Abstract
Abstract. An important part within the German-Indonesian Tsunami Early Warning System (GITEWS) project was the detailed numerical investigation of the impact of tsunamis in densely populated coastal areas of Indonesia. This work, carried out by the German Research Centre Geesthacht (GKSS), in co-operation with DHI-WASY, also provides the basis for the preparation of high resolution hazard and risk maps by the German Aerospace Center (DLR). In this paper a method is described of how to prepare very detailed roughness maps for scenario computations performed with the MIKE 21 Flow Model FM in three highly resolved (~10 m) priority regions, namely Kuta (Bali), Padang (West-Sumatra), and Cilacap (southern coast of Java). Roughness values are assigned to 43 land use classes, e.g. different types of buildings, rural and urban sub-areas, by using equivalent coefficients found in literature or by performing numerical experiments. Comparisons of simulations using differentiated roughness maps with simulations using constant values (a widely used approach) are presented and it is demonstrated that roughness takes considerable influence on run-up and inundation. Out of all simulations, the results of the worst case scenarios for each of the three priority areas are discussed. Earthquakes with magnitudes of MW=8.5 or higher lead to considerable inundation in all study sites. A spatially distinguished consideration of roughness has been found to be necessary for detailed modelling onshore.
Highlights
The Sumatra earthquake of 26 December 2004 was one of the largest ever detected rupture in the Earth’s crust
The great number of simulations of different tsunami scenarios enabled us to get a detailed insight of possible hazards during flood events in the priority regions Padang, Cilacap, and Kuta which were investigated by GKSS and DHI-WASY within the German-Indonesian Tsunami Early Warning System (GITEWS) project
Prerequisite for a successful simulation of tsunami run-up and inundation was the careful preparation of bathymetries/topographies of high resolution and detailed roughness maps to take into account the influence of structures smaller than features considered in the topography by using spatially varying Manning coefficients
Summary
The Sumatra earthquake of 26 December 2004 was one of the largest ever detected rupture in the Earth’s crust. The German-Indonesian Tsunami Early Warning System (GITEWS) consists of a variety of components It includes a seismological network consisting of broadband seismometers which rapidly localizes the earthquake and determines its strength, as well as GPS stations monitoring the deformation of the ground. Complete new technologies and scientific concepts have been developed to reduce early-warning times down to 5–10 min (Rudloff et al, 2009) Because such short early-warning times do not allow numerical computations if required, a data base of thousands of pre-computed Indian Ocean Tsunami scenarios was established and substantially compiled from simulations performed by the Alfred-Wegener Institute of Polar and Marine Research (AWI) and the German Research Centre for Geosciences in Potsdam (GFZ).
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