Surge basin. The 3-acre, 9-ft.-deep pond stores 26 acre-ft. of drainage water from 1,700 acres. Ditch flow enters the basin through a 48-in. inlet and is discharged through a 15-in. outlet. Overflow weirs at the inlet and outlet prevent water from backing up in the ditch. The basin traps sediment and slows the flow of water into the lower portion of Ditch 57. The basin will need to be scraped out every 10-15 years.

The basin and 16-ft. buffers are planted with deep-rooted native grasses to hold the soil, filter sediment, and take up nutrients.

The surge basin is located about midway down the ditch in an area that often flooded in the past, says Project Engineer Chuck Brandel, I & S Group, Mankato. Minn. The site was not the first choice from a water management standpoint, he notes, but the preferred site was unavailable, and “the project leaders refused to force this on anybody. They felt it was important not to have animosity.” No wetlands were drained for the project.

Total water storage costs: $250,000

Outlet weir and water storage area. Ditch 57 empties into the Cobb River, and eventually flows into the Minnesota River. A 5-ft.-tall concrete weir, or dam, at the ditch outlet slows water discharge, dissipating its erosive force and allowing sediment to drop out. Drainage water backs up behind the weir into a 6.4-acre storage area within the channel. Stored water is slowly released into the river through an 18-in.-wide gap in the weir.

During a 3-in. rainstorm this spring, the weir prevented a water surge into the Cobb River, says Craig Austinson, Blue Earth County ditch manager. “I was really surprised at how well this worked. For something that cost just $15,000, this is an extremely effective method” of regulating peak drainage-water flows and preventing river-bank scouring, he says. Outlet weirs are a low-cost practice that could be added to many existing Midwest ditch systems, he adds.

Two-stage ditch. This 1,400-ft. open ditch mimics the floodplain of a natural stream. It’s designed to cut flooding, sediment transport and ditch-bank sloughing. The 2-ft.-wide main channel transports tile water from about 2,300 acres of cropland. Ten-ft.-wide grass “benches” on either side of the main channel slow water flow, allowing sediment to settle out without impeding drainage capacity.

Many public ditches could benefit from this modification, says University of Minnesota Extension Engineer Gary Sands. In fact, “Sometimes, a ditch will start to evolve to that form on its own, with a low flow channel and inside benches.”

Cost: $80,000

In-ditch sediment trap. A 3-ft.-deep trench excavated in a portion of the main ditch channel traps sediment from 2,300 acres of cropland. At $2/ft., “this is a very cost-effective way to store sediment and extend the ditch maintenance period,” Brandel says.

Native grass buffers. Grass buffer strips at least 16.5 ft. wide were planted along the entire length of Ditch 57, where there had been no buffers before. “I’m a big fan of buffers,” Austinson says, “not only for environmental reasons but for economic reasons, too.” Buffers cut erosion and lower ditch maintenance and repair costs, he says.

Instead of the usual blend of ditch grasses, more expensive native grasses were planted along Ditch 57. Native grasses’ advantage is deeper root systems to hold the banks and take up nutrients, Austinson says. A side benefit is wildlife habitat.