Effect of Catchment Aspect Ratio on Geomorphological Descriptors

Abstract

In recent years several geomorphic measures have been used to test the ability of landscape evolution models to simulate field catchments. These are the hypsometric curve, area-slope relationship, width function and cumulative area distribution. The geomorphic modelling community is only now developing the statistical tools to assess whether these measures are sufficiently discriminatory for use in comparisons between model and field data. To examine this question and the effect of catchment geometry (and especially catchment aspect ratio), a series of synthetic catchments with varying aspect ratio and area matching that of a well understood field catchment were used. This field catchment, for which a set of calibrated hydrology and erosion parameters had been determined, has been used in previous studies to test the ability of the SIBERIA landscape evolution model to simulate field catchments. These synthetic catchments were then allowed to evolve using the calibrated SIBERIA model and the hypsometric curve, area-slope relationship, width function and cumulative area compared with field catchment data. Results show that for a good match to be obtained between simulation and field data using these descriptors as tools of comparison, all that is needed is a catchment with an aspect ratio matching that of the field data (given calibrated erosion parameters). The findings highlight the strengths and weaknesses of the above geomorphic measures when used as a means of comparison between model and field data.