地表曼寧糙度值對都會區快速淹水模擬模式之影響

Abstract

現今都會區淹水模式發展成熟，大多為以求解淺水波方程式之二維漫地流模式耦合一維雨水下水道模式之都會區傳統淹水模式，其可合理模擬都會區之淹水狀況。然而因其計算時間較長，故尚無法大量運用於即時積淹水預報上。以基於細胞自動機概念發展的二維快速漫地流模式(WCA2D模式)所建構的都會區快速淹水模式，可得到與都會區傳統淹水模式非常相近的模擬結果，且可大幅減少演算時間，使得其具有相當的潛力來應用於即時淹水模擬演算上，然其WCA2D模式僅能考慮全區相同的地表曼寧糙度值。 本研究修改WCA2D模式使其細胞出流計算能考慮地表曼寧糙度值，發展出二維曼寧權重細胞自動機淹水模式(Manning Weighted Cellular Automata 2D, MNWCA2D)。本研究考慮地表曼寧糙度值設置方法、細胞出流計算方法以及細胞交界的地表曼寧糙度值給定方法，交互組合為三種模式情境。設置七種理想地形測試其水體傳遞，並將三種模式情境於理想地形之模擬結果與以求解二維淺水波方程式之台大二維淹水模式以及FLO-2D Pro模式進行比較分析。研究結果顯示地表曼寧糙度值以非均一值設置、細胞出流計算方法採用MNWCA2D模式且細胞交界地表曼寧糙度值給定方法以平均法模擬時，其結果與台大二維淹水模式以及FLO-2D Pro模式之模擬結果最為相近。

Nowadays, urban flood inundation models have gradually matured. Most of them couple the one-dimensional (1D) sewer flow model and the two-dimensional (2D) overland flow model to construct the traditional urban flood inundation model and simulate dynamic flow interactions between storm sewers and overland surface. They can reasonably simulate urban flooding. However, these types of urban flood inundation models are still difficult to be used on real-time forecasting due to long simulation time they require. Utilizing the concept of cellular automata, a two-dimensional rapid overland flow model is developed(WCA2D) and construct the rapid urban flood inundation model. The simulated results of rapid model are quite comparable to those of traditional model. However, the simulation times of the rapid model are significantly reduced of those of the traditional model. So it is evident that the rapid model has potential to be used on real-time forecasting. However, the Manning’s surface roughness in WCA2D model currently can only be the same for whole simulated area. To solve this limitation, we modify WCA2D model to propose Manning Weighted Cellular Automata 2D Model(MNWCA2D). To evaluate the influence of spatial Manning’s surface roughness, we consider Manning’s surface roughness setting methods, cell outflowing calculation methods, and cell interface’s Manning’s surface roughness giving methods, leading to three model scenarios. In this study, seven idea cases were set to test the water transfer situation of four model scenarios. Three model scenarios simulation results were compared with NTU2D model and FLO-2D Pro model which solve two-dimensional shallow water equations. The result shows that when Manning’s surface roughness is set based on spatial Manning’s surface roughness , cell outflowing is calculated by MNWCA2D model and Manning’s surface roughness on cell interface is assigned as the arithmetic mean of two neighbor cells Manning’s surface roughness, the model scenario simulation results are closest to NTU2D model and FLO-2D Pro model .