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Green tech: Corps of Engineers wetland habitat lowers flood risk for Dallas

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U.S. Army Corps of Engineers, Fort Worth District  

by James Frisinger

Dallas skyline peaks through the Wetlands

A string of sky-blue ponds – surrounded by grasslands – unwinds across the North Texas countryside. Overhead hundreds of cormorants crisscross in and out of formation.

This wildscape, nestled just below the historic Joppa Community, is quiet. But there is a lot more going on here.

Skyscrapers peaking up along the northwest horizon are a reminder that this place is just five miles from downtown Dallas. These wetlands, carved out by the U.S. Army Corps of Engineers from the Linfield Dump and Sleepy Hollow Golf Course in the middle of the last decade, serve two purposes.

For most of the year they are managed as a quality wildlife habitat, a natural area populated by diverse native Texas plants and animals.

But they also stand ready for duty whenever the heavy rains come. These wetlands are part of the Dallas Floodway System and are a green tech solution to reduce flood risk for Dallas citizens by forming an alternate Trinity River pathway to efficiently convey floodwaters out of the central part of the city.

Audubon’s Tania Homayoun says changing people’s perception of the Trinity River is one of the goals of the Trinity Bird Count, which co-sponsored Saturday’s walking tour with the corps.

“A lot of people don’t think of it as anything but the channelized section that they see when they drive over the freeway,” she said. “They have no idea that there is a lot of this back here.”

Birders’ data reflects Corps of Engineers wetlands habitat health

The senior manager for conservation and education at the Dogwood Canyon Audubon Center in Cedar Hill heads the quarterly Trinity Bird Count, now working through its second year. It is developing a data baseline for how large and diverse the bird population is along the Trinity.

Dallas County is in the Central Flyway, the great migratory bird corridor that stretches from Canada and Latin America. The wetlands provide a rest and refueling stop for the journey.

The Trinity Bird Count recorded 48 species Saturday including a thousand double-crested cormorants. Also numerous were gadwalls, blue-winged teal and Northern shovelers. In smaller numbers were lesser scaup, pied-billed grebe, black-throated green warbler, red-bellied woodpecker and Lincoln’s sparrow.

The wetlands were designed by the corps, for the city of Dallas, to attract diverse waterfowl.

Dr. Gary O. Dick, research ecologist at the corps’ Lewisville Aquatic Ecosystem Research Facility, says a lot of the emergent aquatic species planted here are seed producers, which provide fuel for mallards, widgeon and pin-tail. Submersed vegetation attracts coots.

A floating aquatic, American lotus, produces big seeds the size of little acorns.

“Mallards just love it. They’ll come in here and load up,” said Dick.

Plants indirectly feed birds by supporting a robust fishery.

“The fact that we have fish in there is going to draw a whole suite of birds – the egrets, the herons, the kingfishers that we’ve seen today,” said Dick. “The cormorants are coming in and they’re looking for fish.”

The Lower Chain of Wetlands run from the I-45 Trinity River Bridge (near downtown Dallas) to Loop 12. It is fed year-round by effluent from the Central Waste Water Treatment Plant, which is nutrient rich with nitrogen and phosphorous. The wetlands naturally clean the water by reducing these concentrations before draining into the Trinity River. Pumps and gates allow wetland managers to control water flow to help establish plants and to seasonally expose mudflats to attract migrating shorebirds.

Three more wetland cells will be built in an upper chain of interconnected wetlands between the Martin Luther King Jr. Bridge and the water treatment plant. Construction has just gotten under way.

The wetlands support two different fisheries. Shallow waters harbor minnows, bluegill and bass. Deeper waters – up to seven feet deep – support filter feeders such as shad, which consume algae thriving in the nutrient-rich water. The deepwater fishery attracts big fish-eating birds, such as the American white pelican flock that came through earlier in the week.

When complete, this new ecosystem restoration project will create 271 acres of improved habitat.

The wetlands have already proven they can convey floods. The corps also measures who well they perform the other mission as quality habitat.

“It’s easy to come out here and take a look and say, ‘It looks pretty good.’ I’ve heard a lot of people say that today. It looks a lot better than what they expected,” said Dick. “How do you know if you’re successful or not? Monitoring is what does it.”

New Dallas wetland habitat reduces flood risk, too

Researchers measure fish, sediment buildup, invertebrates, water quality, plants and waterfowl to judge performance.

“Is there change in the plant community over time in response to what we’re doing? If we see a positive change – and yes, we are seeing greater diversity, we are seeing better establishment of plants – that’s good,” said Dick. That growing health of this new ecosystem seems to coincide with spotting several new bird species every year.

Twenty-nine species of native aquatics were planted here. Identified in the ecosystem as of March 2012 are 12 species of mammals, 91 species of birds, 10 species of reptiles and five species of amphibians, the corps reports. (The Trinity Bird Count has documented additional bird species, pushing the combined count to at least 107.)

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