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