Getting across a Mile-Long Floodplain: Design and Maintenance Considerations

The Tarrant Regional Water District (TRWD) operates and maintains over 200-mi (322 km) of raw water pipelines bringing water from east Texas Lakes to the western side of the Dallas Fort Worth Metroplex. Part of this system includes approximately 50 mi (80.5 km) of two parallel prestressed concrete cylinder pipelines (PCCP) located in a 130-ft (39.6 m) right-of-way between the Rolling Hills Water Treatment Plant in Fort Worth, TX, and the Ennis Booster Pump Station east of Ennis, TX. The older of the two pipelines is the 72-in. (182.9 cm) Cedar Creek PCCP constructed in the 1970s. The second pipeline is the 90-in. (228.6 cm) Richland Chambers PCCP constructed in the 1980s. Over the years, the Cedar Creek pipeline has experienced approximately 20 pipeline failures, and the increased risk profile for this pipeline has led TRWD to consider a larger pipeline replacement program. Based on system growth and improvements, TRWD now has the operational flexibility to take the Cedar Creek pipeline out of service for an extended period of time to tackle a larger pipeline replacement program. In 2019, Black & Veatch was selected to perform engineering services for the replacement of approximately 10 mi (16.1 km) of the Cedar Creek pipeline located in the cities of Mansfield, Grand Prairie, and Midlothian, TX. One stretch of the project crosses the headwaters of Joe Pool Lake in Grand Prairie, TX. This area includes the crossings of Mountain Creek and Soap Creek. Since these pipelines were installed in the 1970s and 1980s, the widths of the creeks have increased due to erosion, and scour has occurred at the flowline of the creeks. This project includes an evaluation of the best method for the pipeline crossing of these creeks as well as a long-term solution for maintenance access across them. The goal of this project is to provide a sustainable pipeline system that reduces the overall risk of system failure while also meeting the needs of future water demands and maintenance access. This paper will provide a brief overview of the need for the 10 mi (16.1 km) pipeline replacement project, discuss the challenges for crossing a mile-long floodplain, and summarize recommendations for the crossings of Mountain Creek and Soap Creek for both the pipeline installation and long-term maintenance access.