Guest Author: Tom Barrett, GreenWater Infrastructure
What would Indianapolis look like if, instead of building more “gray” we planted more “green”?
In our last article, we presented the serious issues that result from Indy’s Combined Sewer System, particularly with the sewer overflow from that system whenever it rains. The chosen remedy for this dilemma is “DigIndy,” a 28-mile super-deep, super-wide, super-long Super Tunnel to hold and dilute the sewage overflow.
Definitely a “gray” solution.
What if we entertained other possibilities, as well — greener ones.
“Green Infrastructure” (or GI) is a general term for a variety of methods that treat stormwater runoff at the local level. This is achieved through the use of either natural systems or engineered systems that mimic natural methods.
So the idea is to capture stormwater where it falls, so it can be infiltrated into the soil, and then slowly released as clean water into rivers and streams. GI is one of the best strategies for alleviating the problem of Combined Sewer Overflows (CSO).
The EPA explains GI this way:
“While traditional gray stormwater infrastructure (including “DigIndy”)… is designed to move urban stormwater away from the built environment, green infrastructure reduces and treats stormwater at its source while delivering environmental, social, and economic benefits.”
Examples of GI methods recognized by the EPA include:
Rain Barrels & Cisterns
Rain barrels and cisterns are designed to capture rainwater for slowed release into natural or engineered stormwater systems. For example, the 10,000-gallon cistern at the Keep Indianapolis Beautiful headquarters captures stormwater used to water plants & trees on site.
Rain gardens are shallow, vegetated basins that collect and absorb runoff from rooftops, sidewalks, and streets. As such, they serve as a filter to treat storm water. Rain gardens mimic nature’s infiltration and evapotranspiration systems.
Examples of rain gardens in Indy can be seen at the Indianapolis Museum of Art and the Athenaeum, as well as along The Cultural Trail.
Stormwater planters are similar to gardens, but with vertical walls. They may have either open or closed bottoms. The planters collect and absorb runoff from sidewalks, parking lots, and streets and are ideal for space-limited sites in dense urban areas and as a streetscaping element. Indy has several stormwater planters located along The Cultural Trail.
Swales (or Bioswales) are vegetated channels that provide treatment and retention as they move stormwater from one place to another. The type of vegetation used in a swale impact both the speed of conveyance and the rate of infiltration, turf grasses are not as effective as deep-rooted, taller grasses and/or shrubs. As linear features, they are particularly well suited to being placed along streets and parking lots.
Rooftop drainage pipes are rerouted so rainwater drains into rain barrels, cisterns, or permeable areas (such as the pebbles in the photo at right). Downspout disconnection is particularly beneficial to cities like Indy, with Combined Sewer Systems. Unfortunately, Indy does not currently have a downspout disconnection program.
Permeable pavements allow water to pass through the surface and sub base for infiltration into the native soil below. They can be made of pervious concrete, porous asphalt, or permeable interlocking pavers. This GI practice is used for paving streets, sidewalks and parking areas.
A green roof is a multi-functional roofing system that utilizes vegetation and growing media to collect and absorb stormwater, in order to reduce the amount of runoff from the site. These systems have been functioning in Europe and other countries for decades, and have recently increased in popularity in the U.S. According to the EPA, they are particularly cost-effective in dense urban areas where land values are high, and on large buildings where stormwater management costs are often high.
Green roofs can currently be found in Indianapolis at the following locations:
Indianapolis Museum of Art
Hilton Garden Inn
Moon Block Building
HealthNet Clinic Southwest
The Nature Conservancy Headquarters
Keep Indianapolis Beautiful Headquarters
The Children’s Museum
John H. Boner Community Center
Urban Tree Canopy
By intercepting precipitation in their leaves and branches, trees reduce and slow stormwater runoff. As a result, many cities have set tree canopy goals to restore some of the benefits of trees that were lost when the areas were developed. American Forests, a nonprofit conservation organization, recommends that a city have an average tree cover of 45%. According to Keep Indianapolis Beautiful, Indianapolis currently has a tree cover of 24%, and Center Township has a tree cover of 15%. Homeowners, businesses, and community groups are encouraged to participate in planting and maintaining trees throughout the urban environment.
Side Benefits of Green Infrastructure
In addition to the reduction in stormwater runoff inherent in each of the GI tools and practices, the EPA has proven there are notable side benefits. Especially evident are the private and public cost savings. Basing stormwater management systems on green infrastructure rather than on gray infrastructure often results in lower capital costs for developers.
These savings result from lower costs for:
- Site grading, paving, and landscaping; and
- Smaller or eliminated piping and detention facilities.
Also, in cities with combined sewer systems (like Indy), green infrastructure often cost less than conventional controls. The EPA also found that a combination of green-gray approaches often reduces public expenditures on stormwater infrastructure.
In our next article, we’ll take a look at one model U.S. city which has successfully implemented a comprehensive green infrastructure campaign to address its combined sewer overflow issues.
Keep Indianapolis Beautiful, http://www.kibi.org,