OPTIMAL CROP PLANNING-MODEL FOR AN EXISTING GROUNDWATER IRRIGATION PROJECT IN THAILAND

A monthly irrigation planning model is formulated for determining the optimal cropping pattern and the groundwater abstraction requirement i n an existing groundwater development project. Two objectives, maximis ation of net economic benefit and maximisation of irrigated area, aspi red to by both the irrigation authority and the individual farmers in the Sukhothai Groundwater Development Project in Thailand are consider ed, To account for uncertainty in water resources availability, the mo del is solved for three levels of reliability of rainfall and groundwa ter resources (80, 50 and 20%). The effects of deficit irrigation on t he net benefit and cropping intensity as well as on the yield of crops are also assessed by considering three levels (no deficit, 25% defici t and 50% deficit) of water application to the crops, To select the be st alternative plan, a multi-objective analysis is carried out using t he Analytic Hierarchy Process considering the preference of the decisi on makers, including farmers and irrigation project managers, The sele cted decision makers in the Sukhothai Project collectively allocate al most half of the total weight to reliability (or risk) factors, while the remaining preference is almost equally divided between the two obj ectives listed above. On average, they seem to prefer the planning alt ernative corresponding to average (hydrologic) conditions and full irr igation without any deficit.