公路生態草溝之水動力研究(第1期)

Abstract

為減少對環境的衝擊，公路排水溝之設計可採用草溝而非混凝土溝來營造多孔隙的地表生態環境，以減少逕流、延長洪峰時間、增加地下水補注量。然而，此時若仍使用曼寧公式設計生態草溝之排水容量，則將面臨曼寧糙度係數值的選取問題。草溝的曼寧糙度係數與其生長的疏密程度息息相關，一般卻僅憑個人的主觀或經驗判斷而為之，是容易失確的。為明瞭草溝排水量設計時受草的生長疏密及高度所影響之程度，本計畫擬以水動力基本理論進行分析、探討草溝之水理設計，以期建立國內公路生態草溝之水動力理論基礎，俾供工程師設計時參考、應用。本研究第一年研究內容包括蒐集國內外草溝設計之相關文獻、建立並初步修正生態草溝之水動力理論，而第二年之主要內容則是進行生態草溝之流速分佈量測實驗，並和第一年的研究成果進行比較，以驗證或修改第一年提出的基本理論。

To reduce the impact of environment, the design of drainage system of highway is supposed to use grassed channels instead of concrete ditches, which will reduce the runoff, delay the peak time and increase the recharge of groundwater. However, if the Manning's formula is still employed to calculate the capacity of the grassed channels, the selection of the coefficient of Manning's roughness will be a big problem. Since this coefficient is much related to the density of the grass, it is easy to lose the accuracy only by artificial or empirical judgment. To realize the effect of the density and the height of grass on the drainage capacity, this project will develop a fundamental theory to analyze and discuss the hydrodynamics of grassed channels. The results of this study could be as a reference for the design of grassed channels in the future.The work of the first year is aimed at collecting the relative documents and handbooks and drawing up a fundamental theory. The work of the second year will include the measurement of velocity in the lab, and the verification of the results in the first year. Therefore, the mathematical model developed in the first year is probably modified according to the experimental data in the second year.