The report presents the groundwater balance for the Southern Channel command area of the Pennar delta canal system as a part of the conjunctive use studies in the area. In a hydrological system, surface water flows, low or high, do not necessarily coincide with the low or high levels in groundwater, because of the sluggishness of the groundwater flow compared to surface water flow. Also excessive development of groundwater in the deltas and coastal areas may lead to salt water ingress into the freshwater aquifer and may contaminate it, if unchecked. This may happen when sufficient surface water supplies do not reach the tail ends of command areas.

With the increasing knowledge of the hydrogeological features of potential aquifers being identified with latest geophysical investigations, the scope for better conjunctive use practices is very good. The prospects of practicing conjunctive use of surface and groundwater will be better, provided one understands the hydroclimatology of the study area along with hydrogeology of the region.

Understanding and monitoring the water balance of the system helps in better conjunctive use. The relevant data from village level of the Southern Channel command area of Pennar delta system in Nellore district of Andhra Pradesh is utilized and analyzed to arrive at the groundwater balance of the system. The various hydrological components are estimated on a seasonal basis for monsoon and non-monsoon seasons from 1989-1993.

Furthermore, the crop water requirements are estimated for this period to find out the system demand. Various supply and use components are computed for the study area using suitable techniques based on the availability of observed data. From the water balance equation, rainfall-recharge during monsoon season is estimated to find out the relationship between rainfall and recharge coefficient for the area.

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