Maintaining Grassed Waterways
Donald L. Pfost
Department of Agricultural Engineering
USDA, Natural Resources Conservation Service
Grassed waterways are commonly used as an outlet for water from terraces or to prevent gullies, where water flowing down a hillside concentrates. Inspect grassed waterways annually or after unusually large storms. Perform needed maintenance promptly to prevent costly damage to the waterway.
Common maintenance problems with grassed waterways include insufficient grass, weeds and brush, sedimentation, gullies and insufficient capacity.
This may be caused by establishment problems, low soil fertility, smothering from lodged growth, accumulated sediment, or competition from weeds, legumes and nearby trees or brush. It may also be caused by not turning off the herbicide sprayer when crossing waterways, from herbicide runoff or from herbicide-laden sediment deposits.
Because of periodic flowing water, it is difficult to re-establish grass in a functioning waterway. Bare spots may be reseeded or sodded. Mulching can help re-establish a grass seeding. Bare spots being reseeded should not be lower than the surrounding channel areas. You may slightly overfill them to divert water while grass becomes established.
Periodic soil tests make a proper soil fertility maintenance program for waterways easier. Waterways can be topdressed with lime, fertilizer or manure. In extreme cases, a waterway may require a major renovation. In these cases, low fertility may be corrected by moving in topsoil and/or mixing in lime, fertilizer, manure or organic matter to obtain the desired fertility level.
Weeds and brush control
A high fertility program and heavy nitrogen fertilization helps grass compete with weeds and legumes and maintain a vigorous stand. Control trees and brush by cutting and/or with herbicides. Contact your local MU Extension center for recommendations on control herbicides.
To prevent smothering from lodged, accumulated growth, mow and remove hay from the waterway as required to maintain a moderate height. If hay is not desirable, more frequent mowing and/or shredding can prevent smothering without removing the residue.
Delay mowing until after July 15 of each year to avoid destroying wildlife habitats.
Some waterways may not be accessible during the normal cropping/haying season. If necessary, growth may be removed at other seasons. Hay quality may be sacrificed for convenience. Carefully controlled grazing may be permissible when the ground is not too wet or too dry.
Gullies may be caused by original construction irregularities, by sediment deposits, by using the waterway as a travelway or by livestock paths. Unstable outlets, which result from a drop-off or an extremely steep slope at the lower end of the waterway, can also cause gullies.
To control unstable outlets, regrade (and reseed) the outlet end or construct a grade stabilization structure.
Gullies must be filled and reseeded or sodded. Fill material should be well compacted. Slight overfilling may be desirable to allow for settling and to divert water flow somewhat while the new grass becomes established.
If possible, sediment deposits should be removed before grass is damaged.
Machine travel up and down waterways should be minimal, especially when the area is wet and soft. Machine travel on waterways will be required during haying and other maintenance operations. Waterways except for those located on the field boundary will usually be crossed or used as a turnstrip for normal field machinery operations.
Livestock may have to be fenced out of waterways when they are grazing fields.
After grass is well established, remove temporary dikes (berms) that were built to prevent runoff from entering waterways during the grass establishment period. The objective is to allow runoff to enter the waterway and prevent water from eroding a channel along the side of the waterway. Soil removed from the berms may be used to fill low spots in the field or to build terrace ridges.
Insufficient waterway capacity may result from sediment accumulation in the channel or from loss of side berm height. (Permanent side berms are commonly used to contain the water flow in shallow waterways located on field boundaries or ridges.)
Higher residue tillage systems or more soil-conserving crop rotations can reduce sediment buildup.
Overflow can cause a gully to form along the side of the waterway. Sediment buildup in the waterway can cause water to pond in the lower end of the terrace channel.
In severe cases, sediment must be removed from the channel and the channel must be reseeded. In other cases, the height of the side dikes (for waterways not in natural drainage ways) may be increased and the dikes reseeded.
Spot removal of sediment from the waterway at the terrace discharge may eliminate ponding in the terrace channel with a minimum of waterway reseeding required. In other cases, the lower end of the terrace may be moved downhill to access the waterway at a lower point to obtain adequate terrace channel drainage.
If the waterway has to be rebuilt or reseeded, water from the terraces may have to be diverted outside of the waterway until the grass is established. Small, temporary cross trenches and dikes with a fall of 6 to 12 inches across the waterway that will interrupt the flow of water on long waterways may be useful in establishing grass.