Groundwater Flashcards
Estimated that there is 3000x more water stored as groundwater in the upper 800m of
the continental crust than water found in ALL the rivers and streams
Groundwater is our most important:
source of freshwater
About 30% of the Canadian pop depends on:
groundwater
Groundwater is present where:
the crust has pores (like sand) or fractures (breaks in rocks)
What is the water table?
The level below which the ground is saturated with water, fills all pore spaces, fluctuates with flooding, etc.
What is the capillary fringe?
the boundary zone b/w unsaturated and saturated zones
Water Table rises and falls with:
The seasons, and is not flat. Has muted topography.
Porosity
- Pores are open spaces within any sediment or rock
- The total volume of open space is term porosity
- Geologic materials exhibit a wide range of porosities (i.e crystal size)
Two categories of porosity:
primary and secondary
Primary porosity
originally formed with the material, ie voids in sediment, vesicles in basalt
Secondary porosity
develops later = fracturing, faulting, dissolution
Permeability
- The ease of water flow due to pore interconnectedness
- Highly permeable material allows water to flow readily
- Water cannot flow through impermeable material
- Many large and straight flow paths enhance permeability
Aquifer
a body of rock or unconsolidated sediment through which groundwater can flow, transmits water easily
Aquitard
impermeable or low permeability sediment or rock that hinders water flow
Why should deep groundwater take many times longer to reach the discharge area than shallow groundwater?
Travels longer distance, works its way far down and recharging is slower rate
Unconfined vs Confined Aquifers
- Unconfined: an aquifer that intersects the surface, in contact with the atmosphere, easily contaminated
- Confined: an aquifer beneath an aquitard, isolated from the surface, less susceptible to pollution
Hydraulic Gradient
- Hydraulic gradient is the slope of the water table
= (h1 - h2)/L - basically rise over run for water table
- Steeper slope means faster water table flows
Darcy’s Law
V = K(dh/dL) or K(h1-h2)/L
V is groundwater flow velocity
K is the coefficient of permeability
(h1-h2)/L or (dh/dL) = hydraulic gradient
Most water wells are drilled with
truck-mounted drill rigs
Groundwater is fed by
snowmelt and rainfall in recharge areas
In some situations, groundwater contributes to the base flow of a stream. In others:
streams contribute to the groundwater
Gaining stream:
water table is above base flow so gains water
Losing stream (connected):
water table is below, but connected to stream, loses water to ground
Losing stream (disconnected):
water table is super far below stream, loses water
Groundwater can maintain a 3D surface because:
pore water moves super slow = topography
Wetlands are critically important for:
storage of both surface and groundwater
Groundwater moves in response to
gravity and hydraulic pressure (pressure from behind)
Aquiclude
aquitard = impermeable layer
Confined or artesian aquifer
contained between 2 aquicludes
Potentiometric surface
an imaginary plane where a given reservoir of fluid will “equalize out to” if allowed to flow, based on hydraulic principles.
Potentiometric surface vs water table:
the difference between the naturally occurring surface of the water in a groundwater aquifer and the surface of the water in a monitoring well in a confined aquifer.
Groundwater is vulnerable to many different sources of
pollution
Any other fluid released into the ground will
try to do as water does
Groundwater contains a wide range of dissolved
ions, most at levels that are higher than in surface water
Hard water
- Water with high levels of calcium or magnesium
- often leaves coatings of white precipitates on plumbing fixtures
- related to the history of where the water has flowed in sediments
Saltwater Intrusion
- Well creates a cone of depression and used so much of freshwater so now where saltwater flows in, near the coast
What can people living near the coast do to reduce the likelihood of saltwater intrusion?
Dig well further inland, limit water use
An improperly functioning septic tank can be a source of
groundwater contamination
Springs (where the water table intersects with topography) exist where
groundwater naturally comes to the surface
Karst topography
A landscape that is characterized by numerous caves, sinkholes, fissures, and underground streams
- usually forms in regions of plentiful rainfall where bedrock consists of carbonate-rich rock that is easily dissolved
- i.e hydrothermal activity like geysers, hot springs, fumaroles
