The Effects of Slack Tides on Turbidity and Horizontal Velocity in an Estuarine System

Katherine Fitzpatrick, Marina McLeod & Ardi Kveven, Ocean Research College Academy, Everett Community College 1205 Craftsman Way Suite 203 Everett, WA 98201

Possession Sound is a dynamic salt wedge estuary system near Everett, Washington. The estuary is fed by the Snohomish River. In salt wedge estuaries, a mix of salt and fresh water creates a salinity gradient between the two sources, with the denser, saltier water making up the lower sections of the vertical gradient, and the freshwater residing above it. Turbulence from river flow and tidal currents decrease the amount of suspended sediment in the water column, measured as turbidity. When stratification increases, turbulence increases too, which causes lower turbidity. This study explores influences on turbidity at the Everett Marina during the years 2017 and 2020. During tidal exchanges, we predicted that when the tide is slack--shown as north/south flow--the horizontal velocities of the water would be shown with an east/west flow. This east/west flow would create vertical mixing and higher turbidity in the water. Two-dimensional horizontal river flow velocities from 0.9 to 4.9 meters from the riverbed at half-meter increments were measured using a grant-supported deployment of an Aquadopp ADCP (Acoustic Doppler Current Profiler). The depth of each velocity measurement was estimated based on pressure measured by the ADCP. Turbidity was collected using a CTD deployed 1.7 meters from the surface. The volume, velocity, and sediment deposition of river water come from the United States Geological Survey (USGS) data, and tide heights are published by the National Oceanic and Atmospheric Administration (NOAA). 

Additional Abstract Information

Presenter: Katherine Fitzpatrick

Institution: Everett Community College

Type: Poster

Subject: Environmental Science & Sustainability

Status: Approved

Time and Location

Session: Poster 7
Date/Time: Tue 3:30pm-4:30pm
Session Number: 5012