Irrigation water requirements and water lifting technology

The thesis consists of nine publications which present the development and results of work in the field of Irrigation. Specifically, the research covers the assessment of how much water is needed to satisfy the evapotranspiration requirements of the crops, which has implications for the engineering design of irrigation works. The impact of crop water consumption on water resources is presented, together with the application of suitable methodologies to raise and utilise water for irrigation in Africa's rural areas. The first six papers presented are concerned with the assessment of evapotranspiration. In response to the lack of field data in remote areas, I have adapted the energy balance method to provide a viable means of measuring crop evapotranspiration \0 the field. The criteria for the equipment used were accuracy, portability and low maintenance requirements. Two sequential sets of instrumentation, which I developed for remote field use, are described. Results are presented from fieldwork which I carried out in Saudi-Arabia, Egypt, and Zimbabwe. The comparison is made between these results and predictions obtained from commonly used empirical and semi-empirical methods, and a significant difference is found in some cases. The final three papers relate to the impact and methodology of irrigation, with particular reference to dambos in Zimbabwe. I applied for and obtained funding from the Overseas Development Administration (ODA) to carry out research in Zimbabwe over the period 1984-1990. Results obtained from the energy balance work are utilised in the assessment of the water resources of a dambo, and to determine the water requirements of crops grown on dambos. A hydrological model is presented which describes the observed behaviour better than a previous model. Formerly. rural farmers in Zimbabwe have been severly constrained by the limitation of lifting water by a simple bucket, the latter part of my work has thus included the development of suitable pumping technology. The performance of four human powered pumps is described, which facilitate a ninefold increase in irrigable area when compared to the bucket. Two of these were selected and developed, and have been adopted on a wide scale in Zimbabwe. Their use is expanding to Kenya and Nepal.