STREAMBED SEDIMENT AND HYDRAULIC GEOMETRY IN THE POST-GLACIAL LANDSCAPE OF NORTHEASTERN OHIO

Streams generally exhibit downstream hydraulic geometry through downstream fining of sediment, a decrease in water surface slope, and channel widening, but external forces such as land use and glaciers can alter these expected trends. The impact of glaciers on the downstream hydraulic geometry of streams in mountainous terrain is recognized, but the potential for persistent and pervasive impacts of Pleistocene glaciation on hydraulic geometry in the Midwestern United States has received little attention. We seek to bridge this knowledge gap by studying the grain size distribution of three tributaries to northeastern Ohio’s Cuyahoga River: Chippewa Creek; Yellow Creek; and Furnace Run. Total drainage areas ranged from 46 to 80 km², with the distance between furthest upstream to downstream reaches covering between 8.5 to 12 km. We quantified grain size distribution using a Wolman Pebble Count, and measured the water surface slope and bankfull width in four reaches of each stream. D₈₄ values for streambed sediment in each study reach showed high variability, ranging from 36 mm to 250 mm. No clear trend in downstream fining was observed. Similarly, we did not see evidence of typical downstream hydraulic geometry in water slope measurements or channel width measurements. We hypothesized that downstream hydraulic geometry was absent because of varying surficial geologic deposits, but ANOVA tests showed no statistically significant difference in bankfull width or local slope across surficial geology map units. The absence of trends may be attributable to varying land use practices and wood abundance, interspersed bedrock reaches, or recruitment of varying grain sizes along the length of the stream that may influence grain size distributions beyond the map unit boundaries.