ERTH2404-L11: Permafrost, Groundwater and Earth Resources

Permafrost

Permafrost: Permafrost is ground (soil or rock, incl. underwater sediments) that remains at a temperature of 0°C or lower for at least two consecutive years. In other words: permanently frozen ground (soils + rock)

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NOTES:

• Definition based exclusively on temperature, regardless of composition, texture or water content

• Refers to the ground that remains below 0°C for at least two consecutive years.

• Permafrost grades from deep (1000 m) and continuous in the North to thin (30 cm) and discontinuous further South

Permafrost in Canada

Permafrost underlies 20% of the Earth’s land surface and 50% of Canada’s

← look at the patterns of permafrost throughout Canada

Changes in the permafrost layer in Northern Canada

Permafrost in high mountains

Subsea Permafrost

It exists! Since the end of the Last Glacial Maximum (~21,000 years ago), rising sea levels have inundated terrestrial permafrost surrounding the Arctic Ocean, resulting in subsea permafrost...

Active layer

Permafrost

Active layer: near-surface layer that thaws in the summer and freezes in the winter. The active layer in Canada is generally 0.5 m to 2 m thick.

Suprapermafrost

Permafrost

Suprapermafrost: active layer and taliks (pockets of material that never freezes)

Permafrost table

Permafrost

Permafrost table: boundary between the suprapermafrost layer and permafrost

Thermal profile

look closely at diagrams

Layers of permafrost

← look closely at diagram

Gelifluction

Permafrost

Gelifluction: mass movement linked to the thawing of the active layer

• Similar to creep but with a permafrost base

• Water cannot drain through the permanently frozen, impermeable layer below

• Soil becomes saturated and weak, and flows down gentle slopes as a lobate mass

Solifluction

Permafrost: Ice-wedge polygons

Why is permafrost changing?

Permafrost is controlled by the energy balance at the ground surface (energy received versus energy dissipated and lost). If that changes, so will ground temperatures and the characteristics of the permafrost.

Changes can come from:

• a warming climate

• deeper snow cover

• surface disturbance (possibly due to human activities).

All of these increase the thickness of the active layer, resulting in thaw of the top layers of the permafrost and if this continues for decades, potentially the loss of the entire permafrost body.

Where permafrost contains a lot of ground ice, its thaw results in thermokarst processes, which include subsidence and landsliding.

Relation between Climate Change and Permafrost

• Future greenhouse gas additions to the atmosphere as organic material (mostly plant matter) currently stored in the frozen ground defrosts and is broken down by bacteria into two greenhouse gases: carbon dioxide (CO2) or methane (CH4).

• This is termed the permafrost carbon feedback.

Engineering considerations for permafrost

Engineering problems linked to permafrost:

Unwanted thawing of the active layer under either unheated (e.g. roads) or heated (e.g. buildings) structures

Result of unwanted thawing :

• Soil loses strength

—• Subsidence

—• Liquefaction and slope instability

Frost heave: uplift of the surface as the active layer freezes in the winter

Noatak National Preserve, Alaska, 300 m long slump

Engineering consideration: Frost heave (1)

Related to permafrost

ex. Pipeline raised above ground as a consequence of buckling in association with frost heave.

Engineering consideration: Frost heave (2)

Related to permafrost

ex. Pipeline exposed as a consequence of erosion of soil and backfill, following loosening of these materials by repeated frost heave and subsequent thaw

Engineering solution to frost heave in pipelines

Engineers elevated sections of the Alaskan Pipeline so the warm oil would not thaw the permafrost.

Melting permafrost and coastal erosion in the Western Canadian Arctic

Dawson City, Yukon

Example that did not consider permafrost

Engineering consideration: Mitigating unwanted thawing of active layer

Mitigation of unwanted thawing of the active layer:

• Where active layer is thin, the ground is allowed to thaw and spread footings are used

• Roads and railroads built on an insulating pad of non-frost-susceptible soil

• Buildings can be constructed on piles

• Artificial ground freezing can be used to increase the strength of the ground temporarily to build tunnels, caverns, or shafts

Strategies for construction on permafrost

• Minimum disturbance of soils and vegetation cover. Keep shading from trees

• Elevate and properly insulate the bottom of houses to prevent heat losses through the floor system from reaching the ground underneath, which can lead to thawing.

• If wood or steel piles or helical piers are used, they must be installed to a depth that will both support the structure and resist frost jacking from seasonal ground movement.

• Keep water away from house; engineered septic systems that does not thaw permafrost

GROUND WATER

Hydrologic Cycle (or Water cycle)

The hydrologic cycle (or Water cycle) describes the constant exchange of water between oceans, atmosphere and continents

• It has been operating on Earth for over 4 billion years

Hydrosphere

Hydrosphere: the global waters of the Earth

• Liquid and solid

• Fresh and salty

Total volume of water on Earth and distribution

Total volume of water on Earth = 1.36 billion km3

• 97.20 % seawater

• 2.15 % glacier ice

• 0.62 % groundwater (20 times the volume of lakes, rivers, etc)

• 0.03 % inland seas, lakes, rivers, moisture in soil, atmosphere

Global freshwater: 8.84 X 106 km3

• If we divide by the surface of Canada: 10 X 106 km2

• It corresponds to 1 km deep layer over the surface of Canada

Why do people rely on groundwater?

Groundwater is the largest reservoir of fresh water readily available to humans

• 94% of Earth’s available fresh water is groundwater (excluding glaciers)

Surface water is often limited in quantity

NOTE: Surface water may need to be extensively treated before drinking (but groundwater does not always imply drinking water)

Statistics on groundwater use in Canada

26% of Canadians rely of groundwater for crop, livestock and domestic use

2/3 of users in rural areas

• Many areas of the Atlantic Provinces are heavily

dependent on groundwater

—• 100% in Prince Edward Island

—• 90% of Ontario farms

1/3 of users in small communities

• Many small communities in the Prairies use groundwater wells for municipal supply (rain can be scarce in some areas)

Zones of subsurface water

Unsaturated zone: near-surface zone of soil moisture, voids contain air and water. Also called the vadose zone.

• Capillary fringe: zone where groundwater is held by surface tension between grains (as in in tiny conduits)

• fluid pressure is less than atmospheric

• Extending upward from the water table

----Boundary where P = Atmospheric pressure = water table---

• Saturated zone: zone where all the open spaces in rock

(pores, fractures) are completely filled with water

Zones of subsurface water; Capillary action or Capillarity

Zone of aeration, capillary fringe, zone of saturation

The capillary fringe is essentially saturated, but groundwater is being held against gravity under negative pressure.

Capillary Action or (Capillarity)

Capillary Action or (Capillarity):

The process by which water is drawn upwards into pore spaces.

The capillary fringe is essentially saturated, but groundwater is being held against gravity under negative pressure.

Zones of subsurface water: unsaturated zone, zone of aeration, saturated zone

Zone of aeration (vadose zone)

Zone of aeration: (vadose zone)

Soil contains air; water in this zone cannot be pumped by wells due to capillary forces

Percolate

Rain water that is not held as soil moisture percolates down to form the saturated zone

Groundwater

Groundwater: water filling the open spaces in soils or rocks in the saturated zone

Water table

Water table: upper limit of the saturated zone; the surface where the water pressure head is equal to the atmospheric pressure (where gauge pressure = 0).

Wetland

Wetland: area where the water table is at the surface

Recharge and discharge

Water flows from areas where water table topography is highest (recharge areas) to topography where water head is lowest (discharge areas)

Variations of the water table depth

Variations of the water table depth

• Shape often follows the surface topography

• There could be seasonal and annual depth variations

Schematic diagram from land surface through vadose zone, capillary fringe and into unconfined aquifer

Surface water is in continuity with water table

Shore of a river

Base flow

Groundwater serves as an equalizer of stream flow

Much of the water in a stream is often not direct runoff of rain and snow melt, but comes from groundwater discharge (base flow)

• Example: 65% of Lake Ontario comes from base flow

Groundwater acts as “storage” to sustain streams when rain is not falling

Springs

Spring: localized discharge point occurring where the water table intersects the Earth’s surface

Springs: Types of streams

Losing stream

Losing stream: water table can be lower than rivers in Western US due to intense pumping (ie the inverse of natural situation)

Spring near Wakefield, QC

Hydraulic conductivity

K: Hydraulic conductivity

High K: Permeable

Low K: Impermeable

Karstic environments

“A karst environment is a landscape formed by the dissolution of soluble bedrock—primarily limestone, dolomite, or gypsum—characterized by sinkholes, caves, sinking streams, and springs. These terrains feature complex underground drainage systems rather than surface streams and are highly susceptible to contamination due to rapid water flow through fissures.”

Darcy’s Law: general info

Henri Darcy: 19th century French engineer

• Founder of modern groundwater

• Experiments of water flow through column of sand

Established volumetric flow rate of water through saturated sand is proportional to the energy gradient

• Loss of energy per unit length of flow path

Void Space

Void Space

Two quantitative measures of the relative amount of void space in a material

• Porosity

• Void ratio

Both difficult to estimate in practice

Darcy’s Law Diagram

Darcy’s Law: actual law

Darcy’s Law: equation describing flow through a porous medium

v = Q / A

v : flow velocity [m/s]

Q : volumetric flow rate [m3/s]

A : cross-sectional area of flow tube [m2]

Hydraulic head

In relation to Darcy’s Law

Hydraulic head h [m]: level to which water rises above a datum

Hydraulic gradient

Hydraulic gradient i [ ]: difference in hydraulic head between two points separated by a distance L [m]

i = (h2 – h1) / L

Measures in the ability to transmit fluids

One qualitative and two quantitative measures of the ability of a material to transmit fluids

Qualitative:

• Permeability

Quantitative:

• Intrinsic permeability

• Hydraulic conductivity

Permeability

Permeability: general qualitative term describing the ability of a material to let fluids flow through it.

(a measure of how easily a fluid can travel through soil or bedrock.)

Permeability is a composite property of:

• Material properties: size, shape, and interconnectivity of the voids

• Fluid properties: temperature, density, viscosity

Intrinsic Permeability

Intrinsic permeability k [m^2]: portion of “permeability" which is representative of the properties of the material alone

Intrinsic permeability is a function of the characteristics of the voids through which the fluid moves

• Interconnectivity of voids

• Size, shape and packing of grains

• Cementation

• Fracturing

Hydraulic conductivity

Hydraulic conductivity K [m/s]: composite property that describes the ease with which a fluid (usually water) can move through pore spaces or fractures.

K = k ρ g / μ

k : intrinsic permeability [m^2]

ρ : density of water [kg/m^3]

g : acceleration due to gravity [m/s^2]

μ : viscosity of water [Ns/m^2]

Important property in hydrogeology

What do high and low hydraulic conductivity values mean?

High values indicate permeable material through which water can pass easily;

Low values indicate that the material is less permeable.

• Because density and viscosity of water does not vary much, K reflects mostly the intrinsic permeability of the reservoir

Porosity vs Permeabbility

A porous rock is not necessarily permeable

– Example: shale and clay: very porous, but almost impermeable

Scale of intrinsic permeability

Notice log scale

Intrinsic permeability of shale compared to others on graph

Darcy’s Law: Expanded equation

v = Q / A = - K (h2 - h1) / L

Negative sign indicates a loss of energy along flow path due to:

• Friction between water and rock/soil

• Friction between water molecules

v : flow velocity [m/s]

Q : volumetric flow rate [m3/s]

A : cross-sectional area of flow tube [m2 ]

K : Hydraulic conductivity [m/s]

Darcy’s Law: in practice

Darcy’s Law: Application

Datum for measuring hydraulic head is sea level

• Difference between elevation and depth to water in well

Direction of ground-water flow is from high to low hydraulic head

Flow velocity (v)

• Typically ≈ cm/day... i.e. generally very slow

Aquifer

Aquifer: saturated body of rock or soil that transmits significant quantities of groundwater

Aquitard

Aquitard: body of rock or soil that does not transmit significant quantities of groundwater

Geological materials that form good aquifers

Sand and gravel

• Moraine, alluvial fans, etc.

Fractured rocks

• Jointed rock masses, fault zones, deeply weathered zones, etc.

Soluble rocks

• Caves and channels in karst geology

Reef carbonates

Types of aquifers

Two types of aquifers depending on the presence or not of an overlying aquitard

Unconfined aquifer:

• Aquifer that lacks an overlying aquitard

—• The water table is the upper boundary

• Hydraulic head ≈ elevation of the water table

—• Contour lines of the well water levels drawn on a map indicate the direction of flow

Confined aquifer (syn. artesian aquifer):

• Aquifer bounded between overlying and underlying

aquitards

• No relation between the hydraulic head and the

water table

—• In some cases, the fluid pressure in the aquifer is so high that the head is above the land surface

——• Flowing artesian well: well flowing without a pump

Diagram of the two types of aquifers

make sure to look at

Water wells

• A typical water well drilled in the Ottawa area

• To ensure a continuous supply of water, well must penetrate into aquifer which is the bedrock

Ontario government regulations for water wells

Each new well:

• Is tagged with an identification number

• Its GPS location is entered in a provincial database

Production of water; CONE OF DEPRESSION in UNCONFINED aquifers

Cone of depression in unconfined aquifers

• Decline in water table in vicinity of well

• Cone-shaped area extending radially from the well

• Material within the cone changes from saturated to unsaturated state

• Reaches a state of equilibrium

Water extraction in unconfined aquifer

Cone of depression in an unconfined aquifer decreases water table in vicinity of well

Production of water; CONE OF DEPRESSION in CONFINED aquifers

Cone of depression in confined aquifers

• Cone of depression develops in the potentiometric surface without dewatering of aquifer

• Decrease in fluid pressure / pressure head

• Reduction in ability to expels water

• Remains saturated

Water extraction in confined aquifer

Cone of depression in a confined aquifer does not dewater the aquifer

Overpumping in relation to the production of water

In this example, overpumping by industry lowers the water table, making it necessary for farmers to drill a deeper well

Contamination by saltwater near salt water bodies

Nanaimo, BC

Issues near Salt water Bodies

Statistics on water as a precious resources

City of Ottawa draws about 340 million litres of water daily at the Britannia and Lemieux Purification Plants.

Numerous other communities and individual homes also rely on the river as their water source.

Bogs developed on top of poorly drained in the East of Ottawa

East of Ottawa, bogs developed on top of poorly drained clay are a local source of horticultural peat and important wetlands.

3D Diagram of water circulation along the Ottawa River

How old the water is depending on where it is in the water circulation

How does water get into the ground?

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Bad water sources

Human problems: Industrial, residential and agricultural pollution

Natural problems: Sulphur, iron and salt

EARTH RESOURCES

General categories of Earth resources

1. Non-metallic

2. Metallic

3. Energy resources (Fossil Fuels+ uranium)

Mineral Resource Use

USA 2014:

~3400 L consumption of refined petroleum products per capita:

Non-metallic resources

1. Rock quarries: building stone

2. Limestone, crushed rock aggregate: cement

3. Sand and gravel: road materials, concrete

4. Gypsum: plaster and wallboard

5. Clay minerals (kaolinite, montmorillonite): medicine, paint, glassy paper, ceramics, tennis shoes, chocolate!

6. Potash – fertilizers

7. Salt (halite): Winter road maintenance

Non-metallic minerals mined in Canada

Marble Quarry, PortugalL

Active and inactive quarries in the Ottawa-Gatineau region

Carlington Quarry (Ottawa West)

• Former quarry with stones used to build the Parliament and other Ottawa buildings.

• It can be a challenge to rehabilitate inactive quarries within cities

Casino Lac Leamy (Hull)

• Former quarry

Goderich Salt Mine, Goderich, ON

• World’s largest underground salt mine

• 7 km2, extending under Lake Huron

Canada’s mineral and metals; statistics on Canada’s rankings among the top 5 producers of 14 mineral commodities and how mineral exploration undertaken across the world is from Canadian companies

• Canada ranks among the world’s top five producers of 14 mineral commodities

– World's leader in production of Potash and third in Uranium

• Canadian-based companies conduct about 40% of all mineral exploration undertaken in the world

Resources versus. Reserves

In short – mineral reserves are the portion of mineral resources that are economically feasible to produce and sell.