What is a Combined Sewer Overflow (CSO)?
Indianapolis’ original sewer system was designed to carry only stormwater away from streets, homes and businesses. Indoor plumbing meant sewage lines were hooked to these same sewers, combining stormwater and sewage in one pipe and sending it directly to our rivers and streams. These “combined sewers” were state of the art at the time.
Today, CEG builds separate sewers for stormwater and sewage. However, combined sewers remain in many of the city’s older neighborhoods. During rain events with ¼-inch of rainfall or more, the combined system can cause raw sewage to overflow, called Combined Sewer Overflows (CSOs), into our streams and rivers causing a threat to public health. In the central part of Indianapolis, even a light rain storm can cause raw sewage to overflow and pollute Indianapolis waterways.
Raw sewage overflows are a major cause of wet-weather pollution in portions of White River, Fall Creek, Eagle Creek, Pleasant Run, Bean Creek, Pogues Run, Lick Creek and State Ditch. Source: Citizens Energy Group
How do trees reduce the amount of stormwater entering sewers?
One large tree can keep thousands of gallons of stormwater out of the sewers every year! Trees hold precipitation on leaves, branches, and trunk. This reduces the amount of raw sewage that overflows into our streams.
Do trees have other benefits beyond stormwater interception?
Yes! Trees positively affect our economy, safety, health, and environment. Here are a few that explain the benefits of trees:
How are CSO basins identified for tree planting?
KIB and CEG mapped Indianapolis to find areas with low existing tree canopy, high plantable space, and high impervious surface area that overlapped with CSO systems.
Where will trees be planted within the selected CSO basins?
KIB will identify tree planting locations within the city right-of-way along streets and in Indy Parks. KIB arborists take into account tree growth, survival factors and distance from existing infrastructure such as power lines, traffic control signs, street lights, and existing trees. For street trees, KIB identifies tree-lawns (the strip of grass between the street and sidewalk) large enough to accommodate large trees.