Water levels in the Grays Harbor and Columbia River estuaries, Washington

We obtained time series of water levels in tidal channels in the Johns River tributary to the Grays Harbor Estuary (46.88919°N, 123.97209°W) from October 2017 to April 2019 and in the Grays Bay region of the Columbia River Estuary (46.32605°N, 123.65428°W) from October 2020 to August 2021 to determine local tidal datums for nearby tidal wetland research sites. We deployed Hobo pressure sensors in PVC wells and surveyed their elevations using real-time kinematic GPS in the North American Vertical Datum of 1988 (NAVD88). At the Grays Harbor station, the sensor was at -0.160 m NAVD88 and water level was collected every 12 minutes. At the Columbia River station, the sensor was at -0.485 m and water level was collected every 6 minutes. Using NOAA CO-OPS’s on-line “Tidal Analysis Datum Calculator” with the direct method and the NOAA Westport, WA tide gauge (Station 9441102) as the control station, we used 18 months of data to determine tidal datums (in meters relative to NAVD88) at the Grays Harbor site as follows: mean high water = 2.303 and mean higher high water = 2.528. We used the calculator with the standard range ratio method and NOAA’s Astoria tide gauge (station 9439040) as the control station in the Columbia River Estuary to determine tidal datums (in meters relative to NAVD88) for six complete months of water level data as follows: mean lower low water = 0.333, mean low water = 0.570, mean tide level = 1.509, mean high water = 2.448, and mean higher high water = 2.639. The time series also provide water temperatures.