Hydraulic Geometry of Debris-Flow Channel Networks With Implications for Discharge Estimation
Loading...
Authors
Ring, Caleb M.
Issue Date
2024
Type
Thesis
Language
Keywords
Debris Flows , Geohazards , Hydraulic Geometry , Natural Hazards , Postfire , Steeplands
Alternative Title
Abstract
In steep landscapes, debris flows scour much of the upper channel network and significantly alter longitudinal profile form at drainage areas less than 1 to 5 km². The degree to which debris-flow processes alter other aspects of the upper channel network is largely unexplored. Here we compile a large data set of bedrock channel cross-sections following debris-flow scour to constrain the downstream hydraulic geometry in the upper channel network. We find that bedrock channel networks scoured by debris flows display systematic power-law relationships between discharge Q and channel width w ~ Q 0.26-0.35 and mean depth d ~ Q 0.40-0.46 and hence display hydraulic geometry akin to that found further downstream in bedrock and alluvial rivers. Observed w / d ratios are narrowly distributed (6.0+/- 2.5) despite w and d not having identical scaling with Q . However, the scaling observed when substituting upstream drainage area A for Q depends on initiation mechanism and network structure. For branching networks scoured by debris flows initiated from rainfall runoff, we find w ~ A 0.31-0.33 as found in many bedrock rivers, whereas for debris flows initiated from failure of shallow landslides we find w ~ A 0.08-0.16 . In all cases, debris-flow channel widths are 2-10 times wider at A =10 5 km 2 than that found in fluvial channels, highlighting that when present, debris flows are systematically larger at a given drainage area than rivers. If channel networks are nonbranching, we find almost no dependence of w on drainage area, w ~ A 0.01-0.05 . We use these relationships in combination with simple empirical velocity relationships and a constant w / d ratio to develop debris-flow discharge estimation techniques that require only measurements of scoured channel width or drainage area. We find good agreement when tested against debris-flow monitoring sites around the world. Hydraulic geometry relationships specific to bedrock channel networks scoured by debris flows should aid in developing more accurate models of landscape evolution that incorporate debris-flow processes, as well as provide first-order guidance on expected discharges emanating from these networks.