(upbeat music)
[Josh Duty] I'm in a program that maps
reservoirs for the state
to help water-controlling authorities
or water resource managers
figure out how much water they have
for future generations with increasing population.
(gears clanking)
Hydrographic survey is basically a two-part survey
where you have the volumetric survey as one part
and then you have the sedimentation survey as a second part.
And depending on the needs of the client,
they can decide if they just want us
to go in and do a volumetric survey
or we can do both.
Volumetric survey is basically an inexpensive,
accurate way for water resource managers
or controlling authorities to determine current capacity
of the reservoirs by looking for current surfaces.
The current surface is the current bottom surface
of the reservoir.
Once you find the current surface, part of data analysis is
we go back in and calculate water storage capacity
as part of the report.
The data we collect often times can be used
for state and regional water plans.
The first thing that we do on a volumetric survey
is we have to generate a lake boundary.
And the way we do that is we take aerial photographs
and digitize what we would consider a current lake boundary.
Once we have our boundary,
then we create our preplanned lines or transect files
that are perpendicular to the historical river channel.
When we go out and survey, we basically go out,
we set up our equipment,
which is a multi-frequency single beam sonar,
and we calibrate that equipment.
We calculate speed of sound, using a velocity profiler.
And then, once we've calibrated,
we calibrate the transducer for depth.
So, we're making sure that if we're in 15 feet of water,
our transducer is reading 15 feet of water.
Once that's calibrated, then we're ready to survey.
Once we begin surveying,
we basically survey from bank to bank
across the reservoir.
And then, once that transect's finished,
we go to the next one
until we've mapped all the transects
throughout the reservoir.
From the boat, we're collecting depth data.
That data will be tied to a specific GPS coordinate
as we move across the reservoir.
So, each depth has a GPS coordinate tied to it.
And with one boat on the water
we can typically survey a thousand surface acres a day.
We finished Lake Travis in 21 to 25 days
and Lake Buchanan in about the same timeframe,
and those reservoirs average around 20,000 surface acres.
Once that data is collected, we bring it back to the office
and that's where our data analysts start
processing the data.
So, the data analysts actually go back in and run models
on that data to where they build a model
that shows the depth contours of the lake.
Reservoirs lose capacity over time
due to increased sediment levels
due to natural runoff and high-flow events.
We recommend surveying reservoirs every 10 years
or after a major high-flow event.
Completing hydrographic surveys for reservoir owners
as well as water resource managers
helps these entities
figure out water storage capabilities
for increased population growth.