Pebble Counts

The Floods, Farms and Fluvial Geomorphology team (FFFGM: ) has been working to gather field data for the Deerfield River Watershed in an effort to develop more detailed stream power and hazard maps for the region, which currently does not have publicly available FEMA flood hazard maps. The need for such maps are especially important following high-powered storm events like tropical storm Irene which greatly affected local areas back in August of 2011. 

By looking at stream power and dimensions, we can determine which areas are more prone to flood risk and in the future help to make informed decisions with regards to land use and safety. Pebble counts are just a small portion of this process. A pebble count is conducted by taking a transect across a stream, and at regular intervals along the transect, measuring the size of whatever sediment particle (from boulder to clay) is found at that precise point. By measuring the average grain size of sediment transported in a river, we find one part of the puzzle. Combining this information along with other measurements like water depth, river width, and slope, we can figure out an approximate volume of water flowing through a given cross-sectional area, and can then use equations to figure out approximately how fast the river was flowing to move sediment from upstream. 

This Pebble Count shows locations around the Deeerfield watershed were pebble counts were conducted.  At each location we show photos of the stream, along with graphs and tables of the measurment results.