沉滓交換機制之模擬與應用

Abstract

河道沉滓之運移機制相當複雜，本研究在一維有限解析法動床模式架構下，參考許氏(2002)之成果，將懸浮載與河床載分開計算，利用van Rijn(1984)公式計算河床載與懸浮載之垂直平衡濃度剖面，並考慮水體實際懸浮載濃度剖面，此二濃度剖面間之差異即為懸浮載與河床載間之沉滓交換速率，並據以模擬渠道底床沖刷或淤積量。 模式之率定部份係採Suryanarayana(1969)均勻與非均勻沉滓動床實驗資料，針對渠道沖刷與淤積案例進行模擬。結果顯示適度的考慮前述沉滓交換機制，將有助於動床沖淤精確之模擬。最後，為顯示本模式之實用性，將模式應用於模擬阿公店水庫空庫防淤策略對下游河道沖淤之影響，模擬水庫不同排砂濃度對下游河道沖淤之短期及長期影響，所得之結果可提供水庫更新改善計畫之參考。

Sediment transport mechanism in rivers is quite complicated. This study is under the framework of the 1-D finite analytic mobile-bed model, and refers Hsu’s (2002) results. In the model, the sediment transport rate is divided into suspended load and bed load. The bed load and the equilibrium vertical concentration profile of the suspended load are calculated by van Rijn’s (1984) formulas. In addition, the actual concentration of suspended load is concerned. The difference between the two concentration profiles determines the exchange rate between the suspended load and the bed load, and also the quantity of channel scour or deposition. Suryanarayana’s (1969) experimental data for the scour and deposition cases of uniform and non-uniform bed material are adopted for the calibration of the proposed model. Results show that consideration of abovementioned exchange mechanism can accurately simulate the experimental data. Finally, to demonstrate the practicability of the model, the impact of the flushing from Ah-Kong-Diann Reservoir on its downstream channel is simulated. The shortterm and longterm impacts on downstream scour and deposition of Ah-Kong-Diann Creek due to various sediment concentrations released from the Reservoir are evaluated. The results provide some useful information for the reservoir flushing operation in future.