EAS 210: Chapter 16

What does groundwater provide?

- 50% of drinking water to the worlds population
- 40% of water of irrigation
- 25% of water for industrial use

How does rainfall collect?

- runoff
- evaporates
- infiltrate the ground (some stays as soil moisture)

What is the saturated zone (phreatic zone)?

- zone where water saturates the soil
- Water in this zone is called groundwater

What is the water table?

- The top of the saturated zone
- change based on type of rock
- varies yearly and seasonally
- Commonly intersects the surface at rivers, lakes and streams

What is the vadose zone (zone of aeration)?

- location with minimal water between zone of saturation and soil moisture

What is the capillary fringe?

- location between the zone of saturation and vadose zone

What is porosity?

- the fraction of the rock volume that consists of voids

What is primary porosity?

- the structures present when rock is formed

What is secondary porosity?

- structures developed afterwards

What is the porosity in rocks?

- porosity reduced when lithified to form sedimentary rock
- cement occupies some pore space
- igneous and metamorphic rocks have low porosity (generally in fractures)
- Well-sorted is more porous than very poorly sorted

What is permeability?

- Measure of how easily fluid can flow through a rock

What is specific yeild?

- Fraction of groundwater that will drain under the influence of gravity

What is specific retention?

- Fraction of groundwater that will be retained

What is an Aquitard?

- impermeable layer that hinders or prevents groundwater flow (clay or shale)

What is an Aquifer?

- permeable layer that holds enough groundwater to be a useful source

What are the trends between porosity and permeability?

- the permeability increases as porosity increases
- groundwater is commonly 1-2 km of the surface

How does groundwater move?

- groundwater flow is the velocity proportional to the slope of the water table
- driven by pressure difference

What is a hydraulic gradient?

- rate of change of head with distance

How does porosity relate to velocity?

- the higher the porosity the slower the velocity

Where are springs formed?

- Occurred when perched water table intersects the surface
- springs can also be found in variations by faulting

How are hot springs formed?

- increased water temperature (6-9 degrees above annual; temperature) that are relased on the surface

What are geysers?

- Regular eruptions of hot water
- needs very specific subsurface structures

What is downdraw?

- lowering of the water able due to withdrawal of water

What is the cone of depression?

- Area of downdraw which forms around a well.
- Groundwater flows in response to extraction
- flows to try to level the water table

What is a confined aquifer?

- aquifer bounded above and below my aquitards

What is an unconfined aquifer?

- aquifer which is overlain by permeable rocks and soil
- pressure increases by elevation changes

What is an Artesian well?

- Water is in a confined aquifer and rises to a level above the aquifer
- may not reach the surface

What are some problems with groundwater?

1. Overproduction
2. Surface subsidence
3. Groundwater contamination (mines, leaking septic tanks, farms)
4. Seawater intrusion (seawater takes space of clean groundwater)
5. Urbanization (reduces infiltration and aquifer recharge)

Where is groundwater collected in Canada?

- highly used in the sedimentary basin
- low withdrawal with less urbanization

What is hard water?

- water with substantial amounts of dissolved calcium and magnesium
- common in the prairies of Alberta

How is groundwater influenced by other activity in the ground?

- fracking and production of oil and gas can contaminate water

What are some geological effects of groundwater?

- erosion and deposition both occur as groundwater moves through the subsurface
- Chemical sediments are formed and deposited (Silica and Calcium Carbonate)
- Caves are formed just below the water table

What are stalactites and stalagmites?

- stalactites (down) and stalagmites (up)
- deposition of chemical sediment

What is Karst topography?

- surface formed from composition of sinkholes that may collapse without warning
- lack of surface streams