Numerical Simulation Of Hydraulic Transients In Drainage Systems

Abstract

Most Cities count on networks of underground tunnels for the conveyance of storm water and wastewater. A storm drainage system usually is designed to operate with freesurface flow regime, however when a storm exceeds the design event, the flow in the tunnels may transition from free-surface flow to pressurized flow. During the pressurization a moving air-water interface advances into the free-surface region with the potential for generating unacceptable hydraulic transients. A dynamic transient model has been developed to simulate the complex and highly dynamic flow during the pressurization of drainage systems. The model is based on the Interface Tracking Method and the Characteristics Method. The numerical results are compared against measurements. The code was used to predict the potential for hydraulic transients in the West Area CSO Tunnel System of the City of Atlanta. Different design alternatives were evaluated to mitigate pressure oscillations, backflows and flooding during storm events.