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 flowPrimary porosity (and dual)Fine grained and Coarse grainedeg: shale, sandstone
Crystalline rocks – fracturesSecondary porosity with water only in the fractures – fracture flowFracture density controls yieldeg: granite, basalt
high η low klow η low k
high η high klow η high k
Different hydrogeological environmentsCrystalline rock with regolith Sedimentary rocks of different types
Karst limestone Unconsolidated sediments
Hydrogeological diversity
UnconsolidatedUnconsolidated rocks: rocks:
• Primary Porosity Primary Porosity
• Large storageLarge storage
•Locally high permeabilityLocally high permeability
ConsolidatedConsolidated rocks: rocks:
• Secondary fracture porositySecondary fracture porosity
• Small storageSmall storage
•Low permeabilityLow permeability
ConsolidatedConsolidated rocks: rocks:
• Karsts (Karsts (enlargedenlarged fractures) fractures)
• Moderate storageModerate storage
•High permeabilityHigh 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 AquifersFlow is from recharge areas to discharge areasAquifers may be unconfined or confined, which affects recharge mechanismArtesian discharge may occur from confined aquifers
Groundwater…a multi-layer system
Groundwater Recharge / DischargeInteraction 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
• 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 AQUIFER REPONSE: WATER LEVELS
Historic data
Example: Water saving to reduce aquifer depletion
Monitoring data
Baseline data (reference)
ACTION PLANACTION PLAN
MANAGEMENT INSTRUMENTS AND MEASURESMANAGEMENT INSTRUMENTS AND MEASURES
RESOURCE SETTINGRESOURCE SETTING
HYDROGEOLOGIC CONDITIONSHYDROGEOLOGIC CONDITIONS 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 SITUATIONSOCIOECONOMIC 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
REGULATORY PROVISIONSREGULATORY PROVISIONS zoning and source protection groundwater use regulation
POLICY ADJUSTMENTSPOLICY ADJUSTMENTS macro-policy interventions linkage with planning
IMPLEMENTATION OF MANAGEMENT MEASURESIMPLEMENTATION OF MANAGEMENT MEASURES investment priorities and scheduling of actions
mobilizing stakeholder engagement and essential roles of government
USER PARTICIPATIONUSER PARTICIPATION knowledge and awareness strengthening user organization local regulation
DEMAND-SIDE MEASURESDEMAND-SIDE MEASURES substitution of uses (crops, agronomy) efficiency measures/ saving water charging
SUPPLY-SIDE MEASURESSUPPLY-SIDE MEASURES natural/ artificial recharge retention alternative sourcing conjunctive management
QUALITY MEASURESQUALITY MEASURES prevention adaptation water treatment remediation
Aquifer Management Type
Summary of key properties of the most widely-occurring aquifer types (GW Mate2, 2006)
Regional distribution Regional distribution of globalof globalfreshwasser - resourcesfreshwasser - 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
• 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 m300 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 IssuesLegislation and Regulation
Economic InstrumentsPolicy Instruments
Human Resources Management IssuesAbstraction Rights
AllocationStakeholder Participation
Capacity Building
Natural Resource Management Issues Aquifer Characterization
Recharge Water Quality
Environmental Services
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?