Download Introduction to Hydrogeology - The University of Texas at Dallas

GEOS 4430 Lecture Notes:
Introduction to Hydrogeology
Dr. T. Brikowski
Fall 2012
file:introduction.tex,v (v. 1.43), printed August 28, 2012
Introduction
See NBC “Thirsty Planet” series, e.g.
American West
1
Why Study Hydrogeology?
Population growth and global warming will lead to severe
freshwater shortages in the near future.
• U.S.
– West: Emphasis on groundwater.
∗ Water is a crucial problem west of 100o W longitude [the
east side of the Texas panhandle, J. W. Powell, 1875,
quoted in Stegner, 1954].
∗ average U.S. precipitation shows distinct drop-off west
of 100o (Fig. 1)
∗ Situation best summarized by Mark Twain (apocryphal):
“[In the West] whiskey is for drinking, water is for
fighting over . . . ”1
1
http://www.twainquotes.com/WaterWhiskey.html
2
– East: emphasis on surface water management (rivers,
lakes, etc.) and drainage, contamination remediation, and
sea water intrusion. Also seawater intrusion.
• World:
– world wide water stress (pg. 61) increasing rapidly, causing
much suffering and potential war. See also decadal
summary
– Upper-vs-lower basin water usage
∗ similar to western U.S.Colorado River (p. 33) issues. See
also USBR Colo. R. sustainability study
∗ Euphrates River (Fig. 3): Turkey vs. Syria and Iraq.
Drying of Iraq marshes.
∗ Nile River basin (Fig. 4). Egypt vs. Sudan and Ethiopia.
See Nile Basin Initiative
3
– Declining snowpack: primarily Himalaya, which supplies
much of India and south Asia (Fig. 5)
4
U.S. Precipitation 2009
Figure 1: Total precipitation, U.S., 2003. Note large dropoff
west of the Texas panhandle. After NOAA.
5
World Freshwater Stress
Figure 2:
Observed and projected world freshwater stress (fraction
produced vs. available). After UNEP, updated at World Economic Forum
2009.
6
Euphrates River Basin
Figure 3: Euphrates river basin. After WorthNews. See also
satellite photos, NPR 2009 of Ataturk Reservoir, Turkey.
7
Nile River Basin
Figure 4: Nile river basin elevation and hydrology.
WaterWatch.
8
After
Himalayan Snowpack Decline
Figure 5: Changes in extent of glaciers in the Western Himalaya
[Fig. 1, Prasad and Singh, 2007]. See more immediate problem
in Peru.
9
Texas 2011 Drought
• worst single-year drought in Texas history
• Drought Monitor, also seasonal drought outlook
• severe impacts, e.g. Amarillo water supply, Lake Meredith
currently “empty” (official dead pool elev is 2850 ft, 2011
record low of 2842.5 ft, depth 28.5 ft)
• North Dallas (NTWMD) in persistent Stage II water
restrictions
• very unusual conditions (see TX State Climatologist blog,
continues trend of high-T departure from historical trends
10
U.S. Trouble Spots
• Western Colorado River
– about 35 million people depend on this river for drinking
water
– since 2002 demand has exceeded supply by 10% (see Fig.
1, USBR Basin Status Report
– 11 year drought has greatly depleted storage in the system
(e.g. Lake Mead, Fig. 6)
– fortunately, per-capita water use has declined significantly
(Figs. 6-7) in that basin, meaning conservation can help a
lot
11
Climate Change and Drought
• see Global Change Impacts in the United States, [USGCRP,
2009]
• Warming predictions:
– U.S. average temperature has risen by 1.1◦C in the past
50 years
– expect additional 5-6◦C warming by 2100 at current CO2
emissions rates [p. 29, USGCRP, 2009]
– greatest warming in mid-continent, especially west (
[Colorado River headwaters, p.
29 USGCRP, 2009]
(compare to 1940-2005 observed trends
– optimistic models of reduced emissions predict 3-4◦C
warming
12
– will result in over half the year with days warmer than
90◦F by 2100 in North Texas [p. 34, USGCRP, 2009]
– around 120 days over 100◦F for North Texas by 2100 [p.
90, USGCRP, 2009]
• only mild changes in precipitation predicted [p.
USGCRP, 2009]
30-31,
• warming will lead to increased evapotranspiration by plants,
leading to significant water stress in part of U.S. and midlatitudes worldwide (Fig. 8)
• Get ready for a wild ride! E.g. Australian example
– 12 year drought began around 2000, part of a general
southern hemisphere drought
13
– forced steep decline in rice production, leading to global
shortages and conversion to wind production
– some reservoirs dropped to 12% of normal (compare to
Lake Lavon, where at 35% of normal Stage 4 Emergency
restrictions apply, no outdoor use of water)
– drought ended 2010 with heavy rains, reservoirs rising, now
at 35% of capacity
– Australian electorate now becoming quite serious about
climate change
– drought has resumed along west coast (Perth)
14
Lake Mead, NV
Lake Mead, NV Monthly Water Elevation
1240
Maximum
1220
Water Elevation (ft)
1200
1180
Average
1160
1140
Drought
1120
1100
Critical Shortage
1080
1060
2010
2005
2000
1995
1990
1985
1980
1975
1970
1965
1960
1955
1950
1945
1940
Figure 6:
Lake Mead, NV monthly water levels 1937-present. Current levels approaching those experienced in shorter
severe droughts 1955 and 1965. Mandatory rationing below shortage line, AZ handles 94% of the rationing, NV the rest. Mead
supplies 90% of LV water.
15
Las Vegas City Water Intake Tunnel
Figure 7:
Las Vegas-Lake Mead water intake tunnel plan. One of two current intakes is at 1,050 ft elev, and may soon
be above water. From TunnelTalk.
16
Warming-Related Water Stress
Figure 8: Warming will greatly affect water availability by 2100; IPCC4
[2007] lower emissions scenario (SRESa1b) mean results.
17
Unique U.S. Water Stresses
• hydrofracing uses considerable water
• 2012 drought is bringing pressure to recycle that water or
halt this use
• others such as beverage industries have recognized that water
access is their most persistent future business risk factor
• i.e. hydrology is important even to oil and other geologists
18
Water Trends
19
Water Sources
• average water usage in U.S. is ∼ 30% groundwater (Fig. 9)
• U.S. water usage trends:
– Consumptive water use up steadily
– ratio of groundwater to surface water also generally
up, partly due to climate (recent droughts ⇒ increased
groundwater extraction)
– since ∼1980 water use down slightly, but
ground/surface water ratio increasing (Fig. 9)
• U.S. Climate trends
– long term climate predictions are for significant heating,
little precipitation change
20
– historical trends show notable warming in the West (1
◦
F /decade) since 1970, and increase in precipitation
21
Total Water Usage in the U.S., 1950-2005
Figure 9: Total water usage by source in the U.S., 1950-2005.
Groundwater use is steadily increasing, total and surface water
use has leveled off. See USGS, and [Hutson et al., 2004].
22
U.S. Water Usage by Category, 1950-2005
Figure 10: Total water usage by category in the U.S., 1950-2005.
Approximately 30% of thermoelectric water was saline (TDS above drinking
water standard of 1000 mg/l), 2.5% of the thermoelectric total was
consumptive use (not returned to surface or groundwater streams).
23
Water Usage
• average groundwater usage in western U.S. is much higher
• average groundwater usage in Texas 60%, and generally
increasing with time (Fig. 11)
• largest users in west are agricultural irrigation, but this is
declining, partly in favor of municipal use (Fig. 12)
• 94% of NTX use is surface water. Current status of N. Texas
reservoirs or NOAA
24
Sources of Consumed Water, Texas, 1974-1993
Figure 11: Sources of consumed water, Texas, 1974-1993.
Texas Water Resources Planning Commision.
25
TX Water Use Categories 1974, 1993 & 2008
Figure 12: Water usage categories, Texas, 1974 (left), 1993 (middle) and
2008 (right). Municipal usage (blue in right two figures, green on left) has
grown from 12% in 1974 to 22% in 1993 to 25% in 2002. Concomitantly
irrigation usage has declined from 78% to 68% to 62% respectively. Texas
Water Resources Planning Commission and TWDB.
26
Projected Water Usage by Category, Texas
Figure 13: Projected water usage by categories, Texas. From
Texas Water Plan 2002. Municipal usage will increase more
rapidly than decrease in irrigation.
27
City Water Usage, Texas, 2006
Per-Capita Water Use 2006
280
260
240
Gallons/Capita/Day (GPCD)
220
200
180
160
140
HOUSTON
EL PASO
SAN ANTONIO
Tucson, AZ
AUSTIN
FORT WORTH
DALLAS
WACO
AMARILLO
MIDLAND
PLANO
Las Vegas, NV
100
RICHARDSON
120
Figure 14: 2006 Estimated water usage for Texas cities with population
greater than 95,000. Richardson has the greatest usage, nearly double that
of San Antonio, and higher than Las Vegas. Data from TWDB, see also
Texas Comptroller.
28
Projected Groundwater Supply, Texas
Figure 15: Projected groundwater availability, Texas major
aquifers. From Texas Water Plan 2002. See aquifer map for
locations.
29
LIPSCOMB
DALLAM
SHERMAN
HANSFORD
OCHILTREE
HARTLEY
MOORE
HUTCHINSON
ROBERTS
HEMPHILL
POTTER
CARSON
GRAY
WHEELER
ARMSTRONG
DONLEY
OLDHAM
40
RANDALL
27
Pr
ai
ri
D
e
LAMB
SWISHER
HALE
HOCKLEY
LUBBOCK
Lubbock
YOAKUM
LYNN
TERRY
o g To w n
BRISCOE
F ork Red River
FLOYD
MOTLEY
CROSBY
DICKENS
B
GARZA
DAWSON
Perennial Stream
16 to 30 years
BORDEN
ve
r
Major Road
Interstate
31 to 50 years
County Boundary
51 to 75 years
Ogallala Aquifer Extent
Outside of Texas
76 to 100 years
No Saturated Thickness Change
between 1990 and 2004
Water Table Rising
0
HOWARD
5
10
20
30
Land Surface Over
the Ogallala Aquifer
in West Texas
40
50
Miles
Co
MARTIN
Ri
Estimated Usable
Aquifer Lifetime
Greater than 100 years
ANDREWS
os
Already Below 30 feet
Less than 15 years
GAINES
az
r
CASTRO
PARMER
COCHRAN
r
Amarillo
DEAF
SMITH
BAILEY
C anadian R
ive
Oklahoma
Te x a s
New Mexico
Te x a s
High Plains Aquifer Lifetime
lo
r
ad
Midland
Odessa
ECTOR
MIDLAND
GLASSCOCK
o
R
iv
er
20
Figure 16: Projections for usable lifetime of Ogallalla Aquifer,
Texas Panhandle. From TTU.
30
India Groundwater Declines
Figure 17: India annual pumping as fraction of recharge. From
NASA.
31
California Snowpack Reduction
Figure 18:
Projected climate-change-related changes to California
snowpack. From Climate Change and Water Resources Factsheet. Lake
Lavon can hold 275,000 acre-ft of water. See 2007-2009 summary , note
2008 La Niña event. Also interactive prediction maps.
32
What Hydrologists Do
• primarily addressed water supply issues until 1970’s (i.e.
finding water)
• emphasis on contamination issues since creation of EPA
– requires a much more quantitative approach
– typically involving governmental regulations and/or lawyers
– current emphasis on “doing nothing”: finding and
preserving uncontaminated water supplies, establishing
natural attenuation as the typical remediation approach
– also Brownfields (development of contaminated properties,
e.g. American Airlines Center’)
• now returning to water supply issues given the problems of
drought, global warming and full allocation of resources
33
• see also USGS Hydrology Primer (last updated 2010)
34
Definitions
35
Definitions
• Ground Water: two overlapping definitions
– subsurface water that occurs beneath the water table in
porous geologic formations that are fully saturated
– that portion of subsurface water that can be collected with
wells, drainage pipes etc., or that flow naturally to the
surface via springs and seeps (NOTE: not all subsurface
water is groundwater)
– important to remember there is accessible and inaccessible
water in the subsurface
36
Definitions (cont.)
• Ground Water Hydrology:
the study of the origin,
distribution, movement and physical/chemical properties of
ground water. A subset of hydrology, the study of all
terrestrial waters.
• Surface Water Hydrology: the study of subaerial waters
(in contact with the atmosphere), excluding oceans. Civil
engineers usually mean “lakes and bays”, geologists usually
mean “rivers and streams” when using this term.
• Hydrogeology: emphasizes the hydrologic aspects of geology,
e.g. lithologic or facies influences on groundwater movement
• Geohydrology: emphasizing geologic aspects of hydrology,
37
particularly the effects of the porous medium through which
groundwater flows.
• in principle Hydrogeology and Geohydrology have different
meanings, in common usage they are identical
• Hydrosphere: that region of the Earth occupied by water,
including lakes, rivers, oceans, subsurface water, glaciers,
+/- atmospheric water (clouds, vapor, precipitation)
38
The Hydrologic Cycle
39
Definitions: Hydrologic Cycle
• the hydrologic cycle refers to the global chemical balance of
H2O in the hydrosphere (Fig. 19)
• start with Precipitation - form is important, e.g. in Nevada
snow is generally biggest contributor to groundwater
• some part of precipitation onto the ground becomes surface
runoff or overland flow
• the rest is infiltration:
Ppore ≤ Patmosphere
driven by gravity and pressure,
• much infiltrated water goes back out to the atmosphere by
40
evaporation or transpiration (uptake by plants and release
to atmosphere)
• infiltration that makes it to the water table becomes
groundwater, and is termed recharge
• while infiltrated water is above the water table, it forms an
unsaturated (or vadose) zone where pores are filled with a
mixture of air and water. Pore pressure is negative in this
zone.
• groundwater in the saturated zone is found in aquifers (rocks
through which water travels most easily). These are generally
separated by aquitards (water travels slowly through these)
or aquicludes (“impermeable” zones or layers)
41
• within the aquifer, water occupies the accessible pore space in
the rock (some pores may be blocked off, or “permanently”
occupied by something else. The accessible space is referred
to as the effective porosity
• groundwater that discharges into a stream is termed baseflow
(total flow in the stream is runoff)
42
Quantified Hydrologic Cycle
Figure 19: An illustration of the hydrologic cycle. After online
textbook. See flux estimates (p. 5) for water balance.
43
Water Balance
• much of hydrology is based on determining the water balance
for all or some part of the hydrosphere (e.g. a groundwater
basin)
• water balance is just a mass balance:
rate of
mass in
−
rate of
mass out
44
=
change in
content
Groundwater Basics
Some good online resources are now
available to provide overviews of hydrology.
My current favorite is the USGS Basic groundwater hydrology publication [Heath, 1987].
The classic textbook Freeze and Cherry [1979]
is now quite old, but is one of the few calculusbased geologic hydrology texts (much more
readable than civil engineering texts).
45
Aquifer Types
See also Fig. 20:
• confining layer (aquiclude): low-permeability bed or unit
• confined aquifer: an aquifer overlain by a confining layer
• unconfined aquifer (phreatic or water table): water table lies
below the top of the aquifer
• semi-confined: an aquifer exhibiting confined and unconfined
behavior at different locations (e.g. a sand layer in an alluvial
fan)
46
• artesian: can simply mean confined, in common usage it
means an aquifer from which water will flow upward to the
surface given an appropriate conduit (e.g. a borehole)
• perched: a saturated zone lying above unsaturated rock
47
Aquifer Features
Figure 20: Important features of groundwater systems,
including aquifer/aquitard, water table, etc. After Heath
[1987].
48
Water Table Definitions
• the undulating plane below the ground surface at which pore
water pressure is equal to atmospheric
• also the dividing line between the unsaturated and saturated
zones
• Phreatic surface: the level to which water will rise in a well
open only within the aquifer
– different than the water table only for confined aquifers
– when phreatic surface lies at or above the ground surface,
an artesian well or spring is possible
49
Motivating Examples
50
Southwest Drought 1998-2010
• 12-year drought (as of 2010) longest in historical record
[Overpeck and Udall, 2010]
• consistent with pre-historic extreme droughts [USGCRP,
2009, p. 130]
• longer and more frequent droughts predicted by climate
change models, would reduce supply to less than current
demand within the decade [Barnett and Pierce, 2008]
• i.e. permanent water shortage in most of the Southwest
51
Gulf of Mexico Dead Zone
The most severe nutrient pollution issue in U.S. is Gulf Coast
“Dead Zone”, with Chesapeake Bay a close second.
• high nutrient loads in Mississippi River discharge lead to large
algal blooms [CENR, 2000, p. 13]
• seasonal stratification leads to hypoxia zone, killing marine
life, e.g. Baltic Sea image
• see summary of nutrient source spatial and temporal
distribution [CENR, 2000, p. 27, 29], also USGS streamflow
& nutrient delivery to Gulf of Mexico
• see LSU Current Status webpage
52
• expanding steadily with time (2010 is largest ever measured,
area the size of New Jersey)
53
Other Resources
54
Useful Links
This is intended to be an ever-evolving list of useful links on
the general topic of this note set.
• groundwater extraction is 40% of sea level rise [Pokhrel et al.,
2012]
55
Bibliography
56
Tim P. Barnett and David W. Pierce. When will Lake Mead go dry? Water Resour. Res., 44
(W03201), 29 March 2008. doi: 10.1029/2007WR006704. URL http://www.agu.org/
journals/pip/wr/2007WR006704-pip.pdf.
CENR. Integrated Assessment of Hypoxia in the Northern Gulf of Mexico. Report, National
Science and Technology Council Committee on Environment and Natural Resources,
Washington, D.C., May 2000. URL http://oceanservice.noaa.gov/products/hypox_
finalfront.pdf.
R. A. Freeze and J. A. Cherry. Groundwater. Prentice-Hall, Englewood Cliffs, NJ, 1979.
R. C. Heath. Basic ground-water hydrology. Water Supply Paper 2220, U.S. Geol. Survey,
Denver, CO, 1987. URL http://water.usgs.gov/pubs/wsp/wsp2220/.
S. S. Hutson, N. L. Barber, J. F. Kenny, K. S. Linsey, D. S. Lumia, and M. A. Maupin. Estimated
use of water in the united states in 2000. Circular 1268, U. S. Geol. Survey, Reston, VA,
May 2004. URL http://water.usgs.gov/pubs/circ/2004/circ1268/.
IPCC4. Climate Change 2007: The Physical Science Basis, Summary for Policymakers (4th
Climate Assessment Report). Technical report, U.N. Intergov. Panel on Climate Change, 5
February 2007. URL http://www.ipcc.ch/SPM2feb07.pdf. 18 pp.
Jonathan Overpeck and Bradley Udall. Dry times ahead. Science, 328(5986):1642–1643, 2010.
doi: 10.1126/science.1186591. URL http://www.sciencemag.org.
Yadu N. Pokhrel, Naota Hanasaki, Pat J-F Yeh, Tomohito J. Yamada, Shinjiro Kanae, and Taikan
Oki. Model estimates of sea-level change due to anthropogenic impacts on terrestrial water
storage. Nature Geosci, advance online publication, May 2012. ISSN 1752-0908. doi:
10.1038/ngeo1476. URL http://dx.doi.org/10.1038/ngeo1476.
A. K. Prasad and R. P. Singh. Changes in Himalayan Snow and Glacier Cover Between 1972
and 2000. EOS, 88(33):326, 17 August 2007. doi: 10.1029/2007EO330002.
W. E. Stegner. Beyond the Hundredth Meridian: John Wesley Powell and the Second Opening
of the West. Houghton Mifflin, Boston, 1954.
57
USGCRP.
Global Climate Change Impacts in the United States.
Cambridge
University Press, 2009. URL http://www.globalchange.gov/publications/reports/
scientific-assessments/us-impacts. Quadrennial report to U.S. Congress.