Modeling economics of conjunctive surface and groundwater irrigation systems

Tank irrigation is one of the oldest sources of irrigation in India. Decline in the area irrigated over the years due to inadequate operation and maintenance, large-scale development of groundwater sources, disintegration of traditional irrigation institutions, heavy siltation, encroachment, etc., has resulted in heavy supplemental well irrigation in order to avoid crop losses. Rice yield from farms with supplemental well irrigation was observed to be high. Even though it is possible to calculate the value of groundwater for different years, it is difficult to obtain the value of the groundwater used to stabilize rice production from tank irrigation. The model developed in this paper is used to calculate the stabilization value of groundwater using the Srivilliputhur Big Tank, which is a representative tank in Tamilnadu, India. A mathematical formula is used to model the economics of conjunctive surface and groundwater irrigation systems. Analytical expressions for the value of groundwater and the stabilization value of groundwater are derived, assuming that the amount of surface water is a general stochastic variable with a probability density function, and that the demand function for irrigation water is also of that general form. Finally, the model is applied to real data collected during the period 1986 to 2000 for the Srivilliputhur Big Tank in Tamilnadu, India, and the value of groundwater and the stabilization value of groundwater are calculated at 1999-2000 constant prices. The results indicated that the stabilization value of groundwater (covering the entire tank area of 402 ha.) was Rs. 166,677, while the value of groundwater was Rs. 1,064,720. Thus, about 15.7% of the value of the groundwater was used for its stabilization. Using the stabilization value of the groundwater in future investment analysis will help to more accurately indicate project benefits due to groundwater supplementation in the tank command areas.