Groundwater Hydraulics: Storage, continuity and groundwater flow equations Flashcards
True or False
Specific yield only applies to confined aquifers.
False (It applies to unconfined aquifers)
Specific yield is the volume of water released per unit area due to a unit drop in the _______ elevation.
water table
What does storativity in a confined aquifer represent?
A) The volume of water per unit volume of aquifer that is drained due to gravitational forces
B) The volume of water released per unit area over the entire thickness of the aquifer as a result of a unit fall in the potentiometric surface
C) The increase in water content due to capillary action
B) The volume of water released per unit area over the entire thickness of the aquifer as a result of a unit fall in the potentiometric surface
What causes the change in storage in an aquifer?
The change in storage is caused by effective stress and fluid pressure, where an increase in effective stress results in a decrease in porosity, and a change in fluid pressure affects the fluid density.
True or False
The specific storage coefficient is determined only by the rock compressibility.
False (It is determined by both rock and fluid compressibility)
In the equation S_s = nρg(c_R+c_F), c_R and c_F represent the compressibility’s of the _______ and the _______, respectively.
rock, fluid
Which formula represents the effective porosity related to specific yield in an unconfined aquifer?
S_y = V_{water released}/V_{areaxdrop}
True or False
Storativity is dimensionless and calculated as
S=HS_S, where H is the aquifer thickness and S_S is the specific storage coefficient.
True
Mass continuity in an aquifer can be described as the change in storage equaling mass _______ minus mass _______.
in, out
Explain why changes in mass occur in groundwater systems according to the principles of mass continuity.
Changes in mass occur due to alterations in fluid density from compression and changes in porosity due to matrix expansion or contraction, which are influenced by variations in effective stress.
If a fluid slight compressible, can be assumed ρ to be ______.
a constant
Formula for c_F?
dρ/ρdP
Formula for c_R?
dn/ndP
What causes the lowering of the water table in specific yield?
The yield (i.e. loss) of water that causes the lowering of the water table is from some pores that were full becoming partially saturated and others about the capillary fringe become less saturated.
Formula for S_y?
S_y = ∆V\∆Az
True or False
In a confined aquifer, the transmissivity T_x and T_y
are calculated as the product of hydraulic conductivity
K_x and K_y with the thickness H of the aquifer.
True
MODFLOW is a USGS computer program that solves the groundwater flow equation using a _______ differences method.
finite
Which equation is specifically used to model transient flow in an unconfined aquifer?
A) Theis equation
B) Boussinesq equation
C) Darcy’s Law
B) Boussinesq equation
What does the Boussinesq equation account for in unconfined aquifers?
It models the transient flow considering changes due to recharge and only considers flow in the x and y directions.
True or False
Barometric efficiency is a measure of how sensitive an aquifer or piezometer system is to changes in atmospheric pressure.
True
If atmospheric pressure rises, the water level in a piezometer in a confined aquifer typically _______.
falls
What will happen to the water level in piezometers if air pressure increases?
A) Water level rises
B) Water level falls
C) No change
B) Water level falls
True or False
Transient flow in confined aquifers does not consider interactions between aquifers and surface water bodies like rivers.
False (Interactions such as those near the River Thames are considered)
In the equation B = 𝛾dⲮ/dP_A, B represents the _____ efficiency, which measures the response of the water level in an aquifer to changes in atmospheric pressure.
barometric
How does the MODFLOW program contribute to understanding groundwater systems?
MODFLOW helps simulate both steady and transient flow in aquifers using a numerical approach, allowing for the prediction and management of groundwater resources.
What does Barometric efficiency denote?
How sensitive the aquifer/piezometer system is to air pressure changes.
What does it mean if B -> 1?
The aquifer is very sensitive
What does it mean if B -> 0?
The aquifer is not sensitive
