Journal of Science, Engineering and Technology 8:93-100 (2020) Southern State University, Sogod, ,

Bathymetric Profile off the Waters of Limasawa Island in Southern Leyte

Anacleta L. Dagaas, Melvin G. Obus, *Julius O. Paler Norberto O. Labata, Jr., Francis Ann R. Sy Southern Leyte State University Sogod, Southern Leyte, Philippines

Abstract This paper attempts to produce a geo-referenced 3D bathymetric profile off the coastal waters of Limasawa Island. It is located 4 miles (6 km) from the southern tip of the island of Leyte just outside the mouth of . This study used an experimental design. Field measurements were gathered using a fish finder and chart plotter. A total of 1,627 waypoints were marked and processed using QGIS. Findings revealed that the western side of the island is relatively deep with readings not exceeding 100 meters, while the eastern side specifically at the northern edge is deep enough for port construction with readings exceeding 150 meters. The bathymetric profile of the coastal waters of Limasawa Island was georeferenced, wherein the numerical values were very consistent with the 3D visualizations. Percentage error is well within tolerance.

Keywords: Fish finder; Coastal waters; Experimental design; Map; Philippines

Introduction coordinates approximately 9°55’55.92” N/125° 4’26.61”E (WGS 84 Datum by Google Earth, Bathymetry offers significant solutions to 2018). It has a population of 5,835, a land area problems in society. The need for correct and of 632.5465 hectares, and is distinguished as current bathymetric charts and gridded data a 6th class municipality (Philippine National sets is rising in the fields of oceanographic Statistic Office, 2010). Presently, the squid modeling to forecast ocean circulation and its fishery and the exchange in its commodities effect on climate, modeling to forecasts tides is the most profit earner among the fishing and tsunami generation, assessing fisheries businesses of the island. Dried squid from resources and environment, evaluating Limasawa is mostly desired after in Cebu the impact of coastal sediment movement and Manila. Limasawa’s future as a tourism and pollution, geographical modeling of harbor is highly known in the region and ocean basin progression, characterizing the strategies are being planned carefully to restrictions of the Continental Shelf (UNCLOS) expand the municipality’s earnings from this and boosting the International Seabed source. The essential tourism commodity Authority to supervise the oceans(General that the municipality aims to advocate is Bathymetric Chart of the Oceans). the periodic occurrence of whale sharks Limasawa is an island municipality, located throughout the shores of the Island(Acebes, 4 miles (6 km) off the southern tip of the 2013). Figure 1 shows the topographic map island of Leyte, and situated generally on the of Limasawa Island. southern section of Southern Leyte province. Bathymetric studies on oceans and lakes It is approximately centered by geographic using echo sounding has already been done

*Correspondence: [email protected] ISSN 2545-9732 Dagaas, Obus, Paler, Labata and Sy JSET Vol.8, 2020 for quite some time now, producing 2D Materials and Methods maps(Renard & Allenou, 1979; Moreno-Amich & Garcia-Berthou, 1989). Lately, bathymetric This study made use of experimental design. studies on oceans, stream depths and rivers A fish finder and chart plotter was used already uses remote sensing techniques in determining the depth of the water at a (Dierssen et al., 2003, Fonstad & Marcus, particular point as shown in Figure 2. The 2005). Many studies have been conducted transducer was placed below a small boat, in Southern Leyte. There was a study at its center as shown in Figure 3. The on Southern Leyte Coral Reef Conservation transducer generates sound waves, and when (Coral Cay, 2003). Another study was on the it hits the seafloor bounce back to the receiver. sustainability of small-scale fisheries(Muallil et The fishfinder/chart plotter will record the al., 2012; Perez et al., 2012). But bathymetric depth, together with its GPS coordinates and profiling of the coastal waters in Sogod Bay time through an external storage device. has never been done before; hence this study.

Bathymetry is the inquiry of the deepness of beds or the basement of water bodies, as well as the ocean, rivers, streams, and lakes(National Oceanic and Atmospheric Administration USDC, National Geographic Society). On the other hand, georeferencing refers to the inherent coordinate structure of a map or an aerial picture can be associated with a ground structure of geographic coordinates (United States Geological Society). Figure 2. Fishfinder and chartplotter

Figure 3. Depth sounding setup

Figure 1. Topographic map of Limasawa The depth soundings in Limasawa were Island(Source:NAMRIA) taken randomly, an interval of 20 meters along the coast and 10 meters offshore at a maximum distance of 100 meters from the This study intends to produce a 3D shoreline. Within the 100 meter line from the bathymetric profile of the coastal waters of shoreline is the coral cover. Figures 5a and Limasawa Island using echo-sounding which 5b show Limasawa Island and the 100-meter in the future can be a guide for urban planning demarcation line. such as sea reclamation, ports, seawall, and The measurements were transferred to a causeway constructions. computer for processing. The bathymetric

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Figure 4. Depth soundings at Limasawa island Figure 5b. Tilted 3D view of Limasawa Island with the 100-meter demarcation line.

Figure 5a. Top view of Limasawa Island with the 100-meter demarcation line Figure 6. Simplified data process flow profile was generated using QGIS. Figure 6 Every waypoint has a depth reading, GPS shows the flow of the data process. coordinates, and time. Shown in the table are some of the readings taken at the western and Results and Discussion eastern sides of the island. Waypoints 1 to 30 are readings taken from Depth readings were taken at the site. A total the western side of the island. Results showed of 1627 waypoints were marked. Figures 7a that the readings within the 100-meter limit and 7b show the top view waypoints taken are quite deep, with a depth not exceeding 70 within the 100-meter limit off the coast of meters. Waypoints 637 to 655 are readings Limasawa Island. taken at the eastern side of the island. Results

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Table 1. Sample depth readings of coastal waters of Limasawa Island within 100 – m demarcation line Waypoint Latitude Longitude Date and Time Depth(m) Number 1 9.91692 125.0717 2015-05-18T13:23:19Z 4.354211 2 9.91692 125.0712 2015-05-18T13:23:19Z 4.474291 3 9.91692 125.0711 2015-05-18T13:23:19Z 5.154211 4 9.91693 125.0708 2015-05-18T13:23:19Z 5.554811 5 9.917 125.0699 2015-05-18T13:23:19Z 4.554211 6 9.91702 125.0695 2015-05-18T13:23:19Z 6.428078 7 9.91703 125.0692 2015-05-18T13:23:19Z 5.692764 8 9.91702 125.0691 2015-05-18T13:23:19Z 9.606537 9 9.91702 125.0691 2015-05-18T13:23:19Z 9.820015 10 9.91702 125.0689 2015-05-18T13:23:19Z 12.59524 11 9.91703 125.0686 2015-05-18T13:23:19Z 17.22061 12 9.91704 125.0681 2015-05-18T13:23:19Z 27.30154 13 9.91705 125.068 2015-05-18T13:23:19Z 31.68971 14 9.91706 125.0677 2015-05-18T13:23:19Z 37.73827 15 9.91706 125.0676 2015-05-18T13:23:19Z 40.65581 16 9.91706 125.0675 2015-05-18T13:23:19Z 41.86553 17 9.91708 125.0671 2015-05-18T13:23:19Z 47.96153 18 9.91713 125.0665 2015-05-18T13:23:19Z 58.42198 19 9.91713 125.0665 2015-05-18T13:23:19Z 60.69908 20 9.9171 125.0662 2015-05-18T13:23:19Z 63.33199 21 9.91709 125.0661 2015-05-18T13:23:19Z 63.18966 22 9.91632 125.066 2015-05-18T13:23:19Z 62.09855 23 9.91613 125.0664 2015-05-18T13:23:19Z 60.29585 24 9.91612 125.0664 2015-05-18T13:23:19Z 59.46565 25 9.91601 125.0667 2015-05-18T13:23:19Z 57.40203 26 9.91571 125.0674 2015-05-18T13:23:19Z 41.39113 27 9.91556 125.0677 2015-05-18T13:23:19Z 25.07187 28 9.91535 125.068 2015-05-18T13:23:19Z 17.695 29 9.91518 125.0683 2015-05-18T13:23:19Z 12.40548 30 9.915 125.0686 2015-05-18T13:23:19Z 9.155861 637 9.93884 125.078 2015-05-18T13:23:20Z 63.68778 638 9.93895 125.0782 2015-05-18T13:23:20Z 78.22804 639 9.93908 125.0784 2015-05-18T13:23:20Z 81.54883 640 9.93927 125.0786 2015-05-18T13:23:20Z 67.07971 641 9.93956 125.0789 2015-05-18T13:23:20Z 94.57101 642 9.93972 125.0791 2015-05-18T13:23:20Z 104.1301 643 9.94017 125.0794 2015-05-18T13:23:20Z 164.1202 644 9.94044 125.079 2015-05-18T13:23:20Z 220.642 645 9.94027 125.0786 2015-05-18T13:23:20Z 165.7543 646 9.94008 125.0782 2015-05-18T13:23:20Z 131.1233

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Figure 7a. Top view of Limasawa Island with the Figure 8. Limasawa Island showing the contour waypoints lines 200 m from the shoreline.

Figure 7b. Limasawa Island displaying the Figure 9. Figure showing Limasawa Island in a 3D enlarged waypoints on the grid of the western and map on the grid with contour lines at 20m eastern sides. intervals. Contour uses lines of equal elevation to show depth. reveal that the eastern side of the island is really deep with readings exceeding 150 The white color represents Limasawa Island meters. while the reddish and bluish color represents As these data are processed using QGIS, the coastal waters of the island. The reddish the bathymetric map and the 3D maps were color indicates shallow water while the bluish generated. Figure 8 shows the contour map; color indicates deep water. Contour uses Fig. 9 shows the 3D view of the western side lines of equal elevation to show depth. This of the island while Fig.10 shows the 3D view bathymetric map shows that the northeastern of the eastern side of the island. side of the island is really deep.

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