Love and marriage, horse and carriage, levee and pumping stationits not as poetic, but the latter is a powerful pairing of infrastructure to protect low-lying assets. And a pumping-station expansion project now beginning in Texas shows how drainage-system design has evolved over the past century, benefiting from the experience of older systems like that of New Orleans. click here to view diagram
Velasco Drainage District, Clute, Texas, last month issued notice to proceed on a $33-million project to expand two pumping stations, adding 1.56 million gal per minute to their existing 1.69-million gpm capacity. The district consists of industrialized coastal floodplain on the Gulf of Mexico that has suffered storm-surge flooding in past hurricanes. The land is low and flat. South of Houston, the elevation falls 1 ft per mile to the coast. "An old engineer once told me, When it rains, the waters home," says George Kidwell, chairman of Velascos board of supervisors.
Two of the districts watersheds, totaling 15,500 acres, sit behind 53 miles of levees that range from 15 to 22-ft elevation, protecting the cities of Freeport, Lake Jackson and Oyster Creek. The first levees were built in the 1940s to shelter chemical plants supplying the war effort during World War II. Today the watersheds contain about 60,000 people and nine industrial plants, says Kidwell.
Over the years, development has altered the hydrology and hydraulics of the area, and various surveys showed that expanded pumping capacity would be necessary to guard the area from flooding in a 100-year event, a Category 3 hurricane. Last month, two contractors began adding the required capacity. Cajun Constructors Inc., Baton Rouge, won a $13-million contract to add four 260,000-gpm Patterson axial-flow pumps to one station. CSA Construction Inc., Houston, won a $10.2-million contract to expand the other station with two 260,000-gpm pumps and three expansion bays. Design and construction management are by Baker Lockwood Joint Venture, composed of Angleton, Texas-based Baker & Lawson Inc. and Lockwood, Andrews & Newnam Inc., Houston.
The levee failure and flooding in New Orleans has focused attention on drainage-system design. The Velasco pump stations, built in the 1970s, place the pump motors on pedestals nearly 1 ft above the levees elevation. Many of New Orleans newer pump stations do the same, but in the oldest ones, built before 1900, the pumps sit just 4 ft above sea level, says Joe Sullivan, general superintendent for the citys Sewerage & Water Board. They were swamped when the levees breached.
Power supply is another major difference. New Orleans system operates on electric power from its own 61-MW central generating station, which was not flooded, and draws 18 MW more from the utility grid. Velascos pumps are driven by diesel engines with enough fuel for three days of operation, says Kidwell. "Electricity is the first thing that goes out" in a flood, he says.
But Sullivan remains sold on electric power. "If power goes out in one location or another, you can switch from another [location] with electric," he says. "Your most reliable supply is electric motors."