CS/AR/2007-08:Paleo Channel Flow Dynamics in Central Godavari Delta, East Godavari District A.P.

Abstract

Demand for fresh water for agriculture as well as drinking purposes in deltas is increasing day by day. In such situation conjunctive use studies to identify fresh water pockets in the deltas and to arrive at different strategies for better utilization of surface and groundwater are gaining importance. One such major Paleo channel of Gautami Godavari in the central delta of East Godavari District has been identified by AP State Ground Water Department (APGWD). The objective of the study is to characterize groundwater of Paleo channel in Godavari delta; evaluation of groundwater quality and isotope characterization of groundwater of the paleo channel; quantification of Paleo channel flow etc. There is striking contrast in chemistry of oceanic water and continental fresh ground water and help in noticing initiation of seawater intrusion. The chemical analysis data indicated that there is no significant seasonal change in groundwater quality in paleo channel and most of the samples belong to calcium-bicarbonate type. In the upstream side of paleo channel groundwater quality is similar at most places. This scenario is mainly due to influent characteristics of river branches at the head of the delta and due to the three major canals of the delta system. However, the groundwater towards down stream is deteriorating from the aspect of major cations and anions. The stable isotope plots for δO18 and δD also indicates that the significance of rainfall recharge is not much and most of the recharge is from river, canal waters. Groundwater levels at Kundalapalli, Machavaram, Modekurru, Vyagreswaram and Naranedra puram indicate an average rise of 1.6 to 1.9 m and a fall of 1.75 to 2.2 m from up stream to down stream in and around paleo channel. In the study area, about 3500 Ha i.e., 18% of the cropland under the Palivela lock (Amalapuram main canal) is irrigated from the Ambajipeta channel i.e accounting to 20 MCM per season. Whereas the actual requirement is about 35 MCM, the balance of 15 MCM is the draft from Groundwater of the paleo channel. From the groundwater balance of the study area, the net groundwater flow into the system is about 3.5 MCM for monsoon season. Thus draft of non-monsoon season is estimated about 40 MCM. The study can be duplicated for other such aquifers facing threat of seawater intrusion and help in undertaking distributed groundwater modelling of the interface.