6-Conjuctive Use of Canal Water and Groundwater Resources in IGNP Stage -I Irrigation Project (Rajasthan).

Abstract

This paper deals with availability of ground and surface water resource in a Command area of 4.79 Lakh ha, their utilisation for different sectors such as irrigation and domestic. The crop water requirements during Kharif and Rabi seasons were computed as 1028 and 1002 MCM for cropping intensity of 97%; 2500 and 2097 MCM for 120% respectively. The surface and ground water resources were estimated as 4215 and 992 MCM. The salt infested lands are spread over 1.57 Lakh ha. The National Water Policy (1987), fully recognizing the adverse impact of the above hazards in realizing the optimal benefits from the land and water resources, has advocated integrated development of surface and ground water resources for their conjunctive use as a major remedial option. IGNP Stage-I has a significant portion of land under water logging, 1.56 lakh ha, 34% of the command area. Though planning for conjunctive use is highly desirable right from Project formulation stage, this was not possible in case of IGNP Stage-I as surface water system is already in existence. Keeping this factor/ constraint in view, the Board initiated multidisciplinary time bound studies for finding out the feasibility for operationalising the Conjunctive Use in IGNP Stage-1. The mathematical modelling studies by USGS 3D MODFLOW Source Code (1984) devised various water use patterns by means of different scenarios/ strategies. The four scenarios were evolved and most viable one is the ground water development to the tune of 18% of the canal water release. The recharge of 6982 MCM in 15 years period to ground water regime is predicted and water logged areas would be 463,626 and 785 in 5th, 10th and 15th year. The pace of spread of water logging can be reduced but cannot eliminate this phenomena even in next 30 years. About 10003 shallow groundwater abstraction structures have been recommended involving cost of Rs. 72.17 crores. The surface and ground water utilisation would be 3995 and 602 MCM respectively. The incremental cost and income are Rs. 393 and Rs. 563 crores showing net present value of benefits Rs. 11 crores giving a benefit-cost ratio of 1.03. The internal rate of return was calculated to be 17.39%.