Lineament Density Modelling to Identify High Potential Aquifers in Hard Rock Areas

Nawapara and Kalahandi districts located in the south western part of Orissa are drought prone areas. Geologically the area comprises Eastern Ghats Group and Purana (Chhattisgarh) Group. Laterite occurs as capping over the older formation and alluvium of Recent origin occurs as thin discontinuous pockets in and around the rivers. Based on visual interpretation of Landsat imagery four sets of prominent lineaments could be identified. The trends of lineament are broadly NE-SW, NW-SE, E-W and N-S. The lineament trending NE-SW is the most prominent one.

Groundwater in the districts occurs under water table condition mainly in the weathered mantle and narrow zones of unconsolidated sediments along major river valleys. The water yielding fracture zones are generally restricted within a depth of 100 m and groundwater occurs under semi confined to confined condition. The average transmissivity of the shallow and deeper aquifers is 36.8 m²/day and 53.4 m²/day respectively. The groundwater flow directions are mainly from SW to NE, NW to SE and SE to NW. Long-term water table fluctuation indicates that in the northern and central parts of the study area the water table during April 1997 has gone down compared to April 1988. On the other hand in the southeastern part the water table in April 1997 has risen. The long-term rise in the water table has taken place in khondalite to the tune of 0.37 m, in granite gneiss there is a long-term fall in the water table by 0.63 m and in charnockite there is practically no fluctuation of the water table. On an average there is a fall in the water table during this period by an average of 0.39 m, which indicates increase use of groundwater during the pre-monsoon periods. Productivity frequency plots indicate that there is no significant difference in the productivity values of the wells tapping at various depth ranges. But it seems that the productivity of wells is relatively on the higher side in the 50-100m depth followed by 100-150 m depth span.

Lineament density modelling indicates that the major lineament density axes show NE-SW and NW-SE trends. These two trends indicate that the regional ground water flow system is controlled mostly by the Tel river. Lineament density in most of the area is low i.e. below 0.2 km/sq. km. To demarcate potential aquifer zones for future development, 'technique of thematic overlay has been utilized using lineament density and long-term water table fluctuation. The overlay procedure indicates that in general the potentiality of the aquifer for future development is medium. In the Nawapara district the potentiality of the aquifer for future groundwater development is more than in Kalahandi district. Therefore in Kalahandi district artificial recharge of groundwater including roof top rainwater harvesting should be carried out to overcome the shortage of water for drinking purpose.