Module 3:

Aquifer characterization for groundwater management

MODULE 3

Expensive process

Groundwater…the “invisible” resource

A resource, stored in underground reservoir (rocks) and transmitted through interconnected spaces

Aquifers have huge differences with respect to their hydrogeological setting.

GW management based on a good understanding of aquifer system.

Facts

All rocks cannot contain water: It depends on the degree of weathering and fracturing (porosity and permeability)

Rocks can be classified as water bearing (Aquifers and aquitards) and non-water bearing (Aquiclude and aquifuges)

Aquifers

AQUIFER - geologic formation that stores a large volume of groundwater and allows it to drain to streams, springs, or wells at rates that humans consider useful

1. Unconfined aquifer – upper boundary of saturated zone is a water table atmospheric pressure and connected directly to the atmosphere

2. Confined aquifer – bounded on its upper surface by an aquiclude, which precludes direct recharge from the overlying land surface, but only from some remote ‘upstream’ zone of the surface

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Aquitard: geological materials with low porosity and permeability

Aquiclude: Extremely low effective porosity and permeability

Aquifuge: blind rocks

Aquifer Aquitard Aquiclude Aquifuge

Aquifers main functions

Storage capacity (storage coefficient or specific yield)

Transfer capacity (transmissivity)

Physical and chemical interaction capacity (reservoir-rock vs GW)

Hydrogeological diversity

Unconsolidated rocks:

• Pore spaces

• Large storage

Consolidated rocks:

• Fractures

• Small storage

Consolidated rocks:

• Karsts (enlarged

fractures)

• Large storage

Hardrock Hydrogeology

Hydraulic Conductivity of bedrock is controlled by:

Size of fracture openings

Spacing of fractures

Interconnectedness of fractures

Different hydrogeological environments

Can rocks hold water? YES

Solid rock may look like it is

solid, but, it actually has tiny

holes or spaces between its

cemented grains.

This is called Pore space

Porosity - The percentage of a material’s

volume that is pore space.

Interstitial Porosity

Permeability

Can rocks transmit Water? yes

If a rock has pore space,

water can pass through.

This is referred to as

permeability. It is a function

of the sizes of particles,

pores, and the way they are

arranged

Groundwater flow

GW in continuous slow movement from recharge areas (usually upland areas) discharge areas (springs, baseflow, wetlands and coastal zones)

Recharge rate quantification

Recharge area vs land-use (GW protection)

Interactions (quantity/ quality) with surface water bodies

Impacts of GW pumping

Critical issues of GW characterization

Aquifer system water balance:

• to check our understanding

Modelling approach:

• to predict implication of impacts

Groundwater cannot be readily observed;

GW may occur in large, and complex aquifer systems;

Aquifers have high spatial variability of its characteristics.

Difficulties and uncertainties

(MacDonald et al., 2012)

Problems in Africa

• Lack of available groundwater

information

• Good Quality Database and data

sharing

• Lack of groundwater professionals on

permanent basis: Hydrogeologists

• Variation in Natural groundwater

quality is a problem (e.g. high salinity

in the coastal parts, AMD, nitrate,

fluoride, arsenic etc..

GW location, a big issue in complexhydrogeological setting

Available GWR for current and future use, for differentuses…sustainably!

Critical elements: safeyield, overexploitation(negative impacts costs)

GW location and storage

Recharge ensuresrenewability of GW storage, input to the system!

Recharge rate estimate, a critical issue for sustainabilityof GW development

Recharge area map, for land-use planning and access to water

Recharge and recharge areas

SW and GW hydraulically interconnected…all too often ignored in water management considerations and policies

Useful management information? maps of high riskareas of extensive GW exploitation

Trend of characteristics as impacted by land-use/change, climate change/variability, water use

GW discharge

GW connection with surface water: through aquifers

Pressure on

groundwater

development

• Rapidly increasing demand for urban water-supply provision

• Expansion of groundwater use for irrigation.

• Water provision for dispersed rural communities.

GW: Intensive irrigation • Abstraction that exceeds

groundwater recharge can lead to declining water‐tables and possible salinization or even land subsidence.

• Fertilizers and pesticides application: degrade groundwater quality

Food security is achieved

but groundwater quality/quantity

could be compromised.

Hydrogeological parameters: Hydraulic conductivity/permeability, Porosity, Storativity/ Storage coefficients

Degree of weathering, Degree of fracturing

Aquifer thickness, Aquifer extent

Borehole or aquifer Yield

Hydrogeochemical/isotopic variables

Some variables to be compiled

1. Geological and Hydrogeological mapping

2. Aquifer thickness/Extent= apply geophysical methods, analyse lithological logs

3. Aquifer parameters: Specific yield, porosity, transmissivity, storativity

4. GW quality= geochemistry, ions, metals

5. Recharge amount= apply water balance methods

6. GW storage= apply water balance methods

7. Recharge history= Environmental isotopes

8. GW yield= conduct pumping test (constant and step drawdown)

9. Water use= gw dependent communities and ecosystem

What do we need to consider?

Groundwater

Other stakeholders Policy level

Understanding of GW system

Information on unit system

Knowledge on aquifer properties, and

Technical solutions

Demand side

Water provision and

management

Policies

Strategies

Regulatory framework

The needed interaction to providesuitable GWR information

Sustainable development

GW protection

Operation & Maintenance of water

points: PART OF MANAGEMENT

O&M dictates groundwater supply, hence, controlling ‘water security”

Water sector corruption

is extravagant in Africa

that affects O & M.

Policy perspective

A thorough understanding of aquifers, storage and groundwater quality, management could help to maintain water security during the most stressful period of climate change.

• Balancing the demand through decentralized use of groundwater and localized augmentation by runoff/treated wastewater and runoff

:Managed aquifer recharge

• Should groundwater be developed widely, effective governance will become increasingly important.

Management aspect

• Develop detailed national scale groundwater availability maps and reports

• Develop groundwater monitoring program: Abstraction, recharge, quality

• Develop strategy on the groundwater use based on the demand.

• Introduce water demand management techniques to minimise loss

Thank You!