A grassed waterway is a constructed grade channel seeded to grass or other suitable vegetation. The vegetation slows the water, and the waterway conveys the water to a stable outlet at a nonerosive velocity. A grassed waterway is considered an in-field practice.
Figure 23. A grassed waterway. Credit: Greg LaBarge, OSU Extension.
A grassed waterway is usually used in the natural waterways of a field, where concentrated flows of surface water left unchecked will form gullies. The waterway is designed to slow and channel water, providing vegetated cover to prevent erosion. Grassed waterways are often located in large fields and can collect water from upslope areas in multiple fields.
A grassed waterway carries runoff without causing erosion or flooding, or it is put into place to prevent gully formation. It is also used to protect or improve water quality.
- A grassed waterway improves removal of surface runoff.
- It reduces soil erosion and sediments. Sediment reduction is mainly the result of decreased transport capacity due to reduced runoff velocity and volumes, potential sieving of large particles by vegetation, and infiltration of sediment-laden runoff (Fiener and Auerswald, 2017).
- Sediment reduction benefits are very site-specific, so generalized improvements of water quality benefits are difficult to quantify.
- A grassed waterway reduces total phosphorus exports. Particulate phosphorus reductions are directly linked to sediment reductions. Dissolved phosphorus reductions are related to increased infiltration resulting in reduced runoff volumes or a more variable effect of adsorption (Fiener and Auerswald, 2017). One study shows no reduction, while a second study shows a 62 percent reduction in phosphorus concentration (Fiener and Auerswald, 2009).
Figures 24a and 24b. An eroded area before (24a) and after (24b) the installation of a grassed waterway. Credit for both images: Greg LaBarge, OSU Extension.
- A grassed waterway might qualify as a Conservation Works of Improvement to conserve soil resources, and to control and prevent soil erosion, flood prevention, and the conservation, development, utilization, and disposal of water within a district.
- Any landowner located in a soil and water conservation district can petition for Construction of Conservation Works of Improvement.
- The SWCD Law (Chapter 1515 of the Ohio Revised Code) enables local soil and water conservation districts, in addition to their other responsibilities, to construct improvements for natural resource conservation and development.
- To meet USDA-NRCS requirements, grassed waterways should not be used where construction would destroy important woody wildlife cover or where the present watercourse is not seriously eroding.
- Grassed waterways should be planned, designed, and constructed to comply with all federal, state, and local laws and regulations.
- Periodic maintenance is required to maintain function so that water is channeled to rather than around the waterway.
- Farming practices such as tillage and herbicide application should be discontinued at the edge of the waterway.
- Vegetation should be maintained and monitored for undesirable plant species.
Figure 25. Water is naturally diverted around a previously functioning grass area, creating erosion. Credit: Greg LaBarge, OSU Extension.
- Costs are site-specific and depend on the area draining to the grassed waterway, the slope of the land, and the length of the waterway. If only seeding costs are needed, installation might be $30–$40 per acre. A waterway that is engineered will cost $1,700 per acre (Fiener and Auerswald, 2017).
- Grassed waterways that are Conservation Works of Improvement might be eligible for cost-sharing. The Environmental Quality Incentives Program (EQIP) or other such programs might provide cost-share. Check with your local SWCD or NRCS for available programs.
- Maintenance costs primarily involve mowing and generally do not exceed $20 per acre annually (Fiener and Auerswald, 2017)
In Ohio, grassed waterways usually act as shallow, grassed field ditches that collect runoff from furrows and areas in fields that slope toward the waterways.
Extensive design details are provided in Ohio NRCS Standard 412: Grassed Waterway