The irrigated area in the Aral Sea basin totals about 7. 5 million hectare. Part of the water supplied to this area is consumed by the irrigated crop; the remainder of the supplied water drains to the groundwater basin, to downstream depressions, or back to the rivers. During its use, however, this drained part of the water accumulates salts and chemicals. The disposal of this polluted water causes a variety of (environmental) problems. If the percentage consumed water of the total water supply to an irrigated area (the so-called overall consumed ratio) can be increased, less water needs to be drained. This alleviates part of the related (environmental) problems. Further, if the overall consumed ratio for the above 7. 5 million hectare is improved, less water needs to be diverted from the rivers. Hence, more water can flow towards the Aral Sea. As mentioned above, part of the non-consumed irrigation water drains to the groundwater basin. Commonly, the natural discharge capacity of this basin is insufficient to handle this imported water. As a result, the groundwater table rises towards the land surface causing waterlogging. In (semi-)arid zones this waterlogging triggers a soil salinity problem resulting to a significant reduction in crop yields. The artificial increase of the discharge capacity, and lowering of the groundwater table, solves the soil salinity problem.

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.

The irrigated area in the Aral Sea basin totals about 7. 5 million hectare. Part of the water supplied to this area is consumed by the irrigated crop; the remainder of the supplied water drains to the groundwater basin, to downstream depressions, or back to the rivers. During its use, however, this drained part of the water accumulates salts and chemicals. The disposal of this polluted water causes a variety of (environmental) problems. If the percentage consumed water of the total water supply to an irrigated area (the so-called overall consumed ratio) can be increased, less water needs to be drained. This alleviates part of the related (environmental) problems. Further, if the overall consumed ratio for the above 7. 5 million hectare is improved, less water needs to be diverted from the rivers. Hence, more water can flow towards the Aral Sea. As mentioned above, part of the non-consumed irrigation water drains to the groundwater basin. Commonly, the natural discharge capacity of this basin is insufficient to handle this imported water. As a result, the groundwater table rises towards the land surface causing waterlogging. In (semi-)arid zones this waterlogging triggers a soil salinity problem resulting to a significant reduction in crop yields. The artificial increase of the discharge capacity, and lowering of the groundwater table, solves the soil salinity problem.