hydrogeology · 2011-04-08 · hydrogeology 101 the objective is to obtain a better understanding...
TRANSCRIPT
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Hydrogeology 101
W. Richard Laton, Ph.D., PG, CPGAssociate Professor of HydrogeologyCalifornia State University, FullertonDepartment of Geological Sciences
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Hydrogeology 101
The objective is to obtain a better understanding of the principles of groundwater, hydrologic cycle and water budgets. The lecture will also cover various types of aquifers and general groundwater quality.
Objective
To understand Basic definitions
Hydrologic Cycle
Groundwater
Aquifers
How water flows
Water Budgets
Wells
Water Quality
Contamination
Investigation Tools
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Definitions
Water on Earth
Hydrologic Cycle
Meteorology
weather
Hydrology
Surface water
Hydrogeology
Groundwater
Unsaturated Zone
Vadose Zone
Aquifers
Water Table
Unconfined
Confined
Darcy’s Law
Safe Yield
Water Chemistry
Distribution of H2O
on Earth
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Hydrologic Cycle
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Meteorology
Climate
Precipitation
Rain
Snow
Temperature
Other factors
Location
Altitude
Rain Shadow Deserts
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Surface Water
Ocean, Lake, Pond
River, Stream
Spring, Wetland
Surface Water Flow
Discharge
Baseflow
Flood Stage
Gaining Stream
Losing Stream
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Gaining - Losing
Groundwater
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Water contained in spaces within soil and bedrock
Less than 1% of all H2O on Earth
40 times more abundant than water found in lakes and streams
Groundwater
zone of aeration: portion of soil and rock near the surface in which open spaces are filled primarily with air (a.k.avadose zone, unsaturated zone)
saturated zone: zone in which pore spaces are filled with water
water table: boundary between zone of aeration and saturated zone
Groundwater terms
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aquifer: body of rock that is sufficiently water permeable to yield economically significant quantities to wells and springs
Unconfined vs Confined
aquitard: body of rock that retards but does not prevent flow of water to or from an adjacent aquifer
aquiclude: body of relatively impermeable rock that is capable of absorbing water slowly but does not transmit it rapidly enough to supply a well or spring
More groundwater terms
Impacts of Faults on Groundwater Flow
Barriers to Groundwater Flow
Conduits of Flow
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Perched Water Table
Confined Aquifer
Aquifers
Vadose Zone
Unconfined Aquifer
Aquitard
Confined Aquifer
Water Table
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Isotropy/AnisotropyHomogeneous/Heterogeneous
Isotropy – The condition in which
hydraulic properties of the aquifer are equal in all directions.
Anisotropy – The condition under
which one or more of the hydraulic properties of an aquifer vary according to the direction of flow.
Homogeneous – A geologic unit
that has the same properties at all locations.
Heterogeneous – Hydraulic
properties vary spatially.
porosity: portion of volume of a material that consists of open spaces
permeability: measure of the speed at which fluid can travel through a porous medium
Imagine two vertical pipes, one filled with gravel, one with sand. Out of which one will the water flow faster?
Soils and rocks are not completely solid
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Poorly‐sorted Sandstone
Well‐sorted Sandstone
Fractured / Unfractured Shale
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Porosity and PermeabilityPrimary and Secondary Porosity
Hydraulic ConductivityTransmissivity
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Slow to very slow (depending on permeability)
Generally within the range of 10 to 100 cm per day
Rates of groundwater movement
Q = discharge (m3/sec)
A = cross-sectional area (m2)
K = coefficient of permeability (m/sec)
h1 = beginning height (m)
h2 = ending height (m)
l = length of flow (m)
Darcy’s Law
Q = AK(h1– h2)l
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Groundwater Movement in Temperate Regions
Wet Period
Dry Period
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In = Out ± change in storage
Simple in concept
Data driven
Difficult in practice
Water Budgets
How and where is the water coming from; Recharge
Return flow
How and where is the water going; Pumping
Surface water
Evapotranspiration
Assumptions – Water Budget
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Variables
Inputs Precipitation
Return flow
Overland Flow Streams
Springs
Groundwater
Outputs Pumping
Evapotranspiration
Overland Flow
Groundwater
Example Water Budget
Annual Average(acre-ft)
DWR [1967] Goodrich [1978]1 Brose [1987]
Total Input 1,744 1,050 1,750
Total Output 4,640 10,145 7,725
Total Water Budget -2,896 -9,095 -6,475
Annual Average (acre-ft) DWR [1967] Goodrich [1978]2 Brose [1987]
Surface Inflow 1,0501 1,0501 1,0501
Subsurface Inflow - - -
Precipitation 694 - 700
Imported Water - - -
Total 1,744 1,050 1,750
Annual Average (acre-ft) DWR [1967] Goodrich [1978]1 Brose [1987]Stamos and Predmore
[1995]
Surface Outflow - - - -
Subsurface Outflow 100 100 500 300 - 600
Consumptive Use 4,540 10,045 7,725 -
Total 4,640 10,145 8,225 -
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The amount of naturally occurring groundwater that can be economically and legally withdrawn from an aquifer on a sustained basis without impairing the native groundwater quality or creating an undesirable effect such as environmental damage. It cannot exceed the increase in recharge or leakage from adjacent strata plus the reduction in discharge, which is due to the decline in head caused by pumping.
C.W. Fetter, 1994.
Safe Yield (sustainability)
Groundwater Hydrographs
Common
Typically easy to interpret
Este Hydrologic Sub-basin(05N01E17D01)
1954-2002
50
70
90
110
130
150
170
1954 1957 1960 1963 1966 1969 1972 1975 1978 1981 1984 1987 1990 1993 1996 1999 2002
Measure Date
Fee
t B
elo
w G
rou
nd
Su
rfac
e
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Long-term monitoring
Frequent monitoring
Quality data you can trust
Assumptions - Hydrographs
0
50
100
150
200
250
300
350
4001
6
11
16
21
26
31
36
41
46
51
De
c-49D
ec-50
De
c-51D
ec-52
De
c-53D
ec-54
De
c-55D
ec-56
De
c-57D
ec-58
De
c-59D
ec-60
De
c-61D
ec-62
De
c-63D
ec-64
De
c-65D
ec-66
De
c-67D
ec-68
De
c-69D
ec-70
De
c-71D
ec-72
De
c-73D
ec-74
De
c-75D
ec-76
De
c-77D
ec-78
De
c-79D
ec-80
De
c-81D
ec-82
De
c-83D
ec-84
De
c-85D
ec-86
De
c-87D
ec-88
De
c-89D
ec-90
De
c-91D
ec-92
De
c-93D
ec-94
De
c-95D
ec-96
De
c-97D
ec-98
De
c-99D
ec-00
De
c-01D
ec-02
De
c-03D
ec-04
De
pth
to
Gro
un
dw
ate
r (F
eet
)
Pre
cip
ita
tio
n (
Inc
he
s)
Este Hydrologic Sub-basinLucerne Valley Sub-Basin
Big Bear Lake Big Bear Dam Lake Arrowhead 06N01W27B001S 06N01W35A001S05N01E06C001S 05N01W01C001S 05N01W01L001S 05N01W01R003S 05N01E08N004S05N01E17D001S 05N01E20F001S 05N01E27H001S 05N01W25G001S 05N01W36F001S
What do the hydrographs say?
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0
50
100
150
200
250
300
350
4001
6
11
16
21
26
31
36
41
46
51
Jan-94
May-94
Jul-94
Oct-94
Jan-95
Ap
r-95
Jul-95
Oct-95
Jan-96
Ap
r-96
Jul-96
Oct-96
Jan-97
Ap
r-97
Jul-97
Oct-97
Jan-98
Ap
r-98
Jul-98
Oct-98
Jan-99
Ap
r-99
Jul-99
Oct-99
Dec-99
Mar-00
Jun-00
Sep
-00
Dec-00
Mar-01
Jun-01
Sep
-01
Dec-01
Mar-02
Jun-02
Sep
-02
Dec-02
Mar-03
Jun-03
Sep
-03
Dec-03
Mar-04
Jun-04
Sep
-04
Dec-04
Dep
th to
Gro
un
dw
ater
(Fee
t)
Pre
cip
itat
ion
(In
ches
)
Este Hydrologic Sub-basinLucerne Valley Sub-Basin
Big Bear Lake Big Bear Dam Lake Arrowhead 06N01W27B001S 06N01W35A001S 05N01E06C001S
05N01W01C001S 05N01W01L001S 05N01W01R003S 05N01E08N004S 05N01E17D001S 05N01E20F001S
05N01E27H001S 05N01W25G001S 05N01W36F001S 04N01E06R001S 04N01E05P002S 04N01E12P001S
04N01W13R001S 04N01E23K001S 04N01E13M001S
Hydrographs – groundwater levels drive the analysis Decline in water levels
Increased water levels
No change
Balancing act
Analysis
z1
z2
z3
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Groundwater and Wells
Drawdown
Cone of depression
Capture zone
Groundwater Withdrawal
Potable (municipal and private)
Irrigation
Industrial
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Drawdown Due to Pumping
Water in aquifers is replenished primarily by infiltration of surface water (groundwater recharge).
Groundwater flows from areas of high pressure (or hydraulic head) to areas of low pressure. In unconfined aquifers, hydraulic head is given by the height of the water table above some reference level.
Left to itself, groundwater flow may intercept a surface water body, and flow into that body (natural groundwater discharge, Q).
Alternatively, it may be removed through wells for human consumption (artificial groundwater discharge).
dischargeto stream
impermeable layer
flow lines
water table
dischargeto well
Q1
Q2
Water flowing underground
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Mans Interaction
Groundwater Withdrawal
Pollutants/Contamination
James W. Borchers/USGS
Fissures, Depressions and Land SubsidenceCaused by Over Pumping
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Water quality can be thought of as a measure of the suitability of water for a particular use based on selected physical, chemical, and biological characteristics. To determine water quality, scientist’s first measure and analyze characteristics of the water such as temperature, dissolved mineral content, and number of bacteria. Selected characteristics are then compared to numeric standards and guidelines to decide if the water is suitable for a particular use.
Some aspects of water quality can be determined right in the stream or at the well. These include temperature, acidity (pH), dissolved oxygen, and electrical conductance (an indirect indicator of dissolved minerals in the water). Analyses of individual chemicals generally are done at a laboratory.
USGS, 2009
Water Quality
Water Quality and Groundwater Movement
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Sources of Contamination
Groundwater Contamination
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Investigation tools!
Remote Sensing
Geophysics
Subsurface Investigations (monitoring wells, soil and rock borings, etc.)
Aquifer Testing
Water level monitoring
Water Chemistry
Computer Modeling
Conclusion
Basic definitions
Hydrologic Cycle
Groundwater
Aquifers
How water flows
Water Budgets
Wells
Water Quality
Contamination
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Thank you
Questions?