3.23 Estuaries
85
instance of maximum sea level. Low tide refers to the minimum sea level. The tidal
range is the difference between high tide and low tide. Slack water refers to times
of no or only little tidal flow.
The tide-generating force involves the gravitational attractive force between the
Earth/Moon and Earth/Sun systems and the centrifugal force. The magnitude of the
gravitational force is proportional to mass and decreases rapidly with the square of
distance between bodies. Therefore, the Moon (due to close distance) and the Sun
(due to large mass) are the only contributors to tides on Earth. Tides are created
owing to a slight imbalance of these forces at the sea surface.
3.23.5 Dynamic Theory of Tides
Oceanic tides are long surface gravity waves of a phase propagation being constrained by the well-known dispersion relation Eq. (3.8). Owing to this constraint
and the existence of coastlines, tidal oceanic waves simply cannot keep pace with
the progress of the astronomical forcing. Instead of this, the tidal signal in the ocean
is rather of the form of a standing-wave response that varies in magnitude according
to the regional geometry of an oceanic basin. This “dynamic theory of tides”, first
proposed by Pierre-Simon Laplace in 1775 (Laplace, 1775), successfully describes
the apparently complex tidal patterns in the ocean.
The influence of the Coriolis force on tidal motion gives rise to a Kevin-wave
response (see Sect. 3.6.2 of K¨ ampf (2009)). Rotational effects support maximum
tidal sea levels propagating along the coast. Amphidromic points are locations that
display no tidal range a tidal constituent (see below). Radiating from such a point are
co-tidal phase lines, which connect points where high tide occurs simultaneously.
Co-tidal range lines, on the other hand, connect points of the same tidal range. To
this end, the tidal signal in the ocean propagates around amphidromic points and
maximum tidal ranges are often found along coastlines. This makes coastal regions
vulnerable to storm surges if these coincide with a high tide.
3.23.6 Tides in Estuaries
Tidal co-oscillations in the estuary follow from the tidal forcing of the adjacent
ocean. As the tidal wave approaches shallower water, its wavelength decreases
according to Eq. (3.8). Dependant on geometry and because of the shortening of
the tidal wave, some estuaries exhibit enormous tidal sea-level variations. The most
amplified response occurs if a wave node establishes close to the estuary’s entrance.
The Bay of Fundy on the east coast of North America, for instance, supports a
tidal range of 17 m at the northern end of the Minas Basin, which makes boating
and fishing activities rather transient ones. Natural oscillations in an enclosed or
partially enclosed body of water are called seiches.
85
instance of maximum sea level. Low tide refers to the minimum sea level. The tidal
range is the difference between high tide and low tide. Slack water refers to times
of no or only little tidal flow.
The tide-generating force involves the gravitational attractive force between the
Earth/Moon and Earth/Sun systems and the centrifugal force. The magnitude of the
gravitational force is proportional to mass and decreases rapidly with the square of
distance between bodies. Therefore, the Moon (due to close distance) and the Sun
(due to large mass) are the only contributors to tides on Earth. Tides are created
owing to a slight imbalance of these forces at the sea surface.
3.23.5 Dynamic Theory of Tides
Oceanic tides are long surface gravity waves of a phase propagation being constrained by the well-known dispersion relation Eq. (3.8). Owing to this constraint
and the existence of coastlines, tidal oceanic waves simply cannot keep pace with
the progress of the astronomical forcing. Instead of this, the tidal signal in the ocean
is rather of the form of a standing-wave response that varies in magnitude according
to the regional geometry of an oceanic basin. This “dynamic theory of tides”, first
proposed by Pierre-Simon Laplace in 1775 (Laplace, 1775), successfully describes
the apparently complex tidal patterns in the ocean.
The influence of the Coriolis force on tidal motion gives rise to a Kevin-wave
response (see Sect. 3.6.2 of K¨ ampf (2009)). Rotational effects support maximum
tidal sea levels propagating along the coast. Amphidromic points are locations that
display no tidal range a tidal constituent (see below). Radiating from such a point are
co-tidal phase lines, which connect points where high tide occurs simultaneously.
Co-tidal range lines, on the other hand, connect points of the same tidal range. To
this end, the tidal signal in the ocean propagates around amphidromic points and
maximum tidal ranges are often found along coastlines. This makes coastal regions
vulnerable to storm surges if these coincide with a high tide.
3.23.6 Tides in Estuaries
Tidal co-oscillations in the estuary follow from the tidal forcing of the adjacent
ocean. As the tidal wave approaches shallower water, its wavelength decreases
according to Eq. (3.8). Dependant on geometry and because of the shortening of
the tidal wave, some estuaries exhibit enormous tidal sea-level variations. The most
amplified response occurs if a wave node establishes close to the estuary’s entrance.
The Bay of Fundy on the east coast of North America, for instance, supports a
tidal range of 17 m at the northern end of the Minas Basin, which makes boating
and fishing activities rather transient ones. Natural oscillations in an enclosed or
partially enclosed body of water are called seiches.