Hydraulic Transient Analysis of the Tarrant Regional Water District and the City of Dallas's Integrated Pipeline System

Abstract

The Tarrant Regional Water District (TRWD) and the City of Dallas Water Utilities (DWU) are designing a raw water conveyance system with a capacity of 347 millions of gallons per day (mgd). The proposed system consists of an approximately 150-mile long Integrated Pipeline (IPL), three lake-intake pump stations and three booster pump stations. The program management team performed a hydraulic transient analysis for the IPL and the pump stations to: (1) determine if there are unacceptable pressures in the pipeline during normal and emergency operating conditions; (2) develop a surge control strategy, if necessary, to mitigate adverse hydraulic conditions; and (3) determine a safe opening time for the discharge control valves during pump startup. The key challenge for these analyses was to avoid full vacuum during a transient event as the full vacuum condition may create column separation in the system that can generate excessive positive pressures due to the rejoining of separated water columns. Transient analysis software HAMMER TM V8i (HAMMER) by Bentley Systems Inc. was used for this study. The model considered air valves at the critical locations along the pipelines and around the pump stations to control negative pressures in the system. This paper presents the analysis and the results for selecting the surge control devices to keep system pressures within allowable limits during normal and emergency operating conditions.