of the beach. The moon is the primary factor controlling the temporal rhythm and height of
tides. The moon produces two tidal bulges somewhere on the Earth through the effects of gravitational attraction. The height of these tidal bulges is controlled
by the moon’s gravitational force and the Earth’s gravity pulling the water back toward the Earth. At the location on the Earth closest to the moon, seawater is
drawn toward the moon because of the greater strength of gravitational attraction. On the opposite side of the Earth, another tidal bulge is produced away from the
moon. However, this bulge is due to the fact that at this point on the Earth the force of the moon’s gravity is at its weakest. Considering this information, any
given point on the Earth’s surface should experience two tidal crests and two tidal troughs during each tidal period.
The second factor controlling tides on the Earth’s surface is the sun’s gravity. The height of the average solar tide is about 50 the average lunar tide. At
certain times during the moon’s revolution around the Earth, the direction of its gravitational attraction is aligned with the suns. During these times the two tides
producing bodies act together to create the highest and lowest tides of the year. These spring tides occur every 14
15 days during full and new moons Roos, 1997.
Figure 2.3. Sun-earth-moon system affecting spring tide a and neap tide b
2.3.2. Tides Constituent
In most estuaries and seas, a periodic rise and fall of the water can be observed, it is known as the vertical astronomical tides. The highest level of
tides called High Water level HW and the lowest level is called the Low Water level LW, whereas the difference between HW and LW is called tidal range.
When the vertical movement of the water level is measured for about one day, than it can be observed that the second HW and LW differ from first HW and
LW. This difference in HW’s and LW’s is called the daily inequality.
Figure 2.4. Daily inequality of tides
When the water level is measured in “A” location and the wave move horizontally, a periodic rise and fall of water level can be observed also. So,
associated with vertical movement of the water surface, there is also horizontal movement of the water particles. In tidal analysis, the tidal signal the observed
water level versus time is decomposed into its constituents. Tidal constituent generally can be distinguish into three main groups, and completely can be seen
in Table 2.1.
Table 2.1. Principal body tide constituents
Semi-diurnal Tidal constituent
Period hours
Vertical amplitude mm
Horizontal amplitude mm
M2 12.421
384.83 53.84
S2 solar semi- diurnal
12.000 179.05
25.05 N2
12.658 73.69
10.31 K2
11.967 48.72
6.82
Diurnal Tidal Constituent
Period hours
Vertical amplitude mm
Horizontal amplitude mm
K1 23.934
191.78 32.01
O1 25.819
158.11 22.05
P1 24.066
70.88 10.36
Φ1 23.804
3.44 0.43
Ψ1 23.869
2.72 0.21
S1 solar diurnal 24.000
1.65 0.25
Long Term Tidal Constituent
Period Vertical amplitude
mm Horizontal amplitude
mm
M1 13.661 days
40.36 5.95
Mm moon monthly
27.555 days 21.33
2.96 Ssa solar semi
diurnal 0.50000 yr
18.79 2.60
Lunar Mode 18.613 yr
16.92 2.34
Sa solar annual 1.0000 yr
2.97 0.41
Modified from Wahr, 1995
2.4 Sea Level Rise SLR
2.4.1. Eustatic and Isostatic Sea Level Change
There are two kinds of sea levels change: eustatic and isostatic sea level change. Eustatic sea level change is general or global sea level change, change in seawater
volume globally which is caused by factor like global warming. Isostatic sea level change is change of sea level at specific site as the sum of sea level rise plus local
land-level change like land subsidence.
