Willamette at Portland streamgage maintenance

Hydrologic technicians survey the Willamette River at Portland’s streamflow gage datum. Every streamgage measures water levels (gage height) relative to a datum, a fixed elevation chosen to ensure consistent, long-term measurements. At this site, the staff plate span requires that one crew operates a level gun from the bridge while another crew takes tape-down measurements from a boat. Depending on the location, streamgages are surveyed every 1–3 years to maintain accuracy. The gage height at this site is referenced to the North American Vertical Datum of 1988 (NAVD88).