A short summary of the PWC's Improving Stormwater Basins, Naturally - Creating and Maintaining Naturalized Stormwater Management Basins is provided here.  Click Here for the complete document. 

Shortcomings of traditional stormwater basin design
Most detention basins constructed in the past have been primarily designed to control the speed of runoff from new developments.

What is the common design process for traditional stormwater control?
Runoff from rainstorms is generated from impervious surfaces like roads, rooftops and parking lots; concentrated into a piping system; and quickly transported off-site or into a detention basin.  This process was designed for the sole purpose of reducing downstream flooding from new developments. However, the construction of numerous basins along the same stream can actually cause new flooding since the speed of stormwater leaving a new development is the same as it was prior to development, but the amount of water has increased, causing stormwater to flow from the site for a longer period of time. Stormwater from neighboring developments can them overlap and produce flooding where none existed before.

What are some other concerns with the traditional process of stormwater detention?
Traditional basins decrease the base flow of streams by quickly sending stormwater downstream.  Water quality is often degraded by sediments, lawn chemicals fertilizers and other pollutants carried directly into streams. Local streambank erosion commonly results which alters or decreases stream habitat.  Traditional designs result in basins that provide very little aesthetic value to the community.  Maintenance costs for the basin owner are high due to required weekly grass mowing.

Benefits of naturalized stormwater basin design
One of the many new methods to help alleviate some of these traditional stormwater problems is to naturalize existing stormwater basins. The goal of naturalizing existing stormwater basins is to maintain the overall design of the basin while increasing environmental, aesthetic and economic benefits.

What are naturalized stormwater detention basins?
A naturalized stormwater basin is one that is attractively landscaped and incorporates native trees, shrubs, and wildflowers.

In what ways are naturalized basins better than traditional basins?
The deeper root systems of trees, shrubs, and wildflowers encourage water infiltration and thereby recharge ground water tables and increase stream base flows.  Plants increase water quality by trapping sediment and many pollutants found in runoff.  The density of vegetation in a naturalized basin helps to slow the stormwater velocity, reduce flooding impacts and cool the water temperature.  Wildflowers, trees and shrubs planted in basins create an improved visual appearance. They can help beautify a neighborhood and increase property values.  Naturalized basins tend to have vegetation that requires only annual mowing. By decreasing maintenance costs your tax dollars can be diverted to more important township services.

To overcome the shortcomings of traditional stormwater basin designs, municipalities should...
Naturalize existing basins under municipal ownership.
Review ordinances to encourage naturalizing basin plantings in all new detention basins.
Educate landowners that maintain private stormwater basins about naturalizing techniques.
There are other methods to enhance existing stormwater basins; when combined with naturalizing techniques, they can further improve water quality.
Remove concrete low flow channels to help decrease water temperatures and allow for more infiltration.
Retrofit or alter outlet structures so that runoff from smaller streams is held in the basin longer to allow for further settling of pollutants.
Add sediment forebays to basins to improve water quality. These forebays collect debris and other pollutants and allow easier maintenance.

A more comprehensive approach to improving stormwater resources and water quality can be achieved if a municipality also:
Adopts ordinances that encourage infiltrating stormwater, improving water quality and incorporating best management practices into site design.
Partners with neighboring communities, especially those within the same watershed, to promote consistent environmental protection ordinances.
Sets and follows through with goals to preserve floodplain, wetland and streamside areas from development.
Creates recreational greenways and trails along streams.
Beyond municipal activities to improve stormwater basins and stormwater resources, we can all be good stewards of the environment by...
Reducing lawn areas in our yards by planting native flowers, trees and shrubs. Doing so will allow for more stormwater to infiltrate into the ground and will save both time and money in long-term maintenance.
Using a rain barrel to collect water from gutters and downspouts. This practice decreases runoff from your property, provides a watering source even in times of drought and saves money.
Planting trees and shrubs along streamside property. Vegetated streambanks help prevent erosion, increase stormwater quality and reduce flooding.
Gardening organically. Or at least reduce the use of chemical pesticides and fertilizers. Overuse of these chemicals pollutes stormwater and local streams.

For more information on naturalizing existing stormwater basins or these other enhancement techniques, call:
Lower Providence Township 610-539-8020
Perkiomen Watershed Conservancy 610-287-9383
Montgomery County Planning Commission 610-278-3722
Philadelphia Suburban Water Company 610-525-1400

Or check out these websites:
Managing Stormwater: Best Management Practices
Montgomery County Planning Commission