A GEOSCIENTIST’S ROLE IN INFORMING STREAM RESTORATION DESIGN: A CASE STUDY OF THE FOUR MILE CREEK RIVER VALLEY, SOUTHWESTERN OHIO

Stream restoration is a method used to try to return function to impaired streams and has become a billion-dollar industry in the U.S. A key limitation to stream restoration success, however, is an insufficient understanding of what streams in the U.S. were like prior to European settlement. Using a case study conducted in an 18-km stretch of the Four Mile Creek River Valley in southwestern Ohio, we highlight the important role geoscientists can play in helping to inform stream restoration design. By combining historical atlases, geographic information systems (GIS), and the surficial geologic record; it is possible to determine channel migration zones, reconstruct the biodiversity of fossil mollusk assemblages, and identify past channel planform and morphology of streams.

A crucial aspect in reconstructing what Four Mile Creek was like prior to European settlement was the creation of a Relative Elevation Model (REM) basemap from high-resolution LiDAR data. The REM displayed elevation relative to river water level and provided clear visualizations of the fluvial terraces and past channels in the river valley. Historic atlases were then georeferenced over this basemap, which showed where the channel has migrated, or been rerouted anthropogenically, since European settlement. Historic atlases showed a single channel for most of Four Mile Creek; however, prior to 1855 a large island surrounded by two active channel segments was present. Based on the REM, similar multi-thread stream patterns are preserved elsewhere in fluvial terraces estimated to be <4,500 years old and may indicate a multi-thread type stream was present in some reaches just prior to European settlement. Age estimates of fluvial terraces were determined through surficial geologic mapping and radiocarbon dating of the channel deposits from excavated trenches and exposed river outcrops. Shells were prevalent in the channel deposits and were used for radiocarbon dating when datable organics were not present. The shells were not used to assess the biodiversity of mollusk species, but are an aspect that could further aid in informing stream restoration design. Understanding what streams were like prior to European settlement is key for understanding how the stream has changed as a result of human impacts and to what extent it can and should be restored.