Chapter 17:
THE HYDROLOGIC CYCLE
AND GROUNDWATER
What Makes water so important?
p
About the Hydrologic Cycle
• Hydrology is the study of movements
and characteristics of (ground)water.
• The hydrologic cycle has a profound
effect upon climate prediction.
• Water is vital so we must understand
where to find water and how water
supplies cycle through the Earth.
Flows and reservoirs
● Reservoirs
R
i include
i l d all
ll the
th places
l
that water is stored in and on the
Earth.
● Flows into a reservoir include
inflows and outflows
Flows and reservoirs
• < 1% of world’s water is readily available for use. Globally,
70% of fresh water is used for agriculture, 20% for industry,
10% for residences.
• If all the polar ice caps melts, then sea-level will rise by 75 m.
Water: Residence times
Flows and reservoirs
● The
Th hydrologic
h d l i cycle
l
● precipitation
i it ti
● infiltration
i filt ti and
d runoff
ff
● evaporation,
ti
ttranspiration
i ti
● groundwater flow
The hydrologic cycle
cycle-powered by solar energy
Hydrology
y
gy and climate
● Key climatic factors
● relative humidity
● rainfall
● landscape
● Key tectonic factors
● ocean–land
l d relationships
l ti
hi
● mountain rain shadows
Hydrology and climate:
the rain shadow effect
Leeward slope
Windward slope
The hydrology of runoff
● Surface storage of water runoff
● lakes and reservoirs
● wetlands and swamps
Groundwater
● Groundwater flow through soil
and rock
● porosity
p
y and p
permeability
y
● groundwater
d t ttable
bl
Groundwater
• Porosity (φ): is the fraction of a porous material, which is
void space
φ = Vvoid/Vtotal
Groundwater:
porosity
porosit and
the amount
of open space
in various
materials
Groundwater
● Above and below the groundwater
table
● unsaturated ((vadose)) zone
● saturated
t t d (phreatic)
( h ti ) zone
Groundwater:
the
water
table
Groundwater
Two major zones of groundwater:
•Vadose Zone: zone above the water table ((zone of aeration,
unsaturated).
•Zone of saturation: upper surface of saturation zone is
[Groundwater] Water Table
Table.
Water Table mimics the ground topography, the height of which fluctuates
with recharge/discharge.
Groundwater
● Inflow and outflow of groundwater
● groundwater recharge (influent
streams or losing
g streams))
● groundwater
d t di
discharge
h
((effluent
ffl
t
streams)
Groundwater:
effluent water
headed for a
stream
Groundwater
• Aquifer: any lithologic formation that
stores
sto
es g
groundwater
ou d ate (gravel,
(g a e , sa
sand,
d,
limestone etc.). It not only stores but also
transmits water at faster rates
rates.
• Aquiclude: is a formation that may
contain water but does not transmit
significant quantities (clays and shales).
• Aquitard: is a formation with relatively low
permeability.
permeability
Groundwater
● Types of aquifers
● unconfined – has an aquiclude
below
● confined – has an aquiclude
above and below
● Perched
Types of
Aquifer:
Unconfined
Aquifer
qu e
Confined Aquifer
● Characteristics of some confined
aquifers
● artesian (flowing) wells
● artesian flow (under pressure)
Groundwater: artesian conditions
Potentiometric (peizometeric) surface: Imaginary
level to which water rises due to hydrostatic
y
pressure.
Groundwater
● Complex
p
g
geological
g
environments
● perched
h d water
t ttables
bl
● unpredictable flow conditions
Groundwater:
perched
water
t
table
Recharge of Groundwater
● Balancing recharge and discharge
● balance = stable water table
● excess recharge = rising water
t bl
table
● excess discharge = falling
water table
Groundwater:
excess
e cess
discharge
g
and the
cone of
depression
What is the consequence of
over pumping (over draft)?
¾compaction and degradation of the aquifer
¾may trigger subsidence
When the well is dry, we learn the worth of water"
- Benjamin
B j i Franklin
F
kli
Groundwater:
Excess discharge and
The intrusion of salt
water
Q. What is the consequence
off salt
lt water
t intrusion
i t
i
into aquifers?
Darcy’s
y LAW:
Darcy’s law provides an accurate description of
the flow of ground water in almost all
hydrogeologic environments.
Head loss h1 - h2 determines
flow rate
Q – KA(dh/
Q=
KA(dh/dL
dL))
Q= – KA(dh/
Q
KA(dh/dL
dL))
Volumetric flow rate (Q)
(m3/s or ft3/s)
hydraulic conductivity (K) (m/s or ft/s)
Area of cross section perpendicular to flow (A)
Hydraulic gradient (dh/dL)
dh =h
hin - hout (difference
(diff
in
i height
h i ht off water
t level
l
l
in inlet and outlet peizometers)
The minus signs on the right hand reflects that the
hydraulic head always decreases in the direction
off fflow.
K represents the measure of the ability for flow
(permeability) through porous media.
• Darcy Velocity or Flux ( or specific discharge) [q]:
volumetric flow per unit area
q = Q /A = -K dh/dl
Unit: L/T
Darcy velocity is a fictitious velocity since it assumes
that flow occurs across the entire cross-section of the
soil sample. Flow actually takes place only through
interconnected pore channels.
The average pore water velocity is termed the seepage
velocity (v) and is given by:
v = q/φ = Q/(Aφ)
where φ is the p
porosity
y of the p
porous media ((varies
from 0 to 1).
Average
g rate of groundwater
g
flow is ~ 15 m/day,
y, mayy
reach up to 125 m/day.
Table. Typical Porosity and hydraulic conductivity of
selected Earth Materials.
Material
Porosity
y (%)
Hydraulic Conductivity
(K) in m/day
Unconsolidated
Clay
45
0.041
Sand
35
32.8
Gravel
25
205
Gravel & Sand
20
82
Sandstone
15
28.7
Limestone/ Shale
5
0.041
Granite
1
0.0041
Rock
Numerical Problem
Q Two
Q:
T
wells
ll are llocated
d 100 feet
f
apart in
i a sand
d aquifer
if with
iha
hydraulic conductivity of 0.04 feet per day and 35%
porosity. The head of well 1 is 96 ft and the head of well 2 is 99
ft.
Q What is the seepage velocity of water between the two
Q.
wells?
Ans: v = q/φ = K/φ × dh/dl
= (0.04ft/day × 1/0.35) × (0.03) = 0.0034 ft/day.
Numerical Problem
4 km
Sedimentary rocks
Valley
Well 1
1 km
Well 2
Flo direction in valley
Flow
alle
Sedimentary rocks
The valley (blue) is 4 km wide, where 2 wells are drilled 1 km apart.
y Porosity
y
The saturated zone below is 25 m thick,, with K = 100 m/day.
(φ) of material is 30% (0.3). The elevation of water in wells 1 and 2 are
98 and 97 m respectively.
3
3
10,000
m
/day
Q What is the discharge,
Q.
discharge Q (m /day) of aquifer?
Q. What is the time travel (T) of groundwater between
wells 1 and 2? This helps in studying contaminant
transport. 3000 days
Erosion by
yg
groundwater
● Features of groundwater erosion
● caves and caverns
● stalactites and stalagmites
● karst features ((karst
karst topography)
● sinkholes
Erosion by
yg
groundwater: karst
Satellite View
— Karst
K
t
Topography
What are the Environmental
concerns in karst terranes?
¾sinkhole collapse
¾Winter Park, Florida 1981: 100 m depression,
13 m deep, $2 million in damage
¾Susceptible to pollution from above
¾hard water problem: amount of Ca2+ and Mg2+ in
water; difficulties with plumbing
¾thin residual soils, terra rosas, which makes
waste burial or disposal management considerably
difficult.
difficult
Erosion by
y
groundwater:
Carlsbad
Caverns,
New
Mexico
Erosion by
y
groundwater:
sinkhole
in
Winter Park,
Park
Florida
100 m wide, 13 m deep, $2 million in
damage
Groundwater Uses
Why should we be concerned about
groundwater pollution?
¾ Groundwater Pollution is difficult to
detect.
¾ Groundwater has long-term residency
(1000 yr), which means if polluted then it
stays
y there for a long
g time.
¾ Difficult and expensive to clean aquifers.
What steps can be taken to
characterize groundwater pollution?
• Geologic characterization
(lithology structure)
(lithology,
• Hydrologic characterization: depth
of water table, thickness of aquifer,
direction and rate flow etc.
etc
• Contaminant (type & source)
identification and understanding the
transport mechanisms.
mechanisms
Aquifer Contamination
¾ Although unconfined aquifers are used for water
supply, they are often contaminated by wastes and
chemicals at the surface.
¾ Confined aquifers are less likely to be contaminated
and thereby provide supplies of good quality.
Water Quality
● Contamination Source of water
supply
l
•
•
•
•
•
•
•
•
Oxygen-demanding waste
Pathogenic organisms
Nutrients
Oil & Petroleum Products
H
Hazardous
d
Ch
Chemicals
i l
Toxic Heavy Metals
Radioactive Materials (Ra 222)
Thermal Pollution
A pollutant is any substance, excess exposure to which is known to be
harmful to living organisms.
Water Quality
• Pathogenic organisms
-Common
C
diseases are C
Cholera, typhoid, hepatitis,
dysentery etc.
-Cryptosporidiosis
Cryptosporidiosis (caused by Cryptosporidium, a
protozoa infection in the gastrointestinal tract
- standard measure of microbial pollution is to count
f
fecal
l coliform
lif
bacteria
b t i (a
( group off bacteria
b t i found
f
d in
i
human & animal intestine & wastes).
E. Coli ((usually
y found in meat p
products),
), a type
yp of
coliform bacteria causes illness and death.
Acceptable limit for drinking water is 1 coliform per
100 mL of sample
sample.
Causes of Contamination: earthquakes, floods, storms
etc., may damage sewer lines resulting in
contamination of water supply.
Eutrophication:
Eutrophication
p
: Nutrients
Acondition in aquatic ecosystem where high
nutrient concentration stimulates growth of
phytoplankton.
Higher amounts of nutrients in a water
body help grow algae & aquatic plants,
which cloud water & block sunlight.
Underwater grasses, which serves as
food for aquatic creatures dies. When
algae die & decompose, O2 is used up,
resulting in depletion of dissolved
Oxygen.
• Hazardous Chemicals:
– Toxic synthetic organic and inorganic compounds
– oxygen additives
dditi
(Methyl
(M th l Terbutyl
T b t l Ether,
Eth MTBE) in
i
gasoline in order to increase oxygen level of
gasoline and decrease CO emissions
emissions. MTBE is
water soluble and commonly detected as Volatile
Organic
g
Compound
p
(VOC)
(
) in groundwater.
g
Conc.
Of 20-40 μg/L (ppb) can cause difference in taste
& odor.
– Common VOC are - gasoline, industrial chemicals
such as benzene, toluene and xylene (a.k.a. BTX),
formaldehyde (carcinogens)
(carcinogens), and
tetrachloroethylene, perchloroethylene (principal
dry cleaning solvent)
Oil & Petroleum Products
• Oil discharge in to water involving oil-tanker accidents in
sea.
Case History: In 03/24/1989, the oil tanker, Exxon Valdez,
spilled > 11 million gallons of crude oil in sea near Valdez,
Al k ((world’s
Alaska
ld’ mostt pristine
i ti & ecologically
l i ll rich
i h marine
i
environment). Out of this 50 % deposited on the shoreline,
20% evaporated, and only 14% was collected by waste
recovery
recovery.
•
•
•
In 1994
1994, N
N. Russia
Russia, pipe line fracture resulted in about 4-80
million gallons of crude oil spill contaminating land & water.
Sept 16, 2008. A crack in the diesel pipeline of the Indian Oil
C
Corporation
((IOC)
OC) has led to oil spillage in G
Ganga
Aug 22, 2009 - oil spill across a 100-km swath on the south
Gujarat
Guja
at coast, threatens
t eate s the
t e marine
a e bio-diversity
b o d e s ty in tthe
e National
at o a
Marine Park and Sanctuary. Two major oil refineries — Reliance
and Essar.
Toxic Substances
•
Heavy Metals:
– Such as Pb, Hg, Zn, Cd, As are often deposited with natural sediments at
the bottom of stream channels. Become incorporated into plants, crops,
and thus animals and humans.
– Inorganic ions of such metals are toxic
– Hg (from volcanic emissions, natural deposits) contamination of aquatic
systems.
Methylation:- Change of inorganic Hg2+ to CH3Hg+ (methylmercury) due to
bacterial activity. CH3Hg+ is more toxic than Hg2+. The conc. of CH3Hg+
increases higher in the food chain.
Residence time of
Hg in ocean = 80,000
yrs
Source of Water Pollution
Surface water Pollution
• Point source pollution:
– readily identifiable localized and/or confined sources
such as industrial/municipal pipes, sewers that empty
into streams or rivers.
– These pollutants controlled by on
on-site
site treatment/
disposal and are regulated by permit.
• Non
Non-point
point source pollution:
– Diffused and intermittent pollution
– Influenced by
y factors such as climate,, hydrology,
y
gy,
topography, vegetation, geology, urbanization etc.
– Includes all sorts of pollutants entering the water
system
t
from
f
any sources (e.g,
(
i
insecticides
ti id from
f
plant
l t
is washed away by rain and added to rivers)
Acid Mine Drainage – non
non--point source pollution
Oxidation of pyrite
FeS2 + 3
3.75
75 O2 + 3.5
3 5 H2O ⇔ Fe(OH)3 + 2 H2SO4
Remediation
● Reversing contamination
● easier if recharge rate is fast
● usually costly and very slow
● decontamination after pumping
● in
in--ground water treatments
Groundwater Treatment
• Treatment processes:
– Extraction Wells: Pump out contaminated
water and treat it by filtration, oxidation,
reverse osmosis etc.
– Vapor Extraction: Using vapor extraction
well and treatment.
– Bioremediation: using microorganisms to
attenuate contamination.
– Permeable treatment bed: contact
treatment as contaminated water plume
moved through beds, which neutralizes
contaminants by chemical, physical and/or
bi l i l processes.
biological
Control System for
C t i t d Ground
Contaminated
G
d
Water
Extraction Wells
Water q
quality
y
Factors that determine the quality of drinking water:
• Acidity
(pH) —should be around 7
• Salinity (TDS) —should be <500mg/L
• Dissolved
Di
l d constituents
tit
t
Organic
Inorganic
g
• Pathogens
• Taste
(bad taste due to too much of some dissolved constituents
such as Fe, Cu, S, Cl))
•Toxic metal and organic contaminant levels
Quality Criteria of Indian Drinking Water
Set by Indian Standards Institution and Indian Council of Medical
Research (ICMR): ISI (IS:10500-1989)
Sl. No.
Substance or Characteristic
(1)
1.
2.
3.
4.
5
5.
6.
7.
8.
9.
(2)
Colour, Hazen Units
Odour
Agreeable
Turbidity
Di l d solids,
Dissolved
lid mg/l
/l
pH value
Total hardness (as CaCO3), mg/l
Calcium (as Ca), mg/l
Magnesium (as Mg), mg/l
10.
10
11.
12.
13.
14.
15.
16.
17.
Copper (as Cu),
Cu) mg/l
0 05
0.05
Iron (as Fe), mg/1
0.3
Manganese(as Mn),mg/1
0.1
Chlorides (as Cl), mg/l
250
Sulfate (as SO4), mg/l
150
Nitrate (as NO3), mg/l
45
Fluride (as F), mg/I
0.6 to 1.2
Phenolic
Compounds
(as 0.001
C6H5OH),mg/I
Mercury (as Hg),mg/l.
0.001
Cadmium(as Cd),mg/l
0.01
Selenium (as Se),mg/l
0.01
Arsenic (as As),mg/l
0.05
Cyanide(as CN), mg/l.
0.05
Lead (as Pb),mg/1.
0.10
Zinc (as Zn), mg/l
5
Chromium (as Cr6+), mg/1
0.05
P ti id
Pesticides
Ab t
Absent
Radio-active materials:
a) Alpha emitters uc**** per ml, 10-8
Max.
b) Beta emitters uc per ml, Max 10-7
18.
19.
20.
21.
22.
23.
24.
26.
30
30.
31.
Prescribed by ISI
Prescribed by ICMR
Requirement
(Desirable Highest Desirable Level
Limit)
Max. Permissible level
(3)
(4)
10
5 units
Unobjectionable
Unobjectionable
Unobjectionable
Unobjectionable
10 NTU
5JTU
500
500
6.5 to 8.5
7.0 to 8.5
300
300
75
75
30
Not more than 50 mg/I
Maximum Permissible level
(5)
25 units
Unobjectionable
Unobjectionable
25 JTU
1500*
6.5 to 9.2
600
200
00.05
05
0.1
0.1
200
200
20
1.0***
0.001
11.55
1.0
0.5
1000
400
**
1.5
0.002
------------
0.001
0.01
0.01
0.05
0.05
0.10
---3 pci/l*****
--
30 pci/1
Oct. 2008
World-wide Hydrological Mapping and Assessment Programme (WHYMAP); United Nations Educational, Scientific and
Cultural Organization (UNESCO) & German Federal Institute for Geosciences and Natural Resources (BGR)
A map of aquifer zones in India (1,2, 3: aquifer zones
zones))
1. Alluvial aquifers of IndoGangetic plains in the northern
and eastern India. Also,
Narmada and Tapi river alluvium,
coastal alluvium, coastal sand
dunes and coastal limestone
aquifers.
2. Aquifers in the alluvium,
li
limestone,
t
sandstone
d t
etc.
t in
i th
the
inland sedimentary basins of
central and southern India.
3. Hard rock aquifers in the Basalt
(Deccan Traps), Metamorphic
rocks and Basement complex
(granite and gneiss).
Source: groundwater resources of the world and their use; United Nations
Educational, Scientific and Cultural Organization (UNESCO) report 2004.
Hydrological map of India and
Yield Potential
Central
C
t l Ground
G
d Water
W t
Board (Ministry of
Water Resources
Government of India)
India)http://cgwb.gov.in
Groundwater Resources of IndiaIndia- Recharge
The map shows groundwater
changes in India during
2002-08, losses in red and
gains in blue, based on
GRACE satellite
observations.
Estimated rate of depletion
of groundwater in
northwestern India (Jaipur
and New Delhi) is 33 cm (1 ft)
of water per year over the
past decade. Increases in
groundwater in southern
India are due to recent
above-average rainfall,
whereas rain in
northwestern India was
close to normal during the
study period.
Loss is almost entirely
due to human activity.
Gravity Recovery and Climate
Experiment (GRACE) satellite data
Credit: II. Velicogna/UC Irvine
published in the August 20
issue of Nature
Watershed of India
Central Ground Water Board
(Ministry of Water Resources
Government of India)http://cgwb.gov.in
-Watershed atlas of India
-Basin wise watershed maps
available
Thought
g questions
q
for this chapter
p
1 If the Earth warmed
1.
warmed, causing evaporation from the
oceans to increase greatly, how would the hydrologic
cycle of today be altered?
2. If you lived near the seashore and started to notice that
your well water had a slightly salty taste, how would
you explain the change in water quality?
3. Why would you recommend against extensive
development and urbanization of the recharge area of
an aquifer that serves your community?
4. Why should communities ensure that septic tanks are
maintained in good condition?
Thought
g questions
q
for this chapter
p
5. Why are more and more communities in cold climates
restricting the use of salt to melt snow and ice on
highways?
6. You are exploring a cave and notice a small stream
flowing on the cave floor. Where could the water be
coming
i from?
f
?
Key
y terms and concepts
p
Aquiclude
Aquifer
Artesian flow
Darcy’s
Darcy
s law
Discharge
Groundwater
Groundwater table
Hydraulic gradient
Hydrologic cycle
Hydrology
yd ot e a water
ate
Hydrothermal
Infiltration
Karst topography
Meteoric water
Permeability
Key
y terms and concepts
p
Potable water
Precipitation
Rain shadow
Recharge
Relative humidity
Reservoir
Runoff
Saturated zone
Sinkhole
Unsaturated zone