WATER LEVEL VARIATIONS III (TIDEINDUCED)

WATER LEVEL VARIATIONS IIITIDE-INDUCED Tide-Induced Water Level Variations Astronomical Tides... Departure from mean net force => tides Newton Schematized Distribution of Forces Because

WATER LEVEL VARIATIONS III

(TIDE-INDUCED)

Tide-Induced Water Level Variations

Astronomical Tides

Gravitational Force

1 2

g

m m

r



Attraction force between two bodies:

Individual water elements on Earth

attracted by slightly different forces

Departure from mean net force =>

tides

Newton

Schematized Distribution of Forces

Because of Earth’s rotation:

two highs and two lows in a day

(approximately)

Types of Tide

semi-diurnal

diurnal

mixed

Influence of the Sun

Sun has different mass and distance to

Earth = > effect less than half the moon’s

influence

Spring and Neap Tides

Typical Tidal Curves

United States coast

Equilibrium Theory

Tide can be predicted as a sum of

harmonic terms:

Assume that water responds instantaneously to

forces of sun and moon (no inertia and friction).

1

N

i



Compute coefficients from water level data.

Tidal Constituents and Arguments

Time and Phase Shift Effects

Dynamic Theory

Laplace

Tidal motion is viewed as a

forced wave

Basin shape + Coriolis

important.

=> Kelvin Waves

FLOOD TIDE EBB TIDE AMPHIDROMIC POINT CO-TIDAL LINES &

t = 0

cross-section cross-section

t = (6/12)T

t = 0 (1/12)T (2/12)T (3/12)T (4/12)T (5/12)T (6/12)T (7/12)T (8/12)T (9/12)T (10/12)T (11/12)T

AMPHIDROMIC

POINT

MOTION OF CREST

IN THE NORTHERN HEMISPHERE:

Co-range lines are concentric curves

about the amphidromic point

Amphidromic Point

Cotidal and coamplitude lines

Global Tidal Variations

Microtides: < 2 m

Mesotides: 2 – 4 m

Macrotide: > 4 m

Tide Gage

ADCIRC Model

Simulates tidal

motion + storm surge

Application to Shinnecock,

Long Island