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Impacts of 150 Years of Shoreline and Bathymetric Change in the Coos Estuary, Oregon, USA

  • Special Issue: Shallow Water Mapping
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Estuaries worldwide have evolved over the past few centuries under development activities like dredging and shoreline reclamation, which commonly lead to increased channel depths and reduced intertidal areas. The Coos Estuary offers a useful example of how these changes, common to diverse global estuaries, have altered tidal and salt dynamics, with implications for estuarine habitats. In the past 150 years, the primary navigation channel has been deepened from ~ 6.7 to 11 m, generating a 12% decrease in estuary area and 21% increase in volume. To evaluate the present and future impacts on the Coos and similar estuaries, a hydrodynamic model was implemented using a detailed bathymetric dataset compiled from multiple data sources including agency charts, water-penetrating lidar, and single-beam-sonar small-vessel surveys. The model was then re-run using grids constructed from 1865 survey data and a future proposed dredging plan. Changes in the hypsometry from 1865 to present have driven a 33% increase in tidal amplitude, an 18% increase in salinity intrusion length, a doubling of the subtidal salt flux, and an increase in ebb dominance of currents. A proposed channel-depth increase from 11 to 14 m is predicted to generate a negligible change in tidal range and a small increase in the salinity intrusion length. These results highlight the utility of curating high-resolution bathymetric datasets for coastal management applications through modeling. The historical and modern models quantify how local bathymetric modifications can significantly alter tidal and salinity regimes and provide context for estuarine response to global climate-change drivers.

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Computations were performed on the University of Oregon high-performance computer Talapas. We thank Kira Bartlett from UO for assistance in digitizing historical maps, Adam DeMarzo and Alicia Helms at SSNERR for helpful discussions about South Slough management, and the Oregon Department of Fish & Wildlife for SEACOR data. We also thank the editors and two anonymous reviewers for their constructive comments, which helped improve the manuscript.


This work was partially sponsored by the National Estuarine Research Reserve System Science Collaborative, which supports collaborative research that addresses coastal management problems important to the reserves. The Science Collaborative is funded by the National Oceanic and Atmospheric Administration and managed by the University of Michigan Water Center (NAI4NOS4190145).

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Correspondence to E.F. Eidam.

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Eidam, E., Sutherland, D., Ralston, D. et al. Impacts of 150 Years of Shoreline and Bathymetric Change in the Coos Estuary, Oregon, USA. Estuaries and Coasts 45, 1170–1188 (2022).

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