Changes in sediment volume in Alder Lake, Nisqually River Basin, Washington, 1945-2011

J. Geophys. Res. Earth Surf.

Pitlick

2014

Sediment fluxes in steep mountain streams remain difficult to quantify, despite their importance in geomorphology, ecology, and hazard analysis. In this work, aerial lidar surveys, acquired in 2002, 2008, and 2012, are used to quantify such fluxes in Tahoma Creek, a proglacial stream on Mount Rainier, Washington. As these surveys encompass all coarse sediment sources in the basin, we are able to translate geomorphic change into total bed material transport volumes for the time steps between surveys. By assuming that the relationship between daily sediment transport and daily mean discharge is of the form Qs=a(Q−Qc)b, our two observed total loads and estimates of daily mean discharge allow us to numerically solve for values of a and b to create a bed material sediment rating curve. Comparisons of our transport estimates with sediment deposition in a downstream reservoir indicate that our transport estimates and derived rating curve are reasonable. The method we present thus represents a plausible means of estimating transport rates in energetic settings or during extreme events, applicable whenever at least two cumulative sediment loads and the driving hydrology are known. We use these results to assess the performance of several bed load transport equations. The equations generally overpredict transport at low to moderate flows but significantly underpredict transport rates during an extreme event. Using a critical shear stress value appropriate for steep streams improves agreement at lower flows, whereas a shear‐partitioning technique accounting for form drag losses significantly underpredicts transport at all flows.

Section: Results—analysis Of Repeat Lidarmentioning

confidence: 99%

Using repeat lidar to estimate sediment transport in a steep stream

J. Geophys. Res. Earth Surf.

Pitlick

2014

“…Although deforestation and associated road building have occurred in the basin and may have had some influence on coarse headwater sediment production (i.e., Madej & Ozaki, ), there are several reasons to think that influence is minor in the context of our results. First, sediment production from the stratovolcanoes is likely to be substantially larger (order of magnitude) than from forested catchments subject to land use (Czuba, Olsen, et al, ). This is consistent with planform characteristics in the Nooksack, where the North and Middle Forks that drain Mount Baker are often broad and braided, indicative of high coarse sediment loads, while the South Fork is generally narrower and has a meandering planform.…”

Section: Discussionmentioning

confidence: 99%

“…The most direct comparison comes from repeat bathymetric surveys of Alder Lake. Alder Lake traps most of the sediment, and all of the bed material, delivered from the south flank of Mount Rainier, another regional stratovolcano located 200 km south of Mount Baker (Czuba, Olsen, et al, ). Additional records come from several varved lake cores collected in lakes draining glaciated terrain in southwest British Columbia, which provide annually resolved records of relative fine‐sediment yields over the past several centuries (Leonard, ; Menounos, ; Menounos & Clague, ; Heideman et al, ).…”

Section: Discussionmentioning

confidence: 99%

“…(a) The regional climate index, plotted both as annual values (gray bars) and as the cumulative departure from the mean (black line). (b) Total sediment yield variations from the south flank of Mount Rainier, based on repeat bathymetric surveys of Alder Lake made in 1956, 1985, and 2011 (Czuba, Olsen, et al, ). (c) Relative accumulations of fine sediment in Cheakamus Lake in southwest British Columbia (Menounos & Clague, ).…”

Section: Discussionmentioning

confidence: 99%

“…The goal of this study was to assess whether historical changes in river bed elevations in a watershed draining glaciated, sediment‐rich terrain on a stratovolcano in western Washington State, USA, could be related to decadal‐scale climate variations. Stratovolcanoes in the Cascades are steep, composed of friable volcanic rock, heavily glaciated, and experience high orographic precipitation, all of which make them a significant source of coarse sediment to down‐valley river systems (Czuba et al, ; Czuba, Magirl, et al, ). Like glaciers around the world (Marzeion et al, ), glaciers in the Cascade Range of Washington State have generally been retreating since reaching maxima in the eighteenth and nineteenth centuries (Burbank, ; Dick, ; Harper, ; Nylen, ).…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Downstream‐Propagating Channel Responses to Decadal‐Scale Climate Variability in a Glaciated River Basin

Konrad

2019

JGR Earth Surface

Regional climate is an important control on the rate of coarse sediment mobilization and transport in alpine river systems. Changes in climate are then expected to cause a cascade of geomorphic responses, including adjustments in downstream channel morphology. However, the mechanics and sensitivity of channel response to short‐term climate variability remain poorly documented. In the Nooksack River, which drains a glaciated stratovolcano in Washington State, bed elevation changes were inferred from shifting stage‐discharge relations at seven U.S Geological Survey stream gages. Decadal‐scale elevation trends can be explained as a downstream‐propagating channel response to regional climate variability, where periods of persistent warm, dry (cool and wet) conditions corresponded to periods of aggradation (incision). The channel elevation response propagated downstream at a rate of 1 to 4 km per year; propagation rate scaled closely with channel slope. Historical trends in glacier extent and flood intensity both show some potential to explain climate‐sediment linkages, though assessing causation is complicated by the shared climate signal in both records. Results show the influence of the Pacific Decadal Oscillation, with relatively high coarse sediment yields prior to 1950 and since 1980, and notably lower sediment yields from 1950 to 1980. Measured sediment yields from nearby glaciated basins corroborate this history, suggesting a regional consistency to these climate‐sediment linkages. These results document consistent relations between climate, sediment supply, and downstream channel response at the basin scale, with channel responses propagating downstream over periods of decades with little apparent attenuation.

Spatial and temporal controls on proglacial erosion rates: A comparison of four basins on Mount Rainier, 1960 to 2017

Earth Surf Processes Landf

Shean

2021

The retreat of alpine glaciers since the mid-19th century has triggered rapid landscape adjustments in many headwater basins. However, the degree to which decadal-scale glacier retreat is associated with systematic or substantial changes in overall coarse sediment export, with the potential to impact downstream river dynamics, remains poorly understood. Here, we use repeat topographic surveys to assess geomorphic change in four partly glaciated basins on a stratovolcano (Mount Rainier) in Washington State at roughly decadal intervals from 1960 to 2017. The proglacial extents of the four basins show distinct geomorphic trajectories, ranging from substantial and sustained net erosion to relatively inactive with net deposition.These different trajectories correspond to differences in initial (1960) valley floor gradients, and can be effectively understood as valley floor grade adjustments. Significant erosion was most often accomplished by debris flows triggered by extreme rainfall or glacial outburst floods, though a single rockfall mobilized more material than all other events combined. Year-to-year runoff events had little measurable geomorphic impact. Exported material tended to accumulate in broad deposits within several kilometers of source areas and largely remained there through the end of the study period. Over 10-to 100-year timescales, we find that the impact of glacier retreat on coarse sediment yield may then vary substantially according to the geometry and storage trends of the newly exposed valley floor; the timing of that response may also be dictated, and potentially obscured, by stochastic and/or extreme events.