Hydrogeology

Question 1

Hydrologic Budget Equation

Answer 1

dSt = P - E +/- R +/- U
dSt - change in total storage
P - precipitation
E - evapotranspirations
R - runoff
U - underflow (GW inflow - GW outflow)

Question 2

Groudwater Inventory Equation

Answer 2

dS = I - O
dS - change in total aquifer storage
I - input or recharge to aquifer
O - output of discharge from aquifer

Question 3

Total Energy of Aquifer Equation

Answer 3

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

Question 4

Total Head in Unconfined Aquifer Equation

Answer 4

E = z1 - z2 = h
E - energy potential
z1 - higher elevation head
z2 - lower elevation head
h - head loss between two points

Question 5

Porosity Equation

Answer 5

n = Vv/V x 100%
Vv - void volume
V - total volume of material (solid + void)

Question 6

Effective Porosity Equation

Answer 6

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

Question 7

Specific Yield Equation

Answer 7

Sy = (Vw drained / V) x 100%
Vw drained - volume of water gravity drained from sample
V - total volume of sample

Question 8

Specific Retention Equation

Answer 8

Sr = Vw retained / V x 100%
Vw retained - volume of water retained in sample after gravity drain
V - total volume of sample

Question 9

What is Sy + Sr

Answer 9

Specific retention plus specific yield is porosity

Question 10

Storativity Equation for Unconfined Aquifer

Answer 10

S = +/- Vw / A dh
Vw - volume of water
A - unit surface area
dh - water level

Question 11

Storativity Equation for Confined Aquifer

Answer 11

S = b Ss
b = saturated thickness of the aquifer
Ss - specific storage

Question 12

Hydraulic Conductivity Equation

Answer 12

K = ki gamma/mew
ki - intrinsic permeability
gamma - specific weight of fluid
mew - dynamic viscosity of fluid

Question 13

Transmissivity Equation

Answer 13

T = K b
K - hydraulic conductivity
b - saturated thickness of aquifer

Question 14

Hydraulic Gradient Equation

Answer 14

i = dh / L
dh - change in head between two wells
L - horizontal distance between two wells

Question 15

Darcy’s Law

Answer 15

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

Question 16

Darcy’s Law in terms of Transmissivity

Answer 16

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

Question 17

Dupuit Equation for Unconfined Flow

Answer 17

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

Question 18

Groundwater Velocity Equation

Answer 18

Vs = K i / ne
K - hydraulic conductivity
i - hydraulic gradient
ne - effective porosity

Question 19

Salt Water Intrusion Equation

Answer 19

Z = 40 ht
Z - depth of fresh water - salt water interface
ht - height of potentiometric surface above sea level

Question 20

Connate Water

Answer 20

water trapped in the pores of a sedimentary rock at the time of deposition

Question 21

Effective Porosity

Answer 21

percentage of total volume of a soil or rock that consists of interconnected pore space. Sometimes used analagously to specific yield.

Question 22

Field Capacity

Answer 22

Quantity of water held by soil or rock against the pull of gravity

Question 23

Head

Answer 23

A measure of the potential energy of a fluid at any given point with respect to a given datum

Question 24

Hydraulic Conductivity

Answer 24

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).

Question 25

Intrinsic permeability

Answer 25

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.

Question 26

Permeability

Answer 26

measures the relative ease of flow through aquifer under unequal pressure

Question 27

Porosity

Answer 27

percentage of bulk volume of rock or soil that is occupied by void space

Question 28

Specific Retention

Answer 28

Ratio of the volume of water a soil or rock can retain against gravity drainage to the total volume of the soil or rock (%)

Question 29

Specific Storage

Answer 29

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.

Question 30

Specific Yield

Answer 30

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 (%)

Question 31

Storativity

Answer 31

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.

Question 32

Transmissivity

Answer 32

The capacity of an aquifer to transmit water of the prevailing kinematic viscosity.

gpd/ft or ft^2/day