In December of 1995 the extreme South of Santa Catarina State was affected by heavy rains concentrated on the valley's headwater (edge of the Brazilian South Plateau). The rainstorm meant a disaster to the local population, killing people, destroying houses and interrupting economical activities. With the objective of identifying areas potentially susceptible to similar natural events, the present study has been developed on the Rio da Pedra valley, located near the area affected in 1995. Both areas present the same morphological characteristics: high declivity on the headwaters (edge of the plateau) and plains formed by fluvial deposits in the form of alluvial fans. The study tries to identify, by the sediment forms found, plains areas subject to different kinds of floods, as well as to monitor the rain precipitation and the changes caused by them on the main fluvial channel. The preliminary data indicates that natural events of great extent, similar to the one occurred on the neighbour valleys in 1995, may have even more serious consequences in this valley: first because of the basin natural characteristics, that has area bigger than that of the neighbour valleys; second, by the human occupation which occurs mainly on the basin areas formed by fluvial deposits. In the sense, the detailed geomorphological cartography of the plain is a basic document for the territorial planning of the area, as well as for the elaboration of alert chart of the areas with possibility of being affected by great extent floods.