1. Introduction
The Maldives is an archipelago of 1190 islands which is grouped in double chains of 26 atolls stretching in a North-South direction in the Indian Ocean. The atolls are composed of live coral reefs and sand bars. The Maldives is a country which bears the lowest Mean Sea Level (MSL) in the world which has an average ground level of 1.5 meters above sea level and the maximum natural ground level is 2.3 meters from the sea level. These coral islands are surrounded by the sea which plays a vital role on the change of the coastal areas of the islands.
Development within coastal areas has increased interest in erosion problems; it has led to major efforts to manage coastal erosion problems and to restore coastal capacity to accommodate short and long-term changes induced by human activities, extreme events and sea level rise. The erosion problem becomes worse whenever the countermeasures (i.e. hard or soft structural options) applied is inappropriate, improperly designed, built, or maintained and if the effects on adjacent shores are not carefully evaluated. Shoreline changes induced by erosion and accretion are natural processes that take place over a range of time scales. They may occur in response to smaller-scale events, such as storms, regular wave action, tides and winds, or in response to large-scale events such as glaciation that significantly alter sea levels (rise/fall) and tectonic activities that cause coastal land subsidence or emergence. Often erosion is addressed locally at specific places or at regional or jurisdictional boundaries instead of at system boundaries that reflect natural processes. This anomaly is mostly attributable to insufficient knowledge of coastal processes and the protective function of coastal systems.
2. Study Area-Fun Island Resort (FIR)
Fun Island Resort (FIR) (Bodufinolhu) is a 100 room three star resort located on the South Eastern corner of South Male’ Atoll [1-6]. Villa Shipping and Trading Company [7] further reported that the reef on FIR exists has an area of about 16 km2 and it is large compared to average Maldivian reefs.
However since the beginning of FIR development in 1983, number of coastal structures have been constructed to maintain white sandy beaches and to protect the island from erosion [1]. As to improve the status of the FIR beach, one of the beach replenishing projects carried out was in 1998/1999 [1]. This project helped to increase the width of the beach to an average 40 - 50 metres all around the island and at 2003 FIR is about 12 hectares in area [1]. CDE had agreed that FIR has undergone major coastal changes on various occasions and coastal modification has resulted [2] (Figure 1).
CDE surveyed FIR in 2008 and concluded from their evaluation that the terrestrial environment specified that there is no significant vegetation (natural vegetation) on the island. Recently research of VSTC in 2010 also proved that the assessment of the terrestrial environment indicated that there is no significant vegetation on FIR, only planted coconut palms and some pioneer vegetation on the reclaimed area with barren areas in between and found from the reef surveys that there are no significant levels of coral community at the proposal locations for the over water structures (jetty, water villas and restaurants) [7].
3. Methodology
The Figure 2 highlights the research methodology used to obtain the data for the study. Primary data was collected with a topographic survey and available secondary data were collected from various government agencies. The data were analyzed using mainly Autocad 2010 and MS Excel software. The study involves mostly of the erosion, abrasion and shoreline instability due to the wind, tide and the costal structures adapted in the study area.
Figure 1. Aerial view of Fun Island Resort Maldives, source [8].
A Topographic Survey of Fun Island Resort was conducted from 24th to 26th May 2011. The purpose of the topographic survey was to gather survey data about the natural and man-made features along the coastline of the island as well as its elevations. A total of eight station points (ST1 to ST8) were set around the island to form a closed traverse. Initially the survey started with the station point one (ST1) based on the main jetty of the island with reference to the bench mark (BM1) on the island. The elevations of several Intermediate points (IS) between the vegetation and the coastline to a depth of −0.7 m was recorded along the west side of the island from station point ST1. The western side of the island consisted mainly of the beach and the main jetty of the island.
A Foresight (FS) was taken to mark the station points ST2 on the southern side of the island and the station point ST3 was marked on the northern side of the island from the station point ST1. The instrument was then moved to the station point ST2 and a back reference Backsight (BS) was taken to the station point ST1. The intermediate points from this station was taken and a Foresight taken to station point ST4. These steps were repeated and the traverse was continued around the island and closed at station point ST3.
3.1. Survey Data Entry and Error Calculations for Traverse
The collected data from the site survey was entered on MS Excel and the error calculations for the traverse were calculated. The rule says that the sum of the interior angles of a traverse should be as follows:
Sum of interior angles = (n – 2) × 180˚
Where n is the number of station points.
Thus sum of interior angles should be
= (8 – 2) × 180˚ = 1080˚
The total of the interior angles we got from the survey data = 1080˚19'20"
Therefore the misclosure of the traverse = 1080˚ – 1080˚19'20" = −0˚19'20"
The misclosure is divided among the eight station points with each
= −0˚19'20"/8
= −0˚02'25"
The misclosure is then deducted from the interior angle to get the corrected angle.
The summation of the corrected angle is now 1080˚.
The Table 1 shows the initial and correct interior angles for the traverse data obtained from Fun Island Resort.
Once the error in the traverse is corrected the data is entered together with the rest of the data obtained from the survey. The elevations of the points are calculated using Height of Plane of Collimation (HPC) method.
Table 1. Tabulation for corrected angles.
After the elevations are calculated this data is then used to draw the coastline and vegetation of Fun Island Resort including the contours of elevations.
4. Results & Discussions
4.1. Wind Data
The daily wind patterns for the two seasons for the years 2010 and 2011 for Hulhule have been studied for the detail analysis of the winds. The analysis of the winds indicates that the central region of the Maldives is predominantly westerly and north easterly (refer Figure 3). It also indicates that there is almost no wind from the quadrant between east and south. The analysis of the wind data for the two seasons indicate that during the Northeast monsoon the wind is predominantly from ENE and E (refer Figure 4) with wind speed reaching 11-17 knots for 16% of this period. Another 12% of the time the wind speed reaches 7 - 10 knots during this period.
The wind direction changes distinctly from W, WSW and WNW throughout the Southwest monsoon. The wind speed for this monsoon reaches 11 - 17 knots for 12% of the period and 7 - 10 knots for 34% of the period.
These results have been confirmed by Kench and Brander [5] to be consistent with the mean long term trend in the wind climate in the central region of the Maldives.
4.2. Wave Data
According to DHI, (1999) the significant height (Hs) in the southern regions of the Maldives exceeds 2.5 m in about 0.1 percent of the time (refer Figure 5). Figure 5 shows that the highest waves are from W and S. Significant wave heights exceeds 1 m in less than about one
Figure 3. Wind Rose Plot for the Northeast monsoon (Dec-Apr) for central region of Maldives obtained from Department of Metrological Center [3].
Figure 4. Wind Rose Plot for the Southwest monsoon (May-Nov) for central region of Maldives obtained from Department of Metrological Center [3].
Figure 5. Wave height, hs, exceedence curves for Southern region of Maldives. Source [4].
percent of the time from N, NW, NE and E.
Table 2, shows the Astronomical tide levels recorded at the Department of Metrological Centre at Hulhule, Kaaf Atoll, Maldives. This station has continuous records of the tide data for the past 30 years. The table shows that the highest astronomical tide level is +0.64 m (MSL) and that the lowest astronomical tide level is –0.56 m (MSL). It is assumed that the tidal signal at Hulhule will be the same as at Fun Island Resort due to the close of the permanent tide station at Hulhule.