Author(s): S. Dr. Suresh.
Keywords: Ground water; Conjunctive use; Crop yield; Irrigation intensity; Ground water flow model
Abstract: Groundwater exploitation has a limited future as, in several places’ ill effects due to over exploitation had been experienced. Even though significant advances had been made in almost all phases of groundwater technology in recent years, understanding the groundwater flow behavior and its interaction with the surface water is very much needed before addressing any problem related to it. For preparing plans for assessment of water resources of a basin and their utilization, accurate assessment of both surface and groundwater together has to be made and its interrelationship has to be studied. Irrigation projects were prepared either on surface water resource or groundwater resource separately which sometime results in either water logging or depletion of groundwater. In either case it was detrimental to the ecology of the region. Further, the two water resources were not being utilized optimally, economically and sustainably. For intensive irrigation and promotion of good crops, adequate and timely irrigation is essential, which in many a case may not be ensured by a single resource. Sometimes the chemical qualities of groundwater may also pose limitations and its dilution with surface water may serve the water quality needs of the crops. In Tamil Nadu state and more so in southern India, tanks were the oldest and most common surface water reservoirs used for irrigation. This tank irrigation is intricately woven with the tradition and lifestyles of the entire community. In Tamil Nadu there are about 39,200 tanks which accounts for 17 per cent of all tanks in the country, irrigating an area of 928,000 ha. Most of these tanks are rainfed tanks. Well irrigation too, was in vogue and the earliest record dates back to Vedic times (5000 BC). Until the recent years the drawl of groundwater was restricted to the length of rope used to draw water. Bullocks were generally employed to draw water and the length of travel was also restricted by the size of the farm holding and thus encouraging sustainable use. Under the present changed conditions, revival of the traditional methods poses a problem of different dimension. Therefore, the computer model for conjunctive use has been developed and applied to Aralikottai tank irrigation system in Thirupathur taluk of Sivaganga district of Tamil Nadu state as a case study. The tank is to its brim during the start of the crop and dry before crop maturity (3-4 months). Also, there are 41 shallow dug wells whose water table is directly correlating with the tank water level. These wells are irrigating about 26 per cent of the tank command of 100.81 ha. Rice is the major crop grown twice in a year. Conjunctive management was almost absent and poor crop yields were noticed. Thus, there exists a great scope for conjunctive management to increase crop yields and cropped area.