變量流作用下滯洪設施之試驗研究

Abstract

山坡地大量的開發，導致植生覆蓋相對減少，地表糙度降低，逕流量增加 ，大量的土石流失及洪峰流量劇增，嚴重影響下游居民生命財產之安全。 為遲滯及降低山坡地開發所增加之洪峰流量，滯洪壩設置係國內目前較常 被採用之限洪構造物。惟往昔有關此類限洪設施之研究，均以定量流之試 驗為研究範疇，故本研究擬從前人學理探討，以室內水槽試驗中模擬流量 歷線之流況，主要是針對以往研究所採定量流試驗與實際現況之差異，改 進利用人工渠槽變量流試驗，配合超音波變位感應器以推導限洪設施之出 流量與水位高之關係，以及了解不同流量歷線分佈型態對滯洪特性之影響 。經由試驗結果及研究分析獲致： (1) 實際降雨之tp／tr值皆以左偏態 峰型分佈居多，提供水工模型試驗之模擬製造變量流歷線型態依據。又實 際降雨類型之tp／tr值、發生週期及降雨延時，經由推算比較結果，對蓄 洪量、出流量之多寡，影響甚鉅。 (2) 限洪設施中出流口開口寬度b、滯 洪池長度L二者，對於滯洪特性之洪峰消減量、洪峰稽延時間、蓄洪體積 及出流體積等變化影響甚鉅。另者，有關歷線分佈型態，tp／tr所模擬之 形狀，亦對滯洪特性有所影響。 (3) 以出流口處之開口寬度b (m)及水頭 高度Hd(m)為參數，藉由迴歸分析獲得出流口流量Q(cms)之經驗公式為 Q=1.71*b**1.03*Hd**1.49 (R=0.99) (5-1)式中 b及Hd之冪次與理 論值近似。 Due to the most developments on the slopelands, that results the reduction of the vegetation covering and the surface rounghness. Also it causes the increasing of the surface runoff and the discharge of the flow is becoming larger. The soils and sands washes away fastly. It threatens the life and fortune of the peoples living at the downstream of the slopelands. In order to delay and reduce the flow peak, this study has progressed sieres of unsteady flow hydrograph by using the computer and the cycling water flume. By means of these experiments, there can be analyzed the characteristic of various flow hydrograph, the discharge equation at flow outlet and the flood storage of the detention structures, and we can compare the peak attenuation, peak lag with different flow hydrogragh to gain the rules by designing the detention structures at the developments on the slopelands. Based on the experimental data and the theoretical analysis, the conclusion are drawn as follows: (1) The tp/tr of the real rainfalls are always left-hand types. And, the tp/tr occurence period duration of the real rainfall types effect the discharge and volume of inflow, outflow and storage. (2) The outlet width and the detention pool length effect the inflow storage, peak attenuation and peak lag. (3) The outlet experimental discharge equation is Q=1.71*b**1.03*Hd**1.49. The power of b and Hd are similar to that of theoretical value. But the discharge coefficient is smaller than that gained by theoretical value. The reason is that the sensor is placed on the above of the outlet. Not at the upstream where the flow depth is normal.