Control of the irrigation water resources of the Al-Hasa oasis
This thesis describes the present situation of the Al-Hasa oasis, which is critically dependent on a single over-used water resource. Evidence is presented to show that water usage is inefficient, and that real improvements are possible, but only if the local farmers are provided with the means of determining the soil moisture levels of their fields. Simple tensiometers and soil moisture cells are considered for this purpose and both would be effective. Soil moisture cells are likely to be the better choice, but more work is needed to evaluate their response to saline soil moisture conditions. The thesis shows that the widely used pressure plate (for laboratory evaluations) is less accurate than is the simpler filter paper system. Such laboratory determinations will be needed to ensure that the chosen field instruments are as accurate as is wanted. An interesting, and still incompletely understood, phenomenon is that the soil grain sizes do affect the accuracy of results from the chosen field instruments. More work is planned on this subject. A crucial factor also affecting the long term security of the oasis is to improve near surface drainage and evidence is presented that details the adverse effects of the present inadequate drainage system. In view of the vast financial investment already made into the drainage of the oasis, improvements that allow a better drainage of each individual field are seen as sensible. Evaluations of more modern soil moisture measuring equipment (transducer and psychrometer systems) reveal that these are inappropriate for use at Al-Hasa. The emphasis of the thesis is on the positive contribution to water use efficiency that can be achieved by the individual farmer. If the thesis conclusions are accepted then the continued prosperity of Al-Hasa can be assured at a very small cost.