In small watersheds of fewer than 40 acres, WASCOBs can achieve the same goals as grassed waterways, Hellermann says.

They work best in hilly fields with irregular slopes not uniform enough for contour practices, such as terraces. The embankments are often built in a parallel series across an area of concentrated water flow.

The structure includes an earthen dike high enough to hold back runoff water from a 10-year storm event. Most dikes are about 4 ft. tall with broadly sloping banks so they can be farmed on both sides. Taller, steeper dikes are planted with grass.

After a cloudburst, water and sediment from upslope are trapped behind the dike. The sediment settles out as the pooled water drains slowly into a discharge pipe and tile line. The field does not need to be tiled, but an adequate, stable outlet must be available, Hellermann notes. The ponding area is designed to drain within 36 hours to avoid permanent crop damage.

Dave and Karen Liebl considered a grassed waterway to solve their erosion problem. But “that would have taken quite a bit of land out of production,” Dave says. Grassed waterways are generally 30 - 50 ft. wide, and they tend to have quackgrass, Dave says. “And you have to be really careful when spraying.”

With today’s wide sprayer booms and faster speeds, it can be hard to avoid damaging grass waterways with herbicide, Hellermann agrees. “Little by little, the edges get sprayed with glyphosate, and after awhile they’re too narrow. Water then flows around the remaining grass, causing gulley erosion.”