Case Studies for Stormwater Best Practices

With finite supply and increasing global demand for fresh water, the management and reuse of stormwater has become one of the most critical environmental concerns in the building design industry.

In September of 2008, the U.S. Green Building Council (USGBC) announced the recipients of its 2008 Green Building Research Fund Grants, the first grants of their kind in the green building industry.

BNIM’s research proposal, which focused on managing stormwater around building sites and removing pollutants from surface runoff, was among the handful of research proposals selected from over 250 submissions to share the $2 million grant fund.

The resulting research addresses business and City Department concerns, such as dollars lost in potable water expenses and stormwater management. The research conducted through this grant impacts building, construction, design and policy to protect water as a precious resource. The study also focuses on additional outcomes including reducing aquifer depletions, becoming good stewards to downstream neighbors and reducing flooding potential. All of these factors create better, more livable communities and neighborhoods.

To conduct the research for this project, the team monitored the performance of various stormwater Best Management Practices (BMPs) such as raingardens, bioswales, and vegetated infiltration beds. By looking at systems used to capture stormwater runoff near the point of generation (e.g. – roofs, patios, parking lots, driveways), slow runoff rates, infiltrate stormwater into site soils, and remove pollutants, they also hoped to substantiate the viability of creating landscaping amenities and habitat enhancements employed for good purpose. The team looked at several projects, including: City Union Mission, Kansas City, MO; Applebee’s Support Center Raingarden and Treatment Train, Lenexa, KS; and The University of Kansas Fitness Center, Lawrence, KS.

Lessons and information gathered from this report and these projects have the capacity to alter design standards, and policymaking and to significantly impact human health and productivity. This document includes thoughts related to the potential to influence building and site design as well as development policy and standards, facility operations and maintenance standards.

Only 3% of the water in the world is fresh water (with a majority of that water held in glaciers and polar ice caps). It has been estimated that less than 1% of fresh water is available for use and consumption with no more water being produced. With increasing demand from growing populations, fresh water will become a valuable commodity (probably more so than oil). Many cities across the nation have embraced and experienced success with green solutions. BMPs should be incorporated into all facets of building, construction, design, and policy to protect water as a precious resource.

View the entire Multi-Variate Study of Stormwater BMPs research document here:

In Summary, the report offers the following recommendations and lessons-learned:

• Preserve the existing landscape. The less site disturbance the better. It is easier to maintain the existing landscape than to rebuild it.
• Site development significantly disturbs site soils. Minimize site disturbance to the maximum extent possible. Greater effort also needs to be placed on restoring soil structure and organic matter before sites are vegetated, in order to help establish healthy, dense vegetation, limit weeds and erosion, and reduce the need for herbicide applications. This can be done through deep tilling/ripping, plus addition of organic matter in the form of compost, a sustainable, recycled product. This will also improve soil moisture retention for plant health, promote healthy root growth in plants, and promote stormwater infiltration across the site.
• Keep designs simple, especially in areas where BMPs are new techniques and have not been widely constructed or maintained yet. Simple designs can still be attractive and elegant. Complex designs are more difficult to build and likely will not be fully maintained.
• Off-line designs limit flow velocities through BMPs, erosion, washing out, and pollutant export. Where water flows through BMPs (“in-line” designs), distribute flows to minimize erosion.
• BMPs are most effective when they are located near the source of stormwater runoff and treat small drainage areas (less than one acre). Such an approach more closely replicates ecological form and function of the natural landscape and replicates hydrology of the natural landscape. End-of-pipe systems are more susceptible to erosion and bypass in large storm events and are less effective in replicating the hydrology and function of the natural environment. This is part of the philosophy of Low Impact Development (LID) and it is totally applicable to sustainable site design approaches as well.
• Size matters. Undersized systems will have problems. BMP design guidelines in many parts of the country recommend that BMPs be designed to capture the “Water Quality Storm Event,” which is often the 90th percentile storm event. That means, over the long-term average, 90 percent of storm events are that size or smaller. This ranges from about 3/4 to 1 1/2 inches in various regions of the country. At the same time, conveyance features in, out, and around BMPs need to be sized to safely pass larger storm events without damage or erosion.
• Design objectives will be different at every site, and the BMP designs can be customized to the site-specific objectives. At some sites, water quantity control (runoff volumes and rates) may be more important than water quality control. In those cases, infiltration BMPs would be preferred. In other locations, water quality issues may be more important, so the designs should be developed with pollutant removal objectives in mind.
• BMP designs can be customized to promote removal of specific types of pollutants. Some pollutants exist in particulate forms, others in dissolved forms. Pollutant removal mechanisms vary with the type of pollutant, and include sedimentation, precipitation, filtration, adsorption, biodegradation, and photodegradation. Depending on the pollutant of most concern, certain removal mechanisms can be enhanced by the design.
• Site characterization is a critical part of the design effort. Soil types and compaction, the presence of fill material, depth to bedrock and groundwater, and the presence of subsurface utilities should all be taken into account in the BMP design process.
• Plant selection is important. Each BMP is different, so plants should be matched to the soil and water conditions created at each site. Take into account how long water will pond in the BMP, how deep the water will stand in the BMP, and how rapidly it will dry out. Native plants are available that are adapted to a wide range of environmental conditions; pick the plants for the conditions created at each site.
• Some plants grow very deep root systems, which help BMP performance as plants mature. Infiltration rates into soils can improve over time as the roots grow larger and deeper.
• BMPs do not have to be expensive to be effective. Low cost and locally available native materials can be used to create attractive and functional designs.
• Till establishment nuissance species of plants are probable based on their quick growing cycle and lack of rooting systems. Additional maintenance should be expected to remove nuissance species until the selected plant species have established.
• Lastly, BMPs can provide additional wildlife habitat compared to traditional mowed detention facilities.