Groundwater in big cities, use, consequences, impacts of climate change and response options Karen...

Groundwater in big cities, use, Groundwater in big cities, use, consequences, impacts of climate consequences, impacts of climate change and response optionschange and response options

Karen G. VillholthKaren G. VillholthGroundwater Specialist, Senior ResearcherGroundwater Specialist, Senior Researcher

GEUSGEUS, Geological Survey of Denmark and Greenland, Geological Survey of Denmark and GreenlandCopenhagen, DenmarkCopenhagen, Denmark

FAU Conference 2000FAU Conference 2000CCopenhagen Business School, Denmark, May 15, 2008openhagen Business School, Denmark, May 15, 2008

Groundwater development in selected countries

0

50

100

150

200

250

1940 1960 1980 2000

Gro

un

dw

ater

wit

hd

raw

al, c

ub

ic k

m/y

ear

India

USA

China

Bangladesh

Pakistan

Mexico

W.Europe

Tunisia

South Africa

Sri Lanka

Vietnam

Spain

Ghana

Ref: Shah, 2004

Importance of GW for citiesImportance of GW for cities

• Groundwater is the main source of Groundwater is the main source of domestic-potable water supply in most domestic-potable water supply in most European countries (European countries (Water Economy Water Economy Prospects for 1990 and 2000, Prospects for 1990 and 2000, 1982)1982)

• In general, GW is the primary source for In general, GW is the primary source for domestic water supply and hence domestic water supply and hence significant for most citiessignificant for most cities

• Quantity-wise, GW use for cities is less Quantity-wise, GW use for cities is less than the use in agriculturethan the use in agriculture

Reasons and advantages of Reasons and advantages of using groundwater for citiesusing groundwater for cities

• Surface water exhausted or pollutedSurface water exhausted or polluted

• New drilling and pumping technologyNew drilling and pumping technology

• Groundwater is generally of a good, Groundwater is generally of a good, reliable and constant quality and reliable and constant quality and temperature suitable for drinking water temperature suitable for drinking water with no or little pre-treatmentwith no or little pre-treatment

• Groundwater can be developed Groundwater can be developed incrementally and with less capital incrementally and with less capital investmentinvestment

Feature Groundwater resources and aquifers

Surface water resources and reservoirs

HYDROLOGICAL CHARACTERISTICSHYDROLOGICAL CHARACTERISTICS

Storage volumeStorage volume Large to very large small to moderate

Resource areasResource areas relatively unrestricted restricted to water bodies

Flow velocitiesFlow velocities very low moderate to high

Residence timesResidence times decades/centuries weeks/months

Drought propensityDrought propensity generally low generally high

Evaporation lossesEvaporation losses low and localized high for reservoirs

Resource assessmentResource assessment high cost and significant uncertainty lower cost and often less uncertainty

Abstraction impactsAbstraction impacts delayed and dispersed immediate

Natural qualityNatural quality generally (but not always) high variable

Pollution vulnerabilityPollution vulnerability variable natural protection largely unprotected

Pollution persistencePollution persistence often extreme mainly transitory

SOCIO-ECONOMIC FACTORSSOCIO-ECONOMIC FACTORS

Public perception of resourcePublic perception of resource unconnected and replenishable limited, aesthetic

Development costDevelopment cost generally modest often high

Style of developmentStyle of development mixed public and private largely public

Knowledge of resource and Knowledge of resource and importanceimportance

Sparse, use underestimated, impacts disregarded

well-developed, use well-documented

Groundwater Surface water

Groundwater flow and Groundwater flow and occurrenceoccurrence

Importance of Importance of groundwater,1groundwater,1

Importance of groundwater, Importance of groundwater, 22

Pre-development

Post--development (T1)

Post--development (T2)

Impact in response to changeImpact in response to change

Effect on riparian vegetationEffect on riparian vegetation

Example from Dhaka, Example from Dhaka, BangladeshBangladesh

Δ=22%

Δ=30m over 30 years

Karen Villholth

Dhaka major GW-dependent city, relies on water from an underlying semi-confined aquidfer. More than 1300 private and public boreholes. The productivity of new wells has also declined by almost 30 %.

Karen Villholth

Rest level = static level

GWL decline, example from GWL decline, example from ChinaChina

Hydrograph depicting water-table elevations beneath Luancheng Agro-Ecological Research Station (Chinese Academyof Sciences), Luancheng County, Hebei Province, 1974-2002.

Δ=20m over 35 years

Dramatic changes of depression cones Dramatic changes of depression cones in Cangzhouin Cangzhou

6-1973

6-2000

6-1995

2-1981

mm

GWL decline, example from GWL decline, example from ChicagoChicago

Saltwater intrusionSaltwater intrusion• Inflow of saltwater into freshwater aquiferInflow of saltwater into freshwater aquifer

• Origin of saltwater:Origin of saltwater:– Seawater in coastal areasSeawater in coastal areas– Geological saline deposits in deeper formationsGeological saline deposits in deeper formations– Influx or accumulation from irrigated Influx or accumulation from irrigated

agricultureagriculture

In coastal areas there is a In coastal areas there is a natural balance between salt natural balance between salt and freshwater and freshwater

fresh groundwater

ground surface

saline groundwater

seaphreatic water table

zone of diffusion

im pervious layer

GW withdrawal in coastal GW withdrawal in coastal auifersauifers

SubsidenceSubsidence

Subsidence, impactsSubsidence, impacts

• Gives problems for infrastructure, Gives problems for infrastructure, buildings, pipelinesbuildings, pipelines

• Flooding and drainage patterns Flooding and drainage patterns changedchanged

• Causes secondary GW contamination Causes secondary GW contamination from breakage of underground pipes from breakage of underground pipes and tanks and tanks

What is subsidence?What is subsidence?Before After

Karen Villholth

Pressure of the water within the pores between the individual sediment particles also helps to support some of this weight. Groundwater pumping has the effect of decreasing the pore water pressure and thus increasing the effective stress from the overlying strata on the matrix of the aquifer. When the increase in effective stress is greater than a critical value, known as the preconsolidation stress, the sediment compaction becomes irrecoverable or inelastic.

Karen Villholth

All sediments are subjected to an increase of effective stress in this situation. However, coarsegrained sandy aquifers form a rigid aquifer matrix which generally resists compaction whereas fine-grained clayey strata are more plastic and hence more prone to compaction. Where relatively coarse-grained aquifers are sandwiched between fine-grained aquitards, groundwater pumping from the coarse layers can induce leakage from the aquitards; the resulting delayed dewatering of the aquitards can result in greater compaction than that of the aquifer.

Example of subsidence,Example of subsidence,San Joaquin ValleySan Joaquin Valley

GWL

Landsurface level

Relation btw. subsidence and Relation btw. subsidence and GWL declineGWL decline

Karen Villholth

Mexico city extreme, 0.4 m settling per year with a GWL decline of 1.0 m/year.

Example of subsidence, Example of subsidence, TexasTexas

Groundwater pollution Groundwater pollution sourcessources

Karen Villholth

Inputs may be intentional (by design or neglect) or unintentional (side-effect or accident).GW contamination is more likely in shallow, porous unconfined aquifers, since most releases occur close to the land surface.

Karen Villholth

GW contamination is closely linked to land use, hence the planning and regulation of landuse and the handling and disposal of hazardous chemicals in the environment is critical to GWQ.

Karen Villholth

Deep GW pollution sources: oil/gas exploration, deep well waste injection, pumping of GW underlain by saltwater.

Karen Villholth

Interaction with surface water may be complex and not constant. E.g. exchange of water between river and GW may release pollution from GW to stream or the other way around.

Karen Villholth

Contamination of GW dependent on flow and transformation processes occurring in UZ.

geus

Very little knowledge of the extent and types of contamination of GW in low income countries

GW pollution riskGW pollution riskPollution risk

low

high

high

Load is high, but vulnerability is low

Vulnerability high, but load is low

Karen Villholth

Within this scheme (Figure 12), it is possible to have high vulnerability but no pollution risk, because of the absence of significant contaminant load, and vice versa. Both are perfectly consistent in practice.Moreover, the contaminant load can be controlled or modified but not the aquifer vulnerability.

UrbanizationUrbanization

• Generally, urbanization decreases the Generally, urbanization decreases the recharge to aquifers (pavements, storm water recharge to aquifers (pavements, storm water drainage)drainage)

• However, depending on the primary source of However, depending on the primary source of water supply and the means of discharging water supply and the means of discharging wastewaters, GWLs may be affected differentlywastewaters, GWLs may be affected differently

Karen Villholth

Examples of this rebound of GWLs include London, Birmingham and liverpool in the UK, and Kuwait, Doha and Riyadh in arid countries.

Climate changeClimate change

• There is accumulating evidence that the climate There is accumulating evidence that the climate is changing on a global scaleis changing on a global scale

• Exact effects not known as well as the speed, Exact effects not known as well as the speed, extent and local distribution of themextent and local distribution of them

• Some effects seem inevitable:Some effects seem inevitable:– Water level rises due to global warmingWater level rises due to global warming– More variability and unpredictability in climate and more More variability and unpredictability in climate and more

‘extreme’ events‘extreme’ events– Dry regions becoming drierDry regions becoming drier

• Effects compounded by other human influences Effects compounded by other human influences (e.g. intensive water exploitation)(e.g. intensive water exploitation)

• Most vulnerable areas: Arid areas, big coastal Most vulnerable areas: Arid areas, big coastal cities, large tropical deltascities, large tropical deltas

Climate change on GW in Climate change on GW in citiescities

• GW can be a drought prevention strategy but GW can be a drought prevention strategy but only to a certain extentonly to a certain extent

• GW over-abstraction and flooding can occur at GW over-abstraction and flooding can occur at the same timethe same time

• Energy intricately linked to GW exploitationEnergy intricately linked to GW exploitation• CC exacerbate existing problems of GWCC exacerbate existing problems of GW

Disaster Disaster managememanagementnt

Post-Modern Water Post-Modern Water BalanceBalance

Changes in Water Availability

Precipitation Change

Increased Valuation/Economic

Breakpoints

Water Contamination

Trans-boundaryDisputes

Salt-water

intrusion

Virtual Water ImportsAnd Exports

Increased Water Demand for Agriculture, People and Ecosystems

Changes in Water Availability

Precipitation/Recharge Change

Cost-Effective WaterTreatment andConservationTechnologies

Ground Water Contamination

Trans-boundary

Flows

Salt-water

intrusion

Virtual Water ImportsAnd Exports

Increased Pumpage to Meet Domestic, Agricultural, Industrial and

Ecosystem Demands

Baseline situation

0

Availability and accessibility of adequate quality groundwater greatly exceeds small dispersed demand

Registration of wells required, together with maps of occurrence of usable resources

Incipient stress an

1

Growth of aquifer pumping, but only few local conflicts between neighbouring abstractors

Simple management tools (e.g. appropriate well-spacing according to aquifer properties)

Significant stress

2

Abstraction expanding rapidly with impacts on natural regime and strong dependence of stakeholders on ressource

Regulatory framework needed, based on comprehensive assessment

Unstable development

3

Excessive abstraction with irreversible aquifer deterioration and stakeholder conflicts

Regulatory framework with demand managemnt and/or artificial recharge urgently needed

Stable development

4

High-level of abstraction, but sound balance between stakeholder interests and ecosystem needs

Integrated management with high-level of user self-regulation, aquifer monitoring and assessment

timeTot

al a

bstr

actio

n

Num

ber

of

wel

lsSustainable level of

ressource development with acceptalbe impacts

under present conditions

Some response optionsSome response options

• More focus on GW, monitoring, permits, More focus on GW, monitoring, permits, • GW mgt. as an integral part of IWRMGW mgt. as an integral part of IWRM• Combine demand and supply mgt.Combine demand and supply mgt.• Awareness of general public => genuine Awareness of general public => genuine

stakeholder participation in groundwater stakeholder participation in groundwater protectionprotection

• Capacity building => Research into mgt. => Capacity building => Research into mgt. => informed mgt.informed mgt.

• Advocacy at the policy level => importance of Advocacy at the policy level => importance of GW acknowledged and incorporated into policies GW acknowledged and incorporated into policies and institutionsand institutions

• Climate change a driver for GW emphasisClimate change a driver for GW emphasis• No blanket policyNo blanket policy

Groundwater in big cities, use, consequences, impacts of climate change and response options Karen...

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