(lilting acoustical guitar)
- [Voiceover] Texas decision makers work
to ensure that groundwater is available
for beneficial use today
and for the next generation.
Managing groundwater is the same
as managing any budget.
A household cannot continuously
spend more money than it earns.
In the same way, an aquifer cannot continuously
give more water than it is taking in.
- [Voiceover] Accounting for the groundwater budget
requires thinking about the water cycle.
The water cycle is the continuous movement of water
on, above, and below the surface of the earth.
Water that enters an aquifer from the surface
is called recharge.
Recharge includes rainwater that seeps down
through the soil to reach the water table.
Only a small portion of total precipitation
gets down this far.
Recharge also includes water draining
into the aquifer from streams and lakes.
Water that enters from another aquifer
is called inflow.
Inflows and recharge are comparable
to a deposit in a bank account.
They add to the overall wealth of an aquifer.
Water exiting an aquifer naturally or artificially
is called discharge.
Examples of naturally-occurring discharge
are evaporation, groundwater use by plants,
springs, leakage into streams or lakes,
and leakage from one aquifer to another.
The most common discharge from an aquifer
by humans is pumping.
Discharge is comparable to a withdrawal
from a bank account.
The amount of water inside an aquifer is called storage.
This is comparable to a balance in a bank account.
Any time we pump water from an aquifer
we are drawing down the water level
in the aquifer storage.
As long as the amount of inflows can replace
what we pump, drawdown is temporary
and does not affect water availability.
When inflows can't keep up with pumping,
we're depleting the aquifer.
Prolonged pumping and excessive inflows
reduces the amount of water in the aquifer
and as a result pumping becomes more difficult
and costly, as water most be lifted from increasing depths.
- [Voiceover] The Ogallala aquifer is located
in northwest Texas, and extends northward
into Kansas and Nebraska.
Since people began tapping its groundwater,
the aquifer has dropped an average of 105 feet.
This is an example of an aquifer
being steadily depleted by pumping.
- [Voicoever] Pumping can also impact water
that isn't underground.
Springs and streams can dry up
and no longer sustain wildlife and vegetation.
This is what has happened to Big Spring in West Texas.
It's spring has long gone dry,
but because of its significance to the town,
the illusion of a flowing spring is kept up
by piping in surface water.
Depletion of certain aquifers can cause the land above
to sink, making it susceptible to flooding.
This sinking, also called subsidence,
happens when too much water is removed
from an aquifer and void spaces that were
once filled with water become empty and collapse
under the weight of the rocks above them.
Subsidence is a serious concern
along the hurricane-prone Gulf Coast.
In parts of East Houston, land elevations
have dropped as much as nine feet since 1900.
In addition to pumping, contamination also affects
the amount of available groundwater.
A variety of activities may introduce contamination
into an aquifer, thus requiring costly treatment
or abandonment of the water source.
Contamination may also result from salt water
movement caused by pumping wells.
This is an obvious problem in Texas aquifers
that are close to the Gulf of Mexico,
but can also impact aquifers that are located far inland.
Some of these aquifers contain ancient
salt water trapped deep underground.
Drawing down deep aquifers can result
in migration of this ancient trapped salt water
into parts of the aquifer that previously contained
fresh water, causing a decline in water quality.
- [Voiceover] To tackle the challenges
of water level declines, the State of Texas
incorporates the best available scientific methods
in groundwater management and planning.
A critical component in the State's planning process
is the Texas Water Development Board's
Groundwater Availability Models Program.
Groundwater availability models are computer programs
that simulate groundwater flow.
They account for the amount of water
entering as a credit, or deposit,
the amount of water leaving as a debit, or withdrawal,
and the amount of water remaining in an aquifer
as the balance.
These models can be used to predict
the impact of large pumping activities on an aquifer.
Because groundwater systems are complex,
these models require extensive amounts
of information to represent the many different
physical properties in an aquifer.
Scientists from the Texas Water Development Board
collect and organize data associated with
groundwater and aquifer properties,
including groundwater levels, well drilling reports,
pumping records, and rock and sediment types.
They add it to data on streams, lakes,
springs, precipitation, climate,
surface water runoff, geologic structure,
vegetation maps, root depth,
evaporation, and more.
- [Voiceover] This information is analyzed,
to quantify aquifer properties and groundwater
inflows and outflows.
The product of this analysis
is a groundwater availability model
of an aquifer system.
The model is used to answer a series
of "what if" questions.
For instance, what happens to an aquifer
if a city increases pumping to satisfy
its growing population?
How much does it impact the flow from a nearby spring?
How much will water levels fall in the aquifer
due to increases in pumping or due to
the placement of large well fields?
The scientists use model simulations
and then interpret numerical output from the model
to answer these questions.
The models generate numbers
that require review and interpretation.
The scientists checks the outputs
to ensure that they reflect reality.
This is often done by comparing model results
against real world measurements,
such as water levels of monitoring wells.
Numerical model results may be converted into graphics.
For instance, water level predictions can be
graphed on charts, plotted on maps,
or even animated in three dimensions.
But most important of all, groundwater availability
models are critical scientific tools
that state and local authorities and citizens
can depend on when making decisions
on groundwater use.