CHANNEL HYDRAULIC GEOMETRY AND THE SCULPTING OF LANDSCAPES: HOW SENSITIVE IS RIVER PERFORMANCE TO CHANNEL ADJUSTMENT AROUND ACTIVELY DEFORMING FOLDS?

Observations in regions of active deformation suggest that rivers respond to tectonically driven gradient increases by decreasing their width-depth ratios and forming a coarser bed. Such channel adjustments have a potentially significant impact on rates and patterns of incision but have been largely neglected in landscape evolution models. Here, we explore several alternative mechanisms of channel adjustment in the vicinity of a growing anticline to test how sensitive fluvial profiles, drainage networks and landscape response are to channel planform development. Most empirical and physically-based equations of channel planform development (e.g., Parker [1978], Hey and Thorne [1986], Huang and Nansen [2000]) include roughness, slope, and discharge but have varying exponents and constants for each of these terms. Because channel slope takes longer to adjust then channel roughness, width and depth, the difference in exponents for slope influences the timescale, as well as the magnitude, of response. We find that the different equations not only impact on the rates of incision but also drainage network patterns, the spatial and temporal delivery of sediment out the system, and the spatial distribution of local depocentres around the fold. Finally, we compare the modeled responses of fluvial profile and pattern and upstream and downstream sedimentation patterns to those observed in modern river channels crossing active structures (i.e., in the Lesser Himalayas [Avouac et al., 2000] and the Sevier River, Utah [Harbor, 1998]).