Download Geology of the Playas and Ogallala Aquifer of the Llano Estacado

Geology of the Playas
and Ogallala Aquifer
of the Llano Estacado
by Steven Schafersman, PhD, Geology
CyberComputing Sciences
Introduction to the
Llano Estacado
The Llano Estacado is Spanish and
literally means the Staked Plain or Plain
of Stakes. But "staked" or “stakes” for
several reasons that have long been the
subject of controversy.
The region was named the Llano
Estacado by Spanish explorer Francisco
Vasquez de Coronado in 1541, when he
crossed what is now the Texas
panhandle. The name still holds today,
but why he named it this is not clear.
Pronounce the name as the Spanish do:
“Yano Estacado,” not “Lano Estacado.”
Introduction to the
Llano Estacado
The most common explanation is that the original Spanish explorers
would drive stakes into the ground to mark their trail to find their way
back, a common practice when exploring an unknown flat, featureless
landscape, which certainly describes the Llano Estacado.
A second idea has it that Coronado’s men had to tether their horses at
night using stakes, because if they wandered off they couldn’t be tracked
on the soft, short grass.
A third suggestion is that the abundant yucca stalks make it appear that
the land is “staked.”
Playas and Playa Lakes
There is a fourth explanation. Spanish explorer Francisco
Vasquez de Coronado in 1541 was the first European to see the
playa lakes. He named them playas because some playas have
sandy shores, and playa means “beach” in Spanish. Coronado’s
trail through the Texas Panhandle—only 49 years after Columbus
discovered the New World for Spain—is the brown one on the
map above. He also was the first European to visit the Pueblo
Indians of New Mexico.
Introduction to the
Llano Estacado
The fourth hypothesis is that the original word was Estacando, not Estacado.
This word means “stagnant,” “pond,” or “many ponds,” and if this hypothesis is
correct, would refer to the many thousands of playa lakes that are a prominent
feature of the Llano Estacado.
Coronado was the first European to see playas. The small ponds eventually dry
up and become stagnant mud pits before turning into typical dry playas. A
simple misspelling may explain it all. Coronado intended to name the region the
Llano Estacando, the “Plain of Many Ponds,” but somehow the “n” got left out
of the name by mistake, leaving it spelled Estacado!
Unfortunately, no one knows precisely which of these explanations for the
origin of the name Llano Estacado is correct!
Introduction to the
Llano Estacado
Where is the Llano Estacado?
The Llano Estacado is about ¾ in
West Texas and ¼ in eastern New
Mexico. The cities of Amarillo,
Lubbock, and Midland are printed
in red. It is bounded on the north by
the Canadian River, on the
southwest by the Pecos River, on
the east by the Caprock
Escarpment, and on the west by
the Mescalero Escarpment.
Introduction to the
Llano Estacado
What is the Llano Estacado?
The Llano Estacado is a plateau, a
regional landmass consisting of
horizontally-bedded sedimentary rocks or
strata that stands higher in elevation than
the surrounding land areas.
Some plateaus are the result of regional
uplift, while others—like the Llano
Estacado—are the result of the
differential erosion of surrounding land
areas, leaving the plateau higher only
because the surrounding land has eroded
downward.
Introduction to the
Llano Estacado
The best example of an uplifted plateau in
the United States is the giant Colorado
Plateau of southern Utah and Colorado and
northern Arizona and New Mexico, the
famous Four Corners Area.
The Llano Estacado is a smaller version of
the Colorado Plateau, but there are some
important differences. In particular, the
Colorado Plateau was uplifted by tectonic
forces while the Llano Estacado sits higher
only because the surrounding land has
eroded downward.
Introduction to the
Llano Estacado
Characteristically, millions of years of
weathering and erosion create
beautiful and scenic landforms on
plateaus, such as canyons, buttes,
mesas, and pinnacles.
Depending on the age and timing and
amount of uplift, these landforms can
have high relief (relief is the difference
in elevation between the highest and
lowest areas) as in the Colorado
Plateau, seen in the photo at right.
The famous East and West Mitten
Buttes in Monument Valley, Arizona.
Note the high relief.
Introduction to the
Llano Estacado
Landforms can also have low
topographical relief, as is the
case with the Llano Estacado.
Low relief means the area is
relatively flat (see photo), and
this certainly characterizes the
Llano Estacado.
Topography refers to mapping
the land in terms of elevation
and relief, so a topographic
map shows a region’s
elevation and relief to one who
can read it. The entire U.S. has
been mapped topographically.
Rattlesnake Racetrack, just off
Rankin Highway in Midland County,
has low relief.
Introduction to the
Llano Estacado
Canyons on the Colorado Plateau are
deep with steep canyon walls, such as
the Grand Canyon, but “canyons” on
the Llano Estacado are relatively
shallow with gentle slopes and low
bluffs that can simply be termed stream
valleys (or draws), not canyons.
The reason is because the Colorado
Plateau has undergone recent uplift, so
erosion now is extremely active, while
the Llano Estacado has never uplifted,
so erosion by now has worn down the
land to a condition of low relief.
Playa Lake on the Llano Estacado.
Note the shallow depression on
otherwise flat topography (low relief).
Introduction to the
Llano Estacado
High relief in the Llano Estacado?
Yes! The Llano Estacado does have some
areas of high topographic relief. These are
found along the edges of the plateau, where
the land drops precipitously from the top of
the plateau to the valley below. These steep
edges or cliffs are called escarpments. The
eastern edge in Texas is the Caprock
Escarpment, and the western edge in New
Mexico is the Mescalero Escarpment. The
escarpments were created by headward
erosion by streams cutting into the Llano
Estacado.
Introduction to the
Llano Estacado
High relief in the Llano Estacado?
The Caprock Escarpment near Amarillo
and Canyon, Texas, is so scenic that a
state park was created to protect the area:
Palo Duro Canyon State Park. The small
Prairie Dog Town Fork of the Red River
created the huge Palo Duro Canyon by
slowly cutting into the Caprock Escarpment
over millions of years. Spectacular
landforms, such as famous Lighthouse
Rock at left, can be found in the park.
Introduction to the
Llano Estacado
Palo Duro Canyon State Park
The Caprock Escarpment is visible in
the photo at right. This wall of
horizontally-layered sedimentary
rock is the eastern edge of the Llano
Estacado. The red color indicates
that the sediments were originally
deposited in non-marine
environments, such as river channels
and alluvial plains, and contain an
oxidized form of iron called hematite
(blood-mineral), a mineral which is
ground to form a red pigment.
Introduction to the
Llano Estacado
The Mescalero Escarpment
The Mescalero Escarpment is
visible in the photo at right. This
wall of horizontally-layered
sedimentary rock is the western
edge of the Llano Estacado or
southern High Plains. Here it
drops off into the Pecos River
Valley just south of Tucumcari,
New Mexico. Once again, note
the considerable topographic
relief between the top of the
plateau and the river valley
below.
Introduction to the
Llano Estacado
Characteristics of the Llano Estacado
The Llano Estacado plateau occupies approximately 37,000 square
miles (22 million acres). It is larger than the combined states of
Maryland, Massachusetts, New Jersey, and Rhode Island, and
larger than the single state of South Carolina! The region is devoid of
native trees except for the tiny shin oak and mesquite. As the
Southern High Plains, the Llano is cut off from the Great Plains to
the north by the Canadian River Valley. The Llano slopes gently to
the southeast by 8-10 feet per mile. With no geological relief, the
only changes in elevation are the approximately 34,000 shallow
depressions called playas. The Llano Estacado is the largest,
isolated non-mountainous geological area in North America, which is
why endemic plants and animals are found here.
Introduction to the
Llano Estacado
Most students are told that we live in the Permian Basin, but they do not
know what the Permian Basin really is. Also, isn't a basin a depression
rather than an elevated area? The Permian Basin is actually a sedimentary
rock sequence, with horizontal (flat-lying) strata (sedimentary rock layers)
found deep underground. Millions of years ago, the Permian ocean basin
was depressed, filled with marine water, and collected sediment, but now
we live on top of the rocks of the Permian Basin, not in it.
Introduction to the
Llano Estacado
The Permian Basin
The “Permian Basin” is actually an
informal name that describes a
number of subsurface geologic
features: the Midland Basin, the
Delaware Basin, the Central Basin
Platform between them, and
several mountain ranges composed
of the same strata that have been
uplifted by various events that are
scattered around and inside the
major basins. The name “Permian
Basin” was given to this area
because it contains an enormous
amount of oil and gas found
primarily in strata of Permian age.
Introduction to the
Llano Estacado
Most of this Permian strata (stratified sedimentary rock) is deep
underground and isn’t visible anywhere on the surface except in mountain
ranges where it has been uplifted and eroded, such as the Guadalupe
Mountains, adjacent to the Llano Estacado.
So we don’t really live in a basin or depression, we live on an
elevated plateau created by differential erosion. We don’t live in the
Permian Basin, we live on the Llano Estacado!
Introduction to the
Llano Estacado
Description of the Llano Estacado
The Llano Estacado is an elevated plateau—created by differential erosion of
surrounding rock—in a dry region of the United States, so its habitats are
characterized by slight elevation or depression, low amount of water, and the
consequences of wind and water erosion.
Availability of water is the most important factor. Most threatened animal
species on the Llano Estacado are endangered because humans have taken
so much groundwater that springs have dried up, not because of over-hunting.
Excessive groundwater removal is an example of habitat destruction, the most
common reason why plants and animals become endangered or extinct.
Introduction to the
Llano Estacado
The Llano Estacado is a semi-arid region that receives more
rainfall than arid regions, such as deserts, but less rainfall
than moist or wet regions, such as forests. A desert receives
between 0 and 10 inches of rain a year, and a forested
region receives over 30 inches a year. So, a semi-arid
region—usually a grassland—receives between 10 and 30
inches (25-75 cm) of rain annually.
The amount of rainfall is one of the two primary controls on
biomes, ecosystems, and habitats. The other is temperature,
controlled by either latitude or altitude (elevation).
Introduction to the
Llano Estacado
Temperature and rainfall amount (mean annual temperature and precipitation)
have been carefully measured by scientists and are used to describe ecological
zones and regions. The chart above—a climograph—illustrates this concept.
Introduction to the
Llano Estacado
The Southern Great Plains was originally
short-grass and mid-grass prairie.
Domestic cattle were introduced to the
region in the 1870s by the first ranchers—
grazing on endless square miles of
grasses—and most crops started to be
cultivated during the 1920s. Overcultivation and over-grazing of the land
replaced the drought-resistant natural
plants with crop plants that required
abundant rainfall, making the topsoil
susceptible to wind erosion when the
1930s drought began.
Introduction to the
Llano Estacado
The massive wind erosion of the loose
topsoil resulted in the “Dust Bowl,” a period
of great hardship for the farmers that forced
many of them to leave the region and
migrate to California in the later 1930s.
The Dust Bowl wind erosion damage was
centered in two areas: (1) the Llano
Estacado in Texas and (2) southeastern
Colorado and southwestern Kansas. The
land must be constantly protected to
prevent further damage.
Introduction to the
Llano Estacado
Water is also the primary agent
responsible for erosion and the
creation of landforms. This is true
even in deserts, a fact that most
people don’t realize (they
incorrectly think wind is totally
responsible). All of the canyons,
gorges, buttes, mesas, pinnacles,
and columns of desert regions are
the result of water erosion, not wind
erosion, acting slowly over time.
The photos at right show the effects
of water erosion in a semi-arid
region.
Palo Duro Canyon State Park, Texas
Habitats of the
Llano Estacado
Canyons and “The Breaks”
“The Breaks” are the semi-arid
canyons that cut into the eastern
and western edges of the Llano
Estacado Plateau, the Caprock
and Mescalero Escarpments.
Here, water erosion over
millions of years has sculpted
the brightly-colored rocks into
spectacular landforms, providing
an unlimited number of niches
and microhabitats for organisms.
Introduction to the
Llano Estacado
Water is abundant in the Llano
Estacada only in aquifers, streams,
springs, and playa lakes, not in rainfall.
In the case of the playas, the water is
ephemeral, that is, the water is not
permanent but rather seasonal or even
episodic, lasting only for a few weeks or
months.
Despite the temporary nature of this
water, it is nevertheless very important
for the plants and animals of the region
and their habitats. Birds use this water
during their migrations, for example.
Playa Lakes, Llano Estacado
Playas and Playa Lakes
Playa lakes are the
unique, freshwater
wetlands of the
Southern Great Plains.
Playas are circular
depressions
on clay soil that hold
water for several
months after a rain.
There are about 30,000
playas and playa lakes
on the Llano Estacado
Playas and Playa Lakes
The existence of playas
is closely associated
with both rainfall and the
freshwater aquifer of the
region, the Ogallala
Aquifer.
Playas dot the
landscape on the High
Plains states, providing
a unique natural
resource.
Playas and Playa Lakes
The number of playas in the
Great Plains has been
estimated to be between
25,000 and 50,000. Most of
these, about 85%, are found in
the Southern High Plains, that
is, on the Llano Estacado.
Along with the prairie
grasslands, the playas are the
major, defining habitat of the
Llano Estacado.
Playas and Playa Lakes
Scattered across the western
prairie landscape are thousands of
playa lakes. Playa lakes are the
most numerous wetlands in the
region, totaling more than 40,000
in eastern New Mexico, Colorado
and Wyoming, western Kansas,
Nebraska and Oklahoma, and the
Texas Panhandle combined. More
than 95 percent of the world's
playa lakes are located in the
western Great Plains.
Playas and Playa Lakes
Thousands of small playas with
clay soil dot the Llano
Estacado. Playas are circular
depressions; when filled with
rain water, they are termed
playa lakes. Playas are actually
small, round, and shallow
individual wetlands that
average 17 acres in size. They
have clay-lined basins and
naturally fill with water
periodically from rainfall and its
associated runoff. These small
depressions hold water for
several months after a rain.
Playas and Playa Lakes
To get a good idea of the number
and distribution of playas on the
Llano Estacado, please examine
this map of the playas around
Lubbock, Texas. Much of the Llano
is covered by this density of playas.
Note that these rounded playas are
not very large—most average about
17 acres in area. Also, remember
that these playa “lakes” are only
filled with water in the spring and
early summer. They are shallow, dry
depressions most of the year.
Playas and Playa Lakes
Playas on the Llano Estacado
provide over 400,000 acres of
wetland habitat. Playas and playa
lakes occupy only approximately 23% of the total landscape, but they
are vital for the survival of many
birds, mammals, and many other
plants and animals. Playas support
37 mammal species, more than 200
bird species, 13 amphibian species,
124 aquatic invertebrates, and more
than 340 species of plants.
Playas and Playa Lakes
Playa lakes may be the
most important wetland
habitat type for birds on
the Great Plains. Playas
are wintering places for
many species of ducks,
geese, and cranes. In the
summer, some ducks and
wading birds nest in or
near playas with water.
Playas and Playa Lakes
Playa lakes are a vital habitat
for wildlife, especially for
migrating birds that depend on
the region's resources to
"refuel" for their journey
between Canada, the United
States and South America.
More than 200 species of
birds use playas during the
breeding, wintering or
migrating seasons.
Given the diversity of wildlife found on playas, the wetlands offer rich experiences
for wildlife-watchers, photographers, and other naturalists.
Playas and Playa Lakes
Big salt playas (playas with very
alkaline or salty water) are not as
common on the Llano Estacado.
Thousands of Sandhill Cranes
winter on the salt playas from
Muleshoe to Midland. No plants
live on the bottom of a salt playa.
The cranes do not feed on playa
vegetation, but fly to them to roost
at night for protection from
predators. During the day, they
feed on surrounding fields, then
return to the playa in the evening
to roost for the night.
Watching the flocks of Sandhill Cranes fly in to
roost in the evening is one of the great local
birding sights.
Playas and Playa Lakes
Playa lakes are shallow,
usually round, wetlands with
clay floors that lie in the
lowest point of a generally
large, closed watershed and
collect rainfall and associated
runoff from surrounding
uplands. Their average size is
17 acres, and all playa lakes
combined make up about 2 to
5 percent of the total western
prairie landscape.
Playa lakes in the Texas Panhandle.
Playas and Playa Lakes
The majority of playa lakes are
located in or adjacent to farms,
grazing lands and feedlots,
which can create a number of
impacts on playas including:
pesticide and fertilizer runoff,
contaminants from feedlot
runoff, overgrazing, and
sedimentation. Sedimentation
is the primary threat to playa
lakes. Sediment runoff into
playa basins reduces the
volume of water they can hold
and may disrupt the wet-dry
cycles necessary for
vegetation growth.
Playas and Playa Lakes
Additional impacts on playas
include: development, oil field
water dumping, and altered water
cycles and basin structure. Most
playa basins have been
manipulated to increase storage
capacity for irrigation purposes.
The presence of additional water
from irrigation runoff also alters
natural playa hydrology. Many
playas are pumped for irrigation
(photo at right).
Playas and Playa Lakes
Playas are ephemeral, or
seasonal, in nature and hold
water only after rainfall or
runoff events. Most of the time,
they are dry, which is partially
why many people don't
recognize them as wetlands.
Playa lakes are sometimes
mistakenly referred to as
buffalo wallows, mud pits or
evaporation pans. But they
are, in fact, an important type
of wetland that is essential for
the natural health of the land,
plants, and animals.
Playas and Playa Lakes
Plants in clay playas must adapt to being
covered with water for months in the
spring and early summer, and then being
dry for many more months the rest of the
year. Note the mud cracks in the dry playa
at right, into which rain water can infiltrate
and recharge the aquifer.
Playas and Playa Lakes
The landscape of Texas is subject to frequent episodes of belowaverage precipitation and recurrent intervals of prolonged,
severe drought. Since 1996, much of the west-central portion of
Texas has experienced severe drought conditions with annual
precipitation falling to less than 60 percent of normal. Drought
has affected regional ranching operations and the harvests of
important cash crops. In addition, statewide reservoir storage
levels have fallen to a 16-year low in a state experiencing a
booming economy and rapid population growth.
Playas and Playa Lakes
Playa Lakes in Texas High Plains
An even closer inspection of drought
conditions is offered by the imagery
acquired by the LANDSAT Earthmapping satellite. During the early
summer of 1999, substantial rainfall
occurred in the High Plains from the
area near Lubbock north to Amarillo.
Water accumulated in small playa
basins throughout the region. By the
winter of 2000, however, following
several months of reduced rainfall,
dramatic changes were visible in the
concentration of surface water. Many
basins have completely dried by early
January.
July 5, 1999
January 13, 2000
Playas and Playa Lakes
August 6, 1999
January 13, 2000
Decreasing Water Availability
Larger playa basins and reservoirs in the southern High Plains exhibit similar changes during
the same period. LANDSAT imagery registered to the same coordinate system can be used
for change detection analysis of surface water availability during drought conditions.
Information of this kind forms a valuable supplement to field reports of rain gages, water well
levels, stream flows and reservoir capacities. Note above how playa lake shorelines have
retreated due to lack of rainfall during drought conditions.
Playas and Playa Lakes
An important natural resource in
any state are its aquifers. Aquifers
are bodies of rock just below the
surface which contain fresh water.
If you drill a well into the aquifer,
the well bore will fill up with water
that you can pump.
The top of the water in the well
and the aquifer are at the same
depth. This depth is termed the
water table.
The land above the aquifer is
called the recharge area. This is
where rainwater enters the aquifer
and keeps it filled.
Introduction to the
Llano Estacado
Most of the habitats and organisms of
the Llano depend on the presence of
water during some time of the year.
Aquifers are fresh water-bearing rocks
in the shallow subsurface. In this case,
the water is not ephemeral, but
constant. However, it is recharged by
rainfall at slow rates, and is thus
subject to being extracted too quickly
for replacement. Springs are fed by
aquifers, and the springs dry up when
the aquifers become depleted due to
drought and human over-use. This is
the case on the Llano Estacado.
Playas and Playa Lakes
The Ogallala Aquifer (pronounced
oh-ga-la’-la) is one of the largest
aquifer systems in the world. It
stretches across all or portions of
eight states generally from north to
south to include South Dakota,
Nebraska, Wyoming, Colorado,
Kansas, Oklahoma, New Mexico,
and Texas, and underlies about
174,000 square miles. The aquifer is
named after the formation it
occupies, and this was named in
1899 after the town of Ogallala,
Nebraska.
Introduction to the
Llano Estacado
Development of irrigation technology during
the 1940s enabled the exploitation of the
Ogallala Aquifer, now being depleted at
unsustainable rates. Since World War II, the
Llano Estacado has experienced expanded
cultivation, making the Llano one of the most
agriculturally-impacted regions in the
Western Hemisphere.
North of the Canadian River near Amarillo,
the Ogallala Aquifer is recharged in the
foothills of the Rocky Mountains. But only
rain that actually falls on the Llano Estacado
recharges the Ogallala Aquifer here, so it
has been depleted much more rapidly.
The Ogallala Aquifer
Introduction to the
Llano Estacado
Another name for the Ogallala Aquifer is the
High Plains Aquifer. Remarkably, this
enormous aquifer lies beneath the driest
grassland in the United States, allowing it to
be used for agriculture irrigation, even during
cycles of drought. This is one of our country’s
greatest natural resources, but few people
know about it, and few protect it.
Cotton, wheat, corn, and sorghum are the
dominant crops, all watered using
groundwater from the aquifer. Livestock are
grazed on the uncultivated rangelands.
The High Plains or Ogallala Aquifer
Introduction to the
Llano Estacado
The Ogallala or High Plains
Aquifer is the largest aquifer
in the world. Much of the
water taken from this natural
resource was unregulated by
either state or federal
agencies. Before depletion
became a problem, the
Ogallala held more fresh
water than all the lakes and
streams on Earth.
Water Saturation of the Ogallala Aquifer
Introduction to the
Llano Estacado
The law in Texas allowed
landowners to extract as much
groundwater as they wished,
and many took too much. The
result was a depletion of the
aquifer, lowering its top (the
water table) hundreds of feet
since the 1940s when irrigation
began. Now, this great aquifer is
in danger of permanent damage.
This law—termed the right of
capture—is still in effect!
Depletion of the Ogallala Aquifer
Playas and Playa Lakes
Texas has many major and minor
aquifers. Two of the largest are the
Ogallala Aquifer (blue) and the
Edwards Aquifer (light green)
shown on the map at left.
The Ogallala Aquifer underlies the
Llano Estacado is the major
source for irrigation water to
support agriculture in this area.
Most crops could not be grown
here without irrigation water from
the aquifer.
Note the location of the Ogallala
Aquifer in Andrews County.
Playas and Playa Lakes
The map of Texas Minor Aquifers shows
a second aquifer in Andrews and Ector
County, the Dockum Group, which is
Triassic in age and lies beneath the
Ogallala Aquifer in this region.
MRT, June 3, 2008, p. 1A, WCS officials
continue education campaign,
“…information from a geologist about
how the site is dry and does not sit over
an aquifer.” “In this particular area, there
are no active geological processes that
would compromise the site.” Geologist:
Robert M. Holt, U Miss. Is this statement
really true?
Current active geological processes:
earthquakes, fracturing, wind erosion,
stream flooding, water erosion.
Playas and Playa Lakes
The Ogallala Aquifer lies relatively near the land surface in most of
its area with a maximum thickness of about 1,000 feet with a few
hundred feet more the norm. Even in those areas of only a few feet
of thickness, the aquifer can almost always be counted on to yield
water to a well drilled into it. Some wells yield only a few gallons of
water per minute, while others yield 1,000 gallons of water per
minute or more. The Ogallala Aquifer not only includes the portion
of the Ogallala that is saturated with water, but may also include
saturated portions of the overlying and underlying formations that
are hydraulically connected to the Ogallala. Water in the aquifer on
the Southern High Plains flows from northwest to southeast at
about 150 feet per year under natural conditions. This rate of
movement can be altered by discharge from the aquifer by
pumping wells.
Playas and Playa Lakes
Deposition of the Ogallala Formation began 10 to 12 million years ago
during late Tertiary (Miocene/Pliocene) geologic time. Sand, gravel, silt,
and clay eroded from upland areas to the west and north were deposited
over the land surface of the present-day High Plains by primarily eastward
flowing streams. The surface on which the sediments were deposited
would have been much like the present area located east of the High
Plains escarpment characterized by low hills, relatively shallow valleys,
and meandering streams. The uppermost layer of the Ogallala Formation
is typically a caliche layer described as the “Caprock Caliche.” This layer
locally varies in thickness and has been reported to be as much as 60 feet
thick in some areas. The caliche layer formed about one million years ago
after the land surface stabilized and soils formed.
Playas and Playa Lakes
Playas and Playa Lakes
Playas and Playa Lakes
Playas and Playa Lakes
Playas and Playa Lakes
Playas and Playa Lakes
The Ogallala Aquifer underlies
approximately 174,000 square miles of
the Great Plains region, primarily in
Texas, New Mexico, Oklahoma,
Kansas, Colorado and Nebraska. The
Ogallala has long been a major source
of water for municipalities, industries,
and most notably agricultural
development since the turn of the
century. In 1990, the aquifer was
measured to contain about 3.270
billion acre-feet of water. Pumping for
irrigation is the primary use of the
aquifer. In 1949, the Ogallala irrigated
3 million acres; by 1997 it irrigated 14
million acres.
Playas and Playa Lakes
The natural recharge rate for the Ogallala Aquifer on the Llano
Estacado is ¾ inch a year, far less water than is being removed each
year for irrigation. Consequently, the aquifer's water supply has
declined steadily since the 1940s. Recent measurements show a 1.35
feet drop per year from 1992 to 1997.
Use of the Ogallala began at the turn of the century, but the rate was
small, probably not greater than recharge. During World War II,
however, irrigation technology improved, and reliance on the Ogallala
now steadily increased. During this time, the Ogallala water supply
progressively declined: From 1950 to 1980 water levels dropped 9.9
feet, and from 1980 to 1999 they dropped 3.2 feet, according to the
U.S. Geological Survey.
Playas and Playa Lakes
Although current dry land farming
techniques have resulted in
reduced pumping, the amount of
groundwater being withdrawn still
greatly surpasses the aquifer's
natural rate of recharge. In many
places in Texas, the water table—
the top of the water level in the
Ogallala Aquifer—has dropped
hundreds of feet, and pores in the
rock are in danger of collapsing or
being permanently damaged.
Playas and Playa Lakes
Over the past several decades, researchers have gathered
substantial evidence pointing to playas lakes as the primary
source of recharge for the Ogallala Aquifer. This is big news for
western Great Plains states, which have relied on pumping the
Ogallala for agricultural, municipal and industrial use since the turn
of the century.
Although this research has been going on for quite some time, the
results are relatively unknown to the general public and even to
conservation professionals. Since about 99 percent of playa lakes
are located on private land, this information is crucial for farmers,
ranchers, and natural resource managers who hope to conserve
water and maintain agricultural economies of the region.
Playas and Playa Lakes
Examine the cross-section of an idealized playa above. The playa is shallow,
only 1’-3’ deep. The water (blue) enters from the surrounding watershed when it
rains. These watersheds are usually agricultural land, so the entering water can
contain chemicals. The water is held in the playa by a clay layer (brown) that
gradually thickens over the years. The clay comes from sediment mixed in the
water from the surrounding land. The water in the playa lake both slowly
evaporates and infiltrates, and the playa gradually dries up.
Playas and Playa Lakes
According to studies conducted in the Southern High Plains region of Texas
and New Mexico, natural recharge occurs throughout much of the landscape
above the Ogallala Aquifer but is focused through playa wetlands. When a dry
playa lake receives rainfall or associated runoff, water flows into the playa
basin and penetrates the clay layer through deep cracks and plant root
openings in the floor. Water then flows through fissures in the cap rock layer,
ultimately reaching the Ogallala formation. Cracks in the playa lake floor
eventually swell shut as the clay absorbs more water, limiting or diminishing
recharge through the basin.
Playas and Playa Lakes
Aquifer recharge occurs both within playas and along the perimeter of playas. When a
dry playa receives a surge of water from rainfall or associated runoff, water flows into
the playa basin and penetrates the clay layer. These cracks eventually swell shut and
become impermeable as the clay absorbs more water. Once a playa is full, recharge
also occurs along playa perimeters where clay is thin or non-existent. Current research
on playas in the Southern High Plains of Texas found that recharge rates in playa
basins exceeds three inches per year in unaltered playas. More than 70 percent of
playas have been altered from their natural state by tilling, pitting, intentional filling, or
filling through sedimentation.
Playas and Playa Lakes
Recharge also occurs along the wetland's perimeter where clay is thin or nonexistent. It is here that playa permeability increases (permeability is a
measure of how easily a substance transmits fluids). Landscape-wide
recharge to the Ogallala in the Southern High Plains is about 11 mm of water
per year, and about 9.2 mm of that is focused through playa lakes. This
means that 85-90 percent of all recharge is occurring on 2-3% of the
landscape, amounting to about 3-6 inches per year under playa lakes. This is
why preserving playas is so important.
Playas and Playa Lakes
Sedimentation is the most critical threat to playa lake function, especially in
regard to groundwater recharge. Sedimentation occurs on all playas that
are surrounded by tilled lands. Water from rain and irrigation carry soil into
playas, gradually filling them. Sediment build up reduces the volume of
water playas can hold and increases the rate of water loss through
evaporation, thus limiting recharge. Incorrect land use by farmers—such as
improper tilling—can lead to playa lake damage.
Playas and Playa Lakes
Playas and Playa Lakes
Playas and Playa Lakes
Playas and Playa Lakes
The important of playas and playa
lakes is now so well recognized, that
a multi-state organization has formed
to study and protect playa lake
wetlands. This is the Playa Lakes
Joint Venture (PLJV). The PLJV’s
mission is to conserve playa lakes,
other wetlands and associated
landscapes through partnerships for
the benefit of birds, other wildlife and
people. The PLJV works in portions
of six states: Colorado, Kansas,
Nebraska, New Mexico, Oklahoma
and Texas.
PLJV Website: www.pljv.org
Playas and Playa Lakes
The PLJV operates similarly to a business, devoting attention to
communications, fundraising, and infrastructure as well as biology.
The PLJV was established in 1989, and is the seventh of 13 habitat
joint ventures throughout the United States, which cover nearly every
eco-region in North America. Joint ventures were originally conceived
by the U.S. Fish and Wildlife Service in 1986 to implement the North
American Waterfowl Management Plan. But with the recent advent of
other bird conservation plans for waterbirds, shorebirds, and landbird
species, many joint ventures, such as the PLJV, are now incorporating
an "all bird" approach to their work.