Level Spreader at Hinkson
Creek: Implementing
a Stormwater BMP
A level spreader is a stormwater best management
practice that transitions concentrated stormflows
from a stream or culvert into sheet flow over the
ground surface. It can be useful to attenuate peak
flows from small developed or impervious areas.
An added benefit of a level spreader is increased
infiltration of stormwater and uptake by plants as
the water is distributed over a larger surface area.
A level spreader works best in conjunction with a
well vegetated and very mildly sloped area down-
stream. An ideal location for this type of BMP is
just upstream of a vegetated or riparian buffer
strip. The level spreader will facilitate infiltration
while also decreasing the stormwater that directly
enters the water body. Increased infiltration can
help trees and grasses in the buffer to be suc-
cessful, and in turn, well-established vegetation
prevents soil erosion from water overtopping
the level spreader and flowing over the ground.
The City of Columbia built a level spreader in a city
park to divert water from a small stream back into
a reforested floodplain of Hinkson Creek. This level
spreader is composed of a vegetated swale, a basin
to still and pond the water, and a concrete level lip
to distribute the water evenly over the floodplain.
A study is taking place to determine the effective-
ness of the level spreader as a stormwater BMP.
Initial results indicate that the level spreader works
to attenuate stormflows differently during small
and large rain events. During smaller storms, all the
water is held inside the level spreader basin and
slowly infiltrates into the soil in this area—similar
to a retention basin. In larger storms, the level lip is
active, and water is distributed onto the floodplain.
Whether the level lip is overtopped during a storm
or not, the level spreader is effective at attenuating
peak flows in the small stream by infiltration and
evapotranspiration. Two consecutive years of tech-
nical reports on the project can be found here.
—Laura Wiseman, EIT, Graduate Research
Assistant-Water Quality, Missouri University
Civil/Environmental Engineering
Ground view of Hinkson Creek level
spreader. Photo by Laura Wiseman
Level spreader aerial view. Courtesy
City of Columbia, Missouri
18 CityTREES
