A NEW METHOD OF DETERMINING PRE-EXISTING CHANNEL SUBSTRATES: A CRITICAL COMPONENT OF RIVER RESTORATION

The Sandusky River watershed, located in northwest Ohio, has been influenced by agriculture since the late 1800s. Restoration efforts on degraded tributaries and reaches in the Sandusky River watershed are based on a study released in 2003 by the Ohio Environmental Protection Agency (OEPA) which identified various tributaries and reaches as failing to meet biological water quality standards mainly due to siltation. However, prior to the implementation of restoration strategies it is important to consider past conditions of stream reaches to assess effectiveness of past best management practices (BMP). Channel cutoffs represent unique archives of substrates that existed prior to full BMP implementation in an area.

In this study, a channel cutoff of the Sandusky River in the vicinity of Bucyrus, Ohio was identified using recent digital aerial photography. Historical aerial photographs and USGS peak discharge data suggest the channel was likely abandoned between 1957 and 1964. Ten sediment cores between two and three meters long were collected with a Vibracore to estimate the extent of change in channel substrates. The channel substrates from the abandoned channel were identified in the sediment cores using subsurface facies analysis. Grain size analyses of the substrates were completed and the percent sand, silt, and clay were determined. These data are being compared to existing 2003 OEPA grain size data to assess the extent of change in substrates.

Preliminary results from one of the cores indicate that at the time of channel abandonment grain size distribution in the channel was 45.8% sand and 54.2 % silt and clay in the channel. Data from the OEPA 2003 report shows 75.1 % sand and 24.9% silt and clay at a nearby location. This 29.3% decrease in silt and clay is likely due to implementation of BMP's. Channel cutoffs can be used to examine relative temporal changes in substrates as the substrates are preserved in sediment cores.