Watershed Strategies to Reduce Flooding in the Doan Brook Watershed

In early 1998, the Northeast Ohio Regional Sewer District began a study of the Doan Brook watershed, which was completed in 2001. Doan Brook's total length is approximately 9.4 miles and its watershed encompasses an area of approximately 8,000 acres, of which half contains combined sewers, and half contains separate sewers. The watershed is completely urbanized, with land use consisting primarily of residential and urban parkland, along with some commercial and institutional uses.The purpose of the Doan Brook Watershed Study was to develop a comprehensive approach for controlling wet-weather impacts on Doan Brook, both in terms of water quality, and also flooding and channel erosion. Flooding has been a concern in the lower watershed for a number of years. This area consists of an urban park called Rockefeller Park, with a major roadway that winds along the stream and crosses it in several places. Typically once or twice a year, flooding occurs that requires closing of the roadway. This not only causes traffic delays, as cars are forced to detour through neighborhoods above the park, but also creates dangerous conditions. In severe storms, flooding can cause significant property damage in the University Circle area just upstream of the park.During the Doan Brook Watershed Study, hydraulic models of the sewer system and of the stream itself were developed. By examining results of these models, and by doing some historical research of the stream and its tributaries, it became obvious that there would be no single solution to flooding problems. It was found that CSOs were contributing a major volume of flow downstream of a retention dam built by the City of Cleveland. In addition, the stream itself had been significantly modified throughout Rockefeller Park. A number of restrictive bridge crossings were built in the early 1900's, and most of the stream walls were channelized with stone walls. This modification to the stream channel not only degraded habitat for aquatic organisms, but it also reduced the floodplain and accelerated flows, which led to an increase in flooding.This paper will describe how the watershed approach was critical to reducing impacts of flooding in the lower Doan Brook watershed. Although the retention basin by itself can not solve the problem, a combination of changes to the outlet of the retention basin, control of CSO flows downstream, and redesign of the stream channel itself in Rockefeller Park can make a significant reduction in flooding levels.