   Fig 2 (a) DEM of study area. (b) & (c) Exaggerated perspective view of DEM  Fig 3 Drainage network of the area overlaid on DEM. Probable recharge sites (R1, R2, R3, R4 and R5) Hydrogeological Logs Hydrogeological logs prepared on the basis of tubewell and receptivity lithologs are shown in Fig 4. These logs depict the geological material occurring in pediment zone, alluvial valley fill and in depressions. In the logs representing pediment region (Log - NR, MP, RN) depth to bedrock is at about 30m bgl. However in boundary areas of pediment and alluvial valley fill (Log- KP) it shows increase in depth to bedrock to about 120m bgl. Within the deep valley fill areas of alluvium plain (Log - DK, KH) and alluvial depressions (Log - ND,MD) they indicate alternating sand and clay - kankar horizons. Within alluvial plain, bedrocks are encountered only below 300m bgl. Areas suitable for Recharge There are three main prerequisites for identifying the areas suitable for artificial recharge.
The contact of pediment and alluvium (boundary between yellow and green zone) is marked by disorganization and dissipation of several drainages due to high rate of infiltration in the coarse granular material of pediment zone (Log-NR, MP, RN, Fig 4). For example, several drainages coming from structural ridges (Location-SD1 & SD2, Fig 3) dry out near this boundary. Similarly a drainage system coming from Bahadurgarh (Location-BD, Fig 3) side disappears prematurely before debauching into the Najafgarh depression in this boundary zone. Also at the Location-AD (Fig 3) drainage is absent, indicating high infiltration zone. The study of depth to water table map of the area (CGWB, 2003) shows that the groundwater level to the west of structural ridges fluctuate between 15 to 20m bgl, which indicates sufficient unsaturated zone available for effective recharge. Based on the above observations, few suitable sites have been marked which satisfy all the prerequisites for conducting large-scale artificial recharge. These are ND and MD (Fig3), within the two naturally occurring depressions, R1, R2 and R3 (Fig 3) within pediment zone and R4 and R5 (Fig3) in alluvial valley fill. Groundwater Management Recharge within the pediment zone (R1, R2 and R3, Fig3) can be carried out by building check dams at the sites where two drainages are joining or by excavating linear trenches across the drainage path for collecting surface runoff or rain water by inhibiting the sheet flow. Also near the boundary of pediment region and alluvium (boundary between yellow and green zone), groundwater should be extracted by tubewells and dugwells before it flows into the deeper aquifers of alluvial valley fills, where the aquifers are saturated with brackish to saline water. Recharge at the high infiltration sites within the alluvial plain (R4 and R5, Fig3) can be done by building large percolation |