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Creating a Wetlands Environment *
Incredible as it sounds, a wetlands is taking shape in the desert outside Boulder City, Nevada. The constructed wetlands are part of a master-planned water reclamation program that will provide irrigation water for a greenbelt area comprised of a public park, four adjoining ball fields, bike tracks, golf courses, and the Nevada Veteran's Cemetery.
"The idea for the wetlands evolved from discussions between the City, the U. S. Bureau of Reclamation (USBR), the Nevada State Division of Wildlife, and Kennedy/Jenks Consultants," relates Alan Gove, the Public Works Director for Boulder City. Gove led the drive to make the wetlands a reality.
Improving Water Quality - "The wetlands are an outgrowth of our search for an efficient, cost-effective method to treat wastewater and improve water quality," Gove says. "With Kennedy/Jenks' help, we are using the Lemna Process to treat effluent in our ponds."
Lemna, or duckweed, is a fast-growing aquatic plant that prevents algae growth and reduces suspended solids (SS) and biological oxygen demand (BOD) in wastewater. The process is simple, efficient, and produces a high quality effluent that can be further treated for reclamation.
"Duckweed serves two functions," says Gove. "It supplies shade to prevent the growth of algae, and it uses the nutrients in the water for growth. Since duckweed is fast-growing, we are constantly harvesting and drying it for compost. This process keeps the plants young and at the most efficient stage for taking up and converting nutrients."
The effluent from the Lemna Process and the treated wastewater from the Boulder City Wastewater Treatment Plant (WWTP) will receive additional treatment as it passes through the wetlands. The cleansing action of the wetlands will make the effluent suitable for irrigating lawns, landscape, ball fields, and golf courses.
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A Living Laboratory - In addition, the wetlands will serve as a research facility. The USBR, State and local agencies, and students at the University of Nevada, Las Vegas (UNLV) will use the wetlands to monitor the effectiveness of wetlands in purifying water and for research on aquatic plants, fish, endangered species, and wildlife habitat.
"The wetlands will also provide local schoolchildren and the public with a living laboratory where they can learn about reclamation, wetlands, wildlife habitat, and conservation," comments Gove.
Project Challenges - "The project presented some interesting design challenges," saya Walter Hines, Kennedy/Jenks Project Manager. "We had to consider the multiple uses of the wetlands and the extreme evaporation rates in an arid environment. We also needed to control salinity in the irrigation water to avoid salt damage to turf and trees. This will be done by diluting the effluent with surface water from the Colorado River."
The wetlands and designed to treat up to 1.0 million gallons per day (mgd) of wastewater effluent, but could handle up to 2.0 mgd without hydraulic limitations. To make the most efficient use of available water supply, Kennedy/Jenks designed a pumping scheme that matches seasonal irrigation demands with the amount of wetland inflow (minus evaporation). In winter, when irrigation needs and evaporation are low, effluent from the wetlands will be recirculated by pumping from the lower to the upper pond.
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The Flow Schematic illustrates the pumping system: Effluent is pumped from the treatment plant to a storage/control pond on the upper side of the wetlands. The wastewater pump station is controlled by water level sensors at the upper pond. Water flows by gravity from the upper pond through a control valve to a waterfall and Parshall flume, through a stream segment and into four ponds. Finally, the water flows to a lower storage pond that holds about half a day's supply of irrigation water for the Veteran's Cemetery. This pond ensures that enough water will be available for the cemetery's 12-hour nighttime irrigation schedule.
A unique feature of the wetlands is the 3,000 ft-long stream segment that simulates a real stream. Sections of rapids alternate with pool reaches, and aquatic plants and stones are placed on the stream bottom and banks to create "natural" stream conditions. The stream feature was designed by the USBR and installed using volunteer labor from the community.
Transforming the Desert - "Now that the infrastructure, plants, and trees are in place, we are working to establish the wildlife habitat," says Gove. When the aquatic plants are in, the USBR will introduce young razorbacks and chubs. Both are endangered species of fish in the Colorado River. The fingerlings will remain in the wetlands environment, where they are safe from predators. When they are large enough to survive in the wild, they will be reintroduced into the Colorado.
"The Clark County Conservation District has taken cuttings from native plants and planted them in the habitat," Gove reports. "This summer we will put in ball parks and other features. It's a slow process. But eventually, we will have an oasis in Boulder City like those that once thrived around the natural springs common to this area before Las Vegas became so heavily populated."
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