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Contemporary sedimentation patterns within Green Lake, southern Coast Mountains, British Columbia Schiefer, Erik Karl


Lacustrine sediments have provided important information on historical sediment transfer processes and past environmental conditions for lake catchment systems over a wide range of temporal scales. In this study, contemporary patterns of lacustrine sedimentation are described and interpreted for Green Lake, a geomorphically active and morphologically complex lake catchment system in the southern Coast Mountains of British Columbia. Emphasis is placed on detailing spatial variability and characterizing stratigraphic signatures associated with major sediment delivery events. Identified trends in the sedimentary record are related to internal and external lake catchment process domains and physical controls. The research program has included a combination of intensive lake sediment coring, laboratory-based sediment analysis, detailed reconstructions of lacustrine sediment deposition, and case studies of the most significant sediment delivery events of the last 70 years. All bulk physical properties investigated exhibit a dominant monotonic pattern of variation from the principal lake inflow to more distal lake settings. An influence of water depth is observed only in shallow, near-shore environments. Highest variability occurs near lake inflows, in shallow water settings, and at sites disturbed by land use activities. There is an overall non-linear decrease in sedimentation rates with increasing distance from the lake inflows; however, this pattern is disrupted in deep water sites of intervening lake sub-basins where locally higher accumulation rates are recorded. This trend of increased sedimentation with water depth is most pronounced in the proximal basin and becomes less significant in more distal sub-basin settings. These relations are quantitatively described by an empirically derived sedimentation model. Discernible patterns of spatial variability exceed resolved temporal variability by an order of magnitude. Major sediment delivery events of the last 70 years, discriminated at intra-annual to annual scales, include rapid glacial recession of the early 20lh century, extreme late-summer and autumn rainstorm floods, and unusual snowmelt conditions. Some years of anomalous sedimentation can be related to the occurrence of multiple sediment delivery events and other associated geomorphic processes, including Quaternary valley fill landslides and major channel destabilization effects. Stratigraphic characteristics and spatial sedimentation patterns vary between different types of moderate and extreme sediment delivery events in relation to the defined average-regime deposition model. Total sediment yield is calculated to average 205 Mg/km²/yr, with suspended load, bedload, and dissolved load components accounting for similar proportions of the total yield when integrated over the contemporary period. At inter-annual time scales, temporal variability primarily reflects sediment delivery processes associated with rapid glacial recession observed during the 1930's and early 1940's and extreme autumn rainstorm effects occurring in the early 1990's. Sediment yield responses between events and transfer components differ considerably with respect to magnitude, lag time, and duration.

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