| Summary: | 碩士 === 國立中興大學 === 水土保持學系所 === 97 === Usually applied in mountain streams, bar-screen water intakes are of small scale and allow for little water intake. However the largest of all bar-screen water intakes in Taiwan so far, the discharge capacity of the bar-screen water intake at Long-En Weir is only 6 cms. In fact, bar-screen water intakes of large discharge capacity are scarce even abroad. Hence, few data could be used as reference. Now under construction by the Water Resource Agency of the Ministry of Economics Affair, R.O.C., the Lao-Nong Weir contains two units of bar screens which of the same size will allow for a total discharge capacity of 50 cms after the construction and hence earn the reputation of the largest bar-screen water intake in Taiwan. This research paper is set to investigate the effectiveness of Lao-Nong Weir’s water intake in order to serve as reference for future practical operations and designs.
To investigate the effectiveness and characteristics of Lao-Nong Weir’s water intake at different medium-low flow rates, the simulation model of Lao-Nong Weir was operated under the following four conditions: the stilling basin with sediments, the stilling basin without sediments, the bar-screens blocked and the bar-screens un-blocked. The research findings showed that with the stilling basin not silted up and the bar-screens not blocked, the water discharge of Lao-Nong Weir exceeds the estimated capacity when designed—the maximum complete discharge capacity (Q0) of a single unit of bar-screens reaches about 27 cms; the maximum discharge capacity reaches about 2 Q0; the maximum complete discharge capacity of the two bar-screen units together reaches about 79 cms (2.9 times that of a single unit); and the maximum discharge capacity of the two bar-screen units together is about 93 cms (2 times that of a single unit). In essence, the lower the flow rate, the less the impact of blocked bar-screens and the greater the impact of silted stilling basin on the discharge capacity. In addition, the research findings indicated that whenever Lao-Nong Weir is at its medium-low flow rate (under 100 cms), proper measures should be taken to discharge surplus water for enough water preservation downstream.
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