By Albert Petrasek, Jr.
PROJECT: Expand stormwater pumping capacity citywide
OWNER:8City of Dallas Trinity Watershed Management Department
CONTRACTOR:8BAR Constructors Inc., Lancaster, Texas
CONSTRUCTION:8 August 2010 — November 2012
Much of Dallas is protected by a 22-mile levee system that runs along both sides of the Trinity River. These levees form the Dallas Floodway, which receives runoff from an upstream area of approximately 9,000 square miles. The system includes six stormwater pump stations, three behind each levee and each with multiple pumping units, that work with a series of sumps to control flooding. A seventh has been recommended for construction.
Dallas County Levee Control District No. 1 built the facilities in the 1930s in conjunction with the levee system. They were expanded in the 1950s when the U. S. Army Corps of Engineers (USACE) improved the system and again in the mid-1970s to add capacity, making the levees and pump stations a federal program.
Because of their age and inadequacy in a 100-year flood event, the city initiated a program to upgrade the pump stations. The number of pumping units will increase from 29 to 50. This represents a significant increase in operations and maintenance, so selecting equipment best suited for such an application was critical.
The city and its consulting team developed a detailed process to evaluate pump types and options. Their subsequent 15-month investigation included visiting four manufacturers:
The team narrowed their options to conventional vertical pumps or concrete volute pumps before settling on the latter.
Although concrete volute pumps are new to the United States, more than 400 units are in service in North America and Europe and have performed well for more than 30 years. They're excellent for high-volume and low to moderate head applications and have an outstanding reputation for reliability, being commonly used in the nuclear power industry without standby units.
|INCREASE THROUGHPUT WITHIN THE SAME FOOTPRINT|
Stormwater managers increase the total capacity of six pump stations 145%.
The City of Dallas Trinity Watershed Management Department is introducing North America to concrete volute pumps for stormwater applications.
The volute is the component in which the velocity imparted to the water by the impeller is converted to pressure by carefully increasing the size of the spiral-shaped flow passage surrounding the impeller assembly. A small unit processes about 80,000 gpm; a very large one, about 400,000 gpm.
Department managers specified the design to increase capacity at six pumping stations and to build a seventh, called Trinity-Portland. Except for Old Baker, which has horizontal pumps obtained from the City of New Orleans in 1930, all are equipped with vertical mixed-flow pumps.
The first table lists the facilities and the second shows how much stormwater each will process as a result. The stations on the East Levee have two separate structures, which is why there are “old” and “new” and “small” and “large.”
At time of publication, Baker No. 3 and New Able were in the design phase. Funding for the other stations is scheduled to be provided through a future bond program.