SEASONAL VARIATION IN GRAVELBAR MORPHOLOGY AND STAGE LEVEL ALONG ROCK CREEK, TIFFIN, OHIO

Gravelbars are common features in meandering and braided streams. Bar morphology and grain size in gravelbars are indicative of stream velocity and local watershed relief. In this research, I determined morphological changes and grain size distribution of three bars in a 2nd order meandering stream in Northwest Ohio. The three bars, all located in Rock Creek, Tiffin, Ohio, are a point bar, a midstream bar, and a second point bar that formed by a stream blockage. These bars are composed primarily of pebble- to cobble-sized particles. Grain size analysis showed that starting at the upstream point bar, and progressing downstream to the other two bars, the largest particle fraction became larger from bar to bar. Although all three bars contained a similar range of pebble- to sand-sized clasts, the point bar furthest downstream contained large amounts (~60%) of cobble while the midstream bar had fewer cobble-sized and more (~50%) pebble-sized clasts, and the upstream point bar had primarily pebble-sized clasts. Gravelbar size and shape in this creek were stable over the 8-month period from April to November; any changes in bar shape and size were due to stage level fluctuations. From April to November, the bars appeared to grow in size; this change resulted from the drop in water level normal for this time of year. Actual changes in bar morphology depend on particle entrainment and deposition, which most likely take place when the range in stream velocity is broader due to snowmelt and spring precipitation. In northwest Ohio, these conditions occur between January and April.