TIDES

I.          Why study?
A.       Part of coastal energy system
B.       Determine kind of coastal form and distribution (tidal range)
C.       Shape of beach (tidal range)

 II.        Why are they important?  Energy source
            Important aspects:  frequency and range

 III.        Source of energy
            A.       All celestial bodies, but mainly the moon and sun    
                       1.            Moon – proximity
                       2.            Sun – mass
            B.        Expressed by Newton’s 2^nd law:  F = G x (m₁ x m₂)/R²
            C.        Proximity is more important than mass as above formula indicates
            D.        Centrifugal force vs. gravitational attraction
            E.        Frequency of tides:  semi-diurnal (2 highs and 2 lows)
            F.         Syzygy = sun force + moon force in a straight line or acting in concert
            G.        Spring tides occur during conjunctionor opposition
            H.         Neap tides occur at times when conjunction or opposition are not
                        present
            I.           Diurnal inequality – differences between the heights of successive
                         highs or lows; caused by moon moving from 28.5^o N of the earth’s
                         equator to 28.5^o of the equator
            J.          Equatorial tides – those bisected by the earth’s equator
            K.         Tropical tides – those that occur around the Tropic of Cancer and
                         the Tropic of Capricorn

IV.        What determines the height of tides?
            A.        Moons orbit (shape) – complete orbit takes 27.5 days; the orbit is
                        elliptical thus the distance between the earth and the moon changes. 
                        When the moon is closest to the earth, this is known as perigee and
                        tides are tides 20% higher. If the moon and the earth are at their
                        greatest distance, this is known as apogee.
            B.        Earth-Sun distance – orbit of earth around sun is elliptical, thus again
                        distance between the two bodies varies.  The earth and sun are
                        closest during November to January; perihelion, thus tides generally
                        are greater during this period of time.
            C.        Worst conditions, thus, are:  perigee, perihelion, either conjunction or
                        opposition; this condition occurs about every 1700 years, and the
                        next occurrence will be AD 3300.

V.        Tides in the Coastal Zone
            A.        Height increases as it propogates into shallow water
            B.        Length decreases as it moves into shallow water
            C.        Tides are forced waves, e.g., speed is controlled by depth of ocean
            D.        Tides do not move from ocean to ocean, except for the extreme
                        southern oceans, thus bounce off continents and form a standing
                        wave.
                        1.        Incident wave
                        2.        Reflected wave
                        3.        Wave re-enforcement and wave cancellation

  E.        Effects of the earth’s rotation on tides
              1.        Amphidromic system and amphidromic point
              2.        Rotating tides
              3.        Co-tidal lines

            F.        Areas of spectacular tides
                        1.        Bay of Fundy – 15.4 m tidal range
                        2.        Bristol Channel, England – 12 m tidal range
                        3.        Wash, England (North Sea) – 6 m tidal range

            G.        Tidal range is a function of:
                       1.         Length of estuary
                       2.         Depth of channel
                       3.         Resonance or tidal beating
                       4.         Width of shelf