UNIDATA
Unidata Manual 6293 - Precision Water Level Instruments Issue 2.1
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6 6541B
APPLICATIONS
The 6541B is suitable for a wide variety of applications. These include
measuring:
•
Surface water levels.
•
Flow in open channels.
•
Ground water levels.
•
Pan evaporation.
6.1 Measuring Surface Water Levels
Water levels in lakes, reservoirs, tidal estuaries and process tanks are monitored
for research and management. The 6541 mounted on a suitable floatwell will
provide accurate and reliable data in these applications.
6.2 Measuring Flow in Open Channels
When measuring the flow in open channels it is common to measure the water
level and convert this into a flow rate using a stage/flow relationship derived
from theory or actual measurements. This relationship can be entered into
UNIDATA loggers as a formulae or look-up table. The flow rate can then be
logged instead of, or in addition to water level. The accuracy of this practice
depends on how well the level/discharge relationship can be defined, and how
stable this is. At many sites the UNIDATA Model 6256 STARFLOW system
will be a better option for flow measurement.
In small channels it is common practice to construct a small weir, flume or other
measuring structure at a location where all flow passes through. There are many
different types of measuring structures. In larger channels measuring weirs may
be constructed that combine some form of calibrated structure for small flows
and a natural channel for larger flows.
The location and design of measuring sites is covered in many standard texts on
hydrology, fluid mechanics and water resources monitoring. The selection of a
suitable site and measuring structure is essential. It is important to understand
the accuracy and limitations of different structures. Poor flow data may result
from an unsuitable site or structure design, despite the measurement of accurate
water level.
6.3 Measuring Ground Water Levels
A borehole can be used as a floatwell provided it is large enough and straight
enough to allow a float system to operate accurately.
See the section Sources of Errors in Float Systems in Appendix C.
An additional source of error in the boreholes is that a floatline will tend to
cling
