Prolegomena to sediment and flow connectivity in the landscape: A GIS and field numerical assessment

This paper presents two new definitions of sediment and water flux connectivity (from source through slopes to channels/sinks) with examples of applications to sediment fluxes. The two indices of connectivity are operatively defined, one (IC) that can be calculated in a GIS environment and represents a connectivity assessment based on landscape's information, and another that can be evaluated in the field (FIC) through direct assessment. While IC represent a potential connectivity characteristic of the local landscape, since nothing is used to represent the characteristics of causative events, FIC depend on the intensities of the events that have occurred locally and that have left visible signs in the fields, slopes, etc.IC and FIC are based on recognized major components of hydrological connectivity, such as land use and topographic characteristics. The definitions are based on the fact that the material present at a certain location A reaches another location B with a probability that depends on two components: the amount of material present in A and the route from A to B. The distance to B is weighted by the local gradient and the type of land use that the flow encounters on its route to B, while the amount of material present in A depends on the catchment surface, slope gradient and type of land use of said catchment.Although IC and FIC are independent from each other, and are calculated using different equations and different inputs, they complement each other. In fact, their combined use improves IC's accuracy. Hence, connectivity classes can afterward be rated using IC alone.This procedure has been applied in a medium-size watershed in Tuscany (Italy) with the aim of evaluating connectivity, identifying connected sediment sources and verifying the effects of mitigation measures.The proposed indices can be used for monitoring changes in connectivity in areas with high geomorphological or human induced evolution rates.