雨水下水道中之流況，可以是明渠流、管流、閘流或混合型的流動型態。設計時，一般要求為明渠流。但雨水下水道因豪雨期間之流入流量超過設計容量而發生滿管流，也可因下游匯流井或人孔之高水位迴水影響而發生滿管流。滿管流時，若匯流井或人孔深度不足，將使得水由人孔或道路邊溝進水口溢流至地表面而泛濫。
陡坡渠道可因下游發生亞臨界流況而導致水躍，但只要有超臨界流段，則此一下游亞臨界流將不影響上游輸水能力，故本研究以緩坡雨水下水道為研究對象。本研究由矩形斷面規則渠道之臨界坡一般化水流關係式導出封頂涵管之緩坡條件，進而推導緩坡雨水下水道發生明渠流，局部滿管流及全部滿管流之條件，以分類雨水下水道內之水流型態，進而推導各流況之輸水能力近似解。此一近似解可用於豪雨期間由人孔或匯流井水位分析雨水下水道之輸水能力。
由各流況之比較分析，顯示一般而言，滿管流況可能有較大之輸水能力，但若出口匯流井或人孔之水位可浸沒出口時，將高入口匯流井或人孔之水位，或降低雨水下水道之輸水能力。
本研究進行水工實驗以驗證所推導之雨水下水道輸水能力模式。由實驗結果可看出因下游匯流井水位或尾水抬高所導致的迴水影響，可在低流量時形成滿管流動，甚至發生溢流的情形，均與理論分析之結果相符。故需維持雨水下水道出口匯流井或人孔之水位不浸沒出口，可確保雨水下水道之輸水能力，進而提升雨水下水道之輸水能力。
由實驗觀察可看出匯流井內之水面呈現傾斜，最大水深皆明顯偏向出口壁面的水位超高現象，並因匯流井內水位之超高而導致溢流情形發生。在本研究之實驗範圍內，此一超高值小於匯流井內平均水位2%。
由實驗資料分析，入口及出口浸沒之矩形斷面雨水下水道，因矩形斷面匯流井或人孔所造成之能量損失係數可取為0.36。此一結果可應用於演算浸沒管流流況之雨水下水道輸水能力。

The storm sewer system in the urban area can be open channel flow, pipe flow, gate flow or compound flow, and it was generally designed for open channel flow. Pipe flow occurs the inflow exceeds the designed capacity during rainstorms and the backwater effect of the high water stage in downstream junction boxes or manholes. If the manhole is not deep enough, the flood occur overflow from the manholes of sewers or street curbs.
The hydraulic jump occurs in subcritical flow at the downstream steep-slope channel, the subcritical flow can not affect the delivery at upstream channels as long as the supercritical flow exists. Therefore, mild-slope sewer flow is discussed in this study. The study deduces condition for mild-slope in the closed conduit by generalized-flow relation of the critical slope for rectangular channel. Also, deduces the conditions for open channel flow, partial-full pipe flow and full pipe flow to classify the flow regime in the urban drainage system and deduces the approximate solution of delivery for each flow regime. According to water depth of the manholes or junction chambers, the approximate solution of delivery in urban drainage can be analyzed during heavy rainfall events.
More drainage ability in pipe flow can be indicated by analyzing flow regime. However, if the water level of junction chambers or manholes submerges the outlet, water level will be increased in the junction chamber or manhole or reduce the delivery of the storm sewers.
The model is verified by hydraulic experiments. Laboratory investigations indicate that the rising of tailwater level are caused by the water level of the manhole in the downstream and backwater effect, and then result in pipe flow for low discharge and overflow even occurs. The experiment results conform to the theoretical analyses. Keeping the water level not submerging junction chambers or manholes, delivery of storm sewers can be maintained and even raised.
Laboratory investigations also indicate that the water surface in the junction chamber is inclined and the maximum depth is approach to wall top in the outlet and overflow occurs. The surcharge value is smaller than 2 percent of average depth in the experiment.
Based on the experimental results, the loss coefficient of the submerged-rectangular sewers is about 0.36. This result can be applied to estimate the delivery of drainage system with submerged pipe flow.

1. 台北市政府工務局，「台北市下水道工程設計標準」，民國80年5月。
2. 張博超，「連續突縮突擴之明渠水流之研究」，國立成功大學水利及海洋研究所碩士論文，2004。
3. 蔡長泰、顏清連，「通用水面線演算模式」，台灣水利季刊，第29卷，第3期，pp.11-18，1981。
4. 賴政佑，「矩形斷面緩坡雨水下水道之水理研究」，國立成功大學水利及海洋研究所碩士論文，2005。
5. 顏榮甫、林延郎、蔡長泰，「箱式涵洞水流之流量連續性及率定曲線」，台灣水利季刊，第42卷，第2期，pp.95-105，1994。
6. 顏榮甫、蔡長泰、林志翰，「箱式涵洞控制長度及流型分界之研究」，台灣水利季刊，第15卷，第4期，pp.545-553，2000。
7. Benjamin, T. B., “On the flow in channels when rigid obstacles are placed in the stream,” Journal of Fluid Mechanics, Vol. 1, part 2, pp. 227-248, 1956.
8. Campbell, C. W. and Sullivan, S. M., “Simulating time-varying cave flow and water levels using the Storm Water Management Model,” Engineering Geology, Vol. 65, pp. 133-139, 2002.
9. Chanson, H., “Hydraulics of large culvert beneath Roman aqueduct of Nmes,” Journal of Irrigation and Drainage Engineering, Vol. 128, No. 5, pp. 326-330, 2002.
10. Chaudhry, M. H., Open-Channel Flow, Prentice Hall, 1993.
11. Chow, V. T., Open-Channel Hydraulics, McGraw-Hill, New York, USA, 1959.
12. Dasika, B., “New approach to design of culverts,” Journal of Irrigation and Drainage Engineering, Vol. 121, No. 3, pp. 261-264, 1995.
13. Day, R. A., “Preliminary observations of turbulent flow at culvert in inlets,” Journal of Hydraulic Engineering, Vol.123, No. 2, pp.116-124, 1997.
14. Del Giudice, G. and Hager, W. H., “Sewer sideweir with throttling pipe,” Journal of Irrigation and Drainage Engineering, Vol. 125, No. 5, pp. 298-306, 1999.
15. Henderson, F. M., Open channel flow, Macmillan, New York, USA, 1966.
16. Hilden, M., “Simulation of floods caused by overloaded sewer systems: extensions of shallow-water equations,” Hydrological Processes, Vol. 19, No. 5, pp. 1037-1053, 2005.
17. Hsu, M. H., Chen, S. H., and Chang, T. J., “Inundation Simulation for Urban Basin with Storm Sewer System,” Journal of Hydrology, Vol. 234, pp. 21-37, 2000.
18. Jones, L. E., and B. N. Tripathy, ”Generalised critical slope for trapezoidal channels,” J. of Hydr. Div., ASCE, pp. 85-91, 1965.
19. Linsley, R. K., Franzini, J. B., Water-resources engineering, McGraw-Hill, New York, USA, 1979.
20. Mark, O., Weesakul, S., Apirumanekul, C., Aroonnet, S. B., and Djordjevic, S., “Potentail and limitations of 1D modeling of urban flooding,” Journal of Hydrology, Vol. 299, pp. 284-299, 2004.
21. Mays, L. W., Urban Stormwater Management Tools, McGraw-Hill, New York, N.Y., USA, 2004.
22. Merlein, J., “Flow in submerged sewers with manholes,” Urban Water, Vol.2, pp. 251-255, 2000.
23. Nasello, C. and Tucciarelli, T., “Dual Multilevel Urban Drainage Model,” Journal of Hydraulic Engineering, Vol. 131, pp. 748-754, 2005.
24. Schmitt, T. G., Thomas, M., and Ettrich, N., “Analysis and modeling of flooding in urban drainage systems,” Journal of Hydrology, Vol. 299, pp. 300-311, 2004.
25. Seckin, G., Yurtal, R., and Haktanir, T., “Contraction and expansion losses through bridge constriction,” Journal of Hydraulic Engineering, Vol.124, No. 5, pp. 546-549, 1998.
26. Subramanya, K., Flow in Open Channel, Tata McGraw-Hill publishing Co., New Delhi, India.
27. Takashi, S., Shuji, T., and Toshihiro, I., “Energy loss at surcharged manholes-model experiment,” Wat. Sci. Tech., Vol.36, No.8-9, pp. 65-70, 1997.
28. Yen, B. C., “Hydraulics of Sewers” in Yen, B. C. ed., Advances in Hydroscience, Vol. 14, Academic Press, Orlando, pp. 1-122, 1986.