San Antonio Springs is the name of a cluster of springs in Bexar
County, Texas. These springs provide a large portion of the water
for the San Antonio River, which flows from San Antonio to the Gulf
of Mexico.
The San Antonio Springs are located about three miles (5 km)
north of downtown San Antonio; most are now on the property of the
University of the Incarnate Word. The springs are fed by water from
the Edwards Aquifer; this water reaches the surface through faults
along the Balcones Escarpment. There have been more than 100
individual springs identified, but many of these are no longer
active due to pumping demands on the Edwards Aquifer and
sedimentation from the upstream Olmos Creek. During periods of
drought, the springs sometimes stop flowing entirely, only to
resume when water levels rise in the aquifer. The mean flow from
the springs is 20 ft³/s (0.6 m³/s).
The Edwards Aquifer is one of the most prolific artesian
aquifers in the world. Located on the eastern edge of Edwards
Plateau in the U.S. state of Texas, it discharges about 900,000
acre feet (1.1 km³) of water a year and directly serves about two
million people. The Edwards Aquifer is also home to several unique
and endangered species. The aquifer's recharge zone, where surface
water enters the aquifer, follows the Balcones Fault line, from
Brackettville (roughly along U.S. Highway 90), through San Antonio,
and north to Austin along but a few miles west of Interstate 35. On
certain stretches of highway in Austin, signs indicate that the
driver is entering or leaving the recharge zone, as the zone's
easternmost sits beneath heavy urban and suburban development. Its
contributing zone, where shed water is transported near the surface
to the recharge zone, extends about 40 miles (64 km) north of the
recharge zone at the west end, and tapers to end at a point in the
east. The artesian zone, where water springs from wells naturally
due to the higher elevation of the recharge zone, extends
10–20 miles (16–32 km) south on the west end to only a
few miles south on the east end. Across the eastern half of the
aquifer, the recharge and artesian zones occupy common area. The
Aquifer has a recharge zone of 1,250 square miles. Most of the
water (75%-80%) that is in the Aquifer originated from some of the
creeks and rivers flowing in the area. Two creeks that flow into
the Aquifer are the Cibilo and Helotes Creeks.
The Edwards Aquifer is an underground layer of porous,
honeycombed, water-bearing rock that is between 300-700 feet thick.
It includes the Edwards and some associated limestones. The San
Antonio segment of the Aquifer extends in a 160 mile arch-shaped
curve from Brackettville in the west to near Kyle in the northeast,
and is between five and 40 miles wide at the surface. At these two
locations, groundwater divides separate the San Antonio segment of
the Aquifer from other Edwards limestones, so their waters do not
mix. The Barton Springs segment extends from Kyle to south Austin.
The San Antonio segment is where most of the major natural springs
occur, where much of the use by humans takes place, and where the
issues are most hotly-debated. A few major Edwards water features
like Barton Springs and San Felipe Springs occur on the other side
of the groundwater divides, to the north and west of San Antonio
portion.
The Aquifer is divided into three main zones: the contributing
zone, the recharge zone, and the artesian zone. The contributing
zone occurs on the Edwards Plateau, also called the Texas Hill
Country. It is about 5,400 square miles, and elevations range
between 1,000 and 2,300 feet above sea level. The rugged, rolling
topography is covered with thick woodlands of oak and cedar. Today,
the Edwards Plateau bears little resemblance to the prairies the
pioneers to the area saw, but it is home to several endangered
species and is itself the subject of increasing environmental
concerns. The contributing zone is also called the drainage area or
the catchment area. Here the land surface "catches" water from
rainfall that averages about 30" per year, and water runs off into
streams or infiltrates into the water table aquifer of the plateau.
Runoff from the land surface and water table springs then both feed
streams that flow over relatively impermeable limestones until they
reach the recharge zone.
The San Antonio River is a major waterway that originates in
central Texas near San Antonio and follows a roughly southeastern
path through the state. It eventually feeds into the Guadalupe
River about ten miles from San Antonio Bay on the Gulf of Mexico.
The river is 240 miles long.
Questions to answer:
- If the river was flowing at this time, how far above the
aquifer would you be? (Use your GPS altimeter)
- Two different man made rings were made around the springs. What
kind of rock was used for each one?
- If the water is not flowing were does the water come from to
start the San Antonio River?
