Don’t Let the Bedform Migrations Bite: Analyzing and Predicting Dune Heights along the Willamette River
Casey Martin, PE, CFM
CDM Smith
Denver, CO
Subaqueous sand dunes on a river or stream bed can be readily mobilized by flowing water. These dunes can cause localized sediment erosion or deposition even if the bed is overall stable or experiencing the opposite trend on a more overarching scale. This makes understanding and predicting dune migration important when designing bed material for stream restoration or protections for contaminated sediment. Localized erosion and deposition can happen during flow events of various energies but are particularly pronounced during flood events. This presentation discusses a bedform analysis conducted along the Willamette River within Portland Harbor in Oregon. The analysis considered both short-term and long-term patterns. An initial analysis was performed using gage data from a gage approximately three miles upstream of the project site to determine whether the long-term bed elevation patterns indicated net erosion or deposition between 2008 and 2024. Next, an empirical approach (Julien and Klaassen 1995) was used with inputs from sediment borings and bathymetry data collected at several locations along the approximately five mile long project site, the average water surface elevation from gage data, and calculated flood water surface elevations to predict the short-term bedform variations during future flood events. . The calculated dune heights were assumed to be the potential degradation depths in the riverbed. These depths were then used to evaluate the risk of exposure to different areas of contaminated sediment buried beneath the riverbed surface and inform possible protection and monitoring measures. The lengths of the predicted dunes were also calculated to inform the dimensions of any armored caps that might be deemed necessary so that dredging the contaminated soil would not be required. The techniques utilized are readily transferrable to other systems to allow for the quantification of risk to life, infrastructure, and property due to bed mobilization during large and small flow events.
Julien, P.Y. and Klaassen, G.J. “Sand-Dune Geometry of Large Rivers During Floods.” Journal of Hydraulic Engineering, 121(9): 657-663. September 1995.
About Casey Martin, PE, CFM
Casey Martin, P.E., CFM, has nine years of experience as a water resources engineer, including performing hydrologic and hydraulic modeling for projects across the country and previously was the MT-2 Region Lead for FEMA Region X. She received her Bachelor’s degree from Purdue University and her Master’s degree from University of Tennessee, Knoxville. Outside of work, she enjoys hiking and white water rafting in the Rocky Mountains, creating stained glass, and reading with her wobbly cat.