For nation’s largest floodplain restoration, novel floating platforms monitor water quality

By on January 31, 2014

Custom floating platforms are supported by buoyant styrofoam blocks (Credit: Christopher Rice)

In 2010, construction crews breached a levee surrounding 16,000 acres of land adjacent to the Ouachita River in northeast Louisiana, reconnecting the river to a swath of its former floodplain for the first time in 40 years.

The breach is part of the largest floodplain restoration in United States, according to the Nature Conservancy, which partnered with the U.S. Fish and Wildlife Service on the project. The new connection allows flood pulses to flow over former soybean fields and rice paddies in the Mollicy Farms tract of the Upper Ouachita National Wildlife Refuge.

The flood water leaving the floodplain carries sediment and nutrients that eventually flow back out to the Ouachita. That’s a water quality cocktail that the project’s scientists want to keep track of, as they hope to see the benefits of additional restoration work going on within the floodplain. But that was no simple task in what Louisiana Nature Conservancy Biologist Chris Rice said is a “crazy environment” with wild fluctuations in water levels.

“We were scratching our heads because this is a site that can flood from zero to 30 feet in a matter of weeks,” Rice said. “The whole place will basically fill up like a 16,000-acre lake. When the water is really high, there are white-capping waves.”

The researchers needed a way to deploy their YSI sondes in a way that would keep the equipment secure amid fluctuating water levels while remaining accessible for maintenance, whether the ground was dry or under 20 feet of water. Rice said he and the rest of the scientists couldn’t find any references to similar applications. Other sources in the industry were stumped as well, short of recommending they spend tens of thousands of dollars on buoy platforms.

So they came up with their own solution: a floating platform built around a telephone pole that rides the water surface as the floods rise and fall. The results were unusual enough to warrant a paper describing their creation that was recently published in the journal River Research and Applications.

A docked platform during a dry period on the floodplain (Credit: Christopher Rice)

Rice designed and constructed the platforms with an iron frame that encloses styrofoam blocks. They support a solar panel and a waterproof box that houses the data logger. A cable connects the platform to the sonde, which is generally secured in a nearby stream channel in a weighted PVC structure at fixed height off the riverbed.

At each station, a telephone pole donated by a local power company was sunk 8 feet into the ground and secured with concrete. The platforms are installed around the poles, which run through a center slot lined with rollers that ease movement.

The styrofoam blocks came from a local company that usually supplies the material for house boats and riverboat casinos, Rice said. The blocks are buoyant enough to support technicians who approach by boat, tie off and climb on to service equipment. Rice said the amount of styrofoam they ended up using may have been overkill.

“The dimensions of styrofoam that we used were way too more than what we needed,” Rice said. “We could have probably put a car on top of it.”

When the first flood pulse came through, Rice said they could do much more than hold their breath and hope for the best. Fortunately, everything worked like it was supposed to. The stations have floated freely up and down the poles for several floods now, including come greater than 10 feet.

Floating platform during a flood (Credit: Christopher Rice)

The data will help track the progress of other restoration projects within like replanting the area’s historical forests that were cleared to create cropland, creating wetlands and reversing manmade changes like roads agricultural ditches. The research could also benefit other projects in the Mississippi Basin and across the country as restoring natural floodplain connectivity becomes a more common flood management and habitat creation strategy.

“As we’re doing this interior restoration work and try to restore this floodplain, we want to monitor for numerous years to come to see these changes on this large of a scale,” Rice said. “The lessons that we’re learning here are going to be valuable for decades to come.”

Image: Custom floating platforms are supported by buoyant styrofoam blocks (Credit: Christopher Rice)

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