RECREATIONAL ENHANCEMENTS on AN URBAN STREAM AND THEIR ROLE IN STREAM RESTORATION

A locally-led initiative to improve the recreational potential of a 9-km reach of Buck Creek and its tributary Beaver Creek in Springfield, Ohio, includes the modification of four lowhead dams with hydraulic heights up to 3 m. Modifications to the dams, two of which have been completed, include replacing the hydraulic height of each dam with a series of 2-4 drop structures equal to the original height in order to maintain the average grade of the stream. The drop structures, engineered to create hydraulic conditions conducive to kayaking, are essentially riffles immediately upstream of the structure and pools downstream. Changes in the stream habitat, water chemistry, and macroinvertebrates in response to dam modification highlight the potential for incorporating stream restoration into the engineering design.

Prior to dam modification, values of the Qualitative Habitat Evaluation Index (QHEI), which quantify the geomorphic characteristics beneficial to aquatic habitat, are lower in the impounded area upstream of the dams and increase downstream as a function of the substrate quality and pool/glide and riffle/run quality prior to modification. The impounded areas upstream of the dams are dominated by pools and glides with finer substrates embedded with fine sand and silt. Water chemistry Though dissolved oxygen (DO) of surface flow upstream and downstream of the dams does not vary significantly, DO in water extracted from the channel substrate in the impounded area is significantly lower than substrate water upstream of the impounded area and downstream of the dam. Trends in macroinvertebrate diversity and abundance parallel this trend. The Pollution Tolerance Index (PTI), based on order-level macroinvertebrates, decreases in the impounded area. Following modification of two of the dams, QHEI and PTI values increased at one site and decreased at the other site, depending on whether the uppermost drop structure at a given site caused excessive pooling during stormflow events. In the best case, coarser gravel substrates grade to the drop structures and are free of fine sand and silt. QHEI values increased DO of the substrate water is greater, and the PTI, though still low during the first year following modification, is greater than prior to modification.