HYDROGEOLOGICAL STUDIES IN SOUTH HARYANA (DISTT. MAHENDRAGARH) WITH REFERENCE TO POSSIBILITIES OF ARTIFICIAL RECHARGE

Abstract

Mahendragarh district of Haryana, located near its border with Rajasthan, is a semi-arid area affected almost perennially by scarcity of water. The average yearly rainfall for the Narnaul rain gauge station, recorded for the 56 years period between 1 95 1 to 2006 is 540.27mm, whereas the annual potential evapo-transpiration is greater than the annual rainfall and varies between 1400 and 1600mm for the district. In recent years, situation has become alarming due to the persistent decline of the water table, probably due to the over-exploitation of groundwater and deterioration in the quality of groundwater. Keeping in view these problems, the present study was undertaken with the following main objectives: (i) Review of geological and structural framework of the area (ii) Evaluation of subsurface geological scenario from the available data of tube wells and newly recorded Vertical Electrical Soundings (VES), identification of aquifer horizons, aquicludes and aquifuge materials. (iii) Hydrogeological conditions including water table configuration, pattern of groundwater flow, fluctuation of water table. (iv) Possibilities of ground water recharge and the area suitable for artificial ground water recharge. The geological formations of the study area belong to the Delhi Supergroup of the Precambrian age and have been divided into the Alwar and the Ajabgarh Groups. The Alwar Group is well exposed in the northern and western parts and is comprised of an immense thickness of hard and compact quartzite, having a few bands of phyllite and mica-schist. The Ajabgarh Group is made up of calc-silicates, marbles, schists, quartzites, amphibolites, pegmatites in the southern, southeastern and southwestern parts. The formations strike between N-S to NE-SW and steeply dip towards NW or SE. The slate and phyllite are also common in this area. The Delhi Supergroup of rocks have been subjected to tectonic stresses and therefore, suffered extensive folding, faulting and igneous intrusions. In the north, two large doubly-plunging folds are observed: the Sohla-Khodana-Siswal-Anticline and the SSW-plunging Narnaul Syncline. The Sohla-Khondana-Siswala-Anticline trends NNE-SSW. The core of this large fold is represented by an open, upright anticline, whereas the western limb of this fold is represented by the longitudinal ridges. The Narnaul Syncline extends NNE-SSW for at least 15 km as a SSW plunging open asymmetric syncline with westerly-dipping axial plane. The eastern limb of this syncline is represented by continuous exposures in the area.. It was observed during the field study that rocks of the Ajabgarh Group have undergone intense deformation in southern parts, which has caused development of folds, faults and joints. A series of isoclinals folds with axial trend in NNE-SSW direction have also been encountered. Subsurface distribution of different geological formations and groundwater conditions have been deduced from resistivity variations with depth along with other field geological evidences. Data of 23 newly-recorded Vertical Electrical Soundings (VES) recorded using Schlumberger electrode configuration, has been utilized in this study. The resistivity ranges, assigned to the different surface formations, are 12 to 240 ohm-m for top soil, 7 to 15 ohm-m for clay & kankar (with find sand) admixtures, 12 to 25 ohm-m for fine stand with clay, 20 to 45 ohm-rn for fine to medium sand mixture, 45 to 200 ohm-m for medium to coarse sand, 25 to 230 for weathered schist and semicompact bed rock (quartzite/granite), 100 to 560 ohm-m for jointed bed rock, and more than 1000 ohm-m for compact bed rock. iv Depth of the bedrock is highly variable and slopes towards northeast and north in the area. As a consequence, thickness of alluvial deposits increases from south to north and from west to east. Hydrogeological inventory and network monitoring have indicated that the principal aquifer is made up of alluvial fine sands and sands mixed with silt, gravel and kankar. However, groundwater also occurs in fractured rocks. Data from observation wells indicates that depth to water table was highly variable in a wide range between 6.30 m and 79.00m at Siyana & Nihalawas respectively during June 2006. It was shallow in NE parts and deepest in the NW and western parts. Further, there has been a considerable decline of upto 50 m of water table in some area during the past few years. In area, especially in the western, northwestern, and southern and eastern parts decline rate of water table is high. . Such notable decline in water table (upto about 0.75 m/year) from 1985 onwards can be explained due to low recharge during lean rainfall years and overexploitation of groundwater. The water table elevation is greater towards south & gradually decreases towards north & northeast. In general, the water table slopes towards north and northeast. The transmissivity of the aquifer is greater in the northern parts, whereas steeper hydraulic gradients occur towards southern parts. The aquifer are mainly unconfined and semi-confined in nature. The specific yield is low in the alluvial as well as bed rock areas. More than 80percent area is having declining water table and requires artificial recharge to arrest this trend of water table. The quality of ground water is also deteriorating during last two decades as observed from June 1986 to June 2006. The area under low electrical conductivity (i.e. upto 2000 micro mhos/cm) has shown a considerable reduction whereas the area with high electrical conductivity (more than 6000 micro mhos/cm) has increased during this period. This may also be explained due to overexploitation of ground water associated with lowering of water table and poor ground water drainage. v The Krishnawati & Dohan are two ephemeral rivers (now almost dry even during rainy season) have beds of coarser material which may contain intervening thin layers of sand and gravels embedded in clay and kankar (with fine sand) at several places. A thick layer of fine sand in north and northeastern part is a prominent aquifer in the area. The two rivers terminate within the study area itself. The bed of these rivers can be used for artificial recharge to ground water by surplus canal water during rainy season/floods. The decline of water table can be arrested by using the canal water for artificial recharge in the area either through existing canals or by constructing additional canals for the purpose. It is observed from the available data that at village Deroli Jat, which is situated on Dohan river, a distributory from SYL link canal is passing through this village. The pump constructed at this site is having an outlet for excess water to pass over the river bed of Dohan. During rainy season (or during failure of pump houses in the downstream/lower part of the canal), excess water passes over to the river at Deroli Jat. Thus, the water table in this area is almost stationary since last 21 years with no significant change in its elevation. On the contrary, in the nearby village at Nihalawas (about 5 km) there is a very high rate of decline observed during the same period. At village Deroli Jat it is almost stationary, where as at Nihalawas it has a decline of more than 50 m since last 21 years. There are so many sites available to recharge the ground water through the beds of river Dohan and Krishnawati in the area. Roof top rain water harvesting may also be helpful initially for domestic use. The artificial recharge to ground water through canal water/river water is the need of the time for controlling the decline of water table and to improve the socioeconomic conditions of the area.