Blacklands drainage critical

Ever so often Mother Nature reminds folks in the Blacklands of North Carolina exactly where they're farming.

Located along the coast of North Carolina, the area rich in high-organic soil is also right in the path of the majority of hurricanes that hit the East Coast.

“Even though we've been farming here for a long time, we're just beginning to learn how to manage the water,” says Joe Landino, president of the Blacklands Farm Managers Association. “We've gone from getting rid of as much water as we could to learning to control it at a depth of 18 inches.

“Without water management in the Blacklands, we couldn't do crop production,” Landino says.

Watching how long it took for fields and ditches to drain after Hurricane Isabel last year, Blacklands farm managers were reminded of the importance of drainage systems. Farm managers at the annual Blacklands Summer Tour listened to experts about the importance of water management.

Robert Evans, North Carolina State University Extension ag engineer, says there are three components when considering drainage system requirements: Magnitude or how much excess water is present, duration and frequency.

In terms of crop production, the ideal scenario is to manage water at a depth of 18 to 20 inches below the surface. The problem is, the water table is not static. “The outflow from a site is what we're dealing with after a hurricane or a storm,” Evans says. In a flooding situation, the water moves through the soil laterally. Field crops can tolerate “wet feet” for 24 to 48 hours; ponding for 12 to 24 hours. Truck crops can tolerate wet feet for 12 to 24 hours and ponding for less than 12 hours. Crops are more sensitive in the late vegetative stage.

On average, the conditions affecting crops happen every two to five years. Structural buildings face the watermark every five years while ag buildings are threatened every 10 years. Residential buildings, on average, face the watermark every 50 years.

Washington County, N.C., gets a 6-inch rainfall four times every 13 years; a four-inch event every four years; and a three-inch rainfall one time every year. A nine-inch rainfall occurs once every 100 years.

“The question is, what event do we want to design for,” Evans says.

Channels are designed to handle the excess water from a four-inch rainfall and remove it over a 48-hour period. Evans says a channel designed to reflect the way a natural canal would handle water is showing more promise than the standard trapezoidal channels that have been used for years.

While channels provide the means to carry the runoff after a storm or heavy rain, control structures provide the measure to even out the flow.

Carl Crozier, North Carolina State University soil scientist, says water control structures in canals can give growers yield benefits and help manage the amount of runoff. “Uniform field topography is needed to achieve a uniform water table,” he says. He's conducting a precision agriculture study designed to help farmers pick the right practice to correct problems in the fields.

Problems occur in the field when the crown in the middle is too high, which causes over-drainage. When the crown in the field is too low, ponding occurs. Both of these situations can lead to yield problems. Crozier showed a cotton plant that was growing 15 inches off the ditch bank and one that was in the middle of the field. The cotton plant at the ditch bank was small, while the one in the middle of the field was the correct size. “Poor drainage leads to the development of a poor root system.” Precision land leveling might be a practice to correct the problem.

Evans says using a water-control measure in the canal in some cases can mean as much as a 50-percent difference.

“If we don't have the right moisture levels, the nutrients will not work,” Evans says.

When the water is leaving the field at too fast a rate, it's likely to be carrying sediment with it.

Control structures have been widely used during the past 15 years through cost-share programs. There's a major push in the Midwest to have the measures implemented as part of the farm bill, Evans says.

Currently, a “two-board rule” is in place for control structures, meaning that the structure has to have two boards to be in compliance.

On sandy soils, the goal is to “hold the water up high during the non-growing periods,” Evans says. If there's an area that's open for improvement, he believes it's the management of the water table during fallow periods of winter.

He recommends using some form of vegetation along ditch banks — not fescue.

“On a watershed scale, water can be held back and released at an even rate,” Evans says. “We have water being drained out that doesn't need to be drained out. In some cases, we're over-draining water from the soil.”

Because water management is such an important topic in the region, special-use water management districts have developed as a way to address drainage issues, says Dwane Hinson, of North Carolina's Natural Resources Conservation Service.

“It's very important to look at drainage on a watershed scale when planning,” Hinson says. Special-use districts provide money for grants while emergency money after the fact can come from FEMA and state agencies.

Currently, five counties in northeastern North Carolina have these special-use water districts. “No longer does a developer come in and build without looking upstream and downstream,” Hinson says.

“This is about focusing on improving drainage,” Hinson says. Most ditches are designed to remove two inches of water in a 24-hour period. Changing the fall and elevation of the channel has the effect of making it act more like a wetland.

In the town of Edenton, N.C., a special-use water management district designed a wetland, and “it's working great,” Hinson says.

Programs such as CRP, CREP, EQIP and North Carolina Ag Cost-Share can help pay for stabilizing and land shaping, as well as buffers along ditches. A control structure in the channel is a relatively inexpensive way to reduce total drainage. The structure costs between $4,000 and $5,000.

A rock structure in the channel can also help slow down the drainage. In-stream wetlands are another way to even out the flow and glean nutrients as the water flows by. “We're trying to restore the hydrology of the swamp.

“It requires water management on a watershed scale to stop seepage,” Hinson says. “Improve your drainage and improvement your environment.”

Traditional drainage districts in the area are operated through self-assessments and operated through county commissions.

“We were talking about water management at the first Blacklands Farm Managers' Tour 34 years ago and we're still talking about it,” Landino says.

e-mail: [email protected]

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