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The time of concentration for surface runoff is the important factor of the rational formula. The propagation process of overland flow on a sloping plane for unsteady rainfall is investigated using the kinematic wave theory. The relationship between time of concentration and mean rainfall intensity during the time is theoretically revealed. Based on such a relationship, we propose the method of estimating the time of concentration from the observed hyetographs and hydrographs. The proposed method is verified through applying it to several river basins. We can appropriately account for the runoff characteristics of each basin by comparing the estimated time of concentration with the geographical factors of the basin.

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IN URBAN SEWER PIPE SYSTEMSFirst, a storm water runoff simulation model of surcharged flow with masses of air at manholes in urban sewer pipe systems is proposed. In this model, the compressibility of the air is considered. Second, the model is applied to runoff experiments in a hydraulic model of storm sewer pipes with manholes, and the air-pressure hydrogiaplis simulated by the simulation model are compared to the observed ones.As a result, it is demonstrated that the simulation model proposed here can simulate very well the temporal variations in air-pressure at manholes.

In this paper, runoff simulation for urban sewer system using SUM combined with computer mapping is discussed.The method of input-output data formation for SUM is modified using computer mapping. To reduce the computation time and capacity, the effect of the simplification of sewer system on the results of simulation is examied as for EXTRAN of SUM and the comparison of the runoff computation accuracy of RUNOFF with kinematic wave model is carried out as for RUNOFF of SWMM.