Dr. Marykutty Abraham and Dr. K. Venugopal
The study deals with hydrologic modeling of a chain of four tanks in Guduvanchery watershed, Tamilnadu, India for 14 water years. The results of hydrological modeling and simulation are used to derive the strategies to increase utilizable water from the watershed of the chain of tanks. The peculiar problems faced by the watershed include i) watershed lying in over exploited; ii) large scale development in this area due to fast
urbanization; iii) continuous reduction in cropping area; and iv) half of the precipitation takes place within a 30 day period due to monsoonal climate. These prompted human interference with the hydrological cycle. Against this background, scientific approach is needed to assess the present status of existing water bodies and surface water budgeting to identify the opportunities for harnessing surface water. Drainage map and
land use map of the watershed were prepared with satellite imagery in GIS platform using ArcGIS.
The watershed area of tanks has an aerial extent of 20.625 km2 with hard rock formation underneath and limited depth of weathered formation to hold water. Land use map shows that among the four tanks studied two tanks are not having irrigated area at present due to urbanization and the irrigated areas of the other two tanks have reduced to half of the registered ayacut mainly due to insufficient availability of water and urbanisation. Domestic water requirement, net losses and crop water requirement were computed.
The applicability of NRCS – model for runoff computation with simulation modelling is used to assess water availability for sustainable management of water resources of ungauged small watersheds. The water balance study for the chain of tanks showed that out of the total available water only 28% is used for irrigation and the rest is lost as evaporation loss, transition loss and spill from the tanks. It was found that there was around 5.46 MCM of surface water available in the watershed and apart from meeting the domestic requirement of 0.672 MCM in the watershed, additional demand due to future development and demand of adjoining areas can also be met if the available water is properly harvested.
The study concludes that for semi-arid region like Tamil Nadu, accurate estimation of runoff is essential for effective management and utilization of the available water resources. As the study deals with rural water supply for domestic and agriculture, the study is relevant to the conference theme.