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3 Basics of Nonhydrostatic Modelling
3.23.7 Tidal Patterns
Oceanic tides are the composite of a set of several tidal constituents also called
partial tides. The most prominent tidal constituents are briefly described in the
following. The Moon creates a semidiurnal lunar tide (abbreviated as M2), with
a period of 12 hrs and 25 min, and a diurnal lunar tide (O1), with a period of 24 hrs
and 50 min. The Sun causes a semidiurnal solar tide (S2), with a 12-hrs period, and a
diurnal solar tide (K1), with a 24-hrs period. The M2 constituent is often dominant.
The longer period of semi-diurnal and diurnal lunar tides compared with solar
tides is caused by progression of the Moon’s location during one full rotation of the
Earth. Dependant on geometry, tides can appear in shelf seas and estuaries as either
semidiurnal tides, diurnal tides, or a mixture of the latter two, called mixed tides.
Tides in the Bay of Fundy, for instance, are mixed tides, but diurnal sea-level variations appear more dominant than semi-diurnal variations. The form factor compares
the amplitudes of semi-diurnal tidal constituents (M2 and S2) with those of diurnal
tides (O1 and K1). These amplitudes can be derived from field observations using a
method called harmonic analysis, not replicated here. The form factor tells the tidal
characteristics of a region.
Wave interference is the partial or full offset of the sea-level elevation of one
wave pattern by a sea-level depression of another wave pattern. Interference of solar
and lunar tides gives rise to regular variation of the tidal range between spring tide,
when it has its maximum, and neap tide, when it has its minimum. The period
between spring and neap tide is about 14 days. In certain regions, such as Gulf St.
Vincent and Spencer Gulf in South Australia, this interference is almost perfect and
leads to almost absent tidal flows during the neap tide. This phenomenon is called
dodge tide, first reported by the explorer Matthew Flinders in 1814 (Flinders,1814).
3.23.8 Classification of Estuaries According to Stratification
and Circulation
The circulation in positive estuaries depends on the amount of freshwater received
from continental runoff and the magnitude of tidal flows inducing vertical mixing.
When using the period of the predominant tidal constituent for reference, estuaries
can be classified in terms of the amount of freshwater received over this period R,
called freshwater volume, and the amount of water that the tidal flow moves into an
estuary over a tidal cycle, referred to as V in the following. The tidal volume can be
calculated from tidal range observations and the surface area of an estuary and it is
a measure of the magnitude of tidal flows in a region. The freshwater volume has to
be derived from measurements of flow rates at the mouth of individual rivers, also
called sub-estuaries, feeding into the parent estuary.
Salt-wedge estuaries are classified by an R/V ratio exceeding unity. The surface
water has small salinities along the entire length of the estuary and this becomes
largely undiluted exported into the adjacent sea. A wedge of salty oceanic water is
3 Basics of Nonhydrostatic Modelling
3.23.7 Tidal Patterns
Oceanic tides are the composite of a set of several tidal constituents also called
partial tides. The most prominent tidal constituents are briefly described in the
following. The Moon creates a semidiurnal lunar tide (abbreviated as M2), with
a period of 12 hrs and 25 min, and a diurnal lunar tide (O1), with a period of 24 hrs
and 50 min. The Sun causes a semidiurnal solar tide (S2), with a 12-hrs period, and a
diurnal solar tide (K1), with a 24-hrs period. The M2 constituent is often dominant.
The longer period of semi-diurnal and diurnal lunar tides compared with solar
tides is caused by progression of the Moon’s location during one full rotation of the
Earth. Dependant on geometry, tides can appear in shelf seas and estuaries as either
semidiurnal tides, diurnal tides, or a mixture of the latter two, called mixed tides.
Tides in the Bay of Fundy, for instance, are mixed tides, but diurnal sea-level variations appear more dominant than semi-diurnal variations. The form factor compares
the amplitudes of semi-diurnal tidal constituents (M2 and S2) with those of diurnal
tides (O1 and K1). These amplitudes can be derived from field observations using a
method called harmonic analysis, not replicated here. The form factor tells the tidal
characteristics of a region.
Wave interference is the partial or full offset of the sea-level elevation of one
wave pattern by a sea-level depression of another wave pattern. Interference of solar
and lunar tides gives rise to regular variation of the tidal range between spring tide,
when it has its maximum, and neap tide, when it has its minimum. The period
between spring and neap tide is about 14 days. In certain regions, such as Gulf St.
Vincent and Spencer Gulf in South Australia, this interference is almost perfect and
leads to almost absent tidal flows during the neap tide. This phenomenon is called
dodge tide, first reported by the explorer Matthew Flinders in 1814 (Flinders,1814).
3.23.8 Classification of Estuaries According to Stratification
and Circulation
The circulation in positive estuaries depends on the amount of freshwater received
from continental runoff and the magnitude of tidal flows inducing vertical mixing.
When using the period of the predominant tidal constituent for reference, estuaries
can be classified in terms of the amount of freshwater received over this period R,
called freshwater volume, and the amount of water that the tidal flow moves into an
estuary over a tidal cycle, referred to as V in the following. The tidal volume can be
calculated from tidal range observations and the surface area of an estuary and it is
a measure of the magnitude of tidal flows in a region. The freshwater volume has to
be derived from measurements of flow rates at the mouth of individual rivers, also
called sub-estuaries, feeding into the parent estuary.
Salt-wedge estuaries are classified by an R/V ratio exceeding unity. The surface
water has small salinities along the entire length of the estuary and this becomes
largely undiluted exported into the adjacent sea. A wedge of salty oceanic water is