都市雨水下水道系統一般採用合理法及明渠定量等速流進行設計。但豪雨期間之雨水下水道流況為緩變量流，因此本研究應用擬似定量流理論建立「緩坡雨水下水道系統水流模式」，分析及評估緩坡雨水下水道系統之輸水能力。本模式中之雨水下水道流量律為依據明渠定量緩變速流及管流理論推導之緩坡雨水下水道流量公式，並發展由兩端人孔水位以流量公式計算流量之數值解法。

本研究以水工試驗之量測資料驗證雨水下水道流量公式數值解法之正確性。本研究並以所建立之「緩坡雨水下水道系統水流模式」分析設計案例之定量流及變量流排水過程，探討出口臨界水深排水及浸沒水深排水之迴水現象以及人孔能量損失所造成影響雨水下水道系統之輸水能力情形。

由模擬演算結果可看出雨水下水道系統出口為臨界水深時，可有最大的輸水能力。雨水下水道中水流匯流及人孔或匯流井之入口及出口損失均將造成迴水影響，因而影響以定量等速流設計之雨水下水道系統之輸水能力。

因此本研究所建立之「緩坡雨水下水道系統水流模式」可應用於評估雨水下水道系統之功能以研擬改善之對策。

The size of storm sewer is decided by rational method and steady uniform flow for designed discharge. According to theory of gradually varied flow and surcharge flow, the paper establishes the model of storm sewer system and analyses the delivery capacity of the mild slope storm sewer systems.

The accuracy of the model was verified by comparing with experimental data. The paper analyses design case for drainage of steady flow and unsteady flow, exploring the critical depth drainage and the backwater effect of submerged depth drainage and manhole energy loss. This could influence the delivery capacity of storm sewer systems.

In view of this, when the storm sewer system is critical depth, it produces the strongest delivery capacity. The storm sewer system can result in backwater effect, such as the exit and entrance loss of the manhole or junction, so it could affect the delivery capacity of storm sewer systems. The sewer is designed by steady uniform flow.

In summary, the model can apply to estimate functions of storm sewer systems.

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