25 October 2004
Cost Data. Grassed swale construction costs are estimated at approximately
.70 per square meter (
.25 per square foot.)29 These costs, however, do not include
design costs, raising the total cost to approximately .40 per square meter (
square foot.) Grassed swale costs compare favorably with other stormwater
Maintenance Issues. The maintenance objectives include keeping up the
hydraulic and removal efficiency of the channel and maintaining a dense, healthy grass
cover. Maintenance activities should include periodic mowing (with grass never cut
shorter than the design flow depth), weed control, watering during drought conditions,
reseeding of bare areas, and clearing of debris and blockages.
Corrective Actions. Cuttings should be removed from the channel.
Accumulated sediment should also be removed manually to avoid concentrated flows in
the swale. Avoid applying fertilizers and pesticides. The grass cover should be thick
and reseeded as necessary. Any standing water removed during the maintenance
operation must be properly disposed of at an approved discharge location.
INFILTRATION TRENCHES. Infiltration trenches are trenches that have been
back-filled with stone. These trenches collect runoff during a storm event and release it
into the soil by infiltration.
Figure 8-7. Infiltration Trench Schematic
Source: SWRPC, 1991. In EPA, 1999c.
Most Appropriate Uses. Infiltration trenches may be used in conjunction
with another stormwater management device, such as a detention pond, to provide both
water quality control and peak flow attenuation.31 Runoff that contains high levels of
sediments or hydrocarbons (oil and grease) that may clog the trench are often
Brown and Schueler, 1997.