[Nathan Leber] In Texas, quite a bit of our water supply
is held in reservoirs across the state.
Over time, these reservoirs lose capacity
due to sedimentation.
We need to understand what our current capacity is
as well as our future capacity in those reservoirs,
to be able to properly plan
for our future water supply needs.
We offer sedimentation surveys
in addition to volumetric surveys.
The sedimentation survey is built upon
the volumetric survey.
The volumetric survey will tell us
what the current capacity is,
while the sedimentation surveys
show us what the capacity used to be
before the reservoir was impounded,
or the dam was built.
We can use these to project out a rate
of sedimentation over time
because we know what it started with
and we know what it's at now.
Once we have that rate, we can project into the future
and determine what the reservoir capacity
might be in 10 or 20 years.
Sedimentation is a natural process
that occurs in reservoirs across the state.
This happens when you have a rain event
and anything from a speck of dust
to a large boulder is washed into tributaries,
and these are ultimately trapped in our reservoir systems.
[Josh Duty] We will use a vibracore vibrator
with a 3-inch core tube attached,
and we'll lower that vibracore down
to the current bottom,
and basically we will vibrate that core tube
down into the ground until it stops.
Once it stops, we winch it back up
and at that point we remove it from the vibracore,
we measure it,
to determine how much sediment we collected
and we cap it.
And then we bring it back to the office
where we'll do post-processing.
Once the core is back to the lab for post-processing
we will cut the core tube in half,
and we'll analyze the unique sediment layers in that sample.
[Nathan Leber] Different layers are
made up of different types,
or textures, or colors of sediment or materials.
We look for things like roots or rocks
within those layers
to determine whether or not
that was a pre-impoundment surface
that was laid down prior to the reservoir being impounded
or if it was laid down after the reservoir was dammed.
[Josh Duty] Sedimentation is basically,
it's going to be land matter,
it could be anything from organic matter such as leaves;
it could be large woody debris,
different classifications of rock or gravel,
sand, silt, clay, a mixture of anything
that you could technically find land based.
[Nathan Leber] We work with river authorities.
We also work with water districts;
we work with cities.
Any manager or owner of water rights in a reservoir
can sponsor a survey with us.
Hydrographic surveys in Texas allow us to monitor
the state of our reservoirs.
This also helps us plan for the future water needs
of our state.
(upbeat music)