Section 2: Coastal processes equations

Question 1

Wave celerity (speed)

Answer 1

C = L/T

Question 2

What are the forces in wave celerity equation

Answer 2

L is wavelength
T is wave period

Question 3

Deep water wave celerity

Answer 3

Depth: D >L/2
C = gT/2π = √ gL/2π

Question 4

What is Hb (little b)

Answer 4

Wave height at breaking

Question 5

What is hb (little b)

Answer 5

Wave depth at breaking

Question 6

Shallow water wave celerity

Answer 6

Depth: D<L/20
C = √gD
L = T √gD

Celerity is only dependent on water depth in shallow water

Question 7

What is the approx. wave depth in relation to breaking wave height

Answer 7

Hb = 0.78hb

Question 8

Distance =

Answer 8

speed x time

Question 9

Celerity =

Answer 9

distance / time

Question 10

Time =

Answer 10

distance / celerity

Question 11

Irribarren number equation

Answer 11

ξ = tanβ / √Hb / Lo

Question 12

What does the Irribarren number show

Answer 12

Wave breaking control, surf similarity parameter

Question 13

C0 (little 0)

Answer 13

= 0.56T

Question 14

L0 (little 0)

Answer 14

= 1.56T^2

Question 15

What is the Universal Law of Gravitational Attraction

Answer 15

The force of gravitational attraction (F) of two particles of masses M1 and M2 separated by a distance r

Question 16

Universal Law of Gravitational Attraction equation

Answer 16

F = GM1M2/ r^2

Question 17

What is the universal gravitational constant

Answer 17

G= 6.67 x 10^11 Nm^2/kg^2

Question 18

Change in sea surface level equation

Answer 18

Δζ = -ΔPA / (ρg)

Question 19

What are the forces in sea surface level equation
* finish*

Answer 19

Δζ is change in sea surface level
-ΔPA is change in local air pressure

Question 20

Inverse barometer effect equation

Answer 20

Δζ ~ 1ΔPA

Question 21

A 1mbar rise (/fall) of air pressure is equal to

Answer 21

1cm rise (/fall) in sea level

Question 22

Change in sea level with distance equation

Answer 22

dζ / dx = τ /gρD

Question 23

What are the forces in change in sea level equation

Answer 23

In equilibrium, the wind stress must balance the pressure gradient caused by a slope in the sea surface ( dζ / dx in cm)
τ is wind stress
g is gravitational acceleration
ρ is water density
D is water depth
Slope is inversely proportional to depth- only in shallow sea that a major change in sea level expected

Question 24

Tide generating force

Answer 24

P = 2G (mpm1a / r^3)

2mp (m1/m2)* (a/r)^3

Tidal generation force is proportional to the mass of the Moon and inversely proportional to the cube of the distance between the Earth and moon

Question 25

Understand: Natural resonance period

Answer 25

Oscillation in a basin
T =2L/ √gd

Question 26

Understand: Wind stress

Answer 26

τ = CDPaU(little10)^2

Question 27

Understand: wind stress forces in equation

Answer 27

U(little10) is wind speed
CD is drag coefficient (dimensionless) (little D)
Pa

Question 28

What are the forces in tide generating force

Answer 28

g is gravitational acceleration 9.81m/s^2
a is the radius of the Earth
mp is 1kg
m1 is the mass of the object being calculated eg the moon
me is mass of the Earth
r is the distance between the objects eg the earth and the moon

Question 29

using tidal generation force, calculate the Lunar force at P

Answer 29

2mp (m1/m2)* (a/r)^3

2mpg (mass of moon / mass of earth) (equitorial redius of the earth / the mean distance between earth and moon)^3

2mpg (7.3510^22 / 5.97 10^24) (6378000 / 384400000)^3

Question 30

Inverse Barometer effect

Answer 30

Δζ ~1ΔPA (little A)
change in sea level is equal to change in air pressure

Question 31

Pressure set up

Answer 31

Δζ ~1ΔPA
new pressure given take away 1013mbar = pressure change which is the same as the rise in sea level in cm