Storm Water Runoff Simulation Method in Urban Drainage Sewer Systems

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8.1 Numerical Scheme of Transition Flow in Urban Storm Sewer SystemsA numerical scheme that is able to simulate a transition between open-channel and surcharged flows in sewer pipe systems with high accuracy and stability were investigated. The principal results obtained are as follows : (1) The time interval DELTAt of the domain in which the transition occurs is divided into several tens of small intervals, and the characteristics equations in the domain are successively integrated so as to reflect the spatial and temporal variations of the values of flow variables along the characteristics ; (2) An appropriate number of divisions for the interval was derived theoretically ; (3) The adaptabilities of the scheme were made clear through laboratory runoff experiments.8.2 Hydraulic Function of Manholes for Surcharged Flow in Urban Sewer SystemsIt has been pointed out that, for surcharged flow simulations in urban drainage sewer systems, manholes are very important runoff elements that govern the pressure-wave celerity of the surcharged flow. The hyraulic functions of manholes were investigated and the following are the principal results obtained : (1) A theoretical expression of the celerity, which evaluates a hydraulic funcuion of manholes, was derived ; (2) Numerical simulations with representative urban sewer systems were made using SWMM-EXTRAN, and the influences of a manhole storage on runoff characteristics of the surcharged flow were revealed.