多方式法模式在沖刷渠道之研究

Abstract

本研究以李氏 (1992)及陳氏 (1994)所發展之多方式特性法結合演算模式 為基礎，探討非均勻質渠道之水力篩選及護甲現象。此外利用緩衝段法計 算上游邊界非均勻床質粒徑組成之變化，並考慮不平衡輸砂過程之空間稽 延效應。模擬水力篩選之過程中，河床予以分層，並以 Allen(1978)之砂 丘高度經驗式計算交換層厚度。 另根據 Karim & Holly(1986)所提出之 護甲理論，修正輸砂量及交換層厚度。由於多方式法在選取輸砂公式上之 限制，本文改採異於 IALLUVIAL 模式之護甲體積推求方式，以模擬護甲 隨時間發展之過程。為了測試模式之適用性，除進行模式敏感度分析外， 並根據顏氏等( 1987) 非均勻質試驗中之C組資料，模擬在清水沖刷情況 下之底床高程及粒徑組成變化之情形，其結果頗令人滿意。 This study, base on the coupled multimode characteristics model developed by Li(1992) and Chen(1994), investigates the hydraulic sorting and armoring phenomenon of nonuniform- sediment channel. Furthermore, the variation of the bed material gradation at the upstream boundary of the channel is computed by the buffer reach method,and the spatial-lag effect of the nonequilibrium sediment transport is also considered. During the hydraulic sorting simulation,the composition of subsurface materials is determined by defining different layers of subsu- rface sediment,and the thickness of the mixed layer is compuated by Allen's(1978)empirical dune-height relationship. The sediment transport rate and the thickness of mixed layer are updated using the armoring theory proposed by Karim and Holly(1986). Due to the limitation of selecting the sediment transport formula in the characteristics model ,this study adopt a new methodology to compute the armoring volume instead of that used in the IALLUVIAL model,and then the armoring process can be simulated. To test the applicability of the proposed model, the model sensitivity analysis is first executed. In addition, the model simulates the variations of bed elevation and bed material gradation under the clear-water degradation condition,based on Yen et al.'s(1987)experiment data.The results of simulation are quite satisfactory.