Hydrogeology Flashcards
Give examples of geofluids
gas, oil, brine, groundwater
What is the difference in pores in the unsaturated and saturated zones?
unsaturated - pores = water and air
saturated - pores = water
What is the pressure compared to atm in unsaturated and saturated pores?
and at gw table
unsaturated = less than atmospheric pressure
p less than atm in unsaturated pores
p =atm at gw table
p >atm in saturated pores
where is soil water found?
in the root zone
What is a cone of depression?
the shape formed around a groundwater extraction well
What are forms of input for the gw system?
recharge usually precipitation. Some of it goes to baseflow for rivers and the rest is extracted
What is a major consequence of groundwater extraction?
subsidence
Consequences of groundwater abstraction?
increase in irrigation needs
land subsidence in unconsolidated aquifers
increasing costs to lift water from deep aquifers
quality of water deteriorates
risk of saltwater intrusion increases
ecological detereoration
How does unsustainable groundwater abstraction impact salinity
the sea level increases with respect to the inland groundwater level and this will cause easier infiltration of brackish water
3 forms of recharge
artificial (managed aquifer recharge), natural (rainwater), indirect (aquitard leakage, cross formational flow)
pros and cons of surface water
accessible, plentiful, unsteady supply, prone to contamination
pros and cons of groundwater
steady, good quality, inaccessible, difficult ot find
aquifer
subsurface formation of a porous medium that contains and transmits significant amounts of groundwater
difference between aquifer and reservoir
reservoir is the word for hydrocarbons and aquifer for groundwater
aquitard
subsurface formation that can store water and has a low transmission capacity. It retards but does not prevent the flow of water to or from the adjacent aquifer.
aquiclude
very reduced storage, cannot transmit groundwater, impermeable.
unconfined aquifer
water table aquifer or phreatic aquifer
directly connected to water level, upper layer is the water table which is free to rise and fall.
confined aquifer
Clarify the pressure wrt atm
restricted by 2 layers of aquitard. Water pressure is >atm.
artesian well
if well is drilled through superposed aquitard into aquifer, water is under enough pressure to rise. If aquiclude is is above, pressure is even higher. A spring forms. An artesian well is when water rises till above the surface.
semi-confined aquifer (leaky)
bounded by aquitard that does transmit water when hydraulic head above and below the leaky boundary are in disequilibrium. The head difference exists between aquifer A and B so water passes through aquitard to aquifer B. Aquifer B is then semi-confined.
Karstic aquifer
controlled by rock dissolution
What are the 3 forms of energy in GW?
And corresponding head
kinetic energy –> velocity head
potential elevation energy –> datum head
pressure energy –> pressure head
Kinetic energy
formula for energy and for head
gained through motion/ velocity
E=1/2mv^2
velocity head = v^2/2g
Potential Energy
measured with respect to the datum (normally NAP)
z meters above datum, particle has z energy