the Characterization of Groundwater Systems for Management

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?