高低交錯排列消能砥墩於渠道中之水理現象探討

台灣島受造山運動影響島嶼南北狹長，山脈呈現南北走向，山坡地地勢高聳且坡面陡峻，使得山脈間的水系陡峭，故大多數河川水流流速相當快。其次，工業革命後造成溫室效應影響，進而造成氣候異常及降雨量變得難以預測。其中因降雨強度不斷提高所形成之洪水，使護岸和渠床不斷掏刷，造成水工結構物損壞及形成潰堤洪災。為降低水工結構物衝擊常使用護床、護坦等保護設施，故本研究於渠道中採用不同高低與交錯之砥墩護床設計，來增加渠底粗糙度及曼寧係數值，探討其消能狀況及降低河川流速之目的。本研究之水工模型試驗，依據現地河川流速、渠道坡度與混凝土材料等資訊，進行製作縮尺消能砥墩模型。利用試驗渠槽，對交錯排列情況之不同高度、間距、流量和渠道坡度等之模型，進行清水流之水理模型試驗。探討在不同狀況下，不同流速中其曼寧係數與水理特性變化。本研究據試驗模型之曼寧係數，以因次分析法進而推估原型曼寧係數，其結果並與前期以規則排列及同高度交錯排列方式之結果做比較，探討是否能節省成本且有效地降低流速並提高消能效果。本研究之消能砥墩模型採高低交錯排列，消能砥墩塊石之間距採3、4、5、10公分分別進行試驗。根據實驗結果，當消能砥墩排列間距在3公分時，其轉換之原型曼寧係數值介於0.0235~0.0333間；並與流量成反比及與坡度成正比，其曼寧係數值相當於原型之乾砌卵石構造。經由不同之排列模型組合，可得其定義之粗糙度fr與曼寧n值關係成正比，其關係式為 n=0.0122+0.022*(1-e-4.6006*fr)。由試驗中水深及曼寧係數關係，當水深和砥墩平均凸出高度比值約為30時，其曼寧係數值會漸趨於定值，即說明在高水深下有浸沒狀況發生，其次亦可得到水深和砥墩平均凸出高度比值與曼寧係數值呈反比關係。

關鍵字

消能砥墩；渠道；高低交錯排列；曼寧係數

並列摘要

The islands of Taiwan was affected by orogeny. Islands give rise to narrow in north-south, resulting the mountains slopes and the rivers get steep. So most rivers flows velocity quite fast. The greenhouse effect caused by the industrial revolution. Because of industrial revolution, gets highly transform of atmosphere. The rainfall climate become unpredictable, and intensity has been higher than before. The revetment, hydraulic structures and bottom of canal are destroyed by floods straight which is cause damage. In order to reduce the damage of hydraulic structures, this paper uses height difference staggered arrangement of stilling baffle pier in the channel to increase the roughness and Manning coefficient to explore stilling and reduce the flow velocity of the river. In the hydraulic model test of this paper. The scaled stilling baffle pier model was based on the original river flow rate, slope and concrete materials. Using water in scaled canal in height difference staggered arrangement, spacing, flow rate and slope of concrete to do the test and explore the Manning coefficient in different hydraulic phenomenon. In this research, the Manning coefficient of the scaled model is obtained, and the Manning coefficient value of the prototype has been estimated by the dimensional analysis method. The result is compared with the Manning coefficient value of the previous model in a regular arrangement and staggered manner to discuss whether it is possible to save cost and effectively reduce the flow velocity and improve the stilling effect. In this research, using the spacing of the blocks are 3 cm, 4 cm,5 cm and 10 cm. According to the results, the spacing of 3 cm indicates the Manning coefficient is the largest, between 0.0235~ 0.0333; which is inversely proportional of flow but proportional in slope relationship. It’s equivalent to the result of the dry grouted rock in test manual. The relationship between the roughness(fr) and the Manning value(n) are: n=0.0122+0.022*(1-e-4.6006*fr), and are proportional. The relationship of the test between the water depth and the Manning coefficient shows that when the ratio of the water depth to the average height of the block of value in 30, the Manning coefficient value will gradually become constant. Thus, the test shows immersed in the design and the ratio of the water depth to the average height of the block is inversely proportional with Manning coefficient.