Some models for coastal and submarine landforms response to sea level rise: fractal reliefs, chaotic reliefs and non linear evolution.

Coastal landforms are monitored with remote sensing techniques and field measurements. Their present day rate of retreat (or accumulation) is known with a great accuracy. In a contexte of coastal management and global change, these measures are used as a base for evolution scenarii. The past evolution of the coastal landform may give some good information about the best extrapolation technique for the future. On some precise site (such as Portugal or western France) geological evolution of the shore line is well known and various rates of retreat may be calculated for different time span. No linear extrapolation of present day rates succeeds in explaining past rates of retreat. A model of a non linear erosion rate has, then, to be coupled with a geomorphological model of the evolution of the erosional landform. It is suspected, from filed work evidences, that a non linear evolution of landform is linked with a scale dependant process. Digital Elevation Models of submarine reliefs have been constructed in Indonesia, Ivory Coast, Columbia, Portugal and France. This sites are also known with field work and oceanographic cruises. First of all the DEM are tested in order to determine if they display a constant fractal dimension. Most of them are not fractal and may be, at meso scale level, modelised with a non linear equation. A qualitative model is build, in order to explain the distribution of scale dependant landforms in space, throught time, with different types of geomorphological crisis. This model may help for understanding the flexible or rigid response of the coastline to sea level rise