Oct 21 Lecture (Water as a resource) Flashcards
if you followed a water molecule all the way through the water cycle, it would take ___yrs
40,000
regionally, water is a renewable resource, but may not be ___
locally
how does groundwater form?
forms as rain infiltrates through soil and unconsolidated material, progressively moving into the bedrock
- the only space for water is pore spaces b/w the grains that comprise the bedrock or space in fractures
rocks that store and transmit water are called ___
aquifers
compared to surface water, groundwater has many advantages:
- it’s naturally ____ through aquifer rock
- it’s less susceptible to ____ and _____ ____
filtered
evaporation
seasonal variations
porosity=
portion of void space in material (soil or rock) where fluid can be stored
permeability=
measures how readily a fluid passes through a material
____ are very porous
___ is not very porous/ permeable
sandstones
clay
porosity varies with:
1.
2.
3.
- % cement
- sorting
- fracturing
gravity will pull water down into the ground until an impermeable layer (an ____) halts it
aquitard
what is the saturated zone?
aka phreatic zone
below the water table; fills with water (all pore spaces)
what is the unsaturated zone?
aka vadose zone
above the water table, above saturated zone
pore spaces are filled with water and air
the water table is at the top of the _____ ___
saturated zone
the water table separates the unsaturated and saturated zones
water stored and transmitted at rates sufficient enough to be useful is called a(n) _____
aquifer
water moving into an aquifer is called ____
recharge
when ___ and ___ are balanced, the groundwater reservoir and water table remain constant
recharge and discharge
an aquifer without an aquitard above it is called a(n) ____ _____
unconfined aquifer
an aquifer with an aquitard above and below it is a(n) ___ ___
confined aquifer
a confined aquifer may see hydrostatic water pressure increase and form a(n) ____ ___
artesian system
what happens if you drill into a confined aquifer that’s under pressure?
it’ll cause water to rise above the aquifer
- the potentiometric surface is the height to which the water would rise
what is the potential energy in an aquifer called?
hydraulic head
the higher the water table, the ___ the hydraulic head
the higher the potentiometric surface in a confined aquifer, the ___ the hydraulic head
higher
higher
groundwater flows spontaneously from areas of ___ hydraulic head to areas with ___ hydraulic head
high to low
discharge is the:
it’s influenced by:
amount of water flowing past a point over a period of time
the porosity and permeability of the rock or sediment of the aquifer
what is a perched water table?
groundwater that forms a “table” above an aquitard well above the actual water table.
caused by distribution of aquitard lenses
describe cones of depression
pumping ground water will lower the water table and form a cone of depression around the well
if not enough recharge, well can run dry
why does saltwater intrusion occur?
because freshwater is less dense than saltwater
- saltwater near a coastline may push freshwater lenses back if recharge is not sufficient to push seawater back towards the sea
What is the GRACE satellite?
2 satellites that can tell how much groundwater has been extracted
- based on mass of earth/ gravitational pull
- originally used for greenland ice caps
what did the GRACE satellites find in India?
India’s groundwater has been nearly depleted
