Download Karst Connections A Virtual Field Experience Click on a focus area

Karst Connections
A Virtual Field
Experience
Welcome to the Edwards Aquifer
Region. The three colors on the map
represent the Drainage Area (green),
Recharge Zone (blue), and Artesian
Zone (tan) of the aquifer. Learn about
all three zones and what the
Edwards Aquifer Authority does to
protect them by taking a virtual field
experience.
Click on a focus
area on the map to
zoom in and
investigate.
Welcome to Seco
Sinkhole
Click on the arrow to enter the
aquifer, or click the focus area
to learn about the Seco Creek
Recharge Enhancement
Project.
A sinkhole is a type of geologic
feature, created by the collapse
of a cave, or dissolution of the
bedrock found in karst terrains.
Karst topography describes a
landscape containing soluble
rocks typified by the presence
of caves, sinkholes, and other
natural dissolution features
produced by the interaction of
water, minerals within the rock,
and many other natural
processes.
Click the focus area
to learn more about
the recharge
project.
Back
The sinkhole is about 60 feet in
diameter at the surface
entrance with vertical walls. The
Woodward Cave Fault crosses
about 0.3 miles north of the
Seco Sinkhole and has a total
displacement of around 500
feet. There are 60 to 100 feet of
Edwards limestone below the
floor of the cave system above
the Glen Rose/Edwards
contact. The water level in the
cave is the approximate local
water table in the Edwards
Aquifer.
Click the arrow to continue the
repel.
Click the focus area
to discover
more about
aquifers.
Back
Upon entering the sinkhole
you’ll reach a ledge at about 90
feet, and then the bottom of the
cave at about 160 feet below
land surface.
The cave system has been
explored to approximately
4,000 feet. The main cavern
system was formed by the
solutioning of fractures in the
lower portion of the Edwards
limestone, aligned along the
northeast-southwest axis of the
Balcones fault system.
Choose an arrow to explore a
cave passageway.
Check out the left passage
Back
Check out the right passage
You’ve reached the water table
of the Edwards Aquifer!
The water table is the
uppermost surface of the water
filled zone within an aquifer.
Click the blue circle to find out
where the water goes after
entering the aquifer at the
recharge zone.
Click on the focus
area to see how the
EAA monitors
water quality.
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Having the right equipment can
make the difference between
an enjoyable field experience
and potential disaster.
Cavers typically carry three
dependable light sources with
them during expeditions. It’s
important to have backup
systems ready so you’re not
left in the dark.
Most Texas caves are on
private property and you must
always get the permission of
the landowner and be properly
trained prior to entering any
cave.
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The Edwards Aquifer is divided into
three hydrologic zones; the
drainage area, recharge zone, and
artesian zone. Rain that falls on the
drainage area, and that emerges
from various springs along the
Edwards Plateau enters several
streams and creeks that flow south,
crossing the recharge zone.
Precipitation and stream flow then
percolate through the highly porous
and permeable Edwards limestone,
exposed at the ground surface in
the recharge zone.
Once in the aquifer, the water
generally flows south and then east
towards large springs and other
smaller discharge points within the
artesian zone, or confined zone of
the aquifer.
You are here
Back
The Seco Creek Recharge
Enhancement Project
The Seco Creek Recharge Project,
completed on November 15, 1982,
was the fourth structure built by the
former Edwards Underground Water
District (EUWD) to enhance natural
recharge to the Edwards Aquifer.
The dam is 13 feet high, 310 feet
long, with the crest of the dam at
1,201 feet above mean sea level.
When Seco Creek is flowing at high
levels, excess water is diverted
through a man-made channel,
terminating at the entrance to the
sinkhole.
Recharge structures, on average,
contribute nearly 5000 acre-feet to
the aquifer annually.
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The Seco Creek Recharge Enhancement Project
Click on the arrow to see how the water reaches the sinkhole, or click on the focus area learn more about recharge stuctures.
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Two words that describe an aquifer’s
flow characteristics are porosity and
permeability.
Porosity refers to the amount of pore
(or open) space within a rock and
permeability describes how
interconnected those pores are with
each other, and how well water can
travel through it.
Connections
How would you describe the porosity
and permeability of this section of
the Edwards limestone? Does it
have low or high porosity? Could
water be easily transmitted through
this rock body?
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Water Quality Sampling
Every month the EAA samples
water quality from numerous wells
and springs from across the region.
In the middle – A team collects
storm water samples in an effort to
assess potential contaminants that
may be present in surface water
runoff generated by storm
events. The storm water sampling
effort was designed to assess what
changes in water quality occur
within each surface water system
during a storm event.
On the right – Surface water
samples are taken downstream of
San Marcos Springs to establish a
baseline of water quality within the
river system.
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Recharge Structures
The EAA operates four recharge
structures in Medina County on
the Edwards Aquifer Recharge
Zone. The total recharge for
each site is calculated using
data from Stage recorders near
these structures.
The approximate historical
median annual recharge
contributed by the combined
structures is 853 acre-feet,
whereas the approximate
historical mean annual recharge
contributed by the combined
structures is 4,970 acre-feet.
The dams slow down the creek’s
flow during rain events, giving
the impounded water more time
to percolate into the aquifer.
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Welcome to
San Marcos Springs
Click on the arrow to follow the
river’s course south of the
springs, or click on a focus area
to lean about the unique
attributes of San Marcos
Springs.
San Marcos Springs, located
just northeast of San Marcos,
comprise the second largest
spring system in Texas. Some
200 springs emerge from large
fissures and many smaller
openings at the bottom of
spring lake, along the San
Marcos Fault.
Click the focus area
to learn more about
the springs.
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The San Marcos River
Beginning with it’s headwaters at the
springs, the San Marcos River flows
south, eventually meeting its
confluence with the Guadalupe River.
The crystal clear waters offer habitat
to an endangered plant, the Texas
wild rice. Texas wild rice is only found
in the upper reaches of the San
Marcos River.
Riparian, or riverside habitat can be
adversely effected by exotic and
invasive species. Click on the
riparian focus area to learn more.
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Texas Wild Rice
Zizania texana
Texas wild rice exists in only one
place: a small segment of the San
Marcos River. In 1967, the plant was
headed toward extinction, with only a
single clump appearing anywhere in
the river. After a researcher began a
long-term restoration project of the
species, the plant began to again
appear in the water, favoring swift
currents, shallow areas near the
middle of the stream, and still pools of
water as much as ten feet deep.
Texas wild rice requires thermally
constant temperatures, clear water,
undisturbed stream-bottom habitat,
protection from floods, and
unimpeded light.
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Invasive Species
These elephant ear plants may look
lush and aesthetically pleasing, but
the are considered an invasive
species along the banks of the San
Marcos river and elsewhere in south
Texas.
An invasive species is a plant or
organism that has been introduced
into an environment where it
competes for food and/or habitat with
native species.
One component of the Edwards
Aquifer Habitat Conservation Plan is
to control non-native species by
removing them and replacing them
with native species.
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Spring Sampling
Water quality samples are taken a
few different spots at the springs.
This location is known as ‘San
Marcos Deep’. Divers take a
sampling tube more than 28 feet deep
to extract pure spring water from an
opening at the base of the lake.
Click on the samplers to learn more
about water quality parameters, or
click on the water to discover more
about sampling.
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Water Quality Parameters
This water quality meter takes four
different types of readings:
temperature, conductivity, dissolved
oxygen, and pH.
Parameters can give early indications
of water quality problems. For
example if a pH reading is coming
back too low or too high it could
indicate potential impact from an
accident spill or wastewater
discharge.
Back
Water Quality Sampling
Every month the EAA samples water
quality from numerous wells and
springs from across the region.
In the middle – A team collects storm
water samples in an effort to assess
potential contaminants that may be
present in surface water runoff
generated by storm events. The
storm water sampling effort was
designed to assess what changes in
water quality occur within each
surface water system during a storm
event.
On the right – Surface water samples
are taken downstream of San Marcos
Springs to establish a baseline of
water quality within the river system.
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Glass Bottom Boats
Years ago San Marcos Springs was
home to an amusement park featuring
Ralph the Swimming Pig, Mermaids,
an underwater submarine, and glass
bottomed boats.
The theme park is gone, but the boats
remain. Texas State University now
operates the boats and manages they
spring system at the Meadows
Center.
Click on the boat to look through the
glass, or click on the water to learn
about the endangered and threatened
species of San Marcos Springs.
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A Look Through The Glass
The glass bottomed boat tours offer
visitors to the springs a unique view at
the hydrogeological, and biologic
features below.
Numerous springs and a variety of
wildlife can be easily seen by peering
through the glass. Click on the glass
to get a view.
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Cream of Wheat Springs
The aptly-named Cream of Wheat
Springs can be easily viewed
through glass of the Meadows
Center boat.
These are high pressure springs
that add thousands of gallons of
water to Spring Lake each day.
Because of down faulting the
Edwards Aquifer drops deep below
land surface in the artesian zone.
The rocks above the Edwards are
relatively less permeable, creating
a confined condition that adds
pressure to the aquifer. Where
pressure is sufficient, and natural
faults or fractures or present, water
will be forced to the surface in the
form of springs.
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Endangered and
Threatened Species
San Marcos Springs is home to three
endangered, and one threatened
species: The Texas Blind
Salamander, San Marcos Gambusia,
Fountain Darter, and San Marcos
Salamander.
These species serve as indicators
These species serve as indicators to
health the health of the springs and
aquifer. Each need clean, fresh at a
near constant temperature springs
and aquifer. Each need clean, fresh
water at a near constant temperature.
If they begin to die out , what does
that say about our aquifer system? If
they begin to die out , what does that
say about our aquifer system?
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The Wetlands Boardwalk
Welcome to the wetlands
boardwalk, a floating dock that
extends out into the marsh area of
the springs.
Why are wetlands important?
What benefit do they bring to the
ecosystem? Enter the boardwalk
to find out…
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Wetlands
Some people may consider
wetlands to be useless swamp
land, but in fact wetlands play an
important role in the ecosystem
for a number of reasons.
Wetlands provide natural filtration
for runoff water entering the
system. The diversity of plants
here allows for the filtration of
many harmful contaminates as
the water slowing passes through
the dense cover. .
Check out two different views of
the wetlands area.
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Wetlands area, viewing
west.
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Wetlands area viewing
southwest.
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Welcome to Government
Canyon State Natural Area
Government Canyon State Natural
Area is a 9,084 acre preserve in
Northwest Bexar County, on all
three aquifer zones – Drainage,
Recharge, and Artesian.
The natural area was purchased
by Texas Parks and Wildlife in
1993, in cooperation with the EAA,
San Antonio Water System, the
Trust for Public Land, and the
federal government Land and
Water Conservation Fund.
(TPWD.state.tx.us)
Click the focus area
to learn more about
the canyon.
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Welcome to the Government
Canyon State Natural Area
Visitor Center
Government Canyon State Natural
Area provides excellent protection
for both the watershed and wildlife
within the Edwards Aquifer
Region. Much of the canyon is
situated on top of the highly
sensitive Edwards Aquifer
Recharge Zone.
A couple of things that make this
visitor center unique are it’s
examples of rainwater collection
and use of xeriscaping. Click on
red boxes to discover more.
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A Closer Look – Rainwater
Collection
Rainwater collection is the process
of capturing runoff water from
rooftops and other impermeable
surfaces with the use of cisterns
and smaller barrels.
The captured water can then be
later used for landscape watering
and other non-potable uses.
When equipped with special filters,
some home owners live
exclusively on the captured
rainwater.
Rainwater collection has gained
more popularity as the drought
continues and other water sources
have declined.
Connections
What are other alternative sources
of water besides the aquifer that
South Texas could utilize?
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A Closer Look – Xeriscaping
Xeriscaping uses a combination of
native and drought resistant plants
together with mulch or decorative
rocks
to
save
water
while
maintaining aesthetic appeal.
Drought resistant plants and mulch
can replace turf grass to save
hundreds or even thousands of
gallons of water for a home annually.
Connections
Some Cities, particularly in the
western United States, require
drought tolerant landscaping. Is this
a policy south central Texas should
consider? Why or why not?
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After a few miles of hiking down
the Joe Johnston trail, the mail
trail of Government Canyon’s
backcountry, you’ll encounter a
nice exposure of both the
Edwards (younger) and Glen
Rose (older) limestones.
Although the Glen Rose is also
limestone, it is relatively less
permeable than the Edwards and
serves as the lower confining
member to the Edwards Aquifer.
Take a closer looks to discover
some unique features within both
limestone formations.
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Trace fossils are the tracks, trails,
or borings of once living organisms.
(Hamblin, Christiansen 2004)
Trace fossils can be found
throughout the Edwards Aquifer
Region.
Connections
This dinosaur print is located in the
Glen Rose limestone, the first
geologic unit below the Edwards
limestone. What clues can this
trace fossil tell us about the relative
age of the Edwards limestone?
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Marine fossils can be found in both
the Glen Rose and Edwards
Limestones. Over millions of years
the bodies of ocean organisms
accumulated in layers on the sea
floor, eventually being compacted
and lithified, or converted into rock.
Connections
Try to determine the geologic
history of Texas based on the clues
found within the rocks. Hint – you
may want to check the other focus
area on the previous image to
determine the relative age of the
rock.
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Monitoring the Effects of
Drought
The photo on the left was taken in
2004, during a normal year for
precipitation. The photo on the
right is from 2013 after three years
of lingering severe to exceptional
drought. The water in the creek
originates from a series of small
springs within Government
Canyon.
Connections
What differences do you spot
between the two photos? What
effects, besides declining water
levels could prolonged drought
have on an ecosystem?
2004
Back
2013
References:
Adapted from Lukes, L. (2014, January). A new take on the field trip. The Science Teacher, 81(1), 24-29.
Hamblin, W. K., & Christiansen, E. H. (2004). Earth's dynamic systems (10th ed.). Upper Saddle River, N.J.: Prentice Hall,
Pearson Education.
Government Canyon State Natural Area. (2014, January 1). - Texas Parks & Wildlife Department. Retrieved April 30, 2014,
from http://www.tpwd.state.tx.us/state-parks/government-canyon
All photos copyright, Edwards Aquifer Authority, 2014.