Evaluation of surface irrigation system design approaches
To feed the increasing world population, the production of food crops from available land resource will need to be expanded. One of the ways to effect this is by increasing the output per unit area of land through use of irrigation. In Kenya the rate of irrigation development has been low. The Irrigation and Drainage Branch of the Ministry of Agriculture, charged with the responsibility of development of small scale irrigation schemes , identified availability of viable irrigation designs as one of the causes of low rate of irrigation development in Kenya. With this in mind, it has been looking for ways to improve the standard of designs and the rate of designing. In this report the possibility of introducing the use of computers for design of small scale irrigation systems and in particular introduction of MIDAS (Minor Irrigation Design Aid Software) has been looked at. A start is made through establishing the main problems with the designs made. This was done through the study of the comments of the Irrigation Panel on the design proposals presented. A questionnaire survey was carried out to establish the main constraints experienced by the irrigation engineers during design of the schemes. This questionnaire was posted to them. Gambela Irrigation Scheme in Isiolo District of Kenya was used for evaluation of MIDAS. This scheme was designed using MIDAS and normal design without using MIDAS. The aim of the evaluation was to establish whether it could be used to alleviate the problems identified through the study of Irrigation Panel minutes and questionnaire survey.During the evaluation, areas of MIDAS that required improvements for use in Kenya were identified. The improvements required were formulated and this information used t by Overseas Development Unit of Hydraulic Research to adapt MIDAS for use in Kenya. It was established that, of the 61 investigation proposals presented to the panel, only 10% had been designed and approved by the panel by the time of the ninth panel meeting. The designs presented were not complete and calculations were not done thoroughly. Availability of time was identified as one of the constraints. Most of the scheme design activities involve repetitive procedures which are tedious. There is no design criteria for most of the structures and irrigation application methods as used in small scale irrigation in Kenya MIDAS handles design steps that take most time due to repetitive procedures,such as production of scheme layout alternatives, canal design, generation of longitudinal profiles for canals and plotting of the maps. It is faster than normal design process. Accurate and clear output is possible from use of MIDAS as compared to normal design process. However, MIDAS does not assist in processing of river flow data, rainfall data and climatic data. It does not assist in calculation of water requirements, design of field application methods and also does not do structural design.
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