Grassed Waterway

A grassed waterway is a natural or constructed channel established in suitable vegetation for safe water disposal. Waterways should generally have less than 5 percent slopes, suitable soils for vegetation, and adequate area for installation. It is critical during the vegetative establishment period to restrict outside water from flowing through the channel. Therefore, it may be necessary to delay construction until the waterway is well established. Grass waterways are also used as filters to remove sediment, but may sometimes loose their effectiveness when too much sediment builds up in the waterways. When trying to reduce the possibility of severe gully erosion, grassed waterways provide a helpful solution. They force storm runoff water to flow down the center of an established grass strip that can carry very large quantities of storm water across a site without erosion.

Generally, grassed waterways should be located to conform with and use the natural drainage system. Waterways may also be developed along roadways and property lines but should avoid sharp changes in direction and grade. Waterways may be trapezoidal, parabolic, or triangular ÒVÓ shaped. The waterway installation must assure that the runoff from the waterway does not cause gullies and/or overfalls to develop. 

The most critical time in successfully installing grassed waterways is when vegetation is being established. The disturbed area of the waterway should be seeded and mulched within 10 days of excavation and shaping work. Special protection such as mulch anchoring, straw or hay bale dikes, or other protective methods are warranted at this critical period. Supplemental irrigation may also be needed to establish
quality vegetation.
 

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Photo: USDA NRCS, Charlie Rahm