PIBS Model for Surcharged Pipe Flow

Abstract

In order to address questions relating to the cause of local flooding in many downstream watersheds in Houston, TX, a computer model has been developed that handles both a surcharged pipeflow condition and a variable tailwater in the outflow. The ILLUDAS model has been adapted to accept surcharged conditions through the incorporation of an iterative hydraulic grade line calculation, which then allows a corrected set of flows through the pipe system. A variable tailwater condition corresponding to a known or predictable flood hydrograph in the main channel is also included. The pressurized ILLUDAS backwater simulator (PIBS) provides a useful extension of ILLUDAS to areas that suffer from surcharge flooding in low‐slope areas, such as the Gulf Coast. The model has been compared with the extended transport model (EXTRAN) for a 53‐pipe storm sewer system, and excellent agreement for the outflow hydrograph was shown under surcharged conditions. The model has been applied to 500 pipes in the Texas Medical Center and Rice Univ. in Houston, TX, which are adjacent to one of the main flood channels. Results from the analysis indicate good agreement with the observed street ponding locations in the area for high‐intensity rainfall events.