The availability of water quality data for LID practices
varies widely. Certain practices may have 20 years worth of
monitoring data, while other relatively newly implemented
practices may have little such data available. These data
are often important to aid municipal managers in the
selection of BMPs needed to implement effective stormwater
management plans. This section presents some of these water
quality data, primarily gathered from academic research or
pilot project monitoring. For many pollutants and parameters
a wide range of percent removals are reported in the
literature. The variability in the data is the often the
result of environmental factors such as geographic weather
patterns, season, antecedent soil moisture conditions and
rainfall intensity and duration. There is also variability
because many LID controls make use of vegetated, natural
systems with designs that can vary on a site by site basis.
The
findings of the research and monitoring programs indicate
that properly designed and maintained LID systems will
significantly reduce total suspended solids and metals
concentrations from stormwater runoff. LID systems also
provide the benefit of nutrient removal through vegetative
uptake and infiltration. However, the effectiveness for
total phosphorus and total nitrogen removals shows a high
degree of variability. Research has indicated that total
phosphorus removals will be influenced primarily by sediment
transport to and export from LID BMPs, while total nitrogen
removals will be influenced primarily by soil conditions.
The data
presented and cited in this section provide pollutant
removals as a measure of concentration. A primary benefit
that LID controls offer is the ability to reduce stormwater
peak flow rates and discharge volumes. The ability to retain
stormwater through infiltration and evapotranspiration
enhances the effect of LID pollutant removal efficiencies.
The combination of stormwater volume reductions and
pollutant concentration reductions minimizes the total mass
of pollutants discharged to receiving streams and waterways.
| Water
Quality Data |
|
Trash and debris collected
in a stormwater detention pond.
Source: LID Center
(click on thumbnail
for enlarged view)
|
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