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Channel system reduces amount of sediment entering lagoons

PD Editor Karen Lee Published on 19 September 2012
dry creek bed

Lagoons and ponds are required storage facilities for large cattle operations. Their purpose is to collect watershed from the livestock areas and hold it until it can be properly dispersed according to nutrient management plans.

However, as the effluent flows to lagoons, it tends to carry solid particles that over time can fill up the settling basin positioned in front of the lagoon to catch those particles.

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When a large feedlot operation in Texas grew sick of incurring the cost of cleaning out its settling basin, it contacted Jim Nankervis of Nankervis Enterprises to find a practical and effective way to reduce this cost.

Feedlot drainage networks consist of pen drains (open, unlined channels) that deliver runoff from cattle pens to conveyance channels. Conveyance channels (open, unlined channels) collect runoff from one to several pen drains and deliver runoff to a settling basin and/or lagoon.

Nankervis, a scientist who studies sediment transport in rivers, found a way within this network to dramatically reduce sludge in the pond without violating federal or state laws by creating backwater in unlined basins or channels.

The Nankervis Velocity Dissipator (or NVD) is an in-channel device used to settle out solid waste while still allowing channels to drain. It is a four-inch, half-round tube with round verticals sticking up. This creates a roughness in the channel to catch the solids but still allows the effluent to flow through.

The devices are five-foot long and positioned across the width of the channel downstream of the cattle pens but upstream of the settling basins and lagoons. By placing several devices in series along the length of the channel, the entire bed surface of the conveyance channel can be used to trap sediment.

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“It will trap a good amount of sediment over time,” Nankervis says. Over a nine-month period one feedlot cleaned the channel twice; once after four months and 7.5 inches of rain and once after five months and 26 inches of snow. Total accumulation of dry manure (less than 23 percent moisture content) cleaned from the channel was 543 yards.

Based on the height of the device, the channel needs to be cleaned when the depth of the dry manure is at 6 inches, Nankervis estimates.

Unless it is a very heavy rain that pushed a lot of solids, the channel won’t need to be cleaned after every rain event. When the rain stops, the channel drains and the solids dry up and shrink. If the solid buildup begins to change the slope of the channel, that’s when it needs to be cleaned out.

As the manure dries in the channel, it does not mix with the substrate below and, according to Nankervis, peels right off in one single pass when scraped.

“It’s pretty clean manure,” he says, noting he’s seen farmers compost the solids, apply them to the field, incinerate them or use them to generate electricity. Others return them to the drylot to repair holes.

Because the sediment does not reach the settling basin, it reduces the frequency of cleaning the lined pond. This service is typically contracted out to excavation companies to remove sludge from the ponds using heavy excavating equipment or suction dredges. Any time large equipment enters a lined pond or basin, the lining needs to be re-certified and, if damaged, replaced.

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The cost of liner replacement and re-certification can often exceed the cost of removing the sludge. Therefore, reducing the frequency of this is a big savings, Nankervis says. In the example, the feedlot estimates it will now need to have its settling basin cleaned every seven years instead of every four to five years.

Because nutrients like nitrogen and phosphorus are primarily tied up in the solids, this system also reduces the nutrient loading of the lagoon. In the 543 yards captured above, there were 5,000 pounds of nitrogen and 5,500 pounds of phosphorus.

Nankervis says it is costing farms about $5 per pound to manage phosphorus in the wet form. Being able to manage it in the dry form is a huge benefit, he says.

In addition, it helps to reduce the erosion to the native substrate of the channel, keeping it intact and out of the basin as well.

A scour apron on the downstream side of the device allows the effluent to run off the apron so head cutting does not occur within the channel.

The materials are UV-resistant and corrosion-resistant. “It is pretty sturdy stuff. The base is PVC and the verticals are polypropylene so nothing sticks to it,” Nankervis says. “If the cows get out it is pretty safe. It won’t hurt or injure them.”

A 5-foot section of the device, including the scour apron and two-year limited warranty, will run $310.

The amount of sections depends on the design, slope and length of the channel. The example feedlot had a 1,500-foot channel and was 40 feet wide. It ran eight devices across the width of the channel in a series of eight lines for a total of 64 devices installed.

Nankervis has placed as few as three in a 300-foot channel and has worked with one channel that was a mile long. “There’s a lot there,” he says.

It is simple to install and can be cut to fit the width of the channel. The device is portable and easy to move.

Depending on the manpower on the farm, they can be removed or left in place for cleaning the channel.

While the number of times it takes to clean it out is completely dependent on the weather, Nankervis says most farms average three times a year. With the drought, some went as long as 18 months without cleaning the channel.

“It’s a passive system,” he says. “It works when it needs to work. Otherwise it just sits there.”

In addition to channels in feedlots, this system can be placed in any channel where debris is a problem. It can be used for irrigation ditches, natural channels, gully restoration after fires, river restoration, etc.

For more information on this manure-handling system, call Nankervis at (303) 210-9803. PD

PHOTO:Developers claim the trap’s efficiency is nearly 100 percent for low to moderate runoff events. In the background, you can see that the downstream substrate is clean. Photo courtesy of Nankervis Enterprises.

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