Hydrogeology Flashcards
Hydrologic Budget Equation
dSt = P - E +/- R +/- U
dSt - change in total storage
P - precipitation
E - evapotranspirations
R - runoff
U - underflow (GW inflow - GW outflow)
Groudwater Inventory Equation
dS = I - O
dS - change in total aquifer storage
I - input or recharge to aquifer
O - output of discharge from aquifer
Total Energy of Aquifer Equation
E = v^2/2g + z + P/rho
E - total energy or total head
v - velocity of groundwater
g - gravity acceleration
z - elevation of groundwater above ref. elevation
P - pressure
rho - specific weight of water
Total Head in Unconfined Aquifer Equation
E = z1 - z2 = h
E - energy potential
z1 - higher elevation head
z2 - lower elevation head
h - head loss between two points
Porosity Equation
n = Vv/V x 100%
Vv - void volume
V - total volume of material (solid + void)
Effective Porosity Equation
ne = (Ws - Wr / Ws - Wo) x Vv/V x 100%
Ws - weight of saturated sample
Wr - weight of sample after gravity drainage
Wo - weight of air dried sample
Specific Yield Equation
Sy = (Vw drained / V) x 100%
Vw drained - volume of water gravity drained from sample
V - total volume of sample
Specific Retention Equation
Sr = Vw retained / V x 100%
Vw retained - volume of water retained in sample after gravity drain
V - total volume of sample
What is Sy + Sr
Specific retention plus specific yield is porosity
Storativity Equation for Unconfined Aquifer
S = +/- Vw / A dh
Vw - volume of water
A - unit surface area
dh - water level
Storativity Equation for Confined Aquifer
S = b Ss
b = saturated thickness of the aquifer
Ss - specific storage
Hydraulic Conductivity Equation
K = ki gamma/mew
ki - intrinsic permeability
gamma - specific weight of fluid
mew - dynamic viscosity of fluid
Transmissivity Equation
T = K b
K - hydraulic conductivity
b - saturated thickness of aquifer
Hydraulic Gradient Equation
i = dh / L
dh - change in head between two wells
L - horizontal distance between two wells
Darcy’s Law
vd = - K dh/L = Q/A or Q = - K i A
vd - specific discharge
K - hydraulic conductivity
dh/L or i = hydraulic gradient
Q - volumetric discharge per unit time
A - cross sectional area thru which flow occurs
Darcy’s Law in terms of Transmissivity
Q = T/b i (b x w) = T i w
T - transmissivity
b - average saturated thickness of aquifer
i - hydraulic gradient
w - average width of aquifer
Dupuit Equation for Unconfined Flow
Q = -1/2 K (ht1^2 - ht2^2)/L x w
K - hydraulic conductivity
ht1 - height of water table in well 1
ht2 - height of water table in well 2
L - distance along flow path between to wells
w - width of aquifer
Groundwater Velocity Equation
Vs = K i / ne
K - hydraulic conductivity
i - hydraulic gradient
ne - effective porosity
Salt Water Intrusion Equation
Z = 40 ht
Z - depth of fresh water - salt water interface
ht - height of potentiometric surface above sea level
Connate Water
water trapped in the pores of a sedimentary rock at the time of deposition
Effective Porosity
percentage of total volume of a soil or rock that consists of interconnected pore space. Sometimes used analagously to specific yield.
Field Capacity
Quantity of water held by soil or rock against the pull of gravity
Head
A measure of the potential energy of a fluid at any given point with respect to a given datum
Hydraulic Conductivity
The capacity of a porous medium to transmit fluid. Depends on fluid properties (specific weight and dynamic viscosity) and properties of the medium (intrinsic permeability).
Intrinsic permeability
property of the porous medium that measures the relative ease with which a fluid can be transmitted through it under a hydraulic gradient. It is dependent on pore size.
Permeability
measures the relative ease of flow through aquifer under unequal pressure
Porosity
percentage of bulk volume of rock or soil that is occupied by void space
Specific Retention
Ratio of the volume of water a soil or rock can retain against gravity drainage to the total volume of the soil or rock (%)
Specific Storage
Amount of water per unit volume of a saturated formation that is stored or expelled from storage due to compressibility of mineral skeleton and pore water per unit change in head.
Specific Yield
Ratio of the volume of water that drains from a saturated soil or rock due to gravity to the total volume of soil or rock (%)
Storativity
Volume of water that a permeable unit releases from or takes into storage per unit surface area of the aquifer per unit change in head.
In unconfined aquifer, storage = specific yield.
Transmissivity
The capacity of an aquifer to transmit water of the prevailing kinematic viscosity.
gpd/ft or ft^2/day
