Impacts of a Cascadia Subduction Zone Earthquake on Water Levels and Wetlands of the Lower Columbia River and Estuary

• Published in: Geophysical research letters Vol. 50; no. 14
• Main Authors: Brand, M. W., Diefenderfer, H. L., O’Connor, J. E., Borde, A. B., Jay, D. A., Al‐Bahadily, A., McKeon, M., Talke, S. A.
• Format: Journal Article
• Language: English
• Published: Washington John Wiley & Sons, Inc 28-07-2023; American Geophysical Union (AGU); Wiley
• Subjects: Bathymetry; Brackishwater environment; Earthquake effects; Earthquakes; Environmental restoration; Estuaries; Estuarine dynamics; Habitats; Hydrodynamic models; Hydrodynamics; Modelling; Restoration strategies; Rivers; Seismic activity; Subduction; Subduction (geology); Subduction zones; Subsidence; Tidal effects; Tidal range; Water levels; Wetland restoration; Wetlands; Cascadia; Columbia River
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2023GL103017

Subsidence after a subduction zone earthquake can cause major changes in estuarine bathymetry. Here, we quantify the impacts of earthquake‐induced subsidence on hydrodynamics and habitat distributions in a major system, the lower Columbia River Estuary, using a hydrodynamic and habitat model. Model results indicate that coseismic subsidence increases tidal range, with the smallest changes at the coast and a maximum increase of ∼10% in a region of topographic convergence. All modeled scenarios reduce intertidal habitat by 24%–25% and shifts ∼93% of estuarine wetlands to lower‐elevation habitat bands. Incorporating dynamic effects of tidal change from subsidence yields higher estimates of remaining habitat by multiples of 0–3.7, dependent on the habitat type. The persistent tidal change and chronic habitat disturbance after an earthquake poses strong challenges for estuarine management and wetland restoration planning, particularly when coupled with future sea‐level rise effects.
Plain Language Summary
The land in many estuaries along the Pacific Rim has been repeatedly changed by major earthquakes. Previous earthquakes, such as the CE 1700 rupture along the 1,000‐km Cascadia Subduction Zone of western North America, produced as much as 2 m of land‐surface lowering. This study employs a hydrodynamic model to show that the relative sea‐level rise resulting from such lowering would increase tidal range and affect nearly all existing wetland habitat in the lower Columbia River Estuary. In our primary scenario, approximately ∼93% of current wetland habitat converts to lower‐elevation types, with changes largely due to land‐surface lowering but also influenced by tidal changes. Thus, the chronic, long‐term disturbance to habitat conditions after an earthquake poses a similar long‐term risk to estuarine ecology as extreme global sea‐level rise scenarios. Understanding such earthquake effects may assist the development of more resilient habitat restoration strategies.
Key Points
Earthquake‐induced subsidence results in the movement of ∼93% of intertidal habitat to lower habitat zones
Post earthquake, tidal range increases by up to 0.25 m in channels; capturing such changes requires a dynamic model
Both subsidence and changes in tidal range alter habitats, especially sandflats and low marshes