Groundwater Flashcards
Roughly _____% of Canada’s population is reliant on groundwater
25-40%
Define Groundwater
water that lies beneath the surface
Ground water makes up for __% of the hydrosphere’s fresh water, while glaciers make up for ___%
22% and 77%, respectively
___% of total precipitation infiltrates the ground and sends up as ground water
15%
True or False: ground water is static
False; it is slow moving
True or False: groundwater is found most commonly in underground lakes and rivers
True, but barely. It can occur, but is extremely rare
Where is groundwater most commonly found
pores of sediment and soil
fractures of bedrock
Porosity
percentage of voids or pore space (vs total volume)
What is porosity used to determine?
How much groundwater can be stored
How to measure porosity
Take a column with a toal volume of 1000 mL and fill it with dry sand (dry sand has a porosity filled with air). replace the air with water. The porosity=volume water/Volume total
Permeability or Conductivity
Capacity of rock or sediment to transmit a fluid
connected pores give a rock permeability
Specific yield
% that can drain by gravity
Specific retention
% that cannot drain by gravity
Distribution of ground water is found in what three places?
1) Unsaturated zone
2) Water Table
3) Zone of saturation
Unsaturated zone
- above water table
- voids filled by water and air
- water is under suction (negative pressure) due to capillary forces (think TLC)
- water cannot be pumped by wells
Water Table
- Upper limit of zone of saturation
- surface of water level in ground
- depth varies seasonally
Zone of Saturation
- below water table
- all voids are filled with water
- water is under positive pressure and can be sucked up by wells
Pressure distribution
unsat:
a) Patmos. P
b) water under (+) pressure
What factors control infiltration?
1) precipitation
2) slope
3) geological material
3) vegetation
In what three places is groundwater stored?
1) Aquifer
2) Acquitard
3) Aquiclude
Aquifer
permeable rock layer or sediment that stores and transmits groundwater
Acquitard
semi-permeable rock layer
Aquiclude
impermeable rock layer (exCLUDEs water)
Types of aquifers
Unconfined and confined
Unconfined aquifer
- no confining layer
- groundwater is not under pressure
- top of water table moves freely up and down
Confined aquifer
- sandwiched between 2 confining layers (usually inclined to allow recharge)
- groundwater is under pressure
- top of water table is above confined aquifer
Types of wells
Non-flowing artesian well and flowing artisan well
Non-flowing artesian well
water table (pressure surface) of a confined aquifer lies below ground level (pressure is not great enough to bring water to the surface)
Flowing artesian well
Water table of a confined aquifer rests above ground level; water reaches ground surface using natural pressure of the confined aquifer
What is the general pattern of movement?
recharge (high) –> discharge (low)
True or False: velocity is highest nearest the surface
true
Darcy’s Law states:
States that if permeability remains uniform, the velocity of groundwater will increase as the slope of the water table (hydraulic gradient) increases
Darcy’s Law equation
v=-(K/fancy n)(i), where K = hydraulic conductivity, n = porosity, i=hydraulic gradient=driving force, v=velocity
Ground water and stream interactions
1) gaining streams
- gain water from the inflow of groundwater through streambed
2) losing streams
- loss of water to the groundwater system by outflow through streambed
The water table is ____ than the stream bed in the gaining streams interaction
higher
The water table is ____ than the stream bed in the losing streams interaction
lower
-zone of aeration present
Sources of groundwater contamination
- road salt
- fertilizers
- pesticides
- chemical and industrial materials
- bacteria and viruses
What are some problems associated with groundwater withdrawal?
Sewage contamination
-sewage often becomes purified as it passes through the aquifer composed of sand or permeable sandstone. However, in extremely permeable aquifers (ie. coarse gravel or fractured bedrock), the groudwater may travel long distances without being cleaned
Saltwater contamination
-excessive groundwater withdrawal causes saltwater to be drawn into wells
What are the consequences of excessive pumping?
1) drawdown (lowering) of the W.T
2) cone of depression in the WT
subsidence
Ground shrinks when water is pumped from wells faster than the recharge process can replace it
Geysers
intermittent surface emission of hot water
occur when groundwater heats, changes to steam, and errupts
Erosional features of groundwater
- caves (underground cavity)
- Karst topography (typically form in limestone bedrock) (ie. caves and sinkholes)
Depositional features
- Groundwater is often mildly acidic, so it dissolves rocks (particularily limestone).
- if rxn reverts and CO2 escapes, CaCO3 is deposited, creating stalactite (point down), stalagmite (point up), column/pillar etc
