Morphometric controls of creek scour on temperate alluvial fans
Abstract
Alluvial fans and colluvial cones form at the base of steep slopes where streams deposit sediment onto floodplains or plateaus. Fans provide lower gradients for infrastructure in mountainous terrain, but they are also exposed to geohazards such as debris flows, debris floods, and floods. While fans are primarily classified as depositional landforms, the hydrogeomorphic processes that have shaped them can also erode these surfaces. To design appropriate mitigation measures for these hazards, a hydrogeomorphic hazard assessment, including an estimate of scour, is required prior to infrastructure development or to protect existing infrastructure from damage. Few guidelines or literature examples are available to estimate scour depth over the lifetime of the infrastructure. We studied approximately 120 alluvial fans in British Columbia, Canada to examine the geomorphic factors controlling scour depth. Scour was measured from high resolution LIDAR digital elevation models as the relative elevation difference between the stream bed and the average adjacent fan surface, excluding debris flow levees which rise above the average fan surface. From these measurements the average and 95th percentile of scour depth was statistically determined for each stream. Several morphometric variables were collected for each fan and watershed, including gradient, area, Melton ratio and drainage density. The dataset was used to create a predictive morphometric model for the scour measurements via statistical multi-model inference. The final model indicated that combination of Melton ratio, fan gradient, and maximum channel length can predict the depth of the scour. Additionally, fans with evidence of past debris flow and debris or fluvial flood events exhibited the highest scour values. The results of this study will assist future scour assessments and could be used to improve debris flood runout models on alluvial fans by specifying variable entrainment rates.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2016
- Bibcode:
- 2016AGUFMEP33D1016L
- Keywords:
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- 1815 Erosion;
- HYDROLOGYDE: 1824 Geomorphology: general;
- HYDROLOGYDE: 1862 Sediment transport;
- HYDROLOGY