Transcript Groundwater in big cities, use, consequences, impacts of climate

Groundwater in big cities, use,
consequences, impacts of climate change
and response options
Karen G. Villholth
Groundwater Specialist, Senior Researcher
GEUS, Geological Survey of Denmark and Greenland
Copenhagen, Denmark
FAU Conference 2000
Copenhagen Business School, Denmark, May 15, 2008
Groundwater withdrawal, cubic km/year
Groundwater development in selected countries
India
250
USA
China
200
Bangladesh
Pakistan
Mexico
150
W.Europe
Tunisia
100
South Africa
Sri Lanka
Vietnam
50
Spain
Ghana
0
1940
Ref: Shah, 2004
1960
1980
2000
Importance of GW for cities
• Groundwater is the main source of domestic-
•
•
potable water supply in most European countries
(Water Economy Prospects for 1990 and 2000,
1982)
In general, GW is the primary source for
domestic water supply and hence significant for
most cities
Quantity-wise, GW use for cities is less than the
use in agriculture
Reasons and advantages of using
groundwater for cities
• Surface water exhausted or polluted
• New drilling and pumping technology
• Groundwater is generally of a good, reliable and
•
constant quality and temperature suitable for
drinking water with no or little pre-treatment
Groundwater can be developed incrementally
and with less capital investment
Feature
Groundwater resources and
Groundwater
aquifers
Surface water resources and
Surface
water
reservoirs
HYDROLOGICAL CHARACTERISTICS
Storage volume
Large to very large
small to moderate
Resource areas
relatively unrestricted
restricted to water bodies
Flow velocities
very low
moderate to high
Residence times
decades/centuries
weeks/months
Drought propensity
generally low
generally high
Evaporation losses
low and localized
high for reservoirs
Resource assessment
high cost and significant uncertainty
lower cost and often less uncertainty
Abstraction impacts
delayed and dispersed
immediate
Natural quality
generally (but not always) high
variable
Pollution vulnerability
variable natural protection
largely unprotected
Pollution persistence
often extreme
mainly transitory
Public perception of resource
unconnected and replenishable
limited, aesthetic
Development cost
generally modest
often high
Style of development
mixed public and private
largely public
Knowledge of resource and
importance
Sparse, use underestimated, impacts
disregarded
well-developed, use well-documented
SOCIO-ECONOMIC FACTORS
Groundwater flow and occurrence
Importance of groundwater,1
Importance of groundwater, 2
Importance of groundwater, 3
Importance of groundwater, 3
Importance of groundwater, 4
Impact in response to change
Pre-development
Post--development (T1)
Post--development (T2)
Effect on riparian vegetation
Example from Dhaka, Bangladesh
Δ=22%
Δ=30m over 30 years
GWL decline, example from China
Δ=20m over 35 years
Hydrograph
depicting
water-table
elevations
beneath
Luancheng
Agro-Ecological
Research
Station
(Chinese
Academy
of Sciences),
Luancheng
County, Hebei
Province,
1974-2002.
Dramatic changes of depression cones
in Cangzhou
m
m
6-1973
2-1981
GWL decline, example from Chicago
Saltwater intrusion
• Inflow of saltwater into freshwater aquifer
• Origin of saltwater:
– Seawater in coastal areas
– Geological saline deposits in deeper formations
– Influx or accumulation from irrigated agriculture
In coastal areas there is a natural
balance between salt and freshwater
ground surface
phreatic water table
sea
fresh groundwater
zone
on
i
s
u
f
f
of di
saline groundwater
impervious layer
GW withdrawal in coastal auifers
Subsidence
Subsidence, impacts
• Gives problems for infrastructure,
buildings, pipelines
• Flooding and drainage patterns changed
• Causes secondary GW contamination from
breakage of underground pipes and tanks
What is subsidence?
Before
After
Example of subsidence,
San Joaquin Valley
GWL
Landsurface level
Relation btw. subsidence and
GWL decline
Example of subsidence, Texas
Groundwater pollution sources
GW pollution risk
Vulnerability high, but
load is low
Load is high, but
vulnerability is low
high
Urbanization
• Generally, urbanization decreases the recharge
to aquifers (pavements, storm water drainage)
• However, depending on the primary source of
water supply and the means of discharging
wastewaters, GWLs may be affected differently
Climate change
• There is accumulating evidence that the climate is
changing on a global scale
• Exact effects not known as well as the speed, extent and
local distribution of them
• Some effects seem inevitable:
– Water level rises due to global warming
– More variability and unpredictability in climate and more
‘extreme’ events
– Dry regions becoming drier
• Effects compounded by other human influences (e.g.
•
intensive water exploitation)
Most vulnerable areas: Arid areas, big coastal cities,
large tropical deltas
Climate change on GW in cities
• GW can be a drought prevention strategy but only to a
certain extent
• GW over-abstraction and flooding can occur at the same
time
• Energy intricately linked to GW exploitation
• CC exacerbate existing problems of GW
Disaster
management
Post-Modern Water Balance
Increased Pumpage to Meet Domestic,
Increased Water Demand for Agriculture,
Agricultural, Industrial and
People and Ecosystems
Ecosystem Demands
Precipitation/Recharge
Precipitation
Change
Ground Water
Water Contamination
Contamination
Cost-Effective Water
Increased Valuation/
Treatment and
Economic
Conservation
Breakpoints
Technologies
Virtual Water Imports
And Exports
Transboundary
Disputes
Flows
Changes in Water Availability
Saltwater
intrusion
Number of wells
Total abstraction
Sustainable level of
ressource development
with acceptalbe impacts
under present conditions
time
0
1
2
3
4
Baseline
situation
Incipient stress
an
Significant
stress
Unstable
development
Stable
development
Availability and
accessibility of
adequate quality
groundwater
greatly exceeds
small dispersed
demand
Growth of aquifer
pumping, but only
few local conflicts
between
neighbouring
abstractors
Abstraction
expanding rapidly
with impacts on
natural regime
and strong
dependence of
stakeholders on
ressource
Excessive
abstraction with
irreversible aquifer
deterioration and
stakeholder
conflicts
High-level of
abstraction, but
sound balance
between
stakeholder
interests and
ecosystem needs
Registration of
wells required,
together with
maps of
occurrence of
usable resources
Simple
management tools
(e.g. appropriate
well-spacing
according to
aquifer properties)
Regulatory
framework
needed, based on
comprehensive
assessment
Regulatory
framework with
demand
managemnt
and/or artificial
recharge urgently
needed
Integrated
management with
high-level of user
self-regulation,
aquifer monitoring
and assessment
Some response options
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•
•
•
•
•
•
•
More focus on GW, monitoring, permits,
GW mgt. as an integral part of IWRM
Combine demand and supply mgt.
Awareness of general public => genuine stakeholder
participation in groundwater protection
Capacity building => Research into mgt. => informed
mgt.
Advocacy at the policy level => importance of GW
acknowledged and incorporated into policies and
institutions
Climate change a driver for GW emphasis
No blanket policy