Once stormwater runs off an impervious surface, it typically flows into a storm drain and is routed directly to a local stream. These streams flow into bigger streams and lakes. In the Great Lakes basin, these streams (and the stormwater they carry) eventually discharge into a downstream Great Lake. Along the way, the added stormwater can affect the stream’s natural structure and aquatic ecosystem through extreme changes in streamflow, increased sedimentation and erosion, higher water temperatures, lower dissolved oxygen, and degradation of aquatic habitat structure. Stormwater can also transport a wide variety of contaminants such as sediment, trash, metals (iron, copper, nickel, arsenic), nutrients (nitrogen and phosphorus), and organic compounds (oil and gas, grease, pesticides) that can affect fish and aquatic organisms.

Problems can also arise during large stormwater runoff events, which can overwhelm the storm drain system and cause urban flooding. In cities that have combined stormwater and sewer systems, large runoff events can cause an untreated mix of industrial and domestic wastewater and stormwater to be released into nearby receiving waters. Other communities with pervasive stormwater issues may convey runoff to a sewage treatment plant where it is treated at significant cost to the rate payer.

Green infrastructure is a type of urban stormwater control measure. The goal of green infrastructure is to slow or retain stormwater runoff where it originates, encourage infiltration and evaporation, decrease or remove pollutants carried by stormwater, and reduce or delay the amount of runoff entering stormwater or sewer systems. 

Implementation options are numerous and varied, and each is selected and customized to fit local conditions such as space limitations, climate, slope, drainage area, soils, and geology. Some common green infrastructure options include:

• Bioswales – Vegetated or mulched channels or depressions that slow and treat stormwater.
• Rain gardens – Shallow, vegetated basins that collect runoff from roofs, sidewalks, and streets, holding it until it infiltrates or evaporates. Large, engineered rain gardens are called bioretention cells.
• Planter boxes – Street-side rain gardens with vertical walls that collect runoff from streets, sidewalks, and parking lots. These are commonly used in dense urban areas where space is limited.
• Permeable pavements – Pervious concrete, porous asphalt, and permeable pavers allow precipitation to infiltrate through the pavement into the soil or fill materials below (as compared to traditional concrete or asphalt pavements, which are impervious).
• Green streets and green parking – Streets and parking lots that are built or converted to encourage infiltration and evaporation. This can include removing impervious surfaces and utilizing permeable surfaces, diverting stormwater into bioswales or planter boxes, and (or) increasing the streetside tree canopy.
• Natural land conservation and conversion – Adding or preserving existing natural areas, or converting developed land to urban agriculture, can reduce runoff and flooding by providing large areas of land for natural stormwater infiltration while producing recreational and community benefits.
• Green roofs – Partially or completely covering a roof with vegetation and a growing medium (planted over a waterproofing membrane) can reduce runoff by storing and treating rainfall on-site.

Visit the U.S. Environmental Protection Agency’s  green infrastructure website  to learn more about green infrastructure options and how to incorporate them into your home and community.

Green infrastructure can provide many potential benefits:

• Reduce flooding and prevent combined sewer overflows
• Improve water quality in streams and lakes
• Protect groundwater quality and enhance recharge
• Reduce the amount of excess sediment and nutrients entering streams, local water bodies, and the Great Lakes, which in turn reduces the risk of oxygen depletion, algal blooms, and habitat degradation
• Protect aquatic habitat and populations
• More cost effective than treating stormwater at a facility
• Provide recreational and community benefits

Compared to traditional stormwater management strategies, green infrastructure is a relatively new option for reducing stormwater. As such, there are many questions and concerns about its use:

• There is no single solution for every community; green infrastructure implementation must be customized for each location.
• There is a lack of standard methodology for evaluating green infrastructure’s effectiveness. This is complicated by the variety of solutions and environmental settings.
• There are questions about its upkeep and maintenance, performance, durability, and long-term cost.
• Many municipalities have not updated their codes and standards to allow for the use of green infrastructure in public spaces and roadways.

The GLRI Urban Stormwater Monitoring effort hopes to provide information that can help address many of these challenges.

The image at right shows a redevelopment design proposal of Niagara Street in Buffalo, NY, a GLRI Urban Stormwater Monitoring case study (Niagara Street Now, 2016).

Since the late 1970s, the  U.S. Environmental Protection Agency   (EPA) , through authorization under the Clean Water Act, has regulated stormwater runoff from drainage systems to waters of the United States including the Great Lakes. The EPA has worked with states to establish maximum contaminant concentrations on priority pollutants, and local and state agencies have established their own pollution-reduction goals. In response, Great Lakes municipalities are implementing watershed management plans that call for the use of green infrastructure and other stormwater control measures to reduce the impacts of polluted runoff. Since 2010, the federal  Great Lakes Restoration Initiative (GLRI)  has sponsored several programs that support the reduction of stormwater pollution impacts on Great Lakes health, including the  Shoreline Cities Grants  program for green infrastructure (see map at right, from EPA). However, high-quality data on the effectiveness of green infrastructure are needed to assess the overall performance and utility of green infrastructure in urban areas of the Great Lakes.

Developing the capability to accurately evaluate the benefits of green infrastructure represents a significant challenge that requires new assessment approaches and evaluation methods. The USGS has a long history of developing innovative technologies and techniques used in the measurement, evaluation, and interpretation of stormwater runoff. Supported by GLRI, the  Urban Stormwater Monitoring  effort brings together the expertise of the USGS with local and national partners to assess the ability of green infrastructure to reduce the stormwater runoff volume stemming from urbanized areas within the Great Lakes basin.

Although the EPA and USGS acknowledge green infrastructure may affect the quality of urban stormwater, the primary objective of the current studies is to measure changes to water quantity. The following are some questions that the GLRI Urban Stormwater Monitoring effort is designed to answer:​

• What effect does green infrastructure have on surface water (streams, rivers, and lakes) and groundwater quantity?
• As green infrastructure ages, does its effectiveness change? If so, how and why?
• What are the seasonal and regional effects on performance?
• What are the limitations and uncertainties of green infrastructure?

​The main goal of the GLRI Urban Stormwater Monitoring effort is to develop meaningful ways to monitor and assess rainfall, runoff, inflow, outflow, and infiltration characteristics of green infrastructure, and the potential benefits to local streams, rivers, lakes, and groundwater.

The key elements of the Urban Stormwater Monitoring effort include:​​

1. ​Develop partnerships between USGS and other local, state, and federal agencies to encourage an open exchange of ideas and information.
2. Develop consistent monitoring techniques and criteria for evaluating the performance of green infrastructure.
3. Identify how green infrastructure practices, both individually and collectively, can affect the volume of urban runoff, including monitoring across different geographic settings and hydrologic and climatic conditions.
4. Develop consistent methods of assessing the health of an urban stream which can potentially be used to measure the overall effectiveness of green infrastructure.
5. Use results to develop decision-support tools that will help communities identify which green infrastructure options will best help them achieve their pollution reduction goals at minimal cost.

The interactive  map  at right shows the locations of three current GLRI Urban Stormwater Monitoring case studies, which are described in the following slides.

In  Buffalo, NY , the USGS partnered with the  City of Buffalo  and the Niagara River Greenway Project to assess the ability of green infrastructure to reduce the volume of stormwater runoff and limit the risk of combined sewer overflows in the  Niagara River Area of Concern.  The city is redeveloping 16 city blocks along Niagara Street to reconnect residential land-use to the waterfront and implement a safer corridor for pedestrians and bicyclists. Instead of using traditional development, aging infrastructure in this 50-acre area will be replaced with green infrastructure such as porous asphalt, planter boxes, and rain gardens. Initial plans for Niagara Street redevelopment have the potential to control 16 million gallons of stormwater runoff per year.

The USGS measured runoff volume, groundwater levels, evapotranspiration, precipitation, and soil moisture to characterize the volume reduction benefits of green infrastructure. Data was also used to develop a model of rainfall runoff and infiltration for both pre-and post-construction, and an urban watershed model, which can be used to simulate the benefits of expanding green infrastructure into other areas of Buffalo. 

The interactive  map  at right shows the location of two USGS storm-sewer flow monitoring sites as well as the existing storm sewer network in the study area.

In  Detroit, Mich. , combined sewer overflows have been adversely affecting the Detroit River, resulting in increased interest in stormwater management and control. The City of Detroit has identified swaths of abandoned urban land as potential locations for the installation of stormwater control measures, including green infrastructure, to mitigate excess stormwater. One of these locations,  RecoveryPark , is a 40-acre area located about 2.5 miles northeast of downtown Detroit. Until recently, most of this city-owned land was vacant, but the nonprofit RecoveryPark has entered into an agreement to purchase the land and convert it into an urban farm staffed by people with barriers to employment. The goals for RecoveryPark also include sustainable resource management including stormwater management.

In collaboration with the EPA, the  Detroit Water and Sewerage Department  (DWSD), and  Lawrence Technological University , the USGS assessed the influence of adding grass swales and infiltration basins on stormwater quantity. Storm-sewer flow at seven locations (installed by DWSD), groundwater levels at 24 locations, soil moisture at multiple depths, and precipitation and potential evapotranspiration at an on-site weather station were measured to identify changes in runoff volume before and after construction of the green infrastructure and identify the processes that have the greatest influence on the local water balance. Although only a small part of the RecoveryPark was monitored, resulting data was incorporated into hydrologic models that estimated the effects of leaky pipes, climate variability, and scale issues on a larger scale. The results of this study helped the City and RecoveryPark design future phases of the proposed redevelopment and expansion of the RecoveryPark urban farm. 

The interactive  map  at right shows the study area and monitoring locations at RecoveryPark.

Like other cities in the Great Lakes basin, the  City of Gary  is investing in the redevelopment of abandoned areas in its urban core and is exploring the potential stormwater-reduction benefits of green infrastructure. The area surrounding Gary’s  City Hall  is currently undergoing redevelopment; as vacant properties are removed, those lands are being repurposed using types of development that enhance direct infiltration of stormwater, increase opportunities for green space, and minimize stormwater loads by redirecting stormwater towards groundwater recharge. This study focused on the redevelopment of an existing parking lot using permeable pavers and rain gardens.

In collaboration with the City, the USGS studied the effect of green infrastructure on storm-sewer flows and groundwater levels to assess potential changes in increased infiltration and effects of leaky sewers. This was done through the assessment of storm-sewer flows, groundwater flow direction, soil moisture, evapotranspiration, and meteorological conditions before and after installation of green infrastructure practices. The data collected helped build a hydrologic model that can help inform future redevelopment plans by simulating the potential benefits of removing impervious cover (homes, commercial buildings, and paved sites) and increasing the density of green infrastructure (such as rain gardens, bioswales, permeable pavers, and urban farming).  

Evaluating the effectiveness and performance of green infrastructure through a comprehensive, scientific assessment will provide valuable information about the viability and benefits of green infrastructure over a range of conditions and settings. Through these and other case studies, the GLRI Urban Stormwater Monitoring effort will collect valuable data and develop innovative methods and monitoring techniques that will improve the design, construction, and assessment of green infrastructure in communities across the Great Lakes and the Nation.

Learn more about this effort and follow the case studies at the  GLRI Urban Stormwater Monitoring  website.