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| Sustainable Building Sourcebook | ||||
| Chapter: Water | ||||
| Alternative Stormwater Quality Controls | ||||
| CSI Numbers: 02630 Stormwater Drainage | ||||
| Introduction: | ||||
Stormwater runoff can result in flooding, excessive stream erosion, and water quality degradation of Austin's creeks, the Edwards Aquifer, and the Colorado River. Stormwater can carry pollutants such as oil, grease, and pesticides, and heavy metals such as copper, zinc, and lead into streams and our drinking water supply and can negatively affect ecosystems. Its unchecked flow is also destructive, causing erosion and flooding. The City of Austin requires stormwater management, but meeting and/or exceeding the requirements through alternative methods may have the added benefits of cleaner water, introduction of bird and other wildlife habitat, and creation of a more pleasant environment for your building site. A good example is the Central Park development between North Lamar and Guadalupe (www.ci.austin.tx.us/watershed/centralpark.htm ). Another development, the Woodlands near Houston, was the first alternative water quality control project in Texas and a very successful development as well. Water, Fig. 1
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| At-A-Glance Notes: | ||||
| Technology: | ||||
| Available. | ||||
| Suppliers: | ||||
| Not Applicable. | ||||
| Cost: | ||||
| Initially somewhat higher. | ||||
| Public Acceptance: | ||||
| Landscaped wet ponds have public appeal. | ||||
| Regulatory: | ||||
| Alternative controls must be submitted by a Civil Engineer and approved by the Director of the Watershed Protection Department (WPD). Applicants are strongly encouraged to contact the WPD staff prior to submitting plans that propose the use of alternative controls. | ||||
| Considerations: | ||||
To minimize the effect of stormwater runoff impacts, development sites should manage the quantity and quality of water on-site to the maximum extent possible. A variety of non-structural and structural control practices can be used to manage stormwater. Non-structural practices include public education, integrated pest management, and retention of native vegetation. Structural controls include detention and water quality treatment ponds. The standard water quality structural controls used in Austin are sedimentation/sand filtration basins, wet ponds, and retention-irrigation systems. These controls are designed to improve water quality by removing suspended particulate matter and associated constituents such as bacteria, nutrients, and metals. Alternative controls, such as rainwater harvesting, bioretention, and vegetative filters may be acceptable, but the applicant must demonstrate that they will provide a level of control equal to or greater than that provided by standard controls. Water, Fig. 2
If land area is a constraint, another option is a subsurface collection chamber. There are several methods. One is to use a pervious paving, which filters water into a graduated rock chamber below. Another method is a stormwater chamber beneath a paved surface. However, the use of systems that rely on direct soil infiltration may not be appropriate for many soils in the Austin area. In addition to stormwater retention ponds, major stormwater management strategies related to restoration and management of natural water cycles in the landscape include:
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| Guidelines: | ||||
The City of Austin allows alternative water quality controls under its Land Development Code/Environmental Criteria Manual. One measure encouraged for its beneficial features other than stormwater detention is a "wet pond" system. A wet pond is a stormwater pond with a permanent pool of water that uses a vegetative filter method of water cleaning. Wet pond criteria are given in Section 1.6 of the Environmental Criteria Manual. The EPA study called The Economic Benefits of Runoff Controls, describes the negative impacts of stormwater from urban areas on the natural environment. Urban runoff management controls are now widely accepted due to lessons learned from not planning properly for the impacts associated with increased urbanization. The City of Austin has stringent requirements for measures that minimize damage from flooding and to reduce pollution of nearby bodies of water. Devices that store or treat stormwater runoff to reduce flooding, remove pollutants, and provide other amenities are usually called best management practices (BMPs). Two types of BMPs are wet ponds and constructed wetlands. Their benefits to the surrounding environment are greater than standard sedimentation/filtration ponds because they remove a range of pollutants from runoff before it enters surrounding water- ways or aquifers. They also benefit the community by increasing property values. Several studies have shown that "when all else is equal, the price of a home located within 300 feet from a body of water increases by up to 27.8 percent" (NAHB, 1993). Office lease spaces facing natural water features may also lease for greater amounts per square foot. Visually, a wet pond or constructed wetland is more appealing than a concrete reservoir. Safety is an issue that must be considered when planning a wet pond as well as for other stormwater controls. The City's regulations require gentle slopes and recommend plantings surrounding the pond that hinder direct access. | ||||
| Resources: | ||||
| Professional Assistance: | ||||
Atlantis Tank Modules Tom Cahill, P.E. Glenrose Engineering Loomis Austin Leslie Sauer |
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| Components/Materials/Systems: | ||||
Hancor Infiltrator Systems, Inc. High Capacity Infiltrator Chamber System is a molded polyolefin chamberInvisible Structures, Inc. |
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| General Assistance: | ||||
Center for Watershed Protection City of Austin City of Austin Land Development Code Rule R 161-97.06 Prince Georges County Department of Environmental Resources United States Environmental Protection Agency |
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