Slowing the water remains Hawk Creek challenge
RENVILLE — Hawk Creek is pouring way too much sediment, nitrogen and phosphorus into the Minnesota River, and as a result continues to fall short of the goals set for it as a prairie stream in an agricultural landscape.
Reaching those goals is largely a matter of putting on the brakes. "We need to be reducing the water quantity and the velocity,'' said Heidi Rauenhorst, director of the Hawk Creek Watershed Project. She reported on the status of the watershed during the organization's annual meeting Wednesday in Renville.
"So if we could be holding water back in the watershed, at least temporarily, that is going to help reduce those peak flows,'' she said. The watershed director added that efforts to "cover the soil'' are also needed to help address the erosion problems in the 958-square-mile watershed.
Hawk Creek flows 65 miles from its start at Eagle Lake in Kandiyohi County to its confluence with the Minnesota River near the Upper Sioux Agency State Park.
Water quality monitoring by the watershed project found that total suspended solids, which mainly represent sediment and soil being washed into the stream, was anywhere from 2 to 2½ times the standard set for it. The total suspended solids standard is 65 milligrams per liter, but the average load ranged from 147 milligrams per liter at a monitoring site near Maynard to 184 milligrams per liter at a site near the confluence with the Minnesota River.
The same trend was evident for phosphorus and nitrate-nitrogen loads. The total phosphorus standard for a stream in Minnesota's corn and soybean country is 0.15 milligrams per liter. Hawk Creek showed levels of 0.368, or two times the standard at Maynard, and 0.464 near the Minnesota River, or three times the standard.
Phosphorus levels downstream of Willmar dropped significantly when the city's $86.2 million wastewater treatment plant began operations in 2010, but farther downstream the levels hold stubbornly above standards.
Nitrogen levels ranged from 6.9 milligrams per liter at Mayard to 7.1 milligrams per liter near the Minnesota River. Minnesota has not yet adopted a nitrogen standard, but these levels are considered "high,'' according to information presented Wednesday at the meeting.
There are ways to address these issues, and reason for optimism, according to Rauenhorst. She pointed out that landowners in the watershed are among the most active in the state in terms of adapting best management practices that can help.
Since its start 17 years ago, the watershed project has worked with 903 landowners on 1,486 projects aimed at improving water quality. The efforts are calculated to have reduced the amount of phosphorus carried to the Minnesota River by 54,277 pounds. The amount of soil saved is 16,536 tons and the amount of sediment is 19,361 tons, according to Rauenhorst.
Erosion problems are a priority issue for the watershed. The flashy hydrology means that large volumes of water at high velocities are moving across the landscape during rain events, carving gullies in farm fields and eroding streambanks.
Rauenhorst said strategies to slow the water include wetland restoration, adding perennial vegetation such as buffers and grass waterways, planting cover crops, reducing tillage, and installing controlled drainage structures.
The watershed has begun to promote cover crops as among the strategies to adopt. In the last two years, it offered a cost-sharing program in cooperation with the Renville County Soil and Water Conservation District and the county's land and water resources offices. Landowners planted cover crops on more than 1,000 acres as part of the effort. These fields served as test plots to demonstrate the effectiveness and economics of using cover crops.