Publication Date:
2021-10-06
Description:
The concavity index, θ, describes how quickly river channel gradient declines downstream.20 It is used in calculations of normalized channel steepness index, k sn , a metric for com-21 paring the relative steepness of channels with different drainage area. It is also used in22 calculating a transformed longitudinal coordinate, χ, which has been employed to search23 for migrating drainage divides. A θ value of 0.45 is typically assumed in studies. Here24 we quantify the variability in θ across multiple landscapes distributed across the globe.25 We describe the degree to which both the spatial distribution and magnitude of k sn and26 χ can be distorted if θ is assumed rather than constrained. Differences between constrained27 and assumed θ of 0.1 or less are unlikely to affect the spatial distribution and relative28 magnitude of k sn values, but larger differences can change the spatial distribution of k sn 29 and in extreme cases invert differences in relative steepness: relatively steep reaches can30 appear relatively gentle as quantified by k sn . These inversions are function of the range31 of drainage area in the considered watersheds. We also demonstrate that the χ coordi-32 nate, and therefore the detection of migrating drainage divides, is sensitive to varying33 values of θ. The median of most likely θ across a wide range of mountainous and upland34 environments is 0.425. This wide range of variability suggests workers should not assume35 any value for θ, but should instead calculate a representative θ for the landscape of in-36 terest, and exclude basins for which this value is a poor fit.
Type:
info:eu-repo/semantics/article
Format:
application/pdf
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