A Solution for Sediment Control at Intakes
A major problem with intakes diverting water for purposes such as irrigation or power generation is the removal of transported sediment from the diverted flow. If this is not performed adequately, canal capacities and effective volumes of retention reserv
- PDF / 1,328,630 Bytes
- 13 Pages / 430.866 x 649.134 pts Page_size
- 10 Downloads / 178 Views
A SOLUTION FOR SEDIMENT CONTROL AT INTAKES J.G. Whittaker Laboratory of Hydraulics, Hydrology and Glaciology, Federal Institute of Technology (ETH), Zurich, Switzerland 1. INTRODUCTION
A major problem with intakes diverting water for purposes such as irrigation or power generation is the removal of transported sediment from the diverted flow. If this is not performed adequately, canal capacities and effective volumes of retention reservoirs are reduced. Because of variations in the site conditions and requirements of each intake, model tesing is the most reliable means of designing a structure that will function correctly. The reproduction of sediment movement that is geometrically and dynamically similar to the prototype situation is the most important factor. However, because this is very difficult to accomplish, model studies become a means of qualitative or comparative evaluation of different options, rather than a quantitative means for predicting entrainment of sediment. Entry of sediment into the canal at the existing intake structure on the Kander River, near Spiez, Switzerland, is a problem. Because of this and the age of the structure, a new intake and associated weir were proposed. The final solution based on model tests is a repelling type supplemented by an excluder. 2. REVIEW OF INTAKE BEHAVIOUR Intakes can be classified into three broad types: 1) Repelling intakes (these are called Umlenkfassungen in German. ~e 45 m3 / s. As unsatisfactory variants were eliminated, increasing attention was paid to flow conditions within the intake and in the vicinity of the excluder. All the initial model tests were performed with excess amounts of the fine sediment being fed, thereby stressing each variant to enhance detection of weak points in the design. Evaluation of performance was based on a qualitative comparison of several factors. These included the percentages and distributions of the material fed that eventually deposited in the canal, visual impressions of prevention of sediment entry (repelling), and flow patterns within the intake. Tests with the final variant were performed using sediment input rates determined from fig. 3. Some of the variants are shown in fig. 5. Variant ~ This variant was rejected because too much sediment was able to enter the intake, even at very high flows. It is possible that the scum-board intended to keep out floating debris aggravated the situation by repelling the sediment free upper layers of flow while allowing in the sediment laden lower sections of the flow. Operation of the excluder tunnels aggra-
Variant 1
Variant 6
2-35
\
Variant 7
Figure 5
Variant 12
Model variants.
vated sediment entry, and secondary flow effects occurred within the intake. This design was very similar to some of those detailed by Ce~en (1973, 1975). However, it should be noted that Qe~en designed his early frontal intakes as remedial measures for existing lateral solutions that were failing because of excess sediment entry, particularly at high flows.
2-36 Variant 6 This variant was th
Data Loading...
