GLRI Urban Stormwater Monitoring Active

The problem with stormwater

The term “urban stormwater” refers to rainfall or snowmelt that is not absorbed by the ground, but rather flows off impervious surfaces such as road, roofs, and parking lots. Urban stormwater flows into storm drains that are typically routed directly to receiving water bodies. During heavy rainfall, excess stormwater runoff can cause localized flooding and lead to combined sewer overflows. In the Great Lakes basin, urban stormwater eventually makes it into the nearest Great Lake through a network of storm drains and pipes that either discharge runoff to surface waters or divert it to a sewage treatment plant, where it is treated at a significant cost prior to being discharged to receiving waters. Stormwater can transport a wide variety of contaminants such as sediment, metals, nutrients, bacteria, and organic compounds. In urban watersheds, excess stormwater can cause problems such as localized flooding, changes in flow, increased sedimentation, increased water temperature, reduced dissolved oxygen, degradation of aquatic habitat structure, loss of fish and other aquatic populations, and decreased water quality.

Stormwater management measures may be implemented as part of state, tribal, or local programs for a variety of purposes, including the protection of water resources, aquatic wildlife habitat, and land from increased contaminants and flood risks. Urban stormwater management options include the implementation of green infrastructure, which is designed to reduce or delay peak flow and volume 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 ideally each is engineered to fit local conditions such as space limitations, climate, slope, drainage area, soil, and geologic materials. Common green infrastructure options include bioswales, rain gardens, and converting impervious to pervious surfaces.

Green infrastructure in the Great Lakes

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. The EPA works with states to establish numerical limitations on priority pollutants specified by Total Maximum Daily Loads (TMDLs). Additionally, state and local agencies have established their own pollution reduction goals in urban areas. In response, municipalities adjacent to the Great Lakes are implementing watershed management plans that call for the implementation of green infrastructure and other stormwater control measures to reduce the impacts of contaminated runoff on nearshore water quality at beaches and other coastal areas. Since 2010, the Great Lakes Restoration Initiative (GLRI) has sponsored several programs that support the reduction of nonpoint source pollution impacts on nearshore health; however, high-quality data on the operational and performance characteristics of green infrastructure and other stormwater control measures are needed to assess their overall performance.

USGS urban stormwater monitoring

Developing the capability to accurately evaluate the water quantity and quality benefits of an increasingly diverse number of urban stormwater control measures represents a significant challenge that requires new approaches and the standardization of evaluation methods. The Urban Stormwater Monitoring effort brings together the expertise of USGS scientists in developing innovative technologies and techniques together with local and national partners to quantify the change in stormwater flows resulting from the use of green infrastructure and to clarify how stormwater control measures affect stormwater flow and water-budget dynamics in urban settings.

The following are common questions that the Urban Stormwater Monitoring effort is designed to answer:

• How effective is green infrastructure at reducing stormwater volume and contaminant transport?
• What effect does green infrastructure have on surface water and groundwater quality, hydrology, and ecology?
• Can consistent methods be developed to assess the overall health of an urban stream by its hydrologic, hydraulic, geomorphic, physiochemical, and biological/ecological functions? Can those methods then be used as an indicator of the overall effectiveness of green infrastructure on a watershed scale?
• As green infrastructure ages, does their effectiveness change and, if so, how and why?
• Which green infrastructure options work best for removal of pollutants?
• What are the seasonal and regional effects on performance?
• What are the limitations and uncertainties for green infrastructure?
• Can water-quality goals be achieved through green infrastructure implementation?

Goals and objectives

The main goal of the Urban Stormwater Monitoring effort is to provide a unified approach to continually improve and develop meaningful ways to describe rainfall, runoff, inflow, outflow, and infiltration characteristics of green infrastructure practices and their potential benefits to receiving waters. The USGS has a long history of developing innovative technologies and techniques used in the measurement, evaluation, and interpretation of stormwater runoff and the contaminants it transports.

Key elements of the Urban Stormwater Monitoring effort include:

• Develop a core of USGS and partner agencies. Our goal is to continue to provide high-quality products to existing partners and develop new partnerships to foster the understanding of how green infrastructure can influence the quantity and quality of stormwater runoff into the Great Lakes. We will develop a forum with academia and private groups to create an open exchange of ideas on current and emerging issues in the urban landscape.
• Develop consistent monitoring techniques, formats for products, and criteria for evaluating the performance of green infrastructure. We will strive to refine existing and develop new monitoring techniques through adoption of advanced technology, such as the Depth-Integrated Sample Arm and other sophisticated real-time sensors, that provides meaningful results with well-defined measurement precision and accuracy. Because there are many different researchers providing results in different formats, one objective will be to develop consistent metrics and criteria for evaluation and comparison.
• Evaluation and optimization of green infrastructure efficiencies. In many cases, a substantial amount of time and money has been invested in green infrastructure without verification of achieving desired results. Our research goals will prioritize how green infrastructure practices, both individually and collectively, can affect the volume and quality of urban runoff. Monitoring across different geographic settings, hydrologic and climatic conditions, and a full range of contaminant concentrations will provide the data needed to improve algorithms in existing and next generation urban pollutant loading models. 
• Develop consistent methods of assessing the overall health of an urban stream. By assessing a stream’s hydrologic, hydraulic, geomorphic, physiochemical, and biological/ecological characteristics, we can assess the overall impact of green infrastructure on urban watersheds.
• Watershed partitioning and source characterization. Identification of which source areas and land uses are primarily responsible for contributing certain contaminants in the urban landscape will help drive targeted selection and placement of green infrastructure practices that have the greatest likelihood of mitigating pollutants. Understanding the spatial link between source areas at the site level and major land-use categories within a watershed can help partition and prioritize areas for cost-effective management efforts.
• Develop the next generation of decision-support tools. Although monitoring effectiveness is ideal, it cannot be done in every case. Therefore, the use of models allows users to assess stormwater volume and pollution reduction goals simply by design. The wealth of data collected through this effort will not only support the improvement of existing models with field-level data, but will also provide a foundation for the next generation of advanced web-enabled decision-support system tools. This process will help identify which models have the greatest likelihood of helping environmental managers in communities surrounding the Great Lakes achieve pollution reduction goals at minimal cost.

Benefits of urban stormwater monitoring and green infrastructure

The potential benefits from proper implementation of green infrastructure include:

• Stormwater discharge: Reduction in volume and peak flow, and improved water quality
• Water balance: Decreased peak flows, water reuse and conservation, and increased groundwater recharge and baseflow to streams
• Aquatic and human health: Improved air quality and water quality (surface and groundwater), increased wildlife habitat and recreational space, reduced erosion, reduced toxicity, urban heat island mitigation
• Economy: Increase in land values, reduced demands on water and energy during peak summer months, improved recreational use

Evaluating these stormwater-reduction benefits through a comprehensive, scientific assessment will provide valuable information about the effectiveness and performance of green infrastructure over a range of conditions. The data collected and the innovative methods being developed to monitor stormwater control measures should help improve the design, construction, and assessment of green infrastructure in a multitude of locations and environments.