水田區調洪減災生態功能之三維度量化分析與試驗研究

3-D Quantitative Investigation and Field Experiment on Flood-Detention Effect for Paddy Fields

張倉榮(Tsang-Jung Chang) ； 高宏名(Hong-Ming Kao) ； 林玫珊(Mei-Shan Lin)

《農業工程學報》 52卷4期 (2006/12) Pp. 80-90

摘要

本研究針對水田區調洪減災生態功能，以三維度量化分析與試驗研究二者並進之方式，探討三維度自由液面水田區之流場受水稻植栽帶的水理阻滯效應，以及水田區對調滯洪水與下游出口流量之影響，藉以量化瞭解水田區對於生態環境之貢獻度。本研究首先針對台灣地區水稻植栽的特性，例如植栽高度、植栽阻水面積、植栽密度、阻力係數等因子，進行水稻體阻水效應參數之現地量測，整理計算各種不同水稻生長時期的特性因子試驗值，以求符合台灣地區水田現地狀況。
本研究繼而進行三維度自由液面水田區水理模擬，數值模式採用有限體積法(finite volume method)離散控制方程式，搭配PISO法耦合速度和壓力，使得整個流場符合質量守恆及動量守恆。紊流計算採用κ-ε紊流模式配合體積分率法模擬自由液面流場，且加入邊牆函數處理底床邊界周圍流場，再應用孔隙介質流理論模擬水田區植栽帶對水流的阻滯效應。模式驗證係參照Nepf及Vivoni在2000年所作的水槽試驗，模擬含有植栽帶之自由液面明渠流。最後，研究案例以單坵塊水田區進行模擬，研究發現當植栽高度愈高時，水田區內的阻水效應愈明顯。水稻植栽介於10~40cm之間可較休耕時期降低2%~10%之洪峰流量。洪水在洪峰過後緩緩地流出水田區，使得出流歷線重新分配，宛如人工濕地，足證水稻田可提供良好的滯洪功能。

關鍵字

水稻田 ； 調洪生態功能 ； κ-ε紊流模式 ； 體積分率法 ； 孔隙介質

並列摘要

The study conducts the 3-D quantitative simulation as well as experimental study to analyze and evaluate the function of flood detention for paddy fields. The 3-D free-surface flow with paddy plants inside are considered to investigate the influences of paddy fields on peak flood attenuation and the temporal distributions of outlet discharge. The ecological multi-functional of paddy fields are quantified. In the present study, a series of in-site experiments are firstly carried out to obtain the characteristics of paddy plants, such as plant height, interceptive area of plant, canopy density and drag coefficient etc, for different growth periods. The experimental results are further inputted into the 3-D numerical model to simulate the 3-D free-surface vegetative flow of paddy fields in Taiwan.
Next, a 3-D numerical model, adopting the finite volume method and the PISO scheme, is introduced to solve the governing equations. The k-ε turbulence model together with the volume of fluid (VOF) technique, wall function and porous media are used in the model to simulate the vegetative free-surface flow fields. The 3-D numerical model is verified by the vegetative free-surface experiment given by Nepf and Vivoni (2000). The agreement between the experiment and numerical result is quite satisfactory. A series of numerical simulations for different plant heights ranging from 10cm to 40cm are conducted. The influences of paddy fields on the detailed flow depths and velocities are also studied. It is concluded that, in comparison with the fallow case, paddy fields can reduce the peak discharge about 2%~10% for different plant heights. Thus, paddy fields can gradually mitigate flood movement and redistribute the outlet flow discharge. It behaves just like artificial wetlands and indeed provides flood detention function.

並列關鍵字

Paddy field ； Flood-detention function ； κ-ε turbulence model ； Volume of fluid ； Porous media