This document provides a framework for planning and documenting your project’s implementation of the Low Impact Development provisions of the Connecticut Stormwater Quality Manual.

In Connecticut and around the country, there is increased interest in balancing community growth and environmental conservation. As undeveloped sites are converted into residential housing or commercial areas, native vegetation and soils are being replaced by impervious surfaces such as roads, roofs, parking lots and driveways. As more stormwater runs off the impervious surfaces of developed sites during precipitation events, oil from vehicles, bacteria, nitrogen, phosphorus and other pollutants that accumulate on the impervious surfaces commingle with and are carried along with the stormwater runoff. Typical development approaches do not provide adequate treatment for this polluted stormwater and receiving waters suffer a variety of impairments due to these human-induced changes in the landscape. In fact, stormwater runoff has been identified as one of the greatest causes of stream quality degradation.

Low Impact Development (LID) is an approach that can help minimize the environmental impacts of traditional development while still allowing for community growth and has been adopted as the preferred method of site design in the 2004 Connecticut Stormwater Quality Manual². Pioneered in Maryland¹, LID is being successfully utilized throughout the country. In addition to protecting ecosystems and receiving waters, the LID approach can often result in cost savings on projects³.

In planning for your project, you should document how each of the following areas will be addressed using the techniques in the SWQM or, if they are infeasible, the reasons why.

1. Assessment of natural resources. LID should be considered early in the site planning process. The objective is to allow for development of the property while maintaining the essential hydrologic functions of the site. A thorough assessment of the existing natural resources on the site needs to be performed, so that essential features can be preserved, and suitable sites for development can be identified.

 

2. Preservation of open space. Cluster subdivision design can complement the LID approach. Cluster subdivisions provide a key way to protect natural resources while still providing landowners with the ability to develop their property. In most cases, the number of residential units allowed in a cluster subdivision equals the number allowed under conventional subdivision regulations.

 

3. Minimization of land disturbance. Once the development envelope is defined, the goal is to minimize the amount of land that needs to be disturbed. Undisturbed forest, meadow, and wetland areas have an enormous ability to infiltrate and process rainfall, providing baseflow to local streams and groundwater recharge. Because construction equipment can cause severe compaction of soils, areas that are thought to be pervious such as grass, can become quite impervious after development.

 

4. Reduce and disconnect impervious cover. With careful planning, the overall percentage of impervious cover in a proposed project can be minimized. Roads, driveways, sidewalks, parking lots, and building footprints can be minimized to reduce impacts, while still providing functionality. Additionally, not all impervious surfaces have the same impact on local waterways. With proper planning, runoff from impervious surfaces can be directed to pervious areas such as grass or forest, or to LID treatment practices. It should be noted that every project is unique, and not every LID practice will be appropriate. For example, sidewalks or bike paths may be an asset to a new subdivision if there is some connection to existing pedestrian travel routes. However, sidewalks may not be needed in other settings, and would only add unnecessary costs and impervious cover. The objective is to evaluate each site individually and determine the most appropriate management techniques to reduce impacts to waterways.

 

5. LID practices installed. There are a variety of practices that can be used to maintain the pre-development hydrologic function of a site. For more detail on the following practices, see the references below:

• Bioretention areas or rain gardens are depressed areas in the landscape that collect and infiltrate stormwater.
• Vegetated swales can be used to convey runoff instead of the typical curb and gutter system, and they can also infiltrate and filter stormwater.
• Water harvesting techniques can be employed, so that stormwater can be a resource rather than a waste product.
• Pervious pavements allow rainfall to pass through them, and can be installed instead of traditional asphalt or concrete.
• Green roofs can reduce stormwater runoff through evaporation and transpiration through plants, and they also can help save on heating/cooling costs.

LID represents a change from typical design approaches. Proper installation and maintenance of LID practices is critical to their performance. Therefore, installation should be performed by someone with LID experience to avoid costly mistakes.

With proper design and installation, LID can provide multiple benefits including decreased construction costs, reduced impacts to receiving waters, increased habitat for wildlife, beautiful landscape features, and increased property values.

References

¹Prince George’s County, Maryland. 1999. Low-Impact Development Design Strategies:  An Integrated Design Approach. MD Department of Environmental Resources, Programs and Planning Division.

²CT DEP. 2004. Connecticut Stormwater Quality Manual. Department of Environmental Protection. 79 Elm St., Hartford CT.

³US EPA. 2007. Reducing Stormwater Costs through Low Impact Development (LID), Strategies and Practices. EPA Publication number 841-F07-006.