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High Plains Aquifer System
Major rivers crossing the High PlainsPlatte River
Canadian River
Arkansas River
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 VsDip 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)
RechargeAve 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?
• Water balance on vadose zone
Precipitation = ET + Interflow + RechargeWhere interflow is small (low slope, far from drainage)
Recharge = Precipitation – ET
• Important factors
Precipitation, Temp, Vegetation, Slope, K of surface materials
One approach….
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
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).
Mean lake evaporation
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
Uniformly distributed recharge
Focused 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
Evidence for gw/sw interaction
Gaining reach
Losing reach
Evidence for recharge
RDiverging flow
Possibly recharge here
Parallel flow, uniform gradient
Recharge?
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
Roughly 4 x106 acre ft/yr in KSSignificance??
Roughly 4 x106 acre ft/yr in KSTranslate to flux to improve understanding
KS, 150x200 miles=30000 mi2
639 acres=1mi219x106 acres
Or4/19=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
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
Irrigated land, 1992
Aquifer sustainability
Water balanceEco-impactChemistry
Water balance on aquifer
Recharge+Irrigation return = Baseflow + Pumping + Riparian ET + rate of change of storage
Predevelopment to 1980
Water storage in aquiferPredevelopment saturated thickness in KS
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
Water Quality
Sulfate from underlying
gypsum
Cl from underlying Permian marine seds
Cl and SO4 from underlying deep marine seds
Increase in TDS near rivers from riparian ET
From marine lower Cretaceous
Sodium
Sodium Absorption Ratio
SAR>13 = Highly sodic soil
Problems with soil structure, plant fertility, drainage
2 2
2
NaSAR
Ca Mg