Precision Water Level Instrument
Unidata Manual 6293 - Precision Water Level Instruments Issue 2.1
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To operate correctly, a floatwell must have the following features. It should:
•
Have sufficient internal diameter to accommodate the float used with the
measuring instrument.
•
Be long enough to allow the float system to move freely from the
minimum to the maximum water levels expected at the site.
•
Be blocked at the bottom and fitted with restricted inlets that allow the
internal water level to change with outside levels, but exclude the effects
of outside waves and surges. Several such inlets should be used.
•
Be designed to protect the float system from damage or interference.
•
Be fitted with a cabinet or housing to protect the instruments.
•
Be accessible to operators.
11.3 Mounting the Instrument on a Floatwell
The recording instrument must be mounted over the float well so that the float
and counterweight hang clear of the wall and can move freely through the full
measurement range. If the floatwell is small, a separate pipe can be used for the
counterweight or offset guide pulleys can be used to re-direct the floatline to a
better location.
The instrument mount should be solid and not allow any vertical movement of
the instrument itself. Any such movement will be recorded as a change in the
water level. Also, some sort of housing or cabinet is required to protect the
instrument from the weather, interference or damage.
11.4 Measuring Location
The floatwell must be located where it will measure the required water level. In
addition to the location of the floatwell there are several other issues that must be
considered before selecting the site and final design.
•
Water velocity.
•
Siltation.
•
Environmental impact.
•
Access and security.
Note that if a calibrated measuring structure such as a weir or flume is being
used, there will be a specific location at which the water level must be measured.
11.4.1 Water
Velocity
If the site is a large still water body such as a lake, pond or reservoir, the water
will be horizontal and the level can be accurately measured anywhere.
If the water is flowing, the water surface will be sloping. The faster the water is
