THE INFLUENCE OF COASTAL CONDITIONS TO TSUNAMI INUNDATION OF BIMA BAY, WEST NUSA TENGGARA

• Main Authors: Yudhicara Yudhicara, Rahayu Robiana
• Format: Article
• Language: English
• Published: Marine Geological Institute of Indonesia 2017-07-01
• Series: Bulletin of the Marine Geology
• Subjects: Tsunami; coastal characteristics; bathymetry; factors influenced to tsunami inundation
• Online Access: http://ejournal.mgi.esdm.go.id/index.php/bomg/article/view/63

Area along the coast that includes the territorial waters of the Bima Bay, West Nusa Tenggara, is prone to tsunamis, evidenced by the historical tsunamis record in 1815 due to the volcanic eruption of Tambora, 1818, 1836 and 1992 caused by earthquakes associated with tectonic system in the north of the island of Sumbawa, and 1892 were sourced from a distant source. Based on the coastal characteristics, the research area was divided into four types of beaches, namely: Steep rocky beach; Coastal walled plain; Flat coastal mangroves; and Flat sandy beaches. According to the lateral measurement, houses were built in the plains with a minimum height difference of 0.04 m at Rababuntu beach and a maximum of 22.63 m in New Asakota area. The settlement closest distance to the coastline is 10.3 m in Rababuntu, while the farthest extent is at Kawananta 194.58 m from the shoreline. The local bathymetry range between 1 and 42.5 m, where the inside of the very shallow waters of the Bay of Bima, gradually steeper at the mouth of the bay to the open sea. This conditions will influence the wave when entering the bay. It will come with large enough speed at the mouth of the bay, spread along the coastal waters of the eastern and continue spreading to all parts with the diminishing velocity, but the height increasing when it reaches shallow water, especially in the waters of the western Gulf of Bima. Several factors can affect the amount of risk that would be caused by the tsunami, in the research area include are: (1) The research area is located in an enclosed bay; (2) The local sea floor depths around the bay is relatively shallow waters; (3) Coastal characteristics of the research area is dominated by a gently sloping beach morphology with low relief, especially in the area of ??Bajo, Rababuntu and Bontokape and other beaches in the city of Bima; (4) Residential location very close to the shoreline; (5) Minimal vegetation cover; and (6) The presence of the artificial protective are inadequate. Based on tsunami modeling using the 1992 Flores earthquake parameter which is placed perpendicular to the research area obtain the maximum tsunami height around 4-5 m at Sowa and Kolo, near to the mouth of Bima Bay, while the minimum is at Kalaki, about 0,2 m which is at the inner bay.