M.G. Bos - Böcker

The irrigated area in the Aral Sea basin totals about 7.5 million ha. Part of the water supplied to this area is consumed by the irrigated crops; the remainder drains into the groundwater basin, downstream depressions, or back into the rivers. But the water accumulates salts and chemicals during its period of use, causing environmental problems which this book discusses. The natural discharge capacity of the groundwater basin is inadequate to handle the unconsumed irrigation water, leading to a rise in the groundwater table and to waterlogging. In (semi-) arid zones, this waterlogging triggers a soil salinity problem, resulting in poorer crop yields. The problem is solved by artificially increasing the discharge capacity and lowering the groundwater table. Since the lands surrounding the Aral Sea have become independent republics, a number of missions have reported on the water-related environmental problems in the basin. Such reports have contributed to a plan of action for solving or alleviating some of the problems identified, high priority being accorded to improving the irrigation efficiency, artificial drainage, and the related environmental effects.

In the context of water management, structures that measure the flow rate in open channels are used for a variety of purposes: (i) In hydrology, they measure the discharge from catchments; (ii) In irrigation, they measure and control the distribution of water at canal bifurcations and at off-take structures; (iii) In sanitary engineering, they measure the flow from urban areas and industries into the drainage system; (iv) In both irrigation and drainage, they can control the upstream water at a desired level. This thesis represents an attempt to place such flow measurements on a solid foundation by explaining the theory of water flow through 'long-throated flumes' and their hydraulically related 'broad-crested weirs'. On the basis of this theory, and on practical experience, these structures are recommended for use whenever the water surface in the channel at the measuring site can remain free. The thesis concludes with a design procedure that will facilitate the application of these structures. The idea to undertake research on discharge measurement structures was born upon my appointment as the first civil engineer with the International Institute for Land Reclamation and Improvement (ILRI). Because my recruiter, Ir. J.M. van Staveren, then Director of ILRI, had left the Institute before my arrival, and because I was the 'first of my kind' in an agricultural environment, I looked for contact and found - vii- support from: the late Prof. Ir. J. Nugteren, Prof. Ir.

In the context of water management, structures that measure the flow rate in open channels are used for a variety of purposes: (i) In hydrology, they measure the discharge from catchments; (ii) In irrigation, they measure and control the distribution of water at canal bifurcations and at off-take structures; (iii) In sanitary engineering, they measure the flow from urban areas and industries into the drainage system; (iv) In both irrigation and drainage, they can control the upstream water at a desired level. This thesis represents an attempt to place such flow measurements on a solid foundation by explaining the theory of water flow through 'long-throated flumes' and their hydraulically related 'broad-crested weirs'. On the basis of this theory, and on practical experience, these structures are recommended for use whenever the water surface in the channel at the measuring site can remain free. The thesis concludes with a design procedure that will facilitate the application of these structures. The idea to undertake research on discharge measurement structures was born upon my appointment as the first civil engineer with the International Institute for Land Reclamation and Improvement (ILRI). Because my recruiter, Ir. J.M. van Staveren, then Director of ILRI, had left the Institute before my arrival, and because I was the 'first of my kind' in an agricultural environment, I looked for contact and found - vii- support from: the late Prof. Ir. J. Nugteren, Prof. Ir.

Managing land and water is a complex affair. Decisions must be made constantly to allocate and use natural resources. Decision and action in any use of resources often have strong interactions and side-effects on others, therefore it is extremely important to monitor and forecast the impacts of the decisions very carefully. Reliable information and clear data manipulation procedures are compulsory for monitoring and forecasting. Remote Sensing has considerable potential to provide reliable information. A Geographic Information System is an easy tool for manipulating and analysing the data in a clear and fast way. This book describes in seven practical examples how GIS and Remote Sensing techniques are successfully applied in land and water management.