Shaw: Bioretention cell planned in Sylvania

In partnership with the Ohio Environmental Protection Agency (OEPA) and St. Joseph Parish, the City of Sylvania is ready to embark on a project to correct flood plain sedimentation and erosion problems at the westerly end of Harroun Community Park.

In July, the city learned it a Surface Water Improvement Fund grant from the OEPA. The overall cost is estimated to be $106,000, with the OEPA committing over $82,000 toward the project. The remaining project costs are to be shared between the city and parish.

The location of the project is near the Lathrop House adjacent to the easterly parking lot for St. Joseph Church on Main Street. During rain events, uncontrolled stormwater runoff from the approximately one acre parking lot flows to the park’s westerly perimeter. Large erosion channels, up to one foot deep, are cut into the side of the embankment as runoff heads down to the bottom of the Ten Mile Creek floodplain. The large furrows are safety hazards to park users and transport unwanted sediment to the floodplain. In addition, the city expends resources to restore eroded areas after each significant rainfall.

A bioretention cell, often referred to as a rain garden, has been designed to correct the problem. These facilities are usually implemented in urban developments and are sized to treat the first flush of runoff (0.5 inches or less) for small drainage basins. First-flush runoff accounts for 85 percent of the storm events in Ohio and is most attributed with distributing harmful pollutants to our watersheds.

The surface of the cell, consisting of a 3-inch layer of shredded hardwood mulch, is slightly depressed from its surroundings allowing shallow ponding as water enters the basin. The mulch layer protects the filter bed surface from erosion and creates an organic layer conducive to filtering and degrading pollutants.

The cell surface is planted with specific plants capable of withstanding both wet and dry conditions. Tickseed, coneflower, red twig dogwood, Washington hawthorn and pussy willow are scheduled to be used in this application. These species of plants have elongated vertical root systems, which can absorb moisture from deep within the cell. As the root systems mature, more water is absorbed by the cell reducing the overall runoff to the flood plain.

As runoff gradually percolates through the mulch layer it is further filtered by an engineered soil mix, usually between 2 feet and 4 feet thick. The mix is thoroughly blended and is comprised of mostly sand, some native soil and decomposed organic matter. Most of the targeted pollutant removal is achieved in this zone with enhanced microbial activity, ion exchange and plant material absorption. Any excess runoff not used by the cell can exit via an underdrain system to a storm sewer or will infiltrate into the surrounding native soils.

Construction is scheduled to begin in October and the rain garden should be complete and in place by the end of the month.

This publication was financed in part through a grant from the Ohio Environmental Protection Agency under the provisions of the Surface Water Improvement Fund and the U.S. EPA Great Lakes Restoration Initiative. The contents and views, including any opinions, findings, conclusions or recommendations contained in this publication are those of the authors and have not been subject to any Ohio Environmental Protection Agency peer or administrative review and may not necessarily reflect the views of the Ohio Environmental Protection Agency and no official endorsement should be inferred.

Toledo Free Press received no compensation for printing this column.

Joseph E. Shaw is deputy director of the City of Sylvania’s Department of Public Service. He can be reached at jshaw@cityofsylvania.com.