A Rain Garden's Ripple Effect: An Introduction to Green Stormwater Infrastructure and Why it Matters

CSO, or Combined Sewer Overflow dumps excess waste water into a nearby water body, posing a serious hazard to the health of the environment and people in the area.  [1] 

Water that falls on built surfaces, such as parking lots or roofs, usually finds its way into a storm drain and those drains either empty directly into a natural water body or into a larger sewer system. When the larger sewer system is overloaded during heavy rains it will dump its untreated excess water into the environment. If the system is a combined sewer overflow it will expel a mixture of runoff water, human waste water, and (sometimes) industrial waste water, directly into natural water sources, such as local lakes, rivers, and streams.

Riparian zone schematic typical of the Florida Everglades. [2]

Water that falls across a paved surface generally collects salt, petrochemicals, and other pollutants directly from asphalt and whatever has leaked out of on-site features, such as automobiles. Having this hazardous waste-water dumped directly into a natural water source poses a serious threat to the aquatic ecosystem as well as to residents and farmers that encounter the water body. Riparian zones, the area near the banks of waterways, often serve as habitat and migratory pathways for numerous threatened and endangered species. It is important to approach landscape planning and design with sensitivity to the consequences of point-source pollution to these areas, caused by adding water volume and pollution runoff into a sewer system.

Another consequence of directing water into storm drains is that the water that would normally be falling on the earth’s surface as rain and locally and being absorbed into the watertable is running off an area and being redirected directly into water bodies. When green stormwater infrastructure is installed the ecosystem’s natural hydrological processes remain more intact due to offset of rapid water input to waterbodies during rainstorms (which also means decrease in flooding, especially on downstream properties).

  A bioretention system, or rain garden, in Oregon, US, decreases runoff.*

An example of green stormwater infrastucture is an infiltration basin. These are created simply by grading the landscape’s topography towards an area where the water can collect and sink into the ground. The intercepted water no longer goes straight to a natural water source. The plants included in one of these intercepting depressions can be phytoremediators--meaning they remediate the soil from many of the harmful chemicals now being directed into the storm water catchment area.

The primary result of the addition of green stormwater infrastructure to a landscape is that water is slowed, it sinks and recharges the water table, and the toxic chemicals in it are filtered or remediated before it reaches an aquatic ecosystem.

Because of green stormwater infrastructure, the delicate aquatic ecosystem is no longer bombarded with dirty water from the property during heavy rains.  The pipe from drain to output area may become almost negligible to maintain in price. This can save tens of thousands of dollars in the long run, and this saving adds up quickly when many properties are being considered at once. To give an idea - as of 2008, the total reported water infrastructure needs for the United States included $63.6 billion for combined sewer overflow control and $42.3 billion for stormwater management. Green stormwater infrastructure reduces the need for complex sewage systems and uses natural processes to treat storm water throughout the landscape.


Author: Molly A. Burhans
goodlandproject.org


Sources

[1] Hartford, CT Combined Sewer Overflow. © Molly Burhans, 2015.

[2] Wikipedia. Riparian zone schematic typical of the Florida Everclades. From '' The Impact of Federal Programs on Wetlands - Vol. II'' source: http://www.doi.gov/oepc/wetlands2/images/fig12-1.gif {PD-USGov}

[3] A photograph of a bioretention system, or rain garden, in Portland, Oregon, US. Wikipedia, User:
EmilyBlueGreen.