Testing different topographic indexes to predict wetlands distribution

Rural landscapes are characterized by great heterogeneity, thus for any policy of landscape protection and management, the delineation of landscape structures is a prerequisite and the demand for such information at the scale of large catchments or basins. Focusing on wetlands, different studies proposed indexes to predict their extension, based on topographic and climatic information, mainly within small order catchments. The topic of this paper is to determine the validity of different indexes for different orders of catchments and to propose an improved index predicting the delineation of wetland for large order catchments. The work is based on a 830 km2 basin where the actual extension of wetlands is partially known on the base of a soil map. We checked the efficiency of different topographic and hydrological indexes as the climato-topographic index and others, by comparing the map of predicted and actual wetlands, for different stream orders. Results have showed that we improved the prediction of wetland delineation for large catchments when we took into account the importance of the flatness of the bottomland. We proposed the ordinated climato-topographic index that reflects this effect in including the local downhill difference in level to the stream, weighted by the drained volume by the stream as an indicator of the stream order. Such index allows environmental stakeholders a better prediction of wetlands at the management scale.