High Plains Aquifer System

Major rivers crossing the High Plains Platte 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 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 m 2 /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? 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 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, 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 = 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 R Diverging 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: 2x10 6 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: central pivot systems, 13x10 6 acres Pumping exceeds recharge by 100+x Water levels drop 100 ft+. GW mining. Pumping costs increase

Roughly 4 x10 6 acre ft/yr in KS Significance?? Roughly 4 x10 6 acre ft/yr in KS Translate to flux to improve understanding KS, 150x200 miles=30000 mi acres=1mi2 19x10 6 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

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 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 Predevelopment 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