Because so much of the urban area is covered with buildings or blacktop, there are vast volumes of runoff.  Undeveloped agricultural land sheds about 20 percent of rain volume. Forested land sheds even less. Paved commercial and business areas are calculated to run off 80% of precipitation—and greater volumes of stormwater move more quickly. There is increased erosion when flooding carries away sediment and rocks and scours stream channels. Stormwater flowing on streets goes through inlets into storm sewer pipes, which empty into a river or stream.  Higher peak volumes can cause flooding damages along with erosion.

New regulations for land development in the City of Columbus require keeping stormwater release rates below certain levels, installing controls like basins or ponds to filter pollutants, and leaving setback strips along streams.

“Stormwater quantity controls” are constructed features to catch and hold peak stormwater volumes so they can be released more slowly.  While the new requirements do allow increases in stormwater runoff volumes after development, they require that the rate of release be controlled.  Suggested quantity controls include detention basins, parking lot storage, underground tank storage, and even “green roofs” (planted areas on top of buildings that take up precipitation and reduce runoff).

 “Post-construction quality controls” are permanent features to catch small rain events on-site and reduce pollutants. The specific list of these controls in the manual includes: stormwater basins, media filters, vegetated swales and filter strips, and controls for commercial activities.  Stormwater basins can be dry, seasonally wet, or constructed wetlands.  Media filters remove pollutants by passing stormwater through a bed of sand, peat, or some other substance to trap contaminants - they can look like a large box or a planted garden with shrubs. Vegetated swales are usually broad, shallow ditches with grass or other plants. Filter strips are gently sloping areas with robust vegetation to treat storm water from small areas less than 5 acres.  The Manual requires that commercial enterprises conduct activities indoors, cover materials, or use approved controls.

One of the biggest changes is the requirement for a stream corridor protection zone—50 feet on the smallest streams and a maximum of 250 feet on the largest waterways.  The required corridor is wider for steep slopes or wetlands. Building, commercial activities, dredging and filling, mining, and disturbance of vegetation are restricted. Unfortunately, the City continues its policy of allowing the filling of floodplains if a nearby area is dredged. Also, the stream corridor protection zone is not required downtown or in redevelopment areas.

For development, a stormwater report and plan prepared by professional engineers must be submitted. Long-term maintenance must be provided. Existing requirements to control erosion and sediment during construction remain in place.

The biggest improvement in the manual, other than the stream corridor protection zone, is the emphasis on choosing native plants for stormwater facilities. It is a great achievement that the Columbus Division of Sewerage and Drainage will now be promoting the use of adapted native plant species.

The Manual unfortunately does not change the City’s development policy that allows filling of the floodplain if an equivalent volume is removed nearby.  The Manual only applies to new development and will not remedy or restore the many degraded existing waterways in the City - incentives for stream restoration would help.  Controls reduce post-development rate of release but allow increased volumes.  The new requirements will result in many more detention basins dotting the landscape. 

The clay soils of Central Ohio make managing urban stormwater even harder because water cannot percolate through soil easily here.  Given these soil challenges and the constraints of past history, the new Columbus Stormwater Drainage Manual is an important step forward. Based on Sierra Club recommendations, Columbus Division of Sewerage and Drainage included wetlands in protection zones and is promoting the use of native plants. Mud from construction is one of the biggest polluters of area waterways.

For information on how to report sediment eroding into streams, go to the MORPC Greenways site.

 COG Chair’s note: Cyane Gresham supplied excellent comments on the Stormwater Manual to the City of Columbus. These comments can be found here.

Thank You!

The Edwin H. and Nellie M. Rausenberger Fund of the Columbus Foundation has awarded the Ohio Sierra Club a grant to continue the Central Ohio Sewers Campaign. Please see in-depth article on page 7 of the Ohio Sierran newsletter.

Contact Us Today for a Presentation to Your Community Group

The Columbus Foundation grant is helping the Sierra Club offer a slide show to civic, religious, neighborhood and other organizations. The program explains how sewers and stormwater affect your streams and neighborhoods. Find out what you can do to reduce stormwater runoff and how to deal with basement sewage backups. There are exciting success stories. Contact .