|Environmental Review Toolkit|
|NEPA and Project
|Section 4(f)||Water, Wetlands,
|Water, Wetlands, and Wildlife|
Great Lakes Stormwater Workshop
Quantification Initiative Concept Paper
Conventional development practices often result in a high percentage of impervious surfaces, which can have serious adverse consequences for the environment. Among the significant ways development practices can affect the environment are increased run-off volumes (and flow velocities), increased pollutant loadings to streams, rivers and lakes, and decreased groundwater recharge.
Traditional storm water management design features are intended to efficiently remove excess rain water from sites by limiting peak flow amounts and storing the run-off in a controlled manner. These practices do help reduce some impacts on streams and rivers and lakes, however, they do not completely solve the run-off problem. Traditional storm water sewers move the water - and the pollutants typical of urban areas - quickly away from the site and release it from holding systems over a longer period of time, resulting in run-off volumes that are still much higher than the pre-development conditions. This may lead to downstream flooding, degraded stream quality, and disruptions in aquifer recharge.
"Green" design features and management practices, such as rain gardens, vegetated swales, and permeable paving systems, are intended to address some of these water management issues by managing some or all of the storm water on a site through infiltration and evapotranspiration. By increasing the time of concentration and decreasing the volume of run-off, green design features and management practices can help protect water resources. Additionally, many green design features and management practices may result in improved groundwater recharge. Also, in some cases, using green design features and management practices may be more cost-effective than conventional design practices which focus on use of "grey" infrastructure for managing storm water.
Quantification Project Objectives
The lack of compiled, analyzed, and easily-accessible information on the performance of green design features and management practices is a barrier to their implementation. Storm water engineers, planners, lenders, developers, and project decision-makers need accurate, reliable, and quantified information on the performance and benefits of green design features and management practices, and they need that data presented - at least initially - as part of their commonly used models. Without performance data, engineers working on sites or infrastructure projects cannot account for the performance of the green features, and may end up designing redundant systems or may even avoid green design features entirely. Without the information being presented in a professionally accepted mode, it is unlikely that the data will be consistently used. Project decision-makers also need quantified information on the performance and benefits of green design features and management practices so they can ensure their project dollars are being well-spent.
There are numerous case studies examining the performance of management practices at individual sites. Many of these case studies are documented in the International Storm Water Best Management Practices Database (http://www.bmpdatabase.org/). However, the database does not include case studies for all types of green design features and management practices at all types of sites (sites will vary in terms of climate zone, soil types, and other factors which will influence green design feature and management practice performance). Performance varies with surficial soils, lower soil horizons, depth to water table, climate, slope size of catchment, size of BMP, season, maintenance, antecedent conditions, storm characteristics, etc. The number of possible combinations of site, green design feature or management practice, and hydrologic conditions is effectively infinite. As a result, developing a database that describes all combinations is not feasible. In addition, there has not been a systematic analysis of the performance of green design features and management practices across the case studies to generalize about and predict performance in different settings. However, with data from a well-designed sampling of a subset of the different possible combinations, we can describe the anticipated behavior of the feature as different parameters are changed. This can be incorporated into simulation models that allow reasonable prediction of the anticipated performance of many combinations of sites, green design features and management practices, and hydrologic conditions. In parallel, research projects can be conducted across the country to fill gaps in performance data.
The long-term goal of the project is to feed the run-off prediction models with enough complete, precise, and quality-assured data that engineers and planners will have the same level of confidence in their green storm water management features as they currently have in their conventional systems. It is also expected that analyses of alternatives will reveal that in many cases the green approaches will perform as well or better than conventional storm water features, and at a comparable or possibly lower cost. This will result in increased implementation of green design features and management practices, and better protection of water resources.
Analysis of Existing Information
Integration of Performance Data into Models
Development of Methodology, Initiation of Research Projects, and Rollout of Enhanced Data