A geo-environmental study on groundwater recharge zones and groundwater management in the Guwahati municipal area

The city of Guwahati, inspite of being located on the bank of the mighty river Brahmaputra, has been facing the problem of scarcity of water, especially during the lean season. At present only about 27% of the population has access to piped water supply based on Brahmaputra river flow, while the rest depends on sources such as dug wells, shallow tube wells and deep tube wells for their domestic water requirements. However, during the last few years rapid increase in the population of the city has resulted in unprecedented exploitation of the groundwater resource. This, coupled with a decrease in infiltration rate due to increased concretisation and other landuse changes, has considerably depleted the groundwater table in many parts of the city. The groundwater resource of an area basically has two components viz., dynamic and static. The dynamic groundwater resource of the city is around 11 mcm, while the static groundwater resource down to the depth of 200 m is about 625 mcm. Although this indicates the presence of ample groundwater resource, yet, its utilisation should be done in a scientific and systematic manner, with due emphasis on the prevailing hydrogeological conditions of the area. It is imperative that designing of wells should be based on the aquifer characteristics, hydrogeological setup and water requirement of the area. Moreover, it is observed that the city of Guwahati experiences an average annual rainfall of around 162 cm with about 110 – 115 rainy days per year. The city thus has enough potential for harvesting the rainwater it receives, instead of allowing it to flow untapped. Rainwater outlets can be connected to storage tanks or allowed to pass into gravel filled trenches, pits, existing open wells and bore wells. Initiatives can also be taken to reclaim and revive the various wetlands and ponds in and around the city, as these water bodies act as natural groundwater recharge zones.