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UBC Theses and Dissertations

Efficiency in irrigation water use : a case study in the Okanagan Valley, British Columbia O'Riordan, Jonathan

Abstract

Increasing costs associated with the construction of new water supplies support the need to examine alternative measures for solving water supply problems in semi-arid environments. Because irrigation consumes a very large proportion of water supplies in such regions, it has the greatest potential for water saving through more efficient management. Research based on an analysis of the physical processes controlling the movement of water through the soil-plant-atmosphere system leads to the development of an irrigation control model, which could improve the productivity of irrigation water in the Okanagan Valley, B. C. Data from experiments with irrigated alfalfa conducted on the Summerland Research Station are used to test three hypotheses concerning the optimum timing and quantity of irrigation applications. Using the Bowen Ratio approach to examine the fluxes of water and energy to and away from the alfalfa surface during different weather periods, alfalfa crop water requirements (ET) are found to be a function of the latent evaporation from Bellani plate atmometers (E), the maturity of the crop (M) and the prevailing weather type (W). ET = f(E, M, W) Three different weather types significantly influence the relationship between E and ET -- cool and cloudy, partly clear and hot and dry (advective) conditions. The frequency distribution of these weather types is shown to follow a first-order Markov chain model. The optimum timing of irrigations occurs when the soil water content reaches turgor loss point (θ[subscript K]). Using the water balance model and from an examination of the alfalfa rooting distribution, θ[subscript K] is found to be a function of the level of atmospheric demand (ET) and soil water content in the upper two feet of soil (θ[subscript U]) θ[subscript K]= f(ET, θ[subscript U]) Decision rules controlling the depth of irrigation are developed from an analysis of the drainage component (D), which is related to soil water content in the lower root zone before irrigation (θ[subscript LI]) depth of irrigation (I). D = f(θ[subscript LI’] I) The set of decision rules prescribing the timing and quantity of irrigation applications are then incorporated into a "model" irrigation treatment, which is verified to be a more efficient user of irrigation water than present methods used in the Okanagan Valley. Under the conditions of the experiment, savings of at least 20 per cent of present water applications could be achieved without reducing crop yields. The theory of inventory control is used to construct the framework for an irrigation control model (based on the decision rules developed for the "model" treatment), that could be employed to areal units in the study area. The procedure for using Monte Carlo simulation to generate outputs of seasonal crop water use is demonstrated and consequences of these generated outputs on irrigation water allocation both on a regional scale and on the individual farm are discussed. The final chapter examines various implications of the irrigation control model on present Provincial water policy and agricultural economic systems in the Okanagan, with the conclusion that implementation of the efficient control model would require a change in the present attitude and capabilities of the irrigator. This change could be induced by the inclusion of incentives in Provincial water policy and law, such as pricing schedules based on incremental costs, monitoring of water applications, and by a reorganization of existing farm units and irrigation districts.

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