SUMMARY: NOAA’s National Ocean Service, Center for Operational Oceanographic Products and Services (CO-OPS) has updated the reference values for Columbia River Datum (CRD) at 5 active Physical Oceanographic Real-time System (PORTS®) stations on the Columbia River, based on updated offsets for CRD provided by the USACE in 2014. These stations had been previously set such that Station Datum (STND) for each station was equal to CRD, as published by the U.S. Army Corps of Engineers (USACE) in 1978.

CRD is a non-tidal gradient datum developed from an observational study by USACE, Portland District in 1912 (R.E. Hickson, 1912), originally defined at distinct river miles relative to National Geodetic Vertical Datum of 1929 (NGVD29), now defined relative to North American Vertical Datum of 1988 (NAVD88). CRD is the adopted low water reference plane for the area and is used as NOAA chart datum above river mile 22 on the Columbia River. Tidal datums are computed using observations from the low river stages of the year, generally August through October, due to the masking of the tidal signal from strong seasonal river runoff during other portions of the year. Depending on river flow, water levels can be significantly higher than Columbia River Datum.

CO-OPS had previously set water level stations in this region such that STND was equal to CRD so that users could obtain water level observations relative to CRD by referencing them to STND. To accommodate the updated CRD offsets provided by USACE in 2014, CO-OPS has modified data access options for the active stations in this area so that users may select CRD as a reference datum for water level data instead of STND to obtain water level data relative to the updated CRD. Station Datum (STND) for these stations has not been changed, but is no longer be equal to the latest CRD following these updates.

These five active PORTS stations have been updated with the following differences between STND and the updated CRD:

9440569 Skamokawa, WA = -0.018 m (-0.709 in)
9439099 Wauna, OR = -0.044 m (-1.732 in)
9440422 Longview, WA = 0.082 m (3.228 in)
9439201 St. Helens, OR = 0.006 m (0.236 in)
9440083 Vancouver, WA = -0.050 m (-1.969 in)

The major CO-OPS products updated for these stations are data access options at Tides & Currents water level web pages & data services, PORTS® station information web pages, Published Benchmark Sheets, PORTS® Uniform Flat File Format (PUFFF) water level files, and the Columbia River Estuary Operational Forecast System (CREOFS). All display references for data relative to CRD on CO-OPS Tides & Currents websites have been updated to reflect the new CRD, and a new CRD datum reference option has been added to datum reference selection menus where applicable. There are no changes required to the NOAA tidal prediction products distributed by NOAA as a result of these updates. The online predictions now have the new CRD datum option for plotting and downloading predictions.

Updating the CRD references in these areas is necessary to provide the latest up-to-date information available for applications that are essential to supporting Federal, State and private sector activities such as hydrographic surveys and navigational safety.