| Abstract |
: |
Kolleru Lake, the largest natural fresh water lake in Andhra Pradesh in India, located between Krishna and Godavari deltas is acting as a natural flood balancing reservoir and is fed directly by water from the seasonal rivers Budameru, Ramileru and Tammileru, and is also connected to the Krishna and Godavari drainage system consists of over 68 inflowing drains and channels. Over-exploitation of groundwater and land use conversions to aqua-culture are becoming the sources for salt-water intrusion to this lake and coastal aquifers, in specific, are highly vulnerable to seawater intrusion. Hydrogeomorphological study indicates that the potential aquifers around the Kolleru lake are paleo beach ridges and buried river courses. All other geomorphic features either aquiclude or aquitards are may not be considered as prospective zones for groundwater. Though there are number of open wells present in the villages used for potable water earlier, people switched over to imported water as their drinking water source may be due to significant contamination of groundwater resources. Present land use activities like aqua-culture, agriculture, large-scale industries and allied industries in and around the Kolleru lake region has large contribution for the change of water quality. The paleo beach ridge areas, where the permeability of the sandy soil is very high, are also converted into aqua ponds. Integrated study using remote sensing, hydrogeology, hydrochemistry and geophysical investigations revealed the extent of salt-water intrusion up to the northern part of the lake which is about 40 km from the coast line. The electrical resistivity of aquifers is less than 1.0 (ohm-m) having salinity of more than 1.2 ppt and the resistivity is around 20 (ohm-m) where the salinity is less than 0.5 ppt, has also served as an excellent criteria for delineating the fresh-water and salt-water interface. Lenses of fresh water/ brackish water are noticed only in the beach ridges limiting to 2-8m depth below the natural ground level. |
