Low Impact Development Manual for Michigan - OSEH - University ...

Description and Function
Level spreaders are designed to disperse concentrated
stormwater flows and are often used with other BMPs
over a wide enough area to prevent erosion. Erosion can
undermine a BMP, and can be a significant source of
sediment pollution to streams and other natural water
bodies. By dispersing flows, level spreaders assist
vegetated BMPs in pollutant removal via filtration,
infiltration, absorption, adsorption, and volatilization.
Level spreaders also reduce the impact of a stormwater
outlet to a receiving water body.
Level spreader located between a sediment forebay and a buffer
Source: NCSU-BAE requests acknowledgment for this image
Variations
Inflow
Inflow level spreaders are meant to evenly distribute
flow entering into another structural BMP, such as a
filter strip, infiltration basin, or vegetated swale. Examples
of this type of level spreader include concrete sills
and earthen berms.
Outflow
Outflow level spreaders are intended to reduce the
erosive force of high flows while at the same time
enhancing natural infiltration opportunities. Examples
of this second type include earthen berms and a level,
perforated pipe in a shallow aggregate trench (Figure
7.29). In this example, the flow is from the left (from
an outlet control device from another BMP) and flow
reaches the spreader via the solid pipe.
Figure 7.29
A level spreader with a perforated pipe
Applications
Level spreaders can be used in a variety of applications,
from residential areas to highway/road projects. The
primary requirement is that there must be adequate area
with an acceptable slope to receive the outflow from the
spreader. In ultra-urban settings, there is typically not
adequate space for level spreaders.
Figure 7.30, a close-up of Figure 7.29, shows an outlet
pipe from an upstream BMP that serves as an inflow to
the level spreader.
Figure 7.30
Level spreader with inflow pipe
Level spreader with geotextile surrounding the aggregate
helping to create a sloped area.
LID Manual for Michigan – Chapter 7 Page 223