Skip to main content
U.S. flag

An official website of the United States government

Flushing time variability in a short, low-inflow estuary

May 15, 2023

Flushing time, the time scale for exchange and mixing between embayed and oceanic waters in an estuary, plays an integral role in determining water quality and aquatic ecosystem health. Here, we investigated the spatiotemporal variability of flushing times throughout Morro Bay, a short, low-inflow estuary (LIE) on the California coast, using a calibrated and validated hydrodynamic model (Delft3D). Morro Bay has historically supported an extensive eelgrass (Zostera marina) habitat, which declined substantially from 139 to 5.4 ha during 2007–2017. Eelgrass decline motivated the current research into the role of changing bed roughness and oceanic drivers (i.e., tide and sea-level rise) on estuarine hydrodynamics and flushing times. We found that tidal variability exerts the strongest control on flushing times compared to other effects, i.e., bed roughness or sea-level rise. Additionally, we found that increasing sea level and decreasing bed roughness (associated with declining seagrass coverage) yielded higher rates of mixing (lower flushing times). We detected a strong correspondence between areas having shorter flushing times (e.g., near the estuary mouth) and areas occupied by resilient eelgrass populations in Morro Bay. Our findings further indicated that flushing times in short LIEs are particularly sensitive to several factors (e.g., bed roughness, sea level) that are susceptible to anthropogenic disturbance and future climate change.

Publication Year 2023
Title Flushing time variability in a short, low-inflow estuary
DOI 10.1016/j.ecss.2023.108277
Authors Mohsen Taherkhani, Sean Vitousek, Ryan K. Walter, Jennifer O’Leary, Amid P. Khodadoust
Publication Type Article
Publication Subtype Journal Article
Series Title Estuarine, Coastal and Shelf Science
Index ID 70243592
Record Source USGS Publications Warehouse
USGS Organization Pacific Coastal and Marine Science Center