Tsunamic surf zone and morphogenetic impact in areas of coastal protection (Kalutara, Sri Lanka)

The structure of surf zone, the influence of coastal defences and morphogenetic processes are analyzed for the tsunami of december 2004 in Kalutara. The tsunamic surf structures were compared with intermediate beach types produced by ordinary swell, used as reference models. The tsunamic surf was something like an intermediate transverse bar and rip beach type for the normal swell, if the receding phase after the principal breaker is considered. In this phase, the circulation consisted in mega swash and vortexes (eddies). The vortexes appeared where a breakwater or jetty system exists. Both tsunamic and swell lobes carved the soft cliff forming mega-cusps, which are rare features in cliffs. The removed materials and the product of the terrace removal supplied plenty sediments to the nearshore, where produced overcharge of material. Several months after the cataclym, two facts were relevant: the disappearance

of the mega-cusps and the conservation of a broad surf zone with multiple bars, indicating a long persistente of nearshore sedimentary overcharge. That is to say, in the cliff the equillibrium was reached, but at a different level of operation with respect to the pre-tsunami condition. The cliff new straightening means necessarily its retreating. In exchange, in the nearshore the equillibrium was not

reached yet during the relaxation path, if the features pre and post tsunami are compared. These processes can be modeled and mapped and some schemes could be applied in Chile.