472 CHAPTER 8. LABORATORY MEASUREMENT AND ANALYSIS
are given of instruments used to make various measurements, but details
have been omitted. The best sources for up-to-date information on specific instruments are laboratory reports, manufacturer’s literature, or direct
communication with involved researchers.
8.2.1 Water Level Measurement
Determining the elevation of static or slowly varying water levels is a fundamental measurement in coastal engineering hydraulic model studies. Measured water level elevations, when combined with the elevations of the
model bathymetry, allow us to determine water depths throughout the
model. In addition, the still water elevation typically represents the horizontal reference plane defined in many wave theories.
Measuring the still water level in a laboratory facility containing a fixed
volume of water is relatively easy because the measurement can be obtained
when the fluid is at rest and the surface is stationary. Visual observations
can be made using a graduated staff, or more precision is possible by using
manually operated “point gauges.”
A point gauge consists of a sharply pointed, movable metal rod connected to a graduated scale. The pointed rod is slowly raised or lowered
using a rack and pinion gearing system until the point just makes contact
with the water surface. The observer then reads the graduated scale to
get the distance between the water surface and the point gauge zero reference elevation. In order to get absolute water level elevations relative
to the model datum, the elevation of the point gauge zero reference must
be determined. A potentiometer could be attached to the point gauge to
partially automate the recording of data.
In cases when water is being added to or withdrawn from a laboratory
facility, the still water level becomes a function of time, which can complicate the measurement. For example, a basin model that combines both
waves and tides would need to simulate the tide with an inflow and outflow
of water. Provided the change in water level is not too rapid and water
level elevation measurements do not need to be closely spaced in time, the
time-varying water level could be monitored with a point gauge in a stilling
basin. However, preferable methods include the recording float gauge or
some type of electronic water level monitor, such as a capacitance wave
gauge, placed in a stilling basin and configured to record automatically the
water level at set time intervals.
The recording float gauge consists of an ink pen mounted on a float.
As the water level varies, the elevation is recorded on a chart fixed to a
revolving drum. In recent years these types of analog gauges generally
have seen limited use because of the availability of reliable electronic water
are given of instruments used to make various measurements, but details
have been omitted. The best sources for up-to-date information on specific instruments are laboratory reports, manufacturer’s literature, or direct
communication with involved researchers.
8.2.1 Water Level Measurement
Determining the elevation of static or slowly varying water levels is a fundamental measurement in coastal engineering hydraulic model studies. Measured water level elevations, when combined with the elevations of the
model bathymetry, allow us to determine water depths throughout the
model. In addition, the still water elevation typically represents the horizontal reference plane defined in many wave theories.
Measuring the still water level in a laboratory facility containing a fixed
volume of water is relatively easy because the measurement can be obtained
when the fluid is at rest and the surface is stationary. Visual observations
can be made using a graduated staff, or more precision is possible by using
manually operated “point gauges.”
A point gauge consists of a sharply pointed, movable metal rod connected to a graduated scale. The pointed rod is slowly raised or lowered
using a rack and pinion gearing system until the point just makes contact
with the water surface. The observer then reads the graduated scale to
get the distance between the water surface and the point gauge zero reference elevation. In order to get absolute water level elevations relative
to the model datum, the elevation of the point gauge zero reference must
be determined. A potentiometer could be attached to the point gauge to
partially automate the recording of data.
In cases when water is being added to or withdrawn from a laboratory
facility, the still water level becomes a function of time, which can complicate the measurement. For example, a basin model that combines both
waves and tides would need to simulate the tide with an inflow and outflow
of water. Provided the change in water level is not too rapid and water
level elevation measurements do not need to be closely spaced in time, the
time-varying water level could be monitored with a point gauge in a stilling
basin. However, preferable methods include the recording float gauge or
some type of electronic water level monitor, such as a capacitance wave
gauge, placed in a stilling basin and configured to record automatically the
water level at set time intervals.
The recording float gauge consists of an ink pen mounted on a float.
As the water level varies, the elevation is recorded on a chart fixed to a
revolving drum. In recent years these types of analog gauges generally
have seen limited use because of the availability of reliable electronic water