Have you ever thought of storm water as a valuable, natural resource? Well, it is.
Indianapolis is incorporating sustainable “green” infrastructure into several RebuildIndy projects, such as roads, sidewalks, alleys and sewers, as well as working to increase private sector participation in green infrastructure.
Green infrastructure is a general term used for a variety of methods that manage, convey, and treat storm water runoff at the local level through the use of natural systems or engineered systems that mimic natural methods. The primary goal of green infrastructure is to capture storm water where it falls so that it can be cleaned, infiltrated into the soil, and slowly released into rivers and streams. By slowing the release and reducing the amount of rain water into the sewer system, these strategies also help alleviate the problem of Combined Sewer Overflows (CSO).
The USEPA has made green infrastructure a priority in wet weather programs, encouraging cities to use innovative design: "Green Infrastructure can be both a cost effective and an environmentally preferable approach to reduce storm water and other excess flows entering combined or separate sewer systems."
Below is a list of examples of green infrastructure methods:
Bioretention is the use of a natural, biological system to remove contaminants from storm water. Bioretention basins, also called rain gardens, use plants capable of absorbing and cleaning storm water, provide a depression for water retention and utilizes soil conditions that serve as a filter to collect, store, and treat storm water.
The Cultural Trail has many rain gardens installed to capture storm water during rain events. Several City projects are planned for 2011 that include rain gardens to help alleviate flooding in neighborhoods.
Bioretention/Rain Garden (pdf)
A green roof is a multifunctional roofing system that utilizes plants, a growing media, and waterproof membranes to collect and absorb storm water, thereby reducing the amount of storm water runoff from the site. These systems have been functioning in Europe and other countries for decades, and have increased in popularity in the U.S. in recent years as an alternative to traditional roofing systems for their durability, reduction of first-flush storm events, and for their aesthetic qualities.
The following is a list of green roofs in Indianapolis:
Permeable or porous pavement is a surface that allows water to pass through its surface and sub base for infiltration into the native soil below. These types of pavement provide the structural support of traditional pavement materials, but also provide application benefits such as reduced runoff and impact to surrounding plantings.
In Indianapolis, permeable pavement has been piloted on several RebuildIndy projects, including:
In addition, permeable pavement has been installed in several parking lot projects, including:
Rain barrels and cisterns are storm water storage systems designed to capture rainwater for either slowed release into natural or engineered storm water systems, or for other non-potable uses, such as irrigation or toilet flushing. These systems are fed by downspouts and have a limited capacity for rain water storage, but provide excellent capture of first-flush rain water.
Examples of cistern projects in Indianapolis include:
Filter strips are a vegetated, natural method for capturing and slowing storm water while also trapping sediments and pollutants and are often used adjacent to impervious surfaces. These systems are a pretreatment method for sheet flow storm water and are very cost-effective.
Low impact retentive grading is the use of topographic features such as berms and depressions in combination with specific soil types that slow the vertical movement of storm water and increase the rate of infiltration into the groundwater. These grading techniques are designed to capture and infiltrate storm water from small storm events, but require secondary storm water conveyance & treatment methods in large storm events.
Swales are vegetated channels that collect and convey storm water and serve to slow its speed, while increases its infiltration rate before reaching the outfall. 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.
Subsurface infiltration is a method for storing storm water below grade for slow infiltration into the groundwater. Beds of gravel or other open-graded aggregate, often covered by lawn, are used to create voids where storm water can collect. Storm water can be conveyed to a subsurface infiltration area by surface runoff, via an underground pipe, or downspout from a roof.
Inlet/outlet control is a method of manipulating the movement of storm water on a site to increase its chances for sediment settling and infiltration. For example, curb openings can be used to direct storm water into a rain garden or filter strip.
Filters are structures or excavated areas that use layers of materials to remove sediments and other pollutants from storm water before infiltration or release to a sewer or natural body of water. Filters can be very effective in removing contaminants from storm water. This is especially important in urban areas where pollutant levels are significantly higher.
Subsurface vaults are essentially underground storage structures, commonly used in urban areas with very high land values, and are constructed of either concrete or plastic. These vaults are specifically designed to accommodate both the storm water storage capacity needed and the load-bearing needs of the land use above them, such as parking lots, athletic courts or buildings.
Detention basins are a common form of surface storm water storage and are characterized by a deep depression and an outflow structure. Detention basins vary in their size, depth, and amount of vegetation and can provide aesthetic qualities. Detention basins allow sediments to settle, slow the flow of water and allow for infiltration before being released into the storm sewer or natural water body.