Theme 2-22-Estimation of rainfall recharge in a coastal area through inverse groundwater modelling.

Abstract

Estimation of rainfall recharge is important for optimal development and efficient management of groundwater resource in coastal areas. Rainfall recharge, which is dependent on a number of hydrogeological and meteorological factors, is complex to study and analyze. Normally rainfall recharge is estimated as lumped component by using various empirical relationships between rainfall and soil type. Groundwater Estimation Committee (1984) has suggested a wide range (10-25%) of rainfall recharge for alluvial areas. Tyagi et al (1997) have estimated the recharge during monsoon season in the range of 13.4 –17.2%, 12.1-13.3% and 16.1-19.2% for Central Godavari, Mahanadi and Krishna deltas respectively by lumped groundwater balance approach.

The rainfall recharge, however, varies in space and time and as such, a distributed ground water modelling approach may provide better estimate of this input to the aquifers. Therefore, the inverse groundwater modelling technique was adopted in the present study to estimate the rainfall recharge and its spatial variation in the coastal aquifer of Central Godavari Delta, Andhra Pradesh (India). The area was discretized into 1x1 km grid and was grouped into various recharge zones according to the hydrogeomorphology of the delta. MODINV (MODular INVerse model) was used to estimate the distributed recharge in these zones during the monsoon season. On a distributed basis, the rainfall recharge coefficient in the lower, middle and upper reaches of the study delta is found to vary from 0.11 to 0.25. The recharge coefficient taken on lumped basis is obtained as 0.17.