Erosion Control Structures: Which is the Right Fit?

Driving by farm fields, sometimes you will see a waterway or terrace breaking up the field. These structures are put into place to help stop soil from leaving the farm field. But how is it decided what kind of structure is put in? Do they just flip a coin or does the landowner decide if one looks prettier than the other on the landscape? There is science behind which type of structure is selected for a site.

On the left: a water and sediment control basin. On the right: a grassed waterway. Each practice is designed depending on the survey and hydrology of the site.

When projects are being completed by the Natural Resource Conservation Services (NRCS) or the Soil and Water Conservation District (SWCD), there is a process to deciding on the type of structure that should be designed for a site. To begin, an elevation survey of the site is completed by staff. This survey is either done in topo style or points based off the rows and distances that help capture the topography of the land the structure will be going on. Staff then need to determine the hydrology of the site. The watershed (how many acres of water flow to one point) is calculated along with how long it takes for the water to flow from the furthest point of the watershed. The slope of the watershed also figures into the calculation. Another factor that affects the design is the land use. Some land uses soak in more water and it takes the water longer to reach the point of the structure, as compared to other surfaces like roads, where the water directly runs off.

The two main structures in Rice County that are found in farm fields are Waterways and Water and Sediment Control Basins (WASCOBS). Staff will use the results from the survey and hydrology to then design a structure. WASCOBS needs grade along the channel of the structure to be able to “tie” into hills to hold the water back and force the water underground into tile which then flows to a stable outlet. These structures need to be able to have that water drain into the tile line by 24 hours to prevent crop damage. These structures are used for smaller watersheds where there is adequate topography. Waterways do not need to tie into hills and since they are not holding back water but instead controlling the flow, they can be used to handle larger watersheds or areas where there is a flatter topography on the landscape.

Other factors that are taken into consideration when designing an erosion control structure is the outlet and maintenance. The structure cannot outlet somewhere that it will cause further erosion downstream, or there is not enough cover for the tile to be able to outlet.

Maintenance is also important during design. These structures are put in place to last ten years or more and adequate maintenance helps ensure that will happen. If a landowner cannot get out to mow a waterway yearly, the site may not be a fit for a waterway.

Staff from the NRCS and SWCD office must design for a standard, however landowners can put structures in without our financial assistance. Staff are willing to meet with landowners and talk options for structures that may work for their site that they can build on their own. To start the conversation about implementing erosion control structures, contact our office at 507-332-5408.

Emmie Scheffler is a District Technician with the Rice Soil & Water Conservation District and is the Plan Administrator for the Cannon River Comprehensive Watershed Management Plan. She also assists landowners and farmers with the implementation of soil erosion control practices and tree windbreaks. Contact Emmie with your questions at 507-332-5408.