Rainier Survey Technician Matt Boles prepares to install a benchmark. Benchmarks are usually placed in bedrock, and set with cement so that their position will be as stable as possible
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The Benchmark (left) represents a vertical datum reference point and establishing its permanence is vital.
The orifice (right) must be attached to a plate, which is then weighted to the bottom with dive weights, chain, or rock. Nitrogen tanks on land are employed to feed gas to the orifice on the sea floor. |
Rainier crew members, trained as NOAA working divers install the bubbler orifice. The neoprene bubbler tube running to the gauge is also secured by divers under the surface
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The graduated staff is installed in the tidal zone by Rainier crew.
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The benchmarks are leveled to a graduated staff (right) that is also semi-permanently installed at sea level, on which water level observations are taken periodically during the station occupation. Leveling is conducted with a collimated optical instrument set on an undisturbed tripod (right), which allows the operator to read the level rod to the nearest millimeter. |
Rainier crewmeber helps level the graduated staff.
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