Optimization model for annual net income in an irrigation scheme.

Every time a project (farm) manager exercises his judgement he is making a decision. This is true whether this relates to the time he will finish work for the day or whether he will authorise the expenditure of some money on a project. Any judgement which he makes involving the interests of the organization on whose behalf he is acting has therefore some significance. There must, however, be some point up to which intuitive decision making is acceptable on the grounds that the opportunity cost of the time taken up by the decision is apparently small and a high degree of discrimination is not required. This does not imply that such an intuitive decision is illogical; suitable account must be taken of a manager's ability to exercise the correct judgement in these circumstances as a result of experience and expertise. In this study one of the widely used management tools viz Linear Programming (LP) is applied in planning and evaluation of an irrigation scheme. The results are promising, although the procedure is quite tedious and calls for the use of a computer package. Developing the Linear Programme itself requires a specialist. To some managers LP may be considered to be a deterministic "black box" which always generates the same output for a given input. Nevertheless the manager should understand the formulation and be able to interpret the output arising from optimizing the objective function. The author first describes an irrigation planning model that can provide estimates of the quantities of all resource inputs and their costs; the location, quantity, and types of crops to plant; and, if appropriate, their market price that together maximize net income. The relationships among these resource inputs and crop yields are defined by the constraints of the model. This model is finally applied on an operational scheme which is managed by the farmers themselves through the central committee. This scheme was implemented by the Government of the Republic of Kenya as a donation to this group of farmers.