This is a map of the major aquifers across the United States.
You can see that there are great number of them.
They all have these different color schemes.
From the Florida Panhandle all the way up to the Pacific Northwest, there are a variety
of geologic formations that allow for the collection of water and we monitor them in
different ways because they are being used in a variety of ways.
We're going to focus the rest of this presentation on the High Plains or Ogallala Aquifer which
reaches from the southern extent of the panhandle of Texas all the way north through the panhandle
of Oklahoma, and into Kansas, Nebraska, and little bit of South Dakota, eastern Wyoming,
and eastern Colorado, and eastern New Mexico.
The High Plains or Ogallala Aquifer is outlined in this figure on the left here.
The area is about 174,000 square miles.
Each one of these black dots indicates a city that has a population of greater than 20,000
people.
You can see that there is significant desire to use local water resources for these cities
across this area.
In fact, the Ogallala Aquifer provides about 82% of the water that is used by the 2.3 million
people that occupy the lands above the High Plains Aquifer.
Remember, we talked about the source of groundwater to aquifers being largely precipitation.
This is the typical distribution of precipitation across the Ogallala Aquifer.
What you'll note here is that the reddish-yellow colors on the left side or the western side
of this map show that there's very low precipitation in those areas.
As we move further east into the yellow-green, light blue, and darker blue colors, we get
to higher and higher annual precipitation averages.
The average annual precipitation in eastern Nebraska is close to 33 inches whereas when
we move over to some of the western regions in eastern Wyoming in those red areas, we
only see about 12 inches of precipitation.
There's quite a vast gradient of precipitation that's applied at the surface annually across
the Ogallala.
The other thing I wanted to note here is that prior to the development of pumping of groundwater
at the Ogallala Aquifer, it was estimated to contain enough water to cover the entire
continental United States with roughly 20 inches of water.
If it were to ever be pumped dry, the expectation is that it would take about 6,000 years to
refill.
An aquifer is only as good as its geological makeup.
We see that we have a variety of geologic formations that makeup the aquifer, from the
Tertiary age geology in the north in Nebraska and moving south into the Permian age rocks
in Texas.
We can also see the contour lines for the altitude for the basin of the aquifer in light
blue along the map here.
You can see that these elevations range from about 2000 feet to over 5000 feet.
Because these rocks are fairly old that makeup the aquifer, it has been collecting water
unimpeded for a long period of time.
The other thing that we can look at is the general direction of groundwater flow across
the aquifer.
The flow velocities are fairly low, one foot per day.
That's much slower than we see in most of the rivers that move over the aquifer.
Generally, we also see that there is a west to east trend or direction of movement as
the highest water table elevations are on the western side and the lowest water table
elevations tend to be on the eastern side of the aquifer.
How far down to we have to go to reach the water surface?
In the year 2000 this map was generated with data collected from the aquifer to try to
determine exactly what that distribution looked like.
What we see are that in the very light shades it tends to be shallow.
In particular, you can see that from the northeastern corner of Colorado, moving through Nebraska
on the southern end, you can see a nice swath of very near-surface groundwater.
That's because that's where the South Platte River comes out and joins with the North Platte
River and moves across southern Nebraska.
If we move further south, you can see through the panhandle of Texas, just south of the
panhandle of Oklahoma, the water table tends to be very deep, in excess of 300 feet in
some cases.
There's quite a bit of diversity in depth to water across the aquifer.
There are a number of large rivers that flow over the aquifer.
We talked about the North Platte and South Platte just a moment ago moving through Wyoming,
Colorado, and Nebraska.
We also see the Arkansas River coming out of the headwaters in Colorado and moving to
the east through southern Kansas.
Then, of course we also have the Pecos River and the Red River moving through headwaters
in New Mexico and Texas respectively and heading to the east.
In general, the northern rivers are draining the Rocky Mountains.
Of course, all of these rivers are also, can have the opportunity to drain water from local
parts of the watershed more proximal to them as they move downstream.
This is a map of water use across the Ogallala Aquifer as determined on a county-by-county
basis.
Essentially this range from southern South Dakota down all the way through south Texas
indicates that groundwater withdrawals in millions of acre-feet go from .01 or about
10,000 acre-feet in a year to more than 250,000 acre-feet within the 2000 water year.
You can see some hot spots here, particularly in Nebraska along the Platte River after the
North and South Platte Rivers have joined together.
We also see a hot spot at the headwaters of the Republican River which starts in Eastern
Colorado.
In Kansas, as the Arkansas River is moving through southern Kansas we see a few hotspots
there as well.
Then, in the panhandles of Oklahoma and Texas, there are a few hot spots there as well.
There is significantly less groundwater use in southern South Dakota which is also overlying
the aquifer and in the headwaters of the Platte River in Wyoming.
Roughly 27% of the irrigated farmland in the United States depends on the Ogallala aquifer.
It is an important resource for agriculture in the United States.
The key agricultural products that that water is used to support include livestock, corn,
wheat, and soy crops.
If we look at the temporal trend of water use by the different states overlying the
Ogallala Aquifer, Colorado, Kansas, Nebraska, and Texas, and then New Mexico, Oklahoma,
South Dakota, and Wyoming all combined in that blue bar, we can see that from the 1950s
to 2000 if we added up these bars in general, there would be a substantial increase.
But, this increase is not monotonic for any one of these states or one of these regions.
If we start back in the 1950s, there was sort of the beginning of center-pivot irrigation
and the growth of groundwater pumping.
We see an increase as we get into the 1970s.
Particularly in Texas there's a bit of a drop-off as we move into the 1980s and 2000.
In Colorado we see very little use in the 1950s and then an expansion to about a steady
rate from say 1980 to 2000.
Kansas tends to ramp up and peak in the mid-1980s and then drop off.
Nebraska tends to ramp up and peak around 1980, drop off in the 90s but then surge again
into the year 2000.
The other regions combined, New Mexico, Oklahoma, and Wyoming, start low much like the other
regions, pick up and tend to be fairly steady from 1970 to 2000.
The management of the High Plains or Ogallala Aquifer has received the attention of the
federal government.
In 1986, Congress passed the Water Resources Development Act recognizing the economic importance
of the High Plains Aquifer to the states, and added Title III to the Water Resources
Research Act of 1984.
Title III essentially states the US Geological Survey in cooperation with "the States of
the High Plains region is authorized and directed to monitor the levels of the Ogallala or High
Plains Aquifer and report annually to Congress."
In 1995, this was changed to biannually but the monitoring still has to occur.
The objectives of this study include assembling water level measurements from the States the
overlie the High Plains aquifer, that is Colorado, Kansas, Nebraska, New Mexico, Oklahoma, South
Dakota, Texas, and Wyoming.
Mapping water level changes in the aquifer from predevelopment, which is generally accepted
to be about 1950 or 1980 when enough data became available to do so more accurately
across the aquifer, to the spring of the report year using water levels measured by Federal,
State, and local agencies.
What that means is that prior to the irrigation season of a particular year, these water levels
will be assessed and the changes from year to year, changes from 1950 or 1980 to current
will be assessed prior to pumping of that year.
To determine the change in water storage in the aquifer using the water-level data and
estimates of specific yield or rather how much water could be pulled from different
parts of the aquifer because it is somewhat heterogeneous in its properties.
Finally, every two years to report water-level changes and changes in water in storage to
Congress and to the public.
Now, this data is largely available from the US Geological Survey and you can find it online
for free.
Here is the results of this study.
If we look at changes from 1980-1995, a 15 year period, you can see that the grey, which
dominates most of the area of the Ogallala Aquifer, indicates an insignificant change.
The blue colors indicate greater and greater increases in water level.
Declines are indicated in red.
For the most part, you can see that where there is a change that has occurred, that
is a color besides grey, we see changes of ten to more than forty feet drop, water level
drop, in many places across the southern part of the Ogallala Aquifer.
All the way from central Kansas to north Texas.
The southernmost part of the Ogallala Aquifer though tends to have an increase in water
level over that period, ten to twenty feet and in some cases maybe a bit more.
It's also interesting to note that it is the drier western side of the Aquifer, drier meaning
drier climate, less average annual average precipitation on the western side of the Aquifer,
that has more substantial water level declines and that where we tend to see, particularly
in Nebraska, the water level increases, those tend to occur where we're on the wetter side
of the Aquifer, wetter climate that is to say.
On the eastern side of the Aquifer, where we tend to have higher annual precipitations,
we tend to see more water level increases.
Here's an example report from the High Plains Water Level Monitoring Study for 2011 produced
by the US Geological Survey, freely downloadable for anyone.
You can see the results on the map in the background here.
The explanation on the right indicates that these redder, darker, yellow to orange to
red colors indicate a decline in water level whereas the bluish colors going from a grey
to a green to a dark blue indicate greater and greater rise of the water level.
These changes are noted not just from the previous year but actually from predevelopment
times which is considered to be about 1950 in this case.
In general, if we look across Nebraska, we see that just north of the North Platte River
before the North Platte joins the South Platte, we see a substantial location of decline of
the water table within one county.
Then, towards eastern Nebraska, we tend to see more water level rises of about ten to
twenty-five feet.
You can see that those are somewhat distributed across eastern Nebraska.
South of the Platte river, we tend to see more and more declines of water levels.
As we move south through southern Nebraska and northern Kansas, we see a lot of grey
and yellow and orange colors indicating water level declines.
As we move through Kansas, we see declines that are more than 150 feet that are from
predevelopment times.
The same is true in the panhandle of Texas, we see substantial areas where the water level
change has been greater than 150 feet from predevelopment.
We've seen significant changes in the water levels throughout the Ogallala Aquifer.
In some places it's beneficial, that is there's an increase, in some places there appears
to be a significant reduction in the amount of water that is stored.
In that case, we think about the Ogallala Aquifer, the challenge of having this as a
sustainable water resource for this region will rely on careful management and making
difficult decisions sometimes about who can use water and when.
The agricultural industry above the Ogallala Aquifer will always be at the mercy of droughts
and other climatic forces that occur.
The use of groundwater in this area is often required to try to keep that industry going
at the surface.
How we do that without completely depleting the Aquifer or depleting it to an extent that
we can no longer use that as a viable resource will ultimately depend on the decisions we
make with respect to how we balance withdrawals and recharge.
Finally, there are a lot of online resources for looking at real-time groundwater data.
Here is one available from the US Geological Survey from the first of October 2013.
Every one of these symbols indicates a different well.
Some of these are only periodically measured, some of them have regular daily measurements
made from them.
You can see that the color range below indicates whether the water table or water table in
the well is low compared to the long-term record or whether it's on the high end in
blue.
You can see that there is quite a bit of data in some places such as North Dakota, Nebraska,
Pennsylvania, and then it tends to be sparser in other locations, in particular looking
at say Oregon, Wyoming, and even Kansas.
Let's just a look at Nebraska versus Kansas for moment.
Nebraska has a lot of dots, very dense data collection being reported to this network,
the state.
Whereas Kansas has a lot of wells also, but for whatever reason does not have them reported
in this particular network.
You can zoom in on a place and look at the current conditions, groundwater conditions
in view of an Aquifer and know that that's used as a municipal and or local, industrial,
or agricultural resource.
I encourage you to look at the conditions of your Aquifer underneath your feet.
The end.