the Characterization of Groundwater
Systems
for Management
What is groundwater?
• Rainfall that soaks into the ground and moves
downwards into pore spaces and cracks in the rocks
becomes groundwater.
• The rocks that store groundwater are aquifers.
• The study of groundwater is called hydrogeology.
• The study of groundwater requires an understanding
of the hydrological cycle as it pertains to the
recharge and discharge of groundwater
and
• The study of the geological formations that store
groundwater is essential for a comprehensive
understanding of groundwater.
Groundwater USE
Advantages
•Widespread availability at point needed
•Low cost simple technologies
•Potable without treatment
•Drought resistant
Disadvantages
•Must be pumped
•Single use only
•Mineralized
•Difficult to assess
other advantages / disadvantages?
Key aspects of Groundwater
• Groundwater occurs as a result of specific geological conditions in
combination with specific hydrological conditions.
• Aquifers exhibit porosity – the capacity to store water.
• Aquifers exhibit permeability – the capacity to transmit water
• Groundwater flows down the hydraulic gradient – from high head to
low head (m).
• Flow occurs as seepage / matrix flow or fracture flow or both.
• Groundwater flows from recharge areas to discharge areas.
• Aquifers may be unconfined or confined – open to atmospheric
pressure or sealed by an overlying impermeable layer.
• Groundwater chemistry changes naturally due to rock-water
interactions in the aquifers.
• Groundwater management requires reliable aquifer characterization.
Porosity (stores) η and Permeability (transmits) k
two basic hydrogeological parameters
Sediments – granular rocks from
detrital material – matrix flow
Primary porosity (and dual)
Fine grained and Coarse grained
eg: shale, sandstone
high η low k
low η low k
high η high k
low η high k
Crystalline rocks – fractures
Secondary porosity with water
only in the fractures – fracture flow
Fracture density controls yield
eg: granite, basalt
Different hydrogeological environments
Crystalline rock with regolith
Karst limestone
Sedimentary rocks of different types
Unconsolidated sediments
Hydrogeological diversity
Unconsolidated rocks:
Consolidated rocks:
Consolidated rocks:
• Primary Porosity
• Secondary fracture porosity
• Karsts (enlarged fractures)
• Large storage
• Small storage
• Moderate storage
•Locally high permeability
•Low permeability
•High permeability
Group discussion
porosity, permeability and rock type.
• What rock / soil types are you familiar with?
• Which have primary porosity and which have fracture
porosity?
• What can you say about the porosity and permeability of
these rock types?
• What do these parameters mean in terms of well yield?
• Do all rocks of the same type have the same groundwater
characteristics?
• Are all rocks aquifers?
• ?? Questions
Groundwater Flow and the Hydraulic Gradient.
Flow from high head to low head. For an unconfined aquifer, the water table
defines the hydraulic head. Water table often mimics land surface.
Groundwater Flow in
Confined and Unconfined Aquifers
Aquifer types:
unconfined (free
surface), water-table
aquifer or phreatic
aquifer. Specific yield.
Perched aquifer
confined (under
pressure) aquifers are
bounded by
impervious or
semipervious layers.
Storage coefficient.
Artesian aquifer
Groundwater flow; confined / unconfined Aquifers
Flow is from recharge areas to discharge areas
Aquifers may be unconfined or confined, which affects recharge mechanism
Artesian discharge may occur from confined aquifers
Groundwater…a multi-layer system
Groundwater Recharge / Discharge
Interaction between groundwater and surface water
Group Discussion:
Groundwater Flow and Aquifer Confinement
• Is groundwater flow important for groundwater
management?
• What is the impact of groundwater flow on recharge and
discharge?
• Will this have an impact of the age of the groundwater and on
the water chemistry?
• What are the management implications (quality and recharge)
for confined and unconfined aquifers?
• What is the impact of confinement on aquifer storage?
Groundwater Management
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What are the key components for aquifer management?
Size of the aquifer – water in storage
Permeability of the aquifer – well yield
Water quality – fracture flow / matrix flow
Natural recharge and discharge - climate
Abstraction and aquifer depletion – pumping and water levels
Aquifer vulnerability – how easily polluted
Pollution – point and diffuse sources of pollution
Monitoring, data storage and analysis.
Policy, institutions and implementation
AQUIFER REPONSE: WATER LEVELS
Example: Water saving to reduce aquifer depletion
Historic data
Baseline data
(reference)
Monitoring data
RESOURCE SETTING
HYDROGEOLOGIC CONDITIONS
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definition of manageable groundwater bodies
resource renewability, recharge rates and sw interactions
aquifer storage characteristics and economic reserves
susceptibility to irreversible aquifer/ecosystem degradation
SOCIOECONOMIC SITUATION
 analysis of groundwater use drivers (urban vs rural)
(waterwell construction costs, macro-policy interactions
such as energy subsidies and crop price guarantees)
 groundwater use and users profile
MANAGEMENT INSTRUMENTS AND MEASURES
POLICY ADJUSTMENTS
 zoning and source protection
 groundwater use regulation
 macro-policy interventions
 linkage with planning
QUALITY MEASURES
 prevention
 adaptation
 water treatment
 remediation
REGULATORY PROVISIONS
DEMAND-SIDE MEASURES
 substitution of uses (crops,
agronomy)
 efficiency measures/ saving
 water charging
ACTION
USER PARTICIPATION
 knowledge and awareness
 strengthening user organization
 local regulation
SUPPLY-SIDE MEASURES
 natural/ artificial recharge
 retention
 alternative sourcing
 conjunctive management
PLAN
IMPLEMENTATION OF MANAGEMENT MEASURES
 investment priorities and scheduling of actions
 mobilizing stakeholder engagement and essential roles of government
Aquifer Management Type
Summary of key properties of the most widely-occurring aquifer types (GW Mate2, 2006)
Regional distribution
of global
freshwasser - resources
Quelle: Igor A. Shiklomanov, State Hydrological Institute (SHI,
St. Petersburg) and UNESCO (Paris), 1999.
Largest Aquifer Systems of the World
Quelle: J. Margat (2006) Les grands systèmes aquifères du monde.
Proceedings IAH Congress Dijon.
SS Africa Hydrogeological setting
After MacDonald et al, 2005
Specific issues for Groundwater Management
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Maintenance of pumping infrastructure
Slowly accumulating water quality threats
The hidden drought – unseen drawdown
Multiple unknown users and unrecorded
abstractions
• Lack of information on aquifers & recharge rates
• Lack of monitoring
• Complex institutional management issues
Maintenance
issues =>
Lack of water
supply
The
groundwater
quality
time-bomb
The
hidden
drought
300 m
Groundwater Status Quo
• Millions of m3 pumped every year
– Monitored? Why? Who? How? Use? quantity / quality
• 100’s of thousands of users
– Registered? Controlled?
• 10’s of thousands of wells / boreholes
– Registered? Maintained? Information - location, abstraction, water
levels, water quality, formation etc -
• 1000’s of sources of pollution
– Location, nature & quantity of pollutants? aquifer vulnerability?
• 100’s of drillers / consultants
– Registered? Development & drilling data recorded & submitted?
• 10’s of characterization parameters
– Sampled / Analysed? Monitored? Equipped to analyse?
• Many governing departments /institutions
– Joint management ? Coordination / cooperation?
• Unified appreciation & integrated management
Government Management Issues
Legislation and Regulation
Economic Instruments
Policy Instruments
Natural Resource Management Issues
Aquifer Characterization
Recharge
Water Quality
Environmental Services
Human Resources Management Issues
Abstraction Rights
Allocation
Stakeholder Participation
Capacity Building
Thank You!
Group Activity.
Characterisation of groundwater systems
Purpose: To appreciate the link between understanding groundwater
systems and strategies for management
Duration: 60 Minutes
Scenario : 2 groups:
1)A multi-national commercial agricultural organizations submits plans
to develop 150,000 ha of irrigated jatropha for biodiesel from an
extensive sedimentary aquifer in south-western Zambia. The
multinational defends its position citing socio-economic benefits and
aquifer protection measures.
2)Catchment managers / NGO’s / small scale farmer communities
raise objections expressing fears of declining water levels, and
associated impacts on the groundwater system.
Activity – Role Play: With reference to specific aquifer and hydrological
characteristics, the two groups discuss their differences. Is the the plan
is safe? What groundwater management activities should to be
introduced? What sort of problems may arise? And how will they be
dealt with?