A bi-objective model for water allocation and scheme water scheduling

[摘要] ENGLISH ABSTRACT: Water is life | this common expression is often referred to as a cliche, but Earth's inhabitantscan truly bear witness to the accuracy of this statement. As a result of global warming, the ElNin~o phenomenon, a growing population and expanding economies, water has globally becomea cherished commodity. In the Western Cape, South Africa, a devastating drought experiencedover the two-year period 2017/2018 has propelled the innovation of more e ective and e cientwater management strategies to the forefront, especially in the farming sector, where farmersare currently compelled to produce agricultural crops with less water. An irrigation and schemewater supply schedule may, for example, be employed with the aim of proposing how cropsshould be irrigated during their various growth stages, if natural water supply is insufficient,and how additional scheme water supply should be scheduled to enhance efficient water use.An open-air irrigation reservoir typically serves as a water storage facility for the purpose ofirrigating agricultural crops. Evaporation (the process of transforming water vapour into theatmosphere) from such a reservoir water surface may, however, result in a reduced reservoircapacity of up to 20%.In this thesis, two novel mathematical models are proposed which form the basis of a decisionsupport system for farmers aimed at providing bene cial agricultural crop irrigation strategies.The first is a single-objective optimisation model which proposes an irrigation schedule in conjunctionwith a scheme water supply schedule in which the goal is to maximise the total profitobtainable from crop yield. This maximisation process is subject to a user-specified reservoirwater capacity that should be left over in an open-air reservoir at the end of a speci ed schedulinghorizon. If possible, additional water resources may be obtained from scheme water supplyin order to aid with the irrigation of crops. These additional water resources, however, usuallycome at a cost, which is also included in the total profit calculation.The second model is a bi-objective optimisation model which aims to maximise the total profitfrom crop yield while simultaneously maximising the reservoir water contents at the end of thelast scheduling period. When plotted in objective space, the solutions to the model form aPareto front that is presented as the basis of decision support to the decision maker (farmer),providing him with an overview of numerous implementable irrigation and scheme water supplyschedules for a variety of end-period reservoir water levels.Both the single-objective and bi-objective optimisation models are validated in three ways,namely by face validation, by random benchmark validation and by consulting an expert in the field of crop irrigation and farming. Embedded in the decision support system, these modelsenable the decision maker to develop a course of action in terms of crop irrigation for a tailoredfarming scenario.

[发布机构] Stellenbosch University