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Andrei Verdeanu - High Plains Ground Water Depletion
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Transcript of Andrei Verdeanu - High Plains Ground Water Depletion
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Ground WaterDepletion
-The High Plains Aquifer
(Ogallala Aquifer)-
Verdeanu Andrei
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Objectives I have tried to achieve in presenting this project:
Introduction:
- Presenting the geographical location and bioclimatic characteristics of the area;- The aquifers general geological characteristics;
Main contents:
- The water regime recharge and discharge;- Economical aspects of the issue agricultural impact of the problems;- Depletion and pollution of the aquifer;
Conclusions.
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Ground Water Depletion
-The High Plains Aquifer (Ogallala Aquifer)-
The High Plains are a subregion of the Great Plains, located mostly in the Western
United States, but also partly in the Midwest states of Nebraska, Kansas, and South Dakota,
generally encompassing the western part of the Great Plains before the region reaches the
Rocky Mountains. The High Plains are lying in southeastern Wyoming, southwestern South
Dakota, western Nebraska, eastern Colorado, western Kansas, eastern New Mexico, western
Oklahoma and northwestern Texas. From east to west, the High Plains rise in elevation from
around 1,160 feet (350 m) to over
7,800 feet (2,400 m).
The Great Plains area
location and the High Plains
Aquifer and the states
containing it, figures 1 and 2.
Figure 1
The High Plains are characterised by
a semi-arid climate, receiving between
1020 inches (250510 mm) of
precipitation annually. The vegetation
coverage is generaly represented by
shortgrass prairie, prickly pear cacti and
scrub formations, with occasional buttes
or other rocky outcrops.
Figure 2
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The High Plains aquifer system underlies 111.4 million acres (460,000 square
kilometers) of surface, being the leading geologic formation in the aquifer system. Although
there are several other minor geologic formations in the High Plains Aquifer System, such as
the Tertiary Brule and Arikaree and the Dakota formations of the Cretaceous, these several
units are often referred to as the Ogallala
Aquifer.
Tipical aspect from the Great
Plains Area, part of the North American
Prairies Province, figure 3
Figure 3
The Ogallala is composed
primarily of unconsolidated,
poorly sorted clay, silt, sand, and
gravel with groundwater filling
the spaces between grains below
the water table . The aquifer was
laid down about 10 million years
ago by fluvial deposition from
streams that flowed eastward
from the Rocky Mountains
during the Pliocene epoch. It is an
unconfined aquifer, and virtually
all recharge comes from
rainwater and snowmelt. As the
High Plains has a semiarid
climate, recharge is minimal.
Figure 4
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Recharge varies by amount of precipitation, soil type, and vegetational cover and averages
less than 25 millimeters (1 inch) annually for the region as a whole. We can observe in figure 4 that
the aquifer would overlap over the 35 up until 100 mm of mean annual precipitations range, thus
passing through arid to mild conditions, west to east.
In a few areas, recharge from surface water diversions has occurred. Groundwater does flow
through the High Plains Aquifer, but at an average rate of only 300 millimeters (12 inches) per day.
Hypsometric map and satellite image of the aquifer area, figures 5 and 6.
Figure 5. Figure 6.
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The depth to the water table of the Ogallala Aquifer varies from actual surface discharge to
over 150 meters (500 feet). Generally, the aquifer is found from 15 to 90 meters (50 to 300 feet) below
the land surface. The saturated thickness - figure 7, also varies greatly. Although the average
saturated thickness is about 60 meters (200 feet), it exceeds 300 meters (1,000 feet) in west-central
Nebraska and is only one-tenth that in much of western Texas. Because both the saturated thicknessand the areal extent of the Ogallala Aquifer is greater in Nebraska, the state accounts for two-thirds of
the volume of Ogallala groundwater, followed by Texas and Kansas, each with about 10 percent.
The Ogallala
Aquifer, whose total
water storage is about
equal to that of Lake
Huron in the Midwest, is
the single most
important source of
water in the High Plains
region, providing nearly
all the water for
residential, industrial,
and agricultural use.
Because of widespread
irrigation, farming
accounts for 94 percent
of the groundwater use.
Irrigated agriculture
forms the base of the
regional economy. It
supports nearly one-fifth
of the wheat, corn,
cotton, and cattle
produced in the United
States. Crops provide
grains and hay for
confined feeding of cattle
and hogs and for dairies.
Figure 7
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The cattle feedlots support a large meatpacking industry. Without irrigation from the
Ogallala Aquifer, there would be a much smaller regional population and far less economic
activity.
Crop Circles in Kansas
Photo courtesy of NASA Earth Observatory
Because of the Ogallala, the High Plains is the leading irrigation area in the Western
Hemisphere. Overall, 5.5 million hectares (nearly 13.6 million acres) are irrigated in the Ogallala
region. The leading state irrigating from the Ogallala is Nebraska (46%), followed by Texas (30%) and
Kansas (14%).
The Depletion Process
The Ogallala Aquifer is being both depleted and polluted. Irrigation withdraws much
groundwater, yet little of it is replaced by recharge. Since large-scale irrigation began in the 1940s,
water levels have declined more than 30 meters (100 feet) in parts of Kansas, New Mexico, Oklahoma,
and Texas. In the 1980s and 1990s, the rate of groundwater mining , or overdraft, lessened, but still
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averaged approximately 82 centimeters (2.7 feet) per year. Increased efficiency in irrigation continues
to slow the rate of water level decline. State governments and local water districts throughout the
region have developed policies to promote groundwater conservation and slow or eliminate the
expansion of irrigation. Generally, management has emphasized planned and orderly depletion, not
sustainable yield. Depletion results in reduced irrigation in areas with limited saturated thickness andincreased energy cost in all areas as the depth to water increases. Center-pivot sprinklers are among
the irrigation methods used in the High Plains. Large quantities of groundwater pumped from the
Ogallala Aquifer allows these semiarid western lands to yield abundant harvests.
In parts of the area,
farmers began using groundwater for irrigation
extensively in the 1930s and
1940s. Estimated irrigated
acreage in the area overlying
the High Plains aquifer
increased rapidly from 1940
to 1980 and changed slightly
from 1980 to 2002: 19492.1
million acres, 198013.7
million acres, 199713.9
million acres, 200212.7
million acres. Irrigated acres
in 2002 were 12 percent of
the aquifer area, not
including the areas with little
or no saturated thickness.
Water withdrawal, figure 8
and water-level changes
related to the irrigated
surface evolution, figure 9
Figure 8
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Figure 9
Water-level changes in the aquifer figure 10, result from an imbalance between discharge
and recharge. Discharge is primarily ground-water withdrawals for irrigation. Discharge also
includes evapotranspiration, where the water table is near the land surface, and seepage to streams
and springs, where the water table intersects with the land surface. Recharge is primarily from
precipitation. Other sources of recharge are irrigation return flow and seepage from streams, canals,
and reservoirs.
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Figure 10
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The average specific yield for the High Plains Aquifer is about 0.15. This means that only 15
percent of all the water available in the aquifer can be recovered using irrigation pumps, while the
rest remains unused and locked up in the unsaturated zone . Groundwater depletion problems could
be forestalled if this presently nonrecoverable water could be forced to the saturated zone . One
experimental means of accomplishing this is by injecting air into the unsaturated zone, which breaksdown capillary action and permits the movement of water down to the saturated zone. Air injection
experiments have shown positive results for very localized areas. However, the widespread
applicability of this technology has not yet proven effective.
Figure 11
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The map is based on water levels from 3,682 wells, which were measured in the agricultural
predevelopment period and in 2005, and other previously published data in areas with few
predevelopment water levels.
The areas with few predevelopment water levels are in the central part of the Nebraska
Panhandle, west-central Nebraska, and southeastern Wyoming. The water-level changes from
predevelopment to 2005 ranged between a rise of 84 feet and a decline of 277 feet. Area-weighted,
average water-level change from predevelopment to 2005 was a decline of 12.8 feet. Approximately
25 percent of the aquifer area had more than 10 feet of water-level decline from predevelopment to
2005; 17 percent had more than 25 feet of water-level decline, and 9 percent had more than 50 feet of
water-level decline. Approximately 2 percent of the aquifer area had more than 10 feet of water-level
rise from predevelopment to 2005.
In response to these water-level declines, the U.S. Geological Survey (USGS), in cooperation
with numerous Federal, State, and local water-resources agencies, began monitoring more than 7,000
wells in 1988 to assess annual water-level change in the aquifer. A report by the USGS, Water-Level
Changes in the High Plains Aquifer, Predevelopment to 2005 and 2003 to 2005 (McGuire, 2007),
shows the areas of substantial water-level changes in the aquifer from the time prior to substantial
ground-water irrigation development (predevelopment or about 1950) to 2005. Ground-water
withdrawals for irrigation and other uses are compiled and reported by the USGS and agencies in
each State about every 5 years. Ground-water withdrawals from the High Plains aquifer for irrigation
increased from 4 to 19 million acre-feet from 1949 to 1974. Ground-water withdrawals for irrigation in
1980, 1985, 1990, and 1995 were from 4 to 18 percent less than withdrawals for irrigation in 1974.
Ground-water withdrawals from the aquifer for irrigation in 2000 were 21 million acre-feet (McGuire,
2007).
In addition to the water withdrawal and depletion, pollutants and contamination is another
important issue. Groundwater contamination in the Ogallala became an issue in the 1990s. In its
natural state, the High Plains Aquifer is, for the most part, of high quality. The water is generallysuitable for domestic use, stock watering, and irrigation without filtration or treatment. Surveys of
groundwater samples have detected traces of pesticides and nitrates. Sources include irrigated
agriculture and confined livestock feeding operations. The percolation rates of contaminants from the
surface to the water table have not been established in the areas where polluted water has been
found, but a map refering to the aquifers susceptibility of chemical compounds transit to the water
table has been made figure 12
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Analysing the
resulting distribution of
the areas into the
aquifer, tells us that the
coverage area and the
possible recharge areas
at surface are mostly safe
from the reach of
pollutants, at least in thenearby future. The most
prone areas are those
where the water table
meets the topographic
surface through high
piezometric levels,
surfacing or even rises
over the surface, areas
where direct contact
between the phreatic
level and the
topographical surface
are appearing (river
beds, alluvial plains and
areas presenting
advanced errosion
processes).
Figure 12
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Conclusions:
First of all, there should be acknowledged that the aquifer and the related resourcess health
status can still be improved, even saved, in time. Not everything is lost, yet. But action must be taken
quickly. One could say that these times are the last chance available to restore the balance that has
been deply shaken.
The importance of protecting the water resources in this area is even more significant,
considering the geographical location and the climatic characteristics of the aquifer area. Being
situated in an arid area, makes things even more difficult. As stated above, the replenishing and
recharge given by nature are minimal in this area. Relying only on the pluvial input and the even
weaker nival recharge is not an option. From a more religious perspective, people who have settled
around these areas should much appreciate the miracle that has been given to them, in the greatexpanse of these plains. This aquifer represents an unexpected chance for social development,
practically binding the population to the areas inhabited and giving a special character to the lifestyle
and nature of the people.
The future economy of the High Plains and the United States for that matter, depends
heavily on the Ogallala Aquifer, the main source of water for all uses. Economically speaking, the
importance of the water supplied by the aquifer is critical. Even medium variations of the supply, on
mid-term can profoundly affect the countrys economy and agricultural production. A critical balance
point has been achieved. This point was met because once the water was made accessible to industry,agriculture and large scale use, the principle of high production efficency but severe consumption of
the resources has been blindly applied. Until recent years, the depletion was not given the much
needed attention and care. Sensing that the depletion has rised over a certain level, some measures
started to be taken. This is a good thing, but are these measures taken in the context of the same
principle of mass production mass consumption of the resources? Or things have been revised?
Some could be curious to know the answer, but lets hope that the people managing these important
resources know the answer themselves and have chosen the right way... Otherwise, they will realise
too late what serious damage has been done to this valuable resource... Maybe the deadline will raise
some heads, for changing the plans. Who knows...
Otherwise said, the Ogallala will continue to be the lifeblood of the region only if it is managed
properly to limit both depletion and contamination.
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Sources:
- Alley, W.M., Reilly, T.E., and Franke, O.L., 1999, Sustainability of ground-water resources:U.S. Geological Survey Circular 1186;
- Kromm, David E., and Stephen E. White, eds. Groundwater Exploitation in the High Plains.Lawrence: University Press of Kansas, 1992;
- White, Stephen E., and David E. Kromm. "Local Groundwater Management Effectiveness inColorado and Kansas Ogallala Region." Natural Resources Journal 35 (1995);
- McGuire, V.L., 2007, Water-level changes in the High Plains aquifer, predevelopment to 2005and 2003 to 2005: U.S. Geological Survey Scientific Investigations Report 20065324;
- United States Geological Survey -http://ne.water.usgs.gov;- Geology -http://geology.com;- Water Encylopedia -http://www.waterencyclopedia.com;- American Society of Agronomy -https://www.agronomy.org/;- Kansas Department of Agriculture -http://www.ksda.gov/;- University of Nebraska Lincoln -http://www.unl.edu/;- NASA Earth Observatory -http://earthobservatory.nasa.gov/.
http://ne.water.usgs.gov/http://ne.water.usgs.gov/http://ne.water.usgs.gov/http://geology.com/http://geology.com/http://geology.com/http://www.waterencyclopedia.com/http://www.waterencyclopedia.com/http://www.waterencyclopedia.com/https://www.agronomy.org/https://www.agronomy.org/https://www.agronomy.org/http://www.ksda.gov/http://www.ksda.gov/http://www.ksda.gov/http://www.unl.edu/http://www.unl.edu/http://www.unl.edu/http://earthobservatory.nasa.gov/http://earthobservatory.nasa.gov/http://earthobservatory.nasa.gov/http://earthobservatory.nasa.gov/http://www.unl.edu/http://www.ksda.gov/https://www.agronomy.org/http://www.waterencyclopedia.com/http://geology.com/http://ne.water.usgs.gov/