High Plains Aquifer System
Platte River
Arkansas River
Canadian River
Major rivers
crossing the
High Plains
Geologic History
• Deposition of basement rocks, Permian-Tertiary.
Permian contains evaporites, affect water quality,
cause subsidence. Late Cretaceous seds contains
gypsum. Doming centered on OK/TX
• Laramide uplift in early Tertiary, seaway in
midwest.
• Large braided river system transport sed to the
east off Rocky Mtns, Miocene to Pliocene. Coarse
grn, variable sorting. Sand and gravel up to 1000
ft thick. Ogallala frm
Geologic History, Continued
• Continued uplift tilts Ogallala frm.
Removed by erosion near mountains,
locally.
• Dust storms deposit silt (loess) during
Pleistocene, potential confining units
• Eolian processes rework . Dunes formed.
• Modern river systems rework. Alluvium
formed
Basement
geology
• Cretaceous SS
contribute water
• Marine basement
rocks affect water
quality, Cl, SO4
Permian redbeds
underlying HP in
western KS
Geologic units within
the High Plains
aquifer system
•
•
•
•
•
Alluvium
Dune sand
Ogallala Frm
Airkaree Frm
Brule Frm
Stratigraphic section
Regional
dip
Fence diagram
Rule of Vs
Dip of the lower
contact relative to
the gradient of
dissecting rivers
Escarpment from High Plains aquifer in
eastern, CO
•
Physiography of northern
High Plains
Outcrop of
Ogallala frm
Loess
confining
unit in NE
GW/SW interaction variations in KS
Gaining reach, channel cut through
HP to bedrock
Losing reach,
channel underlain
by HP
Regional
dip
Fence diagram
Hydraulic
conductivity
ft/day
Saturated
thickness
Basic Characteristics
• Thick, unconfined aquifer. Locally
confined by loess or caliche
• K: 10 to 100 m/day; 30m/day average
30m/day = 3x10-4 m/s
• b: 300 m max; 30 m average
• T: 1000 m2/day
• S: 0.1 to 0.3; 0.15 average (specific yield)
Recharge
Ave Magnitude: increases from 1 mm/yr in N.TX to
150 mm in dunes in NE
• Infiltration on uplands
• Losing streams; ephemeral streams with
permeable beds (1.3% loss/mile in one study).
Locally streams losing due to pumping
• Irrigation return (irrigation-ET)
• Bedrock (where upward flow occurs)
Factors affecting distribution of recharge…
How to estimate distributed recharge?
One approach….
• Water balance on vadose zone
Precipitation = ET + Interflow + Recharge
Where interflow is small (low slope, far from drainage)
Recharge = Precipitation – ET
• Important factors
Precipitation, Temp, Vegetation, Slope, K of
surface materials
Precipitation on
High Plains
Precipitation
Potential ET
Potential ET produced
when rate is limited by
energy input and plant
metabolism, not limited by
availability of water.
Potential ET >Actual ET
Precip and
Pan
Evaporation
Mean lake evaporation
Figure 3. Mean annual lake evaporation in the conterminous
United States, 1946-55. Data not available for Alaska, Hawaii, and
Puerto Rico. (Source: Data from U.S. Department of Commerce,
1968).
Potential recharge in KS determined using soil model
Playa lake on High Plains aq in TX panhandle
20,000 playa lakes in TX
Playas = important feature affecting recharge
of High Plains aquifer
Focused recharge
Uniformly distributed
recharge
•Amount of recharge
•Distribution
•Water quality
•Timing
Discharge
• Streams; perennial, ephemeral
• Seeps, springs
• Riparian ET. May be significant where w.t.
shallow (near surface water)
• Wells
1.
What is the average horizontal hydraulic head gradient
2.
What is the horizontal gw flux in the aquifer (m/d)?
3.
What is the average gw velocity? (m/d)
4.
Use the head contours to identify an area of suspected
recharge. Circle the area, write “R” and draw gw flux vectors.
List both geologic and meteorologic factors supporting your
choice of recharge area
5.
Identify an area of negligible recharge. List geologic or
meteorologic factors supporting your choice of recharge area.
Circle and write “NR” and draw gw flux vectors.
6.
Identify a gaining stream reach. Circle and write “G” draw gw
flux vectors
7.
Identify a losing stream reach. Circle and write “L” and draw
gw flux vectors
Hydraulic head
contours in High
Plains aquifer
= 40 miles
Hydraulic gradient 400 ft/40 miles
10 ft/mile =1/500 = 0.002
Flux: 0.002* 30 m/d = 0.06 m/day
Velocity = 0.06/0.2 = 0.3 m/d
Gaining
reach
Losing
reach
Evidence for gw/sw interaction
Evidence for recharge
Diverging flow
Possibly
recharge here
Parallel flow, uniform
gradient
Recharge?
R
Water Use
• Pre-1930s: Irrigation from surface water. Dust
Bowl Drought
• 1930s Centrifugal well pump developed.
• 1949: 2x106 acres mostly N TX. Platte R.
• 1950s-60s: Drought. Oil and gas=energy source,
more irrigation
• 1960s: Centrifugal pump improved. 750 gpm
well = central pivot irrigation, r=0.25 mi
• 1978: 27000 central pivot systems, 13x106 acres
• Pumping exceeds recharge by 100+x
• Water levels drop 100 ft+. GW mining. Pumping
costs increase
6 acre ft/yr in KS
Roughly
4
x10
6
Roughly 4 x10 acre ft/yr in KS
Translate to flux to improve understanding
Significance??
KS, 150x200 miles=30000 mi2
639 acres=1mi2
19x106 acres
Or
4/19=0.2 ft/yr
Central pivot
irrigation
Number of central pivot
irrigation systems in NE
Aerial view of area using central-pivot irrigation
Central pivot from the air
Density of land
being irrigated,
1949
Density of land
being irrigated
1979
Irrigated land,
1992
Figure 5. Irrigated cropland 1992, Northern Plains region. USDA, NRCS, Lambert Conformal
Conic Projection, 1927 North American Datum. Source: National Cartography and GIS Center,
NRCS, USDA, Ft. Worth, TX, in cooperation with the natural Resources Inventory Division,
NRCS, USDA, Washington, D.C., using GRASS/MAPGEN software, 09/95. Map based on data
generated by NRI Division using 1992 NRI. Because the statistical variance in some of these areas
may be large, the map reader should use this map to identify broad trends and avoid making highly
localized interpretations
Aquifer
sustainability
Water balance
Eco-impact
Chemistry
Water balance on aquifer
Recharge+Irrigation return =
Baseflow + Pumping + Riparian
ET + rate of change of storage
Predevelopment to
1980
Water storage in aquifer
Change in saturated thickness in KS
Change of water in storage as percent of thickness
Estimated usable lifetime
Change in
stream drainage
with time in KS
Sustainable yield
includes ecological
effects
Water Quality Issues
• Na, Cl, SO4 from basement rocks, N TX, NE NE,
S KS
• Recharge from playas—evap increases TDS
• Riparian ET increases TDS along rivers
• ET during irrigation increases TDS, recirculation
• Na particular problem to ag. Destroy soil
structure, reduce K. Interfere with plant osmosis
• Ag chemicals
• F from fluorite. Teeth staining
From marine lower Cretaceous
Water Quality
Sulfate from
underlying
gypsum
Increase in TDS near rivers from riparian ET
Cl from underlying Permian marine seds
Cl and SO4 from underlying deep marine seds
Sodium
Na
SA R 
Ca
2

 Mg
2
Sodium Absorption Ratio
2
SAR>13 = Highly sodic soil
Problems with soil structure,
plant fertility, drainage