TY - JOUR
T1 - Sediment controls on the transition from debris flow to fluvial channels in steep mountain ranges
AU - Neely, Alexander B.
AU - DiBiase, Roman A.
N1 - Funding Information:
This work was supported by the National Science Foundation grant EAR-1608014 awarded to RAD. Fieldwork performed by ABN and Emily Loucks in the Guadalupe Mountains National Park was supported by the Scholten–Williams–Wright Scholarship in field geology, awarded to ABN. Joanmarie Del Vecchio, Perri Silverhart, Evan Greenberg, and Julia Carr assisted with fieldwork in the San Gabriel Mountains and California King Range. Discussions with Noah Snyder and Josh Roering aided in compiling analysis of headwater channel systems in the California King Range and Oregon Coast Range. Discussions with Joshua Tremba at Riverside County Flood Control and Chris Bartsch at Palm Springs Aerial Tramway aided in analyzing sediment movement during the 2019 storm in the northern San Jacinto Mountains. Historic streamflow data from the gaging stations in small watersheds from the San Gabriel Mountains was prepared by Pete Wohlgemuth at the USDA San Dimas Experimental Forest. The authors would like to thank Doug Choudy, Jason Laird, David Herrero, and Frazier Haney of the Bearpaw Reserve for permitting access to steep terrain on Yucaipa Ridge in the San Bernardino Mountains.
Funding Information:
This work was supported by the National Science Foundation grant EAR‐1608014 awarded to RAD. Fieldwork performed by ABN and Emily Loucks in the Guadalupe Mountains National Park was supported by the Scholten–Williams–Wright Scholarship in field geology, awarded to ABN. Joanmarie Del Vecchio, Perri Silverhart, Evan Greenberg, and Julia Carr assisted with fieldwork in the San Gabriel Mountains and California King Range. Discussions with Noah Snyder and Josh Roering aided in compiling analysis of headwater channel systems in the California King Range and Oregon Coast Range. Discussions with Joshua Tremba at Riverside County Flood Control and Chris Bartsch at Palm Springs Aerial Tramway aided in analyzing sediment movement during the 2019 storm in the northern San Jacinto Mountains. Historic streamflow data from the gaging stations in small watersheds from the San Gabriel Mountains was prepared by Pete Wohlgemuth at the USDA San Dimas Experimental Forest. The authors would like to thank Doug Choudy, Jason Laird, David Herrero, and Frazier Haney of the Bearpaw Reserve for permitting access to steep terrain on Yucaipa Ridge in the San Bernardino Mountains.
Publisher Copyright:
© 2023 John Wiley & Sons Ltd.
PY - 2023/6/15
Y1 - 2023/6/15
N2 - Steep channel networks commonly show a transition from constant-gradient colluvial channels associated with debris flow activity to concave-up fluvial channels downstream. The trade-off between debris flow and fluvial erosion in steep channels remains unclear, which obscures connections among topography, tectonics, and climate in steep landscapes. Here, we analyze steep debris-flow-prone channels across the western United States and observe: (1) similar maximum channel gradients across a range of catchment erosion rates and geologic settings; and (2) lengthening colluvial channels with coarsening sediment cover. Following this compilation, we hypothesize that steep channel gradients are controlled by two competing thresholds of motion for bed-sediment cover: bed failure by mass-wasting and fluvial entrainment. We use downstream patterns in discharge, channel geometry, and sediment size to calculate discharges needed to mobilize sediment cover by both mechanisms across channels in the San Gabriel Mountains (SGM) and northern San Jacinto Mountains (NSJM) in southern California. Across steep colluvial channels in both landscapes, decadal discharges are below fluvial entrainment thresholds but above mass-wasting entrainment thresholds for (Figure presented.) (median) sediment sizes, consistent with recent debris flows captured by repeat imagery. Colluvial channel gradient is similar despite > 3× contrasts in surface sediment grain size. In concave-up fluvial channels downstream, decadal discharges exceed fluvial entrainment thresholds, and mass-wasting is not predicted on lower gradients. In both landscapes, fluvial channels steepen downstream compared to gradients needed to mobilize sediment cover, which we interpret to reflect downstream increases in sediment flux. Coarser sediment supply in the NSJM than the SGM increases fluvial entrainment thresholds, which increases total channel relief in the NSJM by (1) lengthening colluvial channels shaped by debris flows and (2) increasing fluvial channel gradients. Our compilation and downstream analysis show how differing sensitivity of fluvial and debris flow processes to sediment grain size impacts the relative relief of colluvial and fluvial regimes in headwater channel networks.
AB - Steep channel networks commonly show a transition from constant-gradient colluvial channels associated with debris flow activity to concave-up fluvial channels downstream. The trade-off between debris flow and fluvial erosion in steep channels remains unclear, which obscures connections among topography, tectonics, and climate in steep landscapes. Here, we analyze steep debris-flow-prone channels across the western United States and observe: (1) similar maximum channel gradients across a range of catchment erosion rates and geologic settings; and (2) lengthening colluvial channels with coarsening sediment cover. Following this compilation, we hypothesize that steep channel gradients are controlled by two competing thresholds of motion for bed-sediment cover: bed failure by mass-wasting and fluvial entrainment. We use downstream patterns in discharge, channel geometry, and sediment size to calculate discharges needed to mobilize sediment cover by both mechanisms across channels in the San Gabriel Mountains (SGM) and northern San Jacinto Mountains (NSJM) in southern California. Across steep colluvial channels in both landscapes, decadal discharges are below fluvial entrainment thresholds but above mass-wasting entrainment thresholds for (Figure presented.) (median) sediment sizes, consistent with recent debris flows captured by repeat imagery. Colluvial channel gradient is similar despite > 3× contrasts in surface sediment grain size. In concave-up fluvial channels downstream, decadal discharges exceed fluvial entrainment thresholds, and mass-wasting is not predicted on lower gradients. In both landscapes, fluvial channels steepen downstream compared to gradients needed to mobilize sediment cover, which we interpret to reflect downstream increases in sediment flux. Coarser sediment supply in the NSJM than the SGM increases fluvial entrainment thresholds, which increases total channel relief in the NSJM by (1) lengthening colluvial channels shaped by debris flows and (2) increasing fluvial channel gradients. Our compilation and downstream analysis show how differing sensitivity of fluvial and debris flow processes to sediment grain size impacts the relative relief of colluvial and fluvial regimes in headwater channel networks.
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U2 - 10.1002/esp.5553
DO - 10.1002/esp.5553
M3 - Article
AN - SCOPUS:85147589192
SN - 0197-9337
VL - 48
SP - 1342
EP - 1361
JO - Earth Surface Processes and Landforms
JF - Earth Surface Processes and Landforms
IS - 7
ER -