area is classified into different sites suitable for the rainwater harvesting. The final map shows different categories of suitability sites for construction of various ground water harvesting/recharge structures.