EM 1110-2-1100 (Part II)
30 Apr 02
Figure II-6-31. Duration of outflow relative to bay superelevation
Table II-6-2
Semidiurnal and Shallow-Water Tidal Constituents and Harmonic Frequencies
Constituent
Degrees/hr
Designation
a1
28.9841
Lunar semidiurnal
M2
S2
a2
30.0000
Solar semidiurnal
N2
a3
28.4397
Lunar elliptic
M4
2a1
57.9682
Lunar quarter-diurnal
S4
2a2
60.0000
Solar quarter-diurnal
a1+a2
58.9841
Compound harmonic
MS4
MN4
a1+a3
57.4238
Compound harmonic
MSf
a2-a1
1.0159
Lunar long-period
(3) Flow dominance. Entrance area and bay surface area variation impacts flow conditions at the inlet
in terms of the continuity equation (Equation II-6-3), which indicates that
dhb
Aavg
%
(II-6-22)
dt
Ab
The rate of change of bay elevation is directly proportional to channel area and inversely proportional to
surface area of the bay. If Aavg is held constant while Ab increases with the rising tide, then the rate of rise
decreases, while the rate of fall increases over time. This means there is a longer rise and faster fall,
indicating greater ebb velocity peaks (assuming the same amount of water enters and leaves the bay), which
means currents are ebb-dominant when considering only the effect of variable bay area. Similar reasoning
II-6-36
Hydrodynamics of Tidal Inlets
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