Coos Bay sediment dynamics – Coastal & Fluvial Sediment Dynamics

2017-2024

Coos Bay, located along the southern Oregon Coast, is distinguished as the largest estuary between the Columbia River and San Francisco Bay. It provides key services including port facilities for regional lumber and fishing industries, tidal wetlands, and oyster silviculture. The estuary has been modified by developments including dredging and reclamation for more than 150 years, which has impacted the flow of water and sediments throughout the estuary.

Intertidal flats in South Slough National Estuarine Research Reserve,
a protected portion of the Coos Bay Estuary

In 2017-2020, we collaborated with researchers at the University of Oregon (Dr. Dave Sutherland, lead PI), Woods Hole Oceanographic Institute, and the South Slough National Estuarine Research Reserve to observe and model hydrodynamics and resulting sediment transport in the system. This work, which was funded by NOAA NERRS, addressed modern exchange flow processes (Conroy et al., 2020) as well as contrasting tidal dynamics and resultant sediment dynamics for a model representing the estuary in the mid-1800s compared to a present-day model (Eidam et al., 2020, 2021).

*Data collection from the *R/V Pugettia* operated by* OIMB

In 2021-2024 we completed a NOAA NERRS project to study sedimentation patterns and rates. Postdoctoral scholar Dr. Molly Keogh (University of Oregon; now postdoctoral scholar at OSU) used short (~10-cm) cores and short-lived isotope measurements to assess ephemeral deposition and erosion during rainstorm events and fairweather periods, with an eye toward finding where short-timescale seabed changes are occurring which may impact eelgrass and/or oyster restoration efforts. Recent MS grad Tyler Souza (UNC, now at Geosyntec) used longer (~30-80-cm) cores and Pb-210 isotope geochronologies to assess the history of sedimentation related to disturbances like logging and dredging over the past 100 years, and assess spatial variability in different types of intertidal flats (Souza, 2023 MS thesis). The figure below illustrates sites where cores were collected in May 2021.

*Mooring deployments supported by CTCLUSI*

Project publications

Eidam, E., Souza, T., Keogh, M., Sutherland, D., Ralston, D.K., Schmitt, J., Helms, A. (2024) Spatial and Temporal Variability of Century-Scale Sediment Accumulation in an Active-Margin Estuary. Estuaries and Coasts, https://doi.org/10.1007/s12237-024-01407-x

Souza, T. D. (2022). A century of disturbance: How anthropogenic modification has affected sediment accumulation patterns in the coos estuary during the last 100 years (Order No. 29996056). Available from ProQuest Dissertations & Theses Global. (2759261493). Retrieved from http://libproxy.lib.unc.edu/login?url=https://www.proquest.com/dissertations-theses/century-disturbance-how-anthropogenic/docview/2759261493/se-2

Keogh, M., Sutherland, D., Schmitt, J., Souza, T., Eidam, E., Ralston, D., & Helms, A. (2021, December). Estuaries on the Edge: Sediment Dynamics and Resiliency of US Pacific Coast Wetlands. In AGU Fall Meeting Abstracts (Vol. 2021, pp. EP33C-08).

Eidam, E. F., Sutherland, D. A., Ralston, D. K., Conroy, T., & Dye, B. (2021). Shifting sediment dynamics in the Coos Bay Estuary in response to 150 years of modification. Journal of Geophysical Research: Oceans, 126(1), e2020JC016771.

Eidam, E.F., Sutherland, D.A., Ralston, D.K., Dye, B., Conroy, T., Schmitt, J., Ruggiero, P. and Wood, J. (2020). Impacts of 150 years of shoreline and bathymetric change in the Coos Estuary, Oregon, USA. Estuaries and Coasts, pp.1-19.