Hi, my name's John Mazurek and I work
for the U.S. Geological Survey in Asheville, North Carolina.
We put this video together for the HDAC video series
on what hydrologic technicians do, to show you
a Routine Streamgage Inspection.
Streamgage inspections are a major part
of the work hydrologic technicians do in the field
within the U.S. Geological Survey.
This video, we'll look at
a Routine USGS Streamgage Inspection at
a few streamgages located in Western North Carolina
and maintained by the Asheville field office.
When a hydrologic technician first arrives
at a streamgage, they read the primary reference gauge.
This reading is considered the correct reading during
a site visit.
At this site the primary reference gauge is a set
of staff plates.
This plate appears to read 1.62 plus or minus 0.01 feet.
Another example of a primary reference gauge is
a wire weight.
A brass weight is lowered from a spool
and the reading on the dial is read when the bottom
of the weight hits the water surface.
After the primary reference gauge is read,
the electronic data logger is then checked to make sure
the readings agree within two hundreds of a foot.
In this case, the staff plate
and data logger readings agree.
Readings are then recorded in electronic field notes.
Some common components of a USGS streamgage
are a datalogger, the GOES satellite transmitter
and a stage sensor.
At this site, a non-submersible pressure transducer
is used as the stage sensor.
The sensor is located on the inside of the gauge
and reads the back pressure of the water
through thick wall tubing that connects the pressure sensor
to the river.
The tubing is run through a conduit to a position below
the water surface where it is mounted in a fixed position.
Compressed air is blown through the tubing
to regularly purge the line and keep the end
of the tubing clear off debris and vegetation.
The end of the pipe is also serviced regularly
by cleaning debris and algae from the cap.
After maintenance, the data logger is read again
to make sure the pressure sensor readings
did not change after the cleaning.
Next we are going to look at another type of streamgage
that is far less common nowadays, a stilling well.
These large wells are connected to the river by a series
of galvanized pipes and a float and counterweight are used
to record the water level in the well.
The black plastic float is connected to a steel tape
that runs around a metal wheel on the upper shelf
with a sensor that records the stage in the well based
on how much the wheel spins.
This is called a shaft encoder.
A secondary reference gauge in this case, an electric tape
can be used as another check of the water level
in the stilling well.
When the weight hits the water an electric circuit
is completed and the dial on
the volt meter registers a reading.
The values recorded on the electronic data logger
are compared to the values of the reference gauges.
Here you can see the shaft encoder
where the steel tape passes around the wheel.
As the wheel in the encoder spins the stage reading changes.
Max-min clips attached to the steel tape beneath
the instrument shelf mark the maximum and minimum travel
of the steel tape between inspections.
During site visits, the wheel on
the shaft encoders spin until the clip meets the bottom
of the shelf.
The data logger is simultaneously read
and maximum minimum values between visits are recorded.
Max-min clips are one method to validate peaks
in the stream flow record and ensure the accuracy
of peak data recorded at streamgages.
At the first site we looked at there was no stilling well,
so we have to use another method to validate peaks.
Crest-stage gauges are vertical pipes
with specialized tops and bottom caps, used
to measure peak stages at USGS streamgages.
The wooden stick inside the pipe
is removed during site inspections and the distance
from the top of the stick to the cork line
is measured and documented.
Crest-stage gage pipe elevations are surveyed routinely,
so the elevation of the top of the pipe minus
the distance to the cork line equals the elevation
or gauge height of the largest peak since
the last inspection.
Granulated cork used to mark the peaks on the wooden sticks
is replaced in the bottom cap of the pipe to ensure
that future peaks are recorded by the crest stage gauge.
Any cork marks are removed from the stick
and the crest stage gauge is closed back up and ready
for the next peak.
Since the electronic data is based on the readings
from the primary reference gauges, we need to ensure
that the reference gauge elevations are accurate
and not changing through time.
Streamgages surveys or levels are performed
at reoccurring intervals at all USGS streamgages.
During streamgages gauge surveys level rods are held
on multiple reference marks.
Additionally, the reference gauges are surveyed
and if found to be reading off by 15 thousands of a foot
or more, the reference gauges are adjusted to read
the correct gauge height.
A wire weight is surveyed by comparing the elevation
of the bottom of the weight, with the reading
on the wire weight done.
During site visits the condition of the control
is routinely documented.
The control is the part of the river holding the water back
in the pool that the stage sensor and reference gauges
are located in.
In this instance the control is a section control
that consists of cobbles and boulders
and is located 80 feet downstream of the gauge.
Any debris deposition, aquatic vegetation growth
or any obvious changes to the river bed are documented,
because these changes can have a significant impact
on the stage discharge relationship at the site.
Before leaving the site, data from the data logger
is manually downloaded.
At most sites, the data has already been transmitted
to the database and web via satellite.
However, the electronic data log is stored as a backup
and used to fill any gaps in the record.
The site power system
is routinely serviced during site inspections.
Gauge batteries are tested for charge and load capacity
and swapped with fully charged batteries when necessary.
Many USGS streamgages are powered by solar panels.
These panels need to be clean and facing
the correct direction to provide an adequate amount
of solar power to continuously power a streamgage.
For non submersible pressure transducers, desiccant must
be maintained in the air intake system in order to keep
the humidity inside the pressure sensor low.
Thank you for watching
our Routine Streamgaging Inspection video.
I hope you enjoyed this glimpse into some common field tasks
of the USGS hydrologic technician.