Threshold effects in geomorphological parameters extracted from DEM's

The advent of digitisation techniques for maps has allowed the automatic extraction of networks from digitised elevation data. To date, the definition of a stream pixel on which the extraction of a network is based, has depended on an arbitrarily chosen threshold area. In this work we have used three catchments in the South-Western region of Australia varying in size from 40km² to 240km². We have extracted networks using threshold areas varying over two orders of magnitude. Using the extracted networks, we have derived a number of geomorphological parameters or functions including the width function, the area function, Horton's bifurcation, length, and area ratios, and the fractal dimensions of both the stream lengths and of the networks. These results strongly indicate that geomorphological parameters based on Strahler ordering and the Horton order ratios are more dependent on the threshold areas chosen than are the width and area functions. -from Authors