Amarillo MLT_Hydrogeology 101_Ken Rainwater

1. Groundwater Hydrology 101
Texas Style
Ken Rainwater
Texas Tech University
Department of Civil, Environmental,
and Construction Engineering

2. Hydrologic Cycle

3. Hydro-Illogic Cycle
Flood or Drought
Planning Study
Sticker Shock
Procrastination

5. River Basins

6. Basins

7. Add Rivers

8. Add Reservoirs

9. Surface Water Issues
 Renewable water source
 Springflow provides base flow
 Rainfall adds more flow
 Storage in reservoirs
 Multiple purposes
 Floods, supply, recreation, navigation
 Water quality variations
 Natural cycles, treated wastewater
effluents

10. Nine Major Aquifers

11. 21 Minor Aquifers

12. Groundwater Issues
 Water quality variations
 Fresh, brackish
 Arsenic, fluoride, perchlorate, others
 Recharge rate determines renewability
 Fast (Edwards)
 Slow (Ogallala)
 Withdrawal > Recharge = Depletion

13. Subsurface Layer Terms
 Aquifer – geologic layer that holds
water and allows flow to wells
 Unconfined – bounded below only
 Confined – bounded above and below
 Aquitard – layer with low permeability
that allows very little flow
 Aquiclude – layer with no permeability
13

14. 14

15. Aquifer Parameters
 Hydraulic conductivity – K (L/t)
 Measure of permeability of geologic
material to water
 Porosity – n
 Void volume divided by total volume
 Storage coefficient – S or Sy
 Amount of water released per unit decline
in head (larger for unconfined aquifer)
 Saturated thickness – b (L) 15

16. Hydraulic Head
 Unconfined – water table
 Aquifer base may be datum
 Saturated thickness changes
 Confined – well water level
 Datum is usually sea level
 Saturated thickness constant
16
elevationheadpressureh 

17. Darcy’s Law
17
alsodirectionszy,incomponentsVelocity
directionxintyconductivihydraulicK
(L)directionhorizontalx
(L/t)poresinvelocityactualv
dx
dh
n
K
v
x
x
x
x





18. Well
Drawdown
18
 Pump lowers head
at pumping well
 3-D head gradient
to pumping well
 “Drawdown cone”

19. Better Aquifer Definition
 Geologic stratum or layer that
 holds groundwater within saturated thickness, b
 has sufficient hydraulic conductivity, K, for flow
 has enough transmissivity, T = Kb, for useful
production at pumping wells
19

20. Regional Aquifer Flow

21. Moderate Pumping

22. Long-term Depletion

23. Ogallala/High Plains Aquifer
 Alluvial sediments from the Rocky
Mountain area
 Filled river/stream channels
 Complex mix of gravels, sands, silts, clays
 Irrigation source since 1940s
 Improved High Plains yields
 Historical depletion well known

24. McGuire (2017)
Year
Recoverable Volume
(106 acre-ft)
<1950 3200
1980 3250
2000 2980
2009 2960
2013 2920
2015 2910

25. McGuire (2017)
State
Change in
Recoverable Volume
(106 acre-ft)
Colorado -19.6
Kansas -69.3
Nebraska -6.0
Oklahoma -9.7
South Dakota 0.1
Texas -157.6
Wyoming -0.4
Total -273.2

26. Projections for Ogallala
Aquifer in Texas
 Center for Geospatial Technology,
Texas Tech University, 2004,
(http://www.depts.ttu.edu/geospatial/c
enter/Ogallala/Index.html)
 Mapped changes from 1990-2004
 Selected 30 ft as no longer productive
 Same thickness used by Kansas Geological
Survey projections
26

30. Center Pivots in Texas High Plains

31. Area Less Than 30 feet of Saturated Thickness (2004)

32. With Current Center Pivots

33. Area Less Than 30 feet in 15 Years

34. With Current Center Pivots

35. Area Less Than 30 feet in 30 Years

36. With Current Center Pivots

37. Estimating Recharge
 Typical rates
 Historical regional estimates <1 in/yr
 Model calibrations of up to 1.75 in/yr
 Difficult under irrigated lands
 Must know withdrawals
 Irrigation return flow
 Local focus at playa lakes, draws
 Episodic large events dominate
37

38. Projections of Aquifer Life
 Some aquifers are being mined
 Withdrawals exceed recharge, lateral flow
 Groundwater owners choose to pump
 Center pivot requirements
 400-1200 gpm for quarter-mile
 1200-2500 gpm for half-mile
 Municipal supply requirements
 When is aquifer too thin? 30 ft, 50 ft?
38

39. Long-term Drawdown
39
 Effects of single pumping well
 Initial saturated thickness, ho
to
Q
ho

40. Long-term Drawdown
40
 Effects of single pumping well
 Initial saturated thickness, ho
 Transient drawdown increases
to
t1
Q
ho

41. to
t1
t2
Q
ho
ro
Long-term Drawdown
41
 Effects of single pumping well
 Stabilizes within radius of influence, ro
 Can “break suction” if drawdown > ho

42. Drawdown Calculation
 Equilibrium for unconfined aquifer
 Drawdown, s
 Pumping well radius, rw
 Flow rate, Q
 Hydraulic conductivity, K
 ro, ho
42
 
21
w
o2
oow
r
r
ln
K
Q
hhrs 














43. Simplifying Assumptions
 Horizontal aquifer base
 Initially horizontal water table
 Homogeneous K, specific yield, Sy
 Constant Q
 No aquifer boundaries, recharge
 Single value of ro
43

44. Minimum ho for Q, K Values
 Assume ro = 1000 ft, rw = 1 ft
44
0
50
100
150
200
250
0 10 20 30 40 50 60
MinimumSaturatedThickness(ft)
Hydraulic Conductivity (ft/d)
500 gpm
350 gpm
240 gpm
100 gpm

45. Actual Conditions
 Aquifer base topography
 Water table gradient
 More precise shape with capture zone
analysis
 Heterogeneous K, specific yield, Sy
 Multiple wells
 Overlapping drawdown
 Different times of operation
45

46. More Complex Situations
 Computer modeling required
 Limited by size of simulated cells and
time steps
 Calibration challenges
 Benefit from input from GCDs
46

47. Research at Texas Tech
 Regional modeling of Southern High
Plains Ogallala (Dorman 1996, Harkins
1998, Stovall 2001)
 Predated GAMs
 Encouraged GCD involvement in improving
input data and output interpretation

48. Research at Texas Tech
 Recharge studies
 Field observation of playa behaviors at
Pantex
 Impacts on soil contamination
 Perched aquifer contamination
 Field observation of playa recharge (OAP,
with USDA-ARS, Pavur 2010, Ganesan et
al. 2016)

49. Research at Texas Tech
 Water well corrosion at T-Bar well field
 Midland County Fresh Water Supply
District, Winkler County
 Chemical, electrical, and microbial induced
corrosion may exist
 Wind-aided desalination of Dockum
groundwater (Rainwater et al. 2014)
 Seminole demonstration project

50. Research at Texas Tech
 Watershed management
 Texas State Soil and Water Conservation
Board’s Water Supply Enhancement
Program
 Policy support
 Geospatial analyses for effective brush control
 Ecohydrological modeling