Energy loss at manholes is of importance in the design of storm sewer networks and in flood-analysis. Some researchers have already investigated the energy loss at three-way manholes under surcharged conditions. However, formulation to calculate the energy loss at manholes, including all variables of structural elements of the pipes and of the manhole has not yet been accomplished. Therefore, more study to formulate the energy loss at three-way drop manholes is needed. In this study, the ratio of the diameter between inflow pipes and an outflow pipe, the ratio of flow rates between those pipes, water depth in a manhole and the drop gaps between those pipes are considered and the energy loss at three-way circular drop manholes is examined. Finally, a modified formula, more accurate than that in the U.S. Federal Highway Administration's 2001 Urban Drainage Design Manual is proposed. The proposed formula takes the influence of the ratio of the diameter between inflow pipes and outflow pipe and drop gaps between those pipes into consideration. The calculated energy loss coefficients in both straight-through and lateral pipes successfully reproduce the measured values.

Energy loss at manholes under surcharged conditions is as important as the friction loss in pipes in the design of storm sewer networks and in flood analysis. Some researchers have already proposed the formula to calculate the energy loss at three-way manholes under surcharged conditions. However, in most of these proposed formulas, all variables of structural elements for the pipes and the manholes have not been considered enough yet. Therefore, development of the formula to exactly calculate the energy loss at three-way manholes is needed. In this paper, the effect of diameter ratios between inflow pipes and an outflow pipe, the ratios of flow rates between inflow pipes, connected angles among those pipes and drop gaps between inflow pipes and outflow pipe on the energy loss at three-way circular drop manholes were investigated. Based on the experimental results, a new formula that considers all structural elements and the ratios of flow rates between inflow pipes was proposed for the energy loss coefficients at the manholes. In the proposed formula, calculated energy loss coefficients reproduce measured values more exactly than existing formulas do.

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Energy loss at manholes under surcharged conditions is as important as the friction loss in pipes in the design of storm sewer networks and in flood-analysis. Some researchers have already proposed the formula to calculate the energy loss at three-way manhole under surcharged conditions. However, in most of these proposed formulas all variables of structural elements for the pipes and the manhole have not been considered enough yet. Therefore, development of the formula to exactly calculate the energy loss at three-way manhole is needed. In this study, the effect of diameter ratios between inflow pipes and an outflow pipe, the ratios of flow rates between inflow pipes and connected angles among those pipes on the energy loss at three-way manholes were investigated and a new formula was proposed for the energy loss coefficients at three-way manholes that considers all structural elements and hydraulic parameters except drop gap between inflow pipes and an outflow pipe.

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