Evaluating Stormwater Volume Reductions in Constructed Stormwater Wetlands with Native Vegetation
The effectiveness of utilizing native vegetation to enhance water retention capabilities of constructed stormwater wetlands is being investigated at a senior housing development in Muskego, WI in the Root River Watershed which drains into Lake Michigan. This study will evaluate influent and effluent discharge and climatic conditions pre- and post- vegetation establishment to ascertain the influence native vegetation may have on the hydrograph. Additional evaluations will be performed through the use of WinSLAMM (Source Loading and Management Model for Windows) and numerical models.
Background
Constructed Stormwater Wetlands or CSWs are structural stormwater controls built to remove pollutants and sediment through settling and biological uptake. Additionally, CSWs are designed to reduce and delay peak discharge through impoundment and extended release of stormwater. CSWs and wet ponds or retention ponds are widely accepted, low-cost stormwater control practices most commonly used in suburban areas, towns, and villages due to land requirements. Although the primary purpose of CSWs and retention ponds are similar, design characteristics, habitat, biodiversity, and pollutant removal mechanisms differ. This includes the incorporation of shallow water vegetation in marsh areas surrounding a permanent pool, increased vegetation biodiversity in both the marsh and floodplain/upland area, increased fauna biodiversity due in part to increased habitat, and utilization of biological uptake and microbial breakdown in addition to traditional settling to treat pollutants in CSWs.
Many of the benefits realized by CSWs can be enhanced with native vegetation introduction throughout the emergent, wet, and mesic prairies surrounding such treatment systems (Figure 1). Additional benefits from native plant communities may include increased habitat due to plant species polyculture instead of non-native monocultures often found in constructed wetlands; increased animal species richness due to increased habitat; and increased infiltration and erosion prevention due to the extensive root system of native plants among other benefits and ecosystem services.
Although the use of CSWs and wet ponds as structural stormwater mitigation tools is widely accepted and these systems are well understood, little is known about how native vegetation in CSWs may affect and react to urban stormwater. Expected peak flow and volume reductions may be altered due to native plant characteristics such as deep, large root systems; stem clumping and plant growth patterns; growth rates; structural stability during senescence; duration and timing of dormancy, growth, and dieback; evapotranspiration rates; and infiltration rates compared to non-native plants and grasses often found in constructed wetlands. Additionally, the presence of chloride in runoff, often associated with the use of salt as a deicer, may complicate many of these factors and may affect the outcome of native plant communities and any potential boost to CSW stormwater mitigation.
Objectives
This study attempts to ascertain the potential benefits of utilizing native vegetation in a CSW for the purpose of reducing effluent runoff through increased interstorm water usage, potentially resulting in reduced ponding levels and fewer or decreased effluent runoff events, impacting downstream water quantity and quality. Additionally, characterization of chloride interactions with and movement through a CSW with native vegetation will be conducted.
Description
Site selection was finalized in July of 2022 with the help of Milwaukee Metropolitan Sewerage District although construction and final grading was not finished until the end of November. A plan for monitoring and equipment purchases were made between August and September of 2022. Monitoring stations were built out over the winter of 2022-2023 and installation of equipment and monitoring stations happened at the beginning of May 2023. Four solar powered stations, 3 inlet and 1 outlet, collect stage, velocity, discharge, temperature, and specific conductance (chloride surrogate) data. Runoff comes from 7.04 acres of approximately 50:50 impervious and pervious land cover mix. Precipitation, air temperature, wind speed, wind direction, and solar radiation data are also collected to help calculate ET accurately (Figure 2). Continual water quality and quantity data collected from Summer of 2023 to Fall of 2024 is being used to ascertain CSW capabilities.
Benefits
Results from this research will help determine if additional reductions in effluent runoff can be realized by utilizing native emergent, wet, and mesic prairie vegetation in an otherwise traditional CSW. In addition to the benefits of increased property value, increased habitat and other ecosystem services, this information may help developers and stormwater managers determine the appropriate CSW for individual stormwater management projects. Additionally, a reduced number of stormwater effluent runoff events also has the potential to impact nutrient and fine sediment export and overall downstream water quantity and quantity throughout the lifespan of the CSW.
The effectiveness of utilizing native vegetation to enhance water retention capabilities of constructed stormwater wetlands is being investigated at a senior housing development in Muskego, WI in the Root River Watershed which drains into Lake Michigan. This study will evaluate influent and effluent discharge and climatic conditions pre- and post- vegetation establishment to ascertain the influence native vegetation may have on the hydrograph. Additional evaluations will be performed through the use of WinSLAMM (Source Loading and Management Model for Windows) and numerical models.
Background
Constructed Stormwater Wetlands or CSWs are structural stormwater controls built to remove pollutants and sediment through settling and biological uptake. Additionally, CSWs are designed to reduce and delay peak discharge through impoundment and extended release of stormwater. CSWs and wet ponds or retention ponds are widely accepted, low-cost stormwater control practices most commonly used in suburban areas, towns, and villages due to land requirements. Although the primary purpose of CSWs and retention ponds are similar, design characteristics, habitat, biodiversity, and pollutant removal mechanisms differ. This includes the incorporation of shallow water vegetation in marsh areas surrounding a permanent pool, increased vegetation biodiversity in both the marsh and floodplain/upland area, increased fauna biodiversity due in part to increased habitat, and utilization of biological uptake and microbial breakdown in addition to traditional settling to treat pollutants in CSWs.
Many of the benefits realized by CSWs can be enhanced with native vegetation introduction throughout the emergent, wet, and mesic prairies surrounding such treatment systems (Figure 1). Additional benefits from native plant communities may include increased habitat due to plant species polyculture instead of non-native monocultures often found in constructed wetlands; increased animal species richness due to increased habitat; and increased infiltration and erosion prevention due to the extensive root system of native plants among other benefits and ecosystem services.
Although the use of CSWs and wet ponds as structural stormwater mitigation tools is widely accepted and these systems are well understood, little is known about how native vegetation in CSWs may affect and react to urban stormwater. Expected peak flow and volume reductions may be altered due to native plant characteristics such as deep, large root systems; stem clumping and plant growth patterns; growth rates; structural stability during senescence; duration and timing of dormancy, growth, and dieback; evapotranspiration rates; and infiltration rates compared to non-native plants and grasses often found in constructed wetlands. Additionally, the presence of chloride in runoff, often associated with the use of salt as a deicer, may complicate many of these factors and may affect the outcome of native plant communities and any potential boost to CSW stormwater mitigation.
Objectives
This study attempts to ascertain the potential benefits of utilizing native vegetation in a CSW for the purpose of reducing effluent runoff through increased interstorm water usage, potentially resulting in reduced ponding levels and fewer or decreased effluent runoff events, impacting downstream water quantity and quality. Additionally, characterization of chloride interactions with and movement through a CSW with native vegetation will be conducted.
Description
Site selection was finalized in July of 2022 with the help of Milwaukee Metropolitan Sewerage District although construction and final grading was not finished until the end of November. A plan for monitoring and equipment purchases were made between August and September of 2022. Monitoring stations were built out over the winter of 2022-2023 and installation of equipment and monitoring stations happened at the beginning of May 2023. Four solar powered stations, 3 inlet and 1 outlet, collect stage, velocity, discharge, temperature, and specific conductance (chloride surrogate) data. Runoff comes from 7.04 acres of approximately 50:50 impervious and pervious land cover mix. Precipitation, air temperature, wind speed, wind direction, and solar radiation data are also collected to help calculate ET accurately (Figure 2). Continual water quality and quantity data collected from Summer of 2023 to Fall of 2024 is being used to ascertain CSW capabilities.
Benefits
Results from this research will help determine if additional reductions in effluent runoff can be realized by utilizing native emergent, wet, and mesic prairie vegetation in an otherwise traditional CSW. In addition to the benefits of increased property value, increased habitat and other ecosystem services, this information may help developers and stormwater managers determine the appropriate CSW for individual stormwater management projects. Additionally, a reduced number of stormwater effluent runoff events also has the potential to impact nutrient and fine sediment export and overall downstream water quantity and quantity throughout the lifespan of the CSW.