Numerical simulations for Investigation of the Coastline Erosion due to the 2004 Indian Ocean Tsunami

Transcription

1 Numerical simulations for Investigation of the Coastline Erosion due to the 2004 Indian Ocean Tsunami Syamsidik, Musa Al ala, Mirza Fahmi, and Tursina Tsunami Computation and Visualization Laboratory Tsunami and Disaster Mitigation Research Center (TDMRC), Syiah Kuala University, Indonesia

2 Introduction After more than one decade of the 2004 Indian Ocean tsunami, the tsunami affected coastal areas have another state of of its natural balance, shaping a new coastal line. Some of the areas bounced back to re-create a coastal line almost similar to the condition before the 2004 tsunami. However, some of the affected coast could not being recovered until the present due to some factors. The tsunami affected regions in Aceh of Indonesia are mostly located around the South-Western Coast of the Sumatra Island. This area was told to have a number of tsunamis since 1,000 years ago (Monecke et al., 2008). This reflects the vulnerability of the region towards the tsunami. Considering the state of the area towards the tsunami, it would be necessary to understand the process of the coastal recovery around this area that can be used for further coastal zone management. The objective of this paper is to investigate the impacts of the tsunami waves on the area by means of numerical simulations and to monitor the land use changes around the coastal area that were driven by the coastal morphological recovery process. Unlike other areas around the Indian Ocean, less attention has been put to observe the detail coastal process contributing to the impacts of the tsunami waves and the coastal recovery process. Other studies could be found around Tohoku region of Japan after the 2011 Great East Japan Earthwquake and Tsunami/GEJET (Tanaka et al., 2014).

3 Study Area: Teluk Ulee Lheue Before the 2004 tsunami After the tsunami

4 Data Preparation 1. Bathymetri Data GEBCO- Layer 1-3 DISHIDROS TNI AL Layer 4-5 Public Works Dept 2006 layer 5 2. Topography Data Acepmap.com Public Works Indonesia Simulation Domain: Ulee Lheue Bay

5 Simulations Tsunami Wave Propagation Simulations: Initial Waves used Romano (2009) based on mulfi fault scenarios for the 2004 Tsunami; Layer 1-4 were simulated using Cornell Multi-Grid Coupled Tsunami Model (COMCOT); Layer 5 (the innermost layer) was simulated using DELFT3-D Flow, where the boundary condition was adopted from results of tsunami waves propagation produced by COMCOT.

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7 Manning Coefficients Ocean (0.013) Beach (0.020) Ponds (0.017) Paddy Field (0.022) Forest (0.035) Housing (0.040) Sediment Characteristics Mountain Coastline before tsunami Very Fine Sand Fine Sand Medium Fine Sand Coral

8 Results Validation Validation of tsunami wave heights from Jason1 Initial Waves

9 Tsunami wave heights around the near shore area

10 Tsunami Waves Propagation around the Study Site

11 Initial Waves Proses penjalaran tsunami dengan model COMCOT Layer 1 Layer 4

12 Tsunami Inundation Area

13 Proses penjalaran tsunami dengan model Delft3D Water Depth Cumulative erosion and sedimentation

14 Coastal Line Changes Sea Land Coastline before tsunami Simulated Coastline Coastline after tsunami

15 Time after tsunami (sec) Time after tsunami (Local Time)

16 Distance at Cross Shore Coastal Profile Changes Cross 1 Cross 1 Distance at Cross Shore Cross 2 Cross 2

17 Perubahan profil pantai Cross 3 Perubahan profil pantai pada Cross 3 Perubahan profil pantai pada Cross 4 Cross 4

18 Erosion and Deposit of sediment due to tsuanmi waves Hillside Initial coastline

19 Recovery of the Coastal Area after 12- Year of the tsunami

20 Year 2003

21 Year 2005

22 Tahun 2010

23 Year 2011

24 Year 2015

25 Mangrove Area Housing Area

26 Area (m²) Cummulative Area of Housing Complex in the Study Area Shifting closer to the coastline Distance from shore line (m)

27 Conclusions Numerical simulations and spatial analysis were performed in this research to observe the impacts of the 2004 Indian Ocean tsunami and also the coastal area recovery process during one decade after the tsunami. The tsunami inundation area based on the numerical simulations has been confirmed to actual data of the tsunami inundation limit. Although the erosion process due to the tsunami waves has been fairly agreeable to the actual data, the simulation has successfully proven the severe erosion process at some points in the study area. The coastal recovery process around this study area shows a return of new coastal line after one-decade of the 2004 tsunami. Furthermore, the coastal settlement has been seen to take place at the same location where it was before the tsunami. Land use types in the coastal area seem to follow the land use pattern before the tsunami. Despite this, some paddy field areas could not be recovered due to high salinity intrusion around the area.

28 Thank you