Taking Cities by Storm
A state-of-the-art drainage system helps municipalities in flat locales decrease the volume and duration of street flooding
If Buddy Holly, the 1950s rock musician, helped put Lubbock, Texas, on the map, heavy rains and flooding have done their best to take it off. So, when a warning like the one quoted below is published, this major city located in the Texas Panhandle takes it very seriously.
NATIONAL WEATHER SERVICE LUBBOCK TX
603 AM CST THU JUN 26 2003
THE NATIONAL WEATHER SERVICE HAS ISSUED AN URBAN AND SMALL STREAM
FLOOD ADVISORY FOR...LUBBOCK COUNTY IN NORTHWEST TEXAS UNTIL 800 AM CST
EXCESSIVE RUNOFF FROM THIS STORM WILL CAUSE FLASH FLOODING OF SMALL
CREEKS AND STREAMS...HIGHWAYS AND UNDERPASSES. STREET FLOODING WILL
In an extremely flat area that was a lakebed some 150 million years ago, heavy rains have long plagued the city of Lubbock. In order to relieve some of the flooding, the community developed the South Central Drainage System Project. The engineering firm of Parkhill Smith & Cooper, Inc. (PSC), Lubbock, Texas, designed the system that is expected to decrease the volume and duration of flooding in city streets. The storm sewer directs overflow from the playa lake system on the south side of Lubbock to a discharge point near the city’s water reclamation plant.
The Role of Pipes in the Project’s Success
General contractor, Barnard Construction Company, Inc. of Bozeman, Mont., had previously used HOBAS centrifugally-cast, fiberglass reinforced, polymer mortar (CCFRPM) pipe on a sliplining rehabilitation project along Sloan Lane in Las Vegas, Nev. The installation subcontractor, Southland Contracting, Inc., of Fort Worth, Texas, has more than 10 years of history using this manufacturer’s pipes in many types of installations including microtunneling. Consequently, the firms were confident that the pipe would perform excellently.
The specifications included the pipes for both the direct bury and tunnel portions of the project, solid wall and profile wall polyethylene, and corrugated metal pipe alternates for the direct bury portions.
The project manager preferred the CCFRPM pipe due to its versatility and ease of installation. The project team installed the pipe sections around three big tunneled curves and directly under the railroad. They also quickly repaired a piece of pipe that was damaged on site.
Ahead of Schedule
The construction began in July 2001 and finished nine months ahead of schedule. Projections called for the $36 million system to be finished in April 2004. In late June 2003 the first inlets opened and the new storm sewer became functional. Additional inlets opened later and now the entire system is operational.
The project included more than 10,000 feet of CCFRPM pipes ranging from 24-inch to 72-inch diameter at depths of over 50 feet. The majority of the pipe was installed by tunneling methods, either by itself or within a primary liner. The specifications required pipes to meet ASTM D3262 standards for fiberglass sewer pipe with minimum stiffness classes of 36, 46 and 72 psi, depending on the depth of cover and the installation means. PSC inspected the pipe production and testing at the manufacturing plant in Houston, Texas. Robert Torres, EIT, inspector for PSC, said the “pipe performed at or above specification levels in all cases.”
Design practices related to stormwater management now must consider a number of issues: efficient removal of stormwater from urban areas, infiltration, sediment transport, storage, and water quality. The team involved in the South Central Drainage System Project attempted to deal effectively with all these issues.
Nearing the end of the project, Torres summed it up, saying, “With the system now operational, all we need now is some rain to see how well it will work.”
Municipalities Tackle Stormwater Management
Once considered a backwater issue, stormwater management has become an important matter to municipal officials as a result of the enactment in recent years of the National Pollutant Discharge Elimination System (NPDES) permitting program under the Clean Water Act that addresses stormwater discharges.
Published in 1990, Phase I of the NPDES stormwater regulations pertains to operators of large and medium municipal separate storm sewer systems (MS4s). Under the Phase I rules, large MS4s that serve a population of 250,000 or more or medium MS4s that serve a population of 100,000 or more, but less than 250,000 are required to obtain NPDES permits and manage their stormwater discharges. Nine years later, Phase II regulations were enacted that require certain regulated small MS4s, which serve populations of less than 100,000, and construction sites, which disturb 1 to 5 acres, to obtain stormwater management permits. For more information on how to comply with EPA’s NPDES regulations, go to www.epa.gov/npdes/pubs/comguide.pdf.
Stormwater discharges are generated by runoff from land and impenetrable areas, such as paved streets, parking lots, and building rooftops, during rainfall and snow events. Under the NPDES program, most stormwater events are considered point sources and therefore require coverage by an NPDES permit. Stormwater events have two main components that municipalities have to address: the increased volume and rate of runoff from impervious surfaces and the concentration of pollutants in the runoff. According to officials with the U.S. Environmental Protection Agency (EPA), both components are directly related to development in urban areas. Together, these components cause changes in hydrology and water quality that result in a variety of problems, including habitat modification and loss, increased flooding, decreased aquatic biological diversity, and increased sedimentation and erosion.
Typically, cities have several main goals related to stormwater management: reducing pollutant loads, maintaining groundwater recharge and quality, protecting stream channels, and safely conveying extreme floods. As well, effective stormwater management offers a multitude of other possible benefits, including protection of wetlands and aquatic ecosystems, improved quality of receiving water bodies, conservation of water resources, and protection of public health.
This article originally appeared in the 05/01/2007 issue of Environmental Protection.