Webinar to provide a demonstration and introduce new features.
Stormwater discharges continue to cause impairment of our Nation’s waterbodies. Conventional stormwater infrastructure, or gray infrastructure, is largely designed to move stormwater away from urban areas through pipes and conduit. Runoff from these surfaces can overwhelm sewer systems and end up contaminating local waterways. When stormwater runs off impervious streets, parking lots, sidewalks, and rooftops, it can carry pollutants to streams, rivers, and lakes. Runoff flows can also cause erosion and flooding that can damage property, infrastructure, and wildlife habitat. In addition to runoff problems, impervious surfaces also prevent water from penetrating the soil and recharging groundwater supplies.
Green infrastructure, such as rain gardens, and porous pavement, is becoming an increasingly attractive way to reduce the amount of stormwater runoff that flows into wastewater treatment plants or into waterbodies untreated, and to recharge aquifers. It provides many environmental, social, and economic benefits that promote urban livability, such as improved surface water quality, water conservation, and improved aesthetic and property value. EPA researchers have been studying green infrastructure practices and developing models and tools to help communities manage their stormwater runoff and address nutrient impairment.
EPA developed the National Stormwater Calculator (SWC) to help support local, state, and national stormwater management objectives and regulatory efforts to reduce runoff through infiltration and retention using green infrastructure practices as low impact development controls. It is designed to be used by anyone interested in reducing runoff from a property, including site developers, landscape architects, urban planners, and homeowners. It can be used for any location within the United States, including Puerto Rico. This webinar will provide potential and example applications, and will present the new cost module and mobile web application version that can be used on mobile devices, such as smartphones and tablets.
EPA’s National Stormwater Calculator (SWC) is a software application that estimates the annual amount of rainwater and frequency of runoff from a specific site. Estimates are based on local soil conditions, land cover, and historic rainfall records. It is designed to be used by anyone interested in reducing runoff from a property, including site developers, landscape architects, urban planners, and homeowners.
The SWC accesses several national databases that provide soil, topography, rainfall, and evaporation information for a chosen site. The user supplies information about the site’s land cover and selects low impact development (LID) controls they would like to use. The LID controls include the following green infrastructure practices:
- Disconnection (rooftop downspout)
- Rain harvesting (rain barrel or cistern)
- Rain gardens
- Green roofs
- Street planters
- Infiltration basins
- Porous pavement
Green infrastructure promotes the natural movement of water, instead of allowing it to wash into streets and down storm drains. Having less water runoff into storm drains and roadways can help prevent contamination of waterways, infrastructure degradation, flooding, and overwhelming of treatment plants. This allows stormwater to be used as a resource rather than a waste product, and can add aesthetic and economic value to a community.
Capabilities
Hydrology Analysis. The SWC allows users to analyze site hydrology for small- to medium-sized (less than 12 acres) locations within the United States, including Puerto Rico, using LID controls. It estimates the amount of stormwater runoff generated from a site under different development and control scenarios over a long-term period of historical rainfall.
Cost Module. An LID cost estimation module within the application allows planners and managers to evaluate LID controls based on comparison of regional and national project planning level cost estimates (capital and average annual maintenance) and predicted LID control performance. Cost estimation is accomplished based on user-identified size configuration of the LID control infrastructure and other key project and site-specific variables. This includes whether the project is being applied as part of new development or redevelopment and if there are existing site constraints.
Climate Scenarios. The SWC allows users to consider how runoff may vary based on historical weather and potential future climate conditions. To better inform decisions, it is recommended that users develop a range of results with various assumptions about model inputs. Please check with local authorities about whether and how use of these tools may support local stormwater management goals.
Note: The SWC uses the Storm Water Management Model (SWMM) as its computational engine. SWMM is a well-established, EPA developed model that has seen continuous use and periodic updates for 40 years. Its hydrology component uses physically meaningful parameters making it especially well-suited for application on a nation-wide scale. SWMM is set up and run in the background without requiring any involvement of the user.
Real-World Applications
The SWC is most appropriate for performing screening level analysis of small footprint sites up to several dozen acres in size with uniform soil conditions. Its primary focus is informing site developers and property owners on how well they can meet a desired stormwater retention target. It can be used to answer questions such as the following:
- What is the largest daily rainfall amount that can be captured by a site in pre-development, current, or post-development condition?
- To what degree will rainfall from storms of different magnitudes be captured on site?
- What mix of LID controls can be deployed to meet a given stormwater retention target?
- How well will LID controls perform under future meteorological projections made by global climate change models?
- What are the relative planning level costs (capital and maintenance) differences for various mixes of LID controls?
