Patterns and Tidal Characteristics of East Coast of Bintan Island , Riau Archipelago Province

Suhana et al.,/ JAGI Vo2 No 1/2018 98 Patterns and Tidal Characteristics of East Coast of Bintan Island, Riau Archipelago Province Mario Putra Suhana , I Wayan Nurjaya, Nyoman Metta N. Natih Raja Ali Haji Maritime University, Department of Marine Science, Tanjungpinang, Indonesia Bogor Agricultural University, Department of Marine Science and Technology, Bogor, Indonesia Corresponding author e-mail: marioputrasuhana@umrah.ac.id


Introduction
Tidal is a process of sea level change that is characterized by the movement up and down of the sea surface periodically caused by the influence of tensile forces of celestial bodies, especially the sun and moon, where the influence of tensile forces resulted in the movement of water masses on the surface of the earth (Carter, 1988;Adibrata, 2007).
Sea tidal process on a regular basis is one of the important factors that affect oceanographic processes around the waters widely as sea currents.Tides also have a significant influence on the dynamics of the geomorphology of waters, especially coastal waters, this is caused by tidal phenomenon causing changes that occur regularly at sea surface level along the coast (Suhana, et al., 2016).
Tidal is one parameter of oceanography that has an important role in almost all oceanographic phenomena that occur in the waters (Adibrata, 2007).Some examples of the importance of tidal data are as reference data for correction of field measurement data such as water depth (bathymetry) and water level visibility.In addition, can be a reference for the phenomena of other oceanographic parameters which becomes a parameter in carrying out activities of utilization and management of marine and fishery resources in the coastal area.
Seeing the importance of the role of tidal data on all oceanographic phenomena and giving effect to the activities around the coastal areas as well as the fact that tidal in each waters area have different patterns and characteristics, so it is necessary to do research about tidal patterns and characteristics of the waters which are specifically the waters of the east coast of Bintan Island.
East coast of Bintan Island are densely populated waters, population settlements, tourism areas, conservation areas and fishing grounds are the types of existing utilization in this area.This is also one of the reasons why this research is very necessary to do.

Methods
This research was conducted around the area of the east coast of Bintan Island Riau Archipelago Province in December 2017.Tidal data is retrieved from the global tidal modelling using MIKE 21.
Tidal predictions made at four different locations so that the variability of data obtained more diverse so that it can represent the condition of the tidal of the east coast of Bintan Island as a whole (Figure 1).Tidal predictions made during a month (1-31 December) at different time periods during 2007, 2012 and 2017.

Results and Discussion
There are four points of tidal measurement round the east coast of Bintan Island with different depth conditions, namely in the waters of Trikora 4, Trikora 3, Trikora 1 and in the northern part of Poto Island (Figure 1).
The results of the analysis showed that the tidal range of east coast of Bintan Island during 2007-2017 is 0.70-3.50with mean sea level height range is 2.20-2.60 m.Tidal fluctuations of east coast of Bintan Island as general making an asymmetric pattern where this is a common pattern in any waters.This is because when the tide in high level conditions, water volume has given much more toward the land, while the tide in low level conditions the water volume has given much more toward the sea in different time periods (Surbakti, 2012).Tidal fluctuations of east coast of Bintan Island during 2007-2017 in each station measurement can be seen in the following figure.From the pictures above it can be seen the different of tidal time in every year, but overall tidal patterns of the east coast of Bintan Island which is shown in the pictures above are semi-diurnal tide where there is a process of two pairs and two times subsided in a day.It can be seen from the results of analysis of tidal harmonic components in each station measurement in every year.
The results of analysis of tidal harmonics component showed that M2 component is the component with highest amplitude value in three stations, the anomaly was found in station 4 in the northern part of Poto Island where the highest amplitude value is K1 component.
Apart from tidal harmonics component, tidal type of east coast of Bintan Island waters can be seen from the value of formzahl number.Based on formzahl number, tidal type of waters can be classified into four types (Wyrtki, 1961).
The value of formzahl number in each station respectively are 1.19, 1.44, 1.36 and 1.60.from these values it found that the tidal type of east coast of Bintan Island waters is mixed predominantly semidiurnal tide, this is the same with Suhana et al (2016) research results, where in the study mentioned that the type of tidal waters east coast of Bintan Island is mixed predominantly semi diurnal tide with the value of formzahl number is 0.77.
The results obtained are reinforced by the statement of Triatmodjo (1999) that the tidal with mixed predominantly semi-diurnal type in Indonesia waters generally occurring around the waters of the Malacca Strait and the Andaman Sea.This statement is also in accordance with the results of research conducted by Daya, et al., (2017) in the waters of Nongsa Island, Batam which explains that the waters of Nongsa Island located around the Malacca Strait have the type of semi-diurnal tide.Meanwhile, the results of the analysis using the Indian Spring Low Water method obtained tidal characteristics of the east coast of Bintan Island have the highest mean sea level ranges between 3.14-3.25m on spring tide and 2.36-2.55m on neap tide with the tidal ranges between 0.85-0.97m.Interesting phenomenon obtained from the results of this study is from 2007-2017 maximum sea level in each station tend to decrease, this is considered attractive because during the last 20 years the surface temperature tends to increase, resulting in the melting of polar ice that implies the increase in sea water volume.
It must, of course, have linear implications between the melting of polar ice and sea level rise due to the increased volume of water caused by polar ice melting.
The anomalies obtained from this study are interesting phenomena to be carried out a follow-up study on sea level rise, considering that this phenomenon is in contrast to the current condition of sea level changes with sea level at the research sites that are increasingly decreasing years and not vice versa.
However, based on research conducted by Surya, et al., (2017) and Lubis, et al., (2017) on the characteristics of sea surface temperature in the waters of Batam Island showed that sea surface temperature around Batam Island waters tend to be low in period December to January, this may have implications for the east coast of Bintan Island that is quite close to the waters of Batam Island.

Conclusion
From the analysis results obtained that the tidal type of east coast of Bintan Island is mixed predominantly semi diurnal tide.The interesting things found from the results of this research is in every year sea surface height level of east coast of Bintan Island tends to decrease, this becomes an anomaly of its own, with the increase of earth's temperature makes ice at the poles was melt and will increase the volume of sea water on the earth, so it should have a linear impact with east coast of Bintan Island waters level.

Figure. 2 .
Figure. 2. Tidal on east coast of Bintan Island in 2007

Figure. 5 .
Figure. 5. Comparison of sea surface height on station 1 in every year

Table 1 .
Results analysis of tidal fluctuation and characteristics on station 1

Table 2 .
Results analysis of tidal fluctuation and characteristics on station 2

Table 3 .
Results analysis of tidal fluctuation and characteristics on station 3

Table 4 .
Results analysis of tidal fluctuation and characteristics on station 4

Table 5 .
Harmonic components of tidal on station 1

Table 7 .
Harmonic components of tidal on station 3

Table 10 .
Tidal characteristics of east coast of Bintan Island on each station