Reduction of tsunami inundation by coastal forests in Yogyakarta, Indonesia: a numerical study

Abstract

Abstract. Coastal forests are known to protect coastal areas from environmental degradation. In this paper, we examined another important role of coastal forests -to mitigate tsunami devastations to coastal areas. Using a twodimensional numerical model (Harada and Imamura model, 2005), we evaluated the damping effects of a coastal forest to resist tsunami inundation in Yogyakarta, Indonesia. In the simulations, we set up a two-km long control forest with a representative topography of the study site and experimented its damping performance sensitivity under various width configurations, e.g. 20, 40, 60, 80, 100 and 200 m. The initial tsunami wave was set such that the inundation depth at the front edge of the forest would not exceed 4 m (tree fragility limit). The forest variables such as species, density, DBH, height and canopy size were determined from a typical forest of the site (Casuarina plantation, 4 trees/100 m 2 , Diameter at Breast Height = 0.20 m). The results showed that coastal forest with 100 m width reduced inundation flux, depth and area by 17.6, 7.0 and 5.7 %, respectively. Exponential models were found to describe the relationships between forest width and tsunami inundation transmission. An additional experiment was performed using actual topography and a forest plantation plan with 100 m width for 2.46 km 2 . In this experiment, the results showed that the plan would reduce inundation flux by 10.1 %, while the exponential model estimated it to be 10.6 %, close to the numerical model results. It suggests that statistical models of forest width and damping effects are useful tools for plantation planning, as it allows for quicker evaluation of the impact of coastal forest without simulation modeling that requires a lot of data, time and computing power.

Tsunami damping by mangrove forest: a laboratory study using parameterized trees

“…Imai and Matsutomi, 2005;Irtem et al, 2009) as well as numerical modelling (e.g. Harada and Imamura, 2005;Ohira et al, 2012). The results of most of these investigations are representative for the mangrove Rhizophora sp., as its complex root system is believed to significantly contribute to the reduction of tsunami-induced flow.…”

The Implementation of Combined Roughness and Reflected Model (CRRM) in Tsunami Run-up Simulation through Coastal Vegetation

“…Practically, a numerical model is more efficient in conducting tsunami investigations through coastal forests. The effect of coastal forest density was studied by Hiraishi & Harada (2003); Harada & Kawata (2004); Huang et al (2011);and Iimura & Tanaka (2012) whilst the effect of the vegetation in term of dimension was studied by Teh et al (2009) and Ohira et al (2012). The effect of the forest may also be seen in term of the age of the forest trees as was studied by Harada & Kawata (2005).…”

Numerical simulations of land cover roughness influence on tsunami inundation in Ulee Lheue Bay, Aceh-Indonesia

“…Their study revealed flow velocities reduced up to 50 % by mangroves. Another study evaluated the reduction of tsunami inundation by coastal forest in Yogyakarta [7]. They found that the coastal forest with 100 m width reduced inundations flux, depth, and area by 17.6, 7.0 and 5.7 %, respectively.…”