Defining the Reach Scale of a Mountain River from High-resolution Hydraulic Geometry.
Abstract
Natural rivers display a variety of complex geometries comprised of self-organized hydraulics and the influence of stochastic and engineered perturbations (e.g. landslides, floods, wildfires, bridges etc.). This natural variability is absent in quantifications of river geometry as field surveys remain too time intensive to capture sufficient statistics and are biased towards accessible but potentially nonrepresentative locations. The growing availability of high-resolution topography coupled with expanding records of river discharge allows an unprecedented view of downstream hydraulic geometry. Incorporating this variability to understand the impact and extent of perturbations is imperative for resilient infrastructure, restoration design, and natural hazard mitigation. To assess this methodology weve chosen the Logan River, a mixed coarse-grained alluvial bedrock canyon river with mixed seasonal snowmelt floods and springfed flows. Here, we leverage half-meter lidar to extract cross-section profiles and calculate bankfull widths every 10 m of a 53 km stretch. We validated the extracted cross-sections and bankfull widths through a small set of surveyed cross sections. These data allow for a novel definition of the reach scale as the downstream distance over which the probability density function of width converges to a representative distribution with stationary average value. The high-resolution hydraulic geometry allows us to quantify the impact of perturbations as the spatial scale over which significant deviations from the watershed scale width discharge trend are evident in channel width measurements. We document areas within the river where rapid downstream adjustment of the channel geometry can objectively define distinct transitions between river reaches. The extraction of high-resolution hydraulic geometry provides a novel avenue for quantifying river variability and the spatial scale over which perturbations impact river structure. This novel data led approach provides a quantitative framework for extracting a representative river reach and length scale over which a perturbation acts, which can aid in the design of resilient infrastructure and restoration.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2021
- Bibcode:
- 2021AGUFMEP35D1341B