Numerical modeling of storm wave overtopping around a caisson breakwater due to Typhoon Haiyan 2013
Author: Eric C. Cruz, Laurenz Luigi B. Cruz
Presenter: Eric C. Cruz
Most breakwaters used for coastal protection in the Philippines are designed as emergent mound breakwaters mainly because of the relative simplicity of its engineering design and of the use of easily obtainable rocks to form the armor layer. However, the construction cost of a mound breakwater rapidly increases with water depth. Due to the increasing severity of typhoons, breakwaters are recently being designed to be built in depths easily exceeding 8 m. In these depths, caisson breakwater is preferred over the mound type. The simplest caisson breakwater consists of reinforced-concrete shells with reflective vertical faces, but recent designs involve sloping faces with broad crests to increase its dynamic stability against storm waves (Figure 1). However, the overtopping risk of these designs is higher than earlier types. A compromise section is shown as the red outline in Figure 1.
To model the propagation of storm surges along a breakwater-protected coast, a storm surge model based on the nonlinear shallow water equation is typically applied, with the physical domain modeled with finite elements (Figure 2). However the breakwater faces are typically modeled as infinite walls that cannot be overtopped. In order to simulate the overtopping of storm waves on a typically proportioned caisson, wave reflection and transmission due to the actual breakwater geometry, i.e. with finite crest elevation, are incorporated via a reflection-transmission function (Figure 1) based on transient wave conditions in front of the breakwater. The technique is applied to an actual caisson breakwater-protected Philippine marina with depths of about 12 m. Figure 3 shows a comparison of simulated significant wave heights Hs induced by Typhoon Haiyan 2013 around the marina at the time of peak storm tide level. The results indicate that the storm waves are able to propagate into breakwater interior, thereby modulating the maximum waves along the seaward faces. This decrease of wave height is important in the engineering design of these costly infrastructures.
Conference/s:8th Regional Symposium on Infrastructure Development in Civil Engineering, 25-26 October 2018
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