A STATISTIC FOR TESTING THE ELEVATION CHARACTERISTICS OF LANDSCAPE SIMULATION-MODELS

There is an urgent need to test recently constructed conceptual models of landscape evolution and geomorphology against field data. Many sta tistics that have commonly been used, such as Strahler statistics, are poorly suited to this testing being unable to potentially falsify the models when applied in controlled conditions. The relations between t hese statistics and catchment mass movement processes are, in many cas es, indirect. Moreover, they are sensitive to unknowable inputs (e.g., initial conditions). One of the main differences among the competing landscape evolution models is their representation of mass movement an d erosion processes, so that statistics that are directly linked to th ese processes, or their geomorphic signature, are needed. This paper e xamines the use of a log-log linear relation between catchment area, s lope, and elevation. This relation has been previously derived quantit atively from the catchment erosion and hydrologic processes for dynami c and declining geomorphic equilibria. Using a catchment evolution mod el, this paper shows that the relation is robust against deviations fr om the assumptions of spatial and temporal homogeneity of erosion, cli mate, and tectonic uplift made in its derivation. The sensitivity of t he geomorphology to time-varying tectonic uplift and climate and spati ally variable soil erodability is examined. It is thus asserted that t he relation between area, slope, and elevation is suitable for testing of models against field data, where spatial and temporal homogeneity of erosion, climate, and tectonic uplift are only approximately true. In the case of variable soil erodability, planar drainage patterns exh ibit self-organization with the high elevation regions of the catchmen t having low soil erodability. Consequently, a downstream increasing e rodability of the soil material, consistent with a downstream fining t ype of behavior, is observed. It is further argued that the equilibria relation is fundamental and uniquely defines the elevation form of ca tchments so that all other elevation statistics are derived from it.