RIVER CHANNEL WIDTH AND HILLSLOPE RELIEF CORRELATIONS ACROSS TECTONIC AND LITHOLOGIC ENVIRONMENTS

Measuring river channel width continuously downstream is difficult in rugged terrain. Steep canyon walls and dense vegetation can make channels inaccessible in the field and obstruct observation from above. Thus, studies commonly assume W~A^b within a region, where W is channel width, A is upstream drainage area (a parameter easily extractable from digital elevation models (DEMs)), and b is an empirically determined constant. However this assumption is often invalidated by local variations in runoff, substrate strength, and/or tectonic rates of uplift, which can change value of b. Here, we present a potentially useful relationship between upstream drainage area, hillslope relief (R_h), and channel width whereby W~-R_hA^b. We use new methods that link channel width measured from satellite images to upstream drainage area and hillslope relief to test this relationship along 10 rivers draining the Mohand range in northwestern India. These channels cross several lithologic, tectonic, and geomorphic boundaries, yet the relationship between width, upstream drainage area, and hillslope relief exhibits a strong linear correlation across all environments (r = 0.74 ± 0.25). This suggests that (1) channel width and hillslope relief are shaped by common factors (e.g. substrate strength, uplift rate, climate), and/or (2) a connection exists between channel dynamics and hillslope processes. This relationship should be further tested in other settings and, if it holds true globally, could be used to constrain channel width from a DEM.