The relationship between drainage density, erosion rate, and hilltop curvature : implications for sediment transport processes.

Abstract

Drainage density is a fundamental landscape metric describing the extent of the fluvial network. We compare the relationship between drainage density (Dd) and erosion rate (E) using the Channel‐Hillslope Integrated Landscape Development (CHILD) numerical model. We find that varying the channel slope exponent (n) in detachment‐limited fluvial incision models controls the relationship between Dd and E, with n > 1 resulting in increasing Dd with E if all other parameters are held constant. This result is consistent when modeling both linear and nonlinear hillslope sediment flux. We also test the relationship between Dd and E in five soil‐mantled landscapes throughout the USA: Feather River, CA; San Gabriel Mountains, CA; Boulder Creek, CO; Guadalupe Mountains, NM; and Bitterroot National Forest, ID. For two of these field sites we compare Dd to cosmogenic radionuclide (CRN)‐derived erosion rates, and for each site we use mean hilltop curvature as a proxy for erosion rate where CRN‐derived erosion rates are not available. We find that there is a significant positive relationship between Dd, E, and hilltop curvature across every site, with the exception of the San Gabriel Mountains, CA. This relationship is consistent with an n exponent greater than 1, suggesting that at higher erosion rates, the transition between advective and diffusive processes occurs at smaller contributing areas in soil‐mantled landscapes.