On optimisation of sediment exclusion measures at intakes

Abstract

Sediment transported by natural stream flow has often presented the irrigation and hydropower plant designer with major problems, and measures for solving the sediment problems have been proposed. Most of the proposed sediment exclusion measures have been developed based on certain basic hydraulic principles and experiences gained from field observations of typical structures. This qualitative approach together with hydraulic scale model studies have formed the basis of the design for several of the sediment exclusion devices. In recent years, several quantitative methods of design based on experimental and analytical approach have been proposed for some of the sediment exclusion devices. The availability of these quantitative design methods allows for setting up a comprehensive model on optimatisation of sediment exclusion devices. Such a model should allow to select an optimal combination of devices and operational rules to reduce sediment intake, considering also other aspects like irrigation and other system requirements. The development of the comprehensive model is the main objective of this study. Four commonly used sediment exclusion devices, namely tunnel excluder, tunnel extractor, vort ex tube and sandtrap (for which quantitative methods are available) are included. The evaluation is based on the trapping efficiency of sediment exclusion devices and the quantity of used water. The performance of a designed model to predict the efficiency of each sediment exclusion devices was evaluated. For this purpose, field data and an existing (more advanced) model were used for verifying. The evaluations were carried out by considering a range of parameters which are representative for the conditions met in most irrigation schemes and hydropower plants. The results of the evaluation show that the designed model gives a good result as far the trapping efficiency is considered. To test the developed model for its ability, it was used in optimising the design and operation of the proposed sediment exclusion devices of the Ye-U Irrigation Project in Burma. The test results show that the model is handy and capable for this purpose. The results can be included in water management. Finally some proposals for a further development of the model are given.