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Instrumentation at Gages
The USGS in Washington State uses a variety of instruments to collect stage, or gage-height, data at streamflow stations, which is used to compute discharge, and displayed on the Web pages. These includes the traditional stilling well, as well as newer technologies, such as in-situ and remote pressure tranducers, and acoustic rangefinders. The instruments are either developed or tested by the USGS Hydrologic Instrumentation Facility (HIF) to within the acceptable accuracy for USGS use.
In some cases we experience problems with the equipment, often from storm events, other natural events such as mudlfow, landslides, ice, etc., or damage from vandalism. The problems include plugged intakes, broken in-situ sensors, broken or dislodged protective pipes, etc. This causes problems with the gage height, or stage, data where the stage is no longer accurately reflecting the river stage. In these case we will post message to the station Web page warning of this condition, and if there are longer term problems where the damage requires extensive replacement or repairs of gages.
In some cases, we operate several stage sensors at a gage to provide complete data for the conditions at that gage site, such as sensor or instrumentation failure, sites affected by ice, or sensors unable to work in low water. In these cases we may display both sets of stage and discharge datasets on the Web pages, but there will be messages which set to use if there are differences or problems with one set. Additional information about the work necessary with the operation of stage instrumentation and other activities at gages and processing streamflow data is available from the Surface-Water Quality-Assurance Plan for the Washington District (OFR-03490).