The Impact of Water Distribution Rules on Farm Production and Incomes: A Simulation Approach

Abstract

The purpose of this study was to test in terms of comparative efficiency, some alternative water distribution procedures that could be used in the agricultural environment of the Gwydir Valley, New South Wales. The prime interest was on the impact of the alternative water distribution procedures on farm production and income. A simulation model developed by Anderson and Maass (1974, revised 1976) was used to examine effects of water supply restrictions and water delivery rules on farm production and income in the study area. Ten case study farms receiving irrigation water from the Gwydir and Namoi rivers were selected for the study. Technical aspects of water distribution in the area and stream flow data were obtained from the Water Resources Commission. Production data and details of water use at the farm level were obtained from the individual farmers. Irrigation water requirements for each crop were calculated using pan evaporation data and crop coefficient data for the area. Effective rainfall was calculated using the USDA, SCS (1967) method. Yield loss schedules were developed for each crop at each stage of crop development to express crop response to soil moisture stress and various water supply levels. ... An examination of the tradeoffs between efficiency and equity for each of the procedures showed that although tradeoffs do exist it does not hold for all procedures. The ordinal ranking of the procedures which took into account both efficiency and equity criteria ranked the 'demand plan' procedure as the best procedure followed by the 'market' and 'Shares and demand' procedures. Further work on this area will involve the incorporation of a soil-moisture-plant growth simulation model into the Anderson and Maass model and the simulation of the procedures over a number of production seasons. The results also call for a detailed study on the costs of developing a market for water by the Water Resources Commission in the Gwydir Valley.