Vertical Staff Gauges

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VERTICAL STAFF GAUGES
A staff gauge normally consists of a measuring plate fixed to a post set in concrete. The measuring plate is typically made up of coated steel or stable FRP with increasing increments of 0.01 m. The staff gauge is fastened to a concrete or steel pole that has slots to adjust the level of the plate. Staff gauges may also be painted on a well-established and stable structure, like a bridge pier or retaining wall. At all hydrometric stations a staff gauge is required to measure the water level. The staff gauge is used as the main way of obtaining the level, or as a reference gauge to cross reference the water level recorder.
The site requirements for installing a staff gauge should include being attached to a stable bank, or to a bridge pier or reservoir wall. It should be accessible so that it can be read at any time without any obstructions in the way. To reduce measuring errors they should be place in an area of little turbulence and wave action.
If a station has a stilling well with a recorder inside, staff gauges are placed inside and outside the well in order to help level the gauge. Two permanent benchmarks of known level should be close to the site in order to achieve accurate level readings.

Installation aspects
Vertical gauges are typically installed in pieces of 2.0 meter lengths; there should be enough length so that it surpasses the maximum flood level. The zero of the gauges should correspond with the lowest possible water level when dealing with water controlled by a weir. For naturally controlled stations, the zero must be lower than the lowest water level in rivers that are relatively constant year round and lower than the lowest bed level in rivers that do not maintain a water level year round...

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...densation of water in the vent tube and in the sensor.
Advantages and limitations of pressure sensors
Advantages: - they give a direct reading of depth, do not require a stilling well to damp out water level oscillations and are thus relatively easy and cheap to install even though some form of protection is strongly advised. The cable does not have to be installed vertically and transducers are ideally suited for interfacing with data logging systems.
Limitations: - the levels of accuracy are typically limited to 0.1% of full scale, they are susceptible to changes in environment (manufacturer’s stated accuracy is often at a constant reference temperature), they can be affected by changes in density of the water column, are sometimes susceptible to flow (velocity head) and electrical noise effects and are liable to drift over relatively short time scales (< 1 year).

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