Spatial and temporal patterns of sediment storage over 45 years in Carnation Creek, BC, a previously glaciated mountain catchment

Abstract

The movement of sediment through mountain river networks remains difficult to predict, as processes beyond streamflow and particle size are responsible for the entrainment and transport of bedload sediment. In deglaciated catchments, additional complexity arises from glacial impacts on landscape organization. Research to date indicates that the quantity of sediment stored in the channel is an important component of sediment transport in systems which alternate between supply and transport limited states, but limited long‐term field data exist which can capture storage‐transfer dynamics over a timescale encompassing episodic supply typical of mountain streams. We use a 45‐year dataset with annual and decadal‐scale data on sediment storage, channel morphology, and wood loading to investigate the spatial and temporal organization of storage in Carnation Creek, a previously glaciated 11 km2 catchment on Vancouver Island, British Columbia. Sediment is supplied episodically to the channel, including additions from debris flows in the early 1980s just upstream of the studied channel region. Analyzing the spatial and temporal organization of sediment storage along 3.0 km of channel mainstem reveals a characteristic storage wavelength similar to the annual bedload particle travel distance. Over time, two scales of variation in storage are observed: small‐scale fluctuation of 3–10 years corresponding to local erosional and depositional processes, and larger scale response over 25–35 years related to supply of sediment from hillslopes. Complex relationships between storage and sediment transfer (i.e., annual change in storage) are identified, with decadal‐scale hysteresis present in storage‐transfer relations in sites influenced by hillslope sediment and logjams. We propose a conceptual model linking landscape organization to temporal variability in storage and to storage–export cycles. Collectively, our results reaffirm the importance of storage to sediment transport and channel morphology, and highlight the complexity of storage–transport interactions. © 2019 John Wiley & Sons, Ltd.

Does variable channel morphology lead to dynamic salmon habitat?

“…In Carnation Creek, variation in channel morphology is largely driven by sediment supply conditions to the stream channel, and aggradation-degradation cycles have been previously identified in the catchment (Hassan et al, 2008;Reid et al, 2019). The range of variability, sometimes up to a factor of three for A pwc , is significant for planning and design of restoration projects, allocating streamflow in managed systems, and potentially for understanding variations in populations of juvenile salmonids.…”

“…A detailed description of Carnation Creek topographic and wood data collection and preparation can be found in Reid et al (2019). Throughout the period of record, several channel attributes were surveyed and recorded, such as bank tops and bottoms, thalweg position, and margins of the wetted channel.…”

“…Carnation Creek is deglaciated, and a relatively thick layer of drift material ( 0.7 m) covers much of the catchment. Sediment is supplied episodically to the channel from numerous slope failures, primarily in two areas: (1) a confined channel section between 2.9 and 4.5 km from the river mouth, and (2) in the channel headwaters (see details in Reid et al, 2019). The regional climate is temperate and humid, with annual precipitation totals regularly exceeding 2900 mm/yr at low elevations, falling mostly as rain in the autumn and winter months.…”

“…Comprehensive details of Carnation Creek harvesting and the history of data collection can be found in Hartman and Scrivener (1990) and Tschaplinski and Pike (2017). Sediment is supplied episodically to the channel from numerous slope failures, primarily in two areas: (1) a confined channel section between 2.9 and 4.5 km from the river mouth, and (2) in the channel headwaters (see details in Reid et al, 2019). Most slope failures connected to the channel network occurred in the early 1980's and late 1990s .…”

“…These data were collected concurrently with the study area topographic surveys, though wood data are not available for several years in the late 1990s. A detailed description of Carnation Creek topographic and wood data collection and preparation can be found in Reid et al (2019). Hydrometric data have been collected at several locations in the watershed for nearly the duration of the study.…”