Low Flow - Velocity Profiles
[III-A3]
I want to make measurements in rivers/lakes/streams/irrigation canals. [change]
My interest in rivers/lakes/streams/canals is measuring low flows... [change]
...as a velocity profile. [change]
SonTek
makes both the Acoustic Doppler
Profiler (ADP) and the
Pulse-Coherent ADP (PC-ADP) for profiles of water velocity. The
ADP is for larger-scale phenomena (resolution <1.0 cm/s), while the
PC-ADP is for very high resolution work (<0.1 cm/s) that is
typically near the bottom boundary.
For ADPs, there
are two basic questions that quickly get us to the most appropriate system:
- What profiling range is required?
The ADP is available in five
frequencies, with nominal ranges of 6, 25, 40, 90, and 160 m. These are
the expected "medium" ranges under typical conditions. In some cases the
range will be less, in others more.
- How is the ADP to be deployed (e.g., on the bottom, on a mooring, from
a boat)?
If the ADP is to be deployed on the bottom, or in a fixed
location, then a compass/tilt sensor might prove a useful addition for
installation, and also for later analysis to see if the package has moved.
If the ADP is to be deployed on a mooring, then a compass/tilt is
essential for proper vector averaging. If it is to be deployed from a
moving platform (e.g., a boat), then we need to remove the translational
velocity of the platform whether though the use of a DGPS system or our
bottom-tracking feature (or both).
The
PC-ADP is capable of very high resolution measurements, with
cell sizes as small as 1.6 cm and data rates as high as 2 Hz. The PC-ADP is
designed for deployment from a fixed platform, most commonly looking
downward with a range of 1 to 2 m.
There is a complete suite of Windows-based software for the ADPs,
including post-processing and three different application-specific data
acquisition programs.
Any ADP (or
PC-ADP) can be configured for real-time monitoring or for
autonomous deployments with on board logging and power. Also, either system
can be configured with a variety of external sensors, including pressure,
conductivity, temperature, turbidity, etc.
ADPs equipped with pressure sensors can be configured with software that calculates
non-directional wave statistics such as significant wave height and peak period.
Other SonTek instruments capable of low-flow, velocity profile measurements
include our Argonaut systems:
 |
The Argonaut-XR
(Extended Range) is designed for bottom-mounting for measuring depth-integrated velocities
out to a range of 40 m. An on-board pressure sensor can be set to automatically
adjust the measurement parameters with changing water levels. |
 |
The Argonaut-SL
(Side-Looking) is designed for mounting on vertical structures to measure the horizontal
velocity at a given depth. The Argonaut-SL can project its sampling volume up to
120 m
away, allowing it to be easily deployed from large vertical structures, while projecting
its sampling volume away from the possible influence of the structure. |
 |
The Argonaut-SW is bottom
mounted and provides a depth-integrated velocity measurement out to a range of 5
m. A vertical acoustic beam provides water level information. The measurement
cells will dynamically adjust in size as the water level changes. Typically used
in irrigation canals. |
