TN-50 : Impact of forest on ground water

Abstract

Forest influences on groundwater storage can be estimated from evapo- transpiration and discharge relationships. Studies have been done in various countries to establish relationship between forests and groundwater, however, these have not been on extensive scale. The findings of these studies have not been very coherent as studies conducted in the USA claim that water tables collapse as a result of deforestation or forest fires; while studies done in Switzerland do not seem to indicate any effects on ground water as a result of forest cover changing to grass. In an International Symposium held in 1980 in Helsinki, Guillerne (1980keported while describing the influence of deforestation on groundwater in temperate zones that there did not seem to be any historical evidence of any direct influence of deforestation on the lowering of water tables. On the other hand, there have been opinions that logging of tropical forest watersheds had caused wells, springs, streams, and even major rivers to cease flowing. There have also been opinions that roots of forest exhibit 'sponge' effect that soaks up water in the wet periods and let it release slowly and evenly in dry season to keep water supplies adequately restored. In its forestry sector policy paper, the world bank has advocated reforestation of upland watersheds partially on the grounds that it will indicate dry season flows and raise groundwater well levels. On the contrary, most of well conducted experiments have shown that reforestation reduced stream flow experiments have universally given increased total water yield over the year. There are instances where trees have been planted to arrest rising groundwater level in water logged areas.

In view of the prevailing state of knowledge, it is necessary to conduct systematic study to spell out effects of forests on groundwater. For this purpose, a comprehensive review of literature has been carried out. Also a methodology has been presented to determine the forest influence under different land uses.