荖濃溪攔河堰棒柵型取水工取水特性試驗

Abstract

棒柵式取水工常運用於山區溪流，設施規模小、取水量少，目前台灣現有棒柵取水工最大規模為隆恩圳進水口，其設計取水量僅有6 cms，對於大取水量之棒柵取水工案例，即便國外亦不多見，可供借鑑之資料少。經濟部水利署正興建之荖濃溪攔河堰，有二階相同尺寸之棒柵取水工，總取水量高達50cms，完成後將成為國內最大型之棒柵取水工。 為探討該堰取水效能，作為未來營運及相關設計之參考。本文乃透過荖濃溪攔河堰取水工模型試驗，分析棒柵取水工在靜水池淤積、未淤積、棒柵間隙有阻塞及無阻塞之四種情況組合條件下，探討各種中低流量之取水效能及特性。試驗結果顯示，當靜水池未淤積且未卡柵時，取水量可超過設計流量，單階最大完全取水量Q0約27cms，極限取水量約2Q0；荖濃堰整體（2階棒柵取水工）最大完全取水量約79cms，約為單階2.9倍；整體最大引水能力約93cms，約為單階的2倍；卡柵在來流量越低時，影響程度越小；在靜水池淤積的情況下，來流量越低時，影響程度越顯著；另荖濃堰在中低流量（100cms以下）引水時，為兼顧洩放足夠下游保留量，必須有配合措施，將多引之水量排放至下游。

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.