MMSD Watercourse Corridor Study: Green Infrastructure
In urban areas, the term “stormwater” refers to the precipitation (either rainfall or snowmelt) that isn’t absorbed by the ground, but rather flows off impervious surfaces such as roads, roofs, and parking lots. Stormwater flows into storm drains and is typically routed directly to streams, which often results in flooding and sometimes combined sewer overflows (CSO) as well. Stormwater can also transport a wide variety of contaminants such as sediment, trash, metals, nutrients, bacteria, and organic compounds. In urban watersheds, excess stormwater can cause problems such as changes in flow, increased sedimentation, higher water temperature, lower dissolved oxygen, degradation of aquatic habitat structure, loss of fish and other aquatic populations, and decreased water quality.
During the current 5-year study period for Phase VI (2021-2025) of the Milwaukee Metropolitan Sewerage District (MMSD) Watercourse Corridor Study, the following six topics are being addressed by one or more USGS subprojects:
1. Ecological Assessments and Trends
2. Geomorphology and Habitat Studies Related to Stream and Estuary Rehabilitation
3. Contaminants in Water and Sediment
4. Green Infrastructure
a. Assessment of Watershed Renewal through Green Infrastructure
b. Evaluating the Performance of Infiltration-Based Green Infrastructure on Contaminant Removal
6. Continuous Real-Time Streamflow
This webpage focuses on topic 4. Green Infrastructure.
MMSD has been working on a number of different stormwater management measures focused on protecting water resources, aquatic wildlife habitat, and land from increased pollution and flood risks. Urban stormwater management options include the implementation of green infrastructure which is designed to reduce or delay peak flows of runoff by holding stormwater on-site, encouraging infiltration, and enhancing evapotranspiration. The types and scales of green infrastructure options are numerous and varied, and each is engineered to fit local conditions such as space limitations, climate, slope, drainage area, soils, and geology. Common green infrastructure options include bioswales, rain gardens, and removing impermeable surfaces and replacing them with permeable options.
4a. Assessment of Watershed Renewal through Green Infrastructure
BACKGROUND
Urban flooding and water-quality degradation in the MMSD service area is often related to stormwater runoff from the high amount of developed area relative to natural areas. Stormwater runoff, coupled with CSO events, have negatively altered the nearshore and tributary health of Lake Michigan. A 2001 study found that for 16 land-use types in Wisconsin watersheds, connected impervious cover was the best descriptor of variation in fish community attributes, noting an inverse relationship between impervious cover and base flows (Wang et al., 2001). This study also noted connected imperviousness levels between 8 and 12% represented a threshold where minor changes in urbanization could result in major changes in stream condition. The percentage of impervious cover in the MMSD service area greatly exceeds this threshold.
The use of green infrastructure (GI) has been increasingly accepted as a means to reduce the adverse effects of stormwater in urban areas. Over the last decade, much has been learned about how well individual GI practices can reduce stormwater volume or improve water quality; however, of great importance, and less well understood, is watershed response in the context of reduced effective impervious cover (EIC) due to GI implementation. More information is needed to determine the threshold of reduced EIC required in an urban watershed before an impaired stream begins to shift back toward pre-settlement conditions. This information will help MMSD gain insight into the reality of their long-term volume reduction goals as well as advance a targeted approach to reduce stormwater runoff volume from urban sources through implementation of GI.
OBJECTIVES
The goals of this project are to track hydrologic changes in urban catchments through phased implementation of urban GI. The hypothesis is that reducing EIC through additions of GI, as well as other watershed improvements, will result in reduced stormwater volume to receiving streams such that eventual alteration of the hydrologic regime will return the stream towards a more natural state.
Specific objectives are as follows:
- Monitor changes in end-of-pipe storm sewer flows over time in test catchment targeted for accelerated implementation of downspout disconnection and installation of GI practices. Volumetric changes at the catchment level can be observed more rapidly than at the watershed level.
- Assess how changes to effective impervious cover in the test catchment translate into changes in stormwater runoff volume.
- Inventory homes that have disconnected as well as municipal and private GI practices in test catchment and track changes over duration of study.
- Calibrate a watershed model (e.g., WinSLAMM) that can be predictive of effective impervious cover and hydrologic response at the catchment scale.
APPROACH
In 2021, the USGS, in cooperation with MMSD, established two storm sewer monitoring sites to measure the volume of stormwater runoff from urban catchments of known drainage area (figure 1). The test catchment will undergo a transition that disconnects drainage from residential homes that are currently directly connected to the storm sewer as well as add or retrofit GI practices into the urban landscape. The control catchment will serve as a reference and having a similar percentage of effective impervious cover as the test catchment but with no (or limited) plans to disconnect home or implement GI and serve as a baseline condition by which future comparisons to changing contributions of stormwater volume, delivered via the storm sewer network, can be made. The campaign to encourage residents to disconnect their homes will be facilitated by MMSD and their consultants. Both catchments are located within the MMSD service area boundaries but outside the CSO area.
CONTACT
- William Selbig (USGS Upper Midwest Water Science Center)
- Nicolas Buer (USGS Upper Midwest Water Science Center)
4b. Evaluating the Performance of Infiltration-Based Green Infrastructure on Contaminant Removal
BACKGROUND
Water-management agencies worldwide are increasingly using green infrastructure (GI) and other stormwater control measures at various scales to minimize contaminant transport to receiving waterbodies, reduce stormwater volumes, collect stormwater for reuse, and increase groundwater recharge (Masoner et al., 2019). However, despite the increasing application of GI for urban stormwater management, water-quality performance data has been primarily limited to regulated pollutants, such as solids, nutrients, and metals. There is a significant lack of understanding of performance beyond these conventional water-quality metrics. Masoner et al. (2019) noted urban stormwater transports substantial mixtures of contaminants including polycyclic aromatic hydrocarbons, bioactive contaminants (pesticides and pharmaceuticals), and other organic chemicals known or suspected to pose environmental health concern. They also observed positive correlations in concentration with the percentage of impervious surfaces in highly developed urban catchments.
Many GI practices are designed to rapidly infiltrate large volumes of stormwater runoff from impervious surfaces, thus posing a risk of contaminating receiving surface water or groundwater. Oftentimes these practices use engineered media designed for enhanced removal of solids and nutrients; however, evidence suggests some organic contaminants, such as pesticides, may be of greater concern due to their mobility and potential to pass through treatment systems (Zhang et al., 2014). More information is needed to better understand the fate, transport, exposure and toxicity of stormwater contaminant mixtures discharged to and from infiltration-based GI practices.
OBJECTIVES
The objective of this study is to evaluate the performance of an infiltration-based GI practice at removal and retention of organic and inorganic contaminants in stormwater.
Specific objectives are as follows:
- Evaluate, through influent/effluent monitoring, the fate and transport of a suite of regulated contaminants (sediment, nutrients, metals, bacteria, and chloride) and emerging organic contaminants of concern that enter GI in both water and soil.
- Evaluate long-term performance of GI practice to help inform future maintenance decisions.
- Assess the toxicity potential of effluent and soils of GI through use ToxCast and other water and sediment-quality benchmarks. This analysis will be facilitated by the toxEval application.
APPROACH
In 2021, the USGS, in cooperation with the Northwest Side Community Development Corporation, installed equipment to monitor influent and effluent water quantity and quality to a single biofiltration system located at the Green Tech Station in Milwaukee (figure 1).
Influent to the biofilter is derived from an adjacent street surface with considerable traffic volume serving an area comprised of commercial and industrial land use. Runoff influent to the lined biofilter infiltrates into engineered soils before discharging into an underdrain that leads to a secondary observation tank.
Water-quality and sediment samples will periodically be collected from both influent and effluent to determine presence and abundance of sediment, total and dissolved nutrients and metals, chloride, temperature, polycyclic aromatic hydrocarbons, and other trace organic chemicals and waste indicator compounds.
Resulting data will be analyzed to determine what degree the GI practice is or is not capable of reducing pollutant loading in water for all chemicals analyzed and if so, what is the cumulative toxic potential of select pollutants retained in the soil.
CONTACT
- William Selbig (USGS Upper Midwest Water Science Center)
- Nicolas Buer (USGS Upper Midwest Water Science Center)
In urban areas, the term “stormwater” refers to the precipitation (either rainfall or snowmelt) that isn’t absorbed by the ground, but rather flows off impervious surfaces such as roads, roofs, and parking lots. Stormwater flows into storm drains and is typically routed directly to streams, which often results in flooding and sometimes combined sewer overflows (CSO) as well. Stormwater can also transport a wide variety of contaminants such as sediment, trash, metals, nutrients, bacteria, and organic compounds. In urban watersheds, excess stormwater can cause problems such as changes in flow, increased sedimentation, higher water temperature, lower dissolved oxygen, degradation of aquatic habitat structure, loss of fish and other aquatic populations, and decreased water quality.
During the current 5-year study period for Phase VI (2021-2025) of the Milwaukee Metropolitan Sewerage District (MMSD) Watercourse Corridor Study, the following six topics are being addressed by one or more USGS subprojects:
1. Ecological Assessments and Trends
2. Geomorphology and Habitat Studies Related to Stream and Estuary Rehabilitation
3. Contaminants in Water and Sediment
4. Green Infrastructure
a. Assessment of Watershed Renewal through Green Infrastructure
b. Evaluating the Performance of Infiltration-Based Green Infrastructure on Contaminant Removal
6. Continuous Real-Time Streamflow
This webpage focuses on topic 4. Green Infrastructure.
MMSD has been working on a number of different stormwater management measures focused on protecting water resources, aquatic wildlife habitat, and land from increased pollution and flood risks. Urban stormwater management options include the implementation of green infrastructure which is designed to reduce or delay peak flows of runoff by holding stormwater on-site, encouraging infiltration, and enhancing evapotranspiration. The types and scales of green infrastructure options are numerous and varied, and each is engineered to fit local conditions such as space limitations, climate, slope, drainage area, soils, and geology. Common green infrastructure options include bioswales, rain gardens, and removing impermeable surfaces and replacing them with permeable options.
4a. Assessment of Watershed Renewal through Green Infrastructure
BACKGROUND
Urban flooding and water-quality degradation in the MMSD service area is often related to stormwater runoff from the high amount of developed area relative to natural areas. Stormwater runoff, coupled with CSO events, have negatively altered the nearshore and tributary health of Lake Michigan. A 2001 study found that for 16 land-use types in Wisconsin watersheds, connected impervious cover was the best descriptor of variation in fish community attributes, noting an inverse relationship between impervious cover and base flows (Wang et al., 2001). This study also noted connected imperviousness levels between 8 and 12% represented a threshold where minor changes in urbanization could result in major changes in stream condition. The percentage of impervious cover in the MMSD service area greatly exceeds this threshold.
The use of green infrastructure (GI) has been increasingly accepted as a means to reduce the adverse effects of stormwater in urban areas. Over the last decade, much has been learned about how well individual GI practices can reduce stormwater volume or improve water quality; however, of great importance, and less well understood, is watershed response in the context of reduced effective impervious cover (EIC) due to GI implementation. More information is needed to determine the threshold of reduced EIC required in an urban watershed before an impaired stream begins to shift back toward pre-settlement conditions. This information will help MMSD gain insight into the reality of their long-term volume reduction goals as well as advance a targeted approach to reduce stormwater runoff volume from urban sources through implementation of GI.
OBJECTIVES
The goals of this project are to track hydrologic changes in urban catchments through phased implementation of urban GI. The hypothesis is that reducing EIC through additions of GI, as well as other watershed improvements, will result in reduced stormwater volume to receiving streams such that eventual alteration of the hydrologic regime will return the stream towards a more natural state.
Specific objectives are as follows:
- Monitor changes in end-of-pipe storm sewer flows over time in test catchment targeted for accelerated implementation of downspout disconnection and installation of GI practices. Volumetric changes at the catchment level can be observed more rapidly than at the watershed level.
- Assess how changes to effective impervious cover in the test catchment translate into changes in stormwater runoff volume.
- Inventory homes that have disconnected as well as municipal and private GI practices in test catchment and track changes over duration of study.
- Calibrate a watershed model (e.g., WinSLAMM) that can be predictive of effective impervious cover and hydrologic response at the catchment scale.
APPROACH
In 2021, the USGS, in cooperation with MMSD, established two storm sewer monitoring sites to measure the volume of stormwater runoff from urban catchments of known drainage area (figure 1). The test catchment will undergo a transition that disconnects drainage from residential homes that are currently directly connected to the storm sewer as well as add or retrofit GI practices into the urban landscape. The control catchment will serve as a reference and having a similar percentage of effective impervious cover as the test catchment but with no (or limited) plans to disconnect home or implement GI and serve as a baseline condition by which future comparisons to changing contributions of stormwater volume, delivered via the storm sewer network, can be made. The campaign to encourage residents to disconnect their homes will be facilitated by MMSD and their consultants. Both catchments are located within the MMSD service area boundaries but outside the CSO area.
CONTACT
- William Selbig (USGS Upper Midwest Water Science Center)
- Nicolas Buer (USGS Upper Midwest Water Science Center)
4b. Evaluating the Performance of Infiltration-Based Green Infrastructure on Contaminant Removal
BACKGROUND
Water-management agencies worldwide are increasingly using green infrastructure (GI) and other stormwater control measures at various scales to minimize contaminant transport to receiving waterbodies, reduce stormwater volumes, collect stormwater for reuse, and increase groundwater recharge (Masoner et al., 2019). However, despite the increasing application of GI for urban stormwater management, water-quality performance data has been primarily limited to regulated pollutants, such as solids, nutrients, and metals. There is a significant lack of understanding of performance beyond these conventional water-quality metrics. Masoner et al. (2019) noted urban stormwater transports substantial mixtures of contaminants including polycyclic aromatic hydrocarbons, bioactive contaminants (pesticides and pharmaceuticals), and other organic chemicals known or suspected to pose environmental health concern. They also observed positive correlations in concentration with the percentage of impervious surfaces in highly developed urban catchments.
Many GI practices are designed to rapidly infiltrate large volumes of stormwater runoff from impervious surfaces, thus posing a risk of contaminating receiving surface water or groundwater. Oftentimes these practices use engineered media designed for enhanced removal of solids and nutrients; however, evidence suggests some organic contaminants, such as pesticides, may be of greater concern due to their mobility and potential to pass through treatment systems (Zhang et al., 2014). More information is needed to better understand the fate, transport, exposure and toxicity of stormwater contaminant mixtures discharged to and from infiltration-based GI practices.
OBJECTIVES
The objective of this study is to evaluate the performance of an infiltration-based GI practice at removal and retention of organic and inorganic contaminants in stormwater.
Specific objectives are as follows:
- Evaluate, through influent/effluent monitoring, the fate and transport of a suite of regulated contaminants (sediment, nutrients, metals, bacteria, and chloride) and emerging organic contaminants of concern that enter GI in both water and soil.
- Evaluate long-term performance of GI practice to help inform future maintenance decisions.
- Assess the toxicity potential of effluent and soils of GI through use ToxCast and other water and sediment-quality benchmarks. This analysis will be facilitated by the toxEval application.
APPROACH
In 2021, the USGS, in cooperation with the Northwest Side Community Development Corporation, installed equipment to monitor influent and effluent water quantity and quality to a single biofiltration system located at the Green Tech Station in Milwaukee (figure 1).
Influent to the biofilter is derived from an adjacent street surface with considerable traffic volume serving an area comprised of commercial and industrial land use. Runoff influent to the lined biofilter infiltrates into engineered soils before discharging into an underdrain that leads to a secondary observation tank.
Water-quality and sediment samples will periodically be collected from both influent and effluent to determine presence and abundance of sediment, total and dissolved nutrients and metals, chloride, temperature, polycyclic aromatic hydrocarbons, and other trace organic chemicals and waste indicator compounds.
Resulting data will be analyzed to determine what degree the GI practice is or is not capable of reducing pollutant loading in water for all chemicals analyzed and if so, what is the cumulative toxic potential of select pollutants retained in the soil.
CONTACT
- William Selbig (USGS Upper Midwest Water Science Center)
- Nicolas Buer (USGS Upper Midwest Water Science Center)