What Does a USGS Hydrologic Technician Do to Inspect Streamgages?

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Detailed Description

What do USGS Hydrologic Technicians do on the job? This video features two Hydrologic Technicians from the South Atlantic Water Science Center sharing how they inspect streamgages, which is an integral part of a Hydrologic Technician's work. This video was sponsored by the USGS Hydrologic Data Advisory Committee.
 

Details

Date Taken:

Length: 00:08:12

Location Taken: Asheville, NC, US

Video Credits

John Mazurek
Brad Huffman
Jake Wentz
Kyle Corcoran
Bill Hazell
USGS South Atlantic Water Science Center
Asheville Field Office

Transcript

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.