Author(s): R. Triatmadja; S. N. Hijah; N. Azizah; Kuswandi; I. Dewanti
Linked Author(s): Radianta Triatmadja
Keywords: Tsunami; Sand dunes; Force; Simulation; Protection; Erosion; Scour
Abstract: Sand dunes such as those at Parangtritis beach in Yogyakarta province of Indonesia may be useful to protect the beach area from tsunami attack. The shapes, sizes and locations of natural sand dunes however are random. In order to employ their utmost protection to the beach, sand dunes have to be designed and shaped accordingly. The height and the top width of the sand dune relative tothe height and the length of the tsunami surge are important factors that determine the stability of the sand dune against the surge and the reduction of surge force it may cause on downstream structure. The research is aimed to study the effect of tsunami surge on the stability of sand dunes and the possibility of sand dunes as a tsunami protection. Models of sand dunes were built in a flume dedicated for surge simulation based on dam break system. The flume was divided in to two parts. The upstream part was used to store water that will surge downstream when the gate that divided the flume is opened quickly. The models of the dunes were made of fine sand on a flat flume bed. The shape of the dune models were trapezium with both upstream and downstream slopes were 1:3 (vertical to horizontal). The top width was varied from B/L=0.0 to 0.057, where B is the top width of the sand dune and L is the length of the basin which determine the tsunami surge length. Tsunami surge height was varied by varying the basin depth (d0) and the dunes’height (D) from D/d0=0.25 to 1.0. The tsunami surge heights were measured using wave probes, whilst the surge speeds were calculated based on the arrival time of the surge at designated stations. The results indicated that the reosion process started from the downstream part of the dunes. As D/d0 decreases, the erosion increases yielding a significantly reduced height of the dune. At lower D/d0, the protection of the dunes to downstream structure becomes less significant. It is also observed that the top width of the dunes plays important role in stabilizing the dune. Simple numerical models that predict the erosion process was developed and capable of predicting the erosion process with some limitation related to D/d0.