BANK EROSION AND STABILITY MONITORING OF PIKE RUN AND ITS TRIBUTARIES, WASHINGTON COUNTY, PA

Pike Run is a small stream in southwestern Pennsylvania, draining into the Monongahela River from Washington County to the west. Though flows in the stream are typically low and calm, the watershed responds quickly to rainfall events and rapid snowmelt. Steep valley walls, thin, clay-rich soils, and shale-rich bedrock cause Pike Run and many streams of the region to rise rapidly during and after storms. The result of these flashy discharge events is excessive erosion, especially along meandering segments. This study seeks to understand the spatial and temporal rates of lateral incision along the cut banks of Pike Run, correlating loss rates to flow conditions. High-intensity, short-duration flow conditions, such as those resulting from rapid snowmelt or extreme precipitation events, result in a greater volume of eroded material, exacerbating natural migration of stream meanders, compromising existing land use and infrastructure. Landslides and compromised bridges, retaining walls, and culverts are common in the watershed as a result of focused erosion in the stream. Rating curves were developed, using flow measurements and stream stage and crest measurements, and compared to initial incision rates. Incision rates were measured as soil loss using exposure of erosion pins in the stream bank monitored at weekly intervals to calculate the volume of bank material lost over time. At least five meanders are continually monitored for erosion, using 20-pin grids on the exposed cut bank. Experimental erosion rates were compared to modeled values to validate the model for the region and develop a full-stream predictive model. Seasonal variations proved to be an important consideration in estimating and modeling bank erosion. Southwestern Pennsylvania has generally uneven seasonal precipitation characterized by a wet spring and dry summer and fall, with spring as the dominant season for sediment loss and bank erosion.