Manhole Storage Capacity Influence on Transient Flow Modeling during Storm Sewer Flooding Event

Abstract

Drainage systems are designed to quickly convey rainwater from urban areas to areas of natural flow (rivers, streams, lakes, etc). Hence, they are sized with the assumption of steady free surface flow. With the frequent flooding of storm sewers and corresponding damage to public and private infrastructure (Schmitt et al. 2004), numerical modeling of transient flow has now become unavoidable. Several models of transient flow are available, each with its advantages and limitations. This chapter examines the impact of the inclusion of manhole size on the filling celerity of urban drainage systems. It is assumed that the pressurization of the drainage network starts with the rapid filling of a manhole, i.e. as soon as the water level in the manhole reaches the crown of the pipe being filled. Based on this assumption, a filling model is built to analyze the influence of manhole capacity on the propagation of the surge wave. This model uses the method of characteristics within the conduit and an innovative method based on gravity waves. To evaluate the impact of manhole size on the filling speed of the Storm Water System (SWS), the proposed methodology is applied to a theoretical case study. Results show that manhole size can accelerate or reduce the filling speed of connecting conduits.