Significance of event versus post-event sediment transfer processes in a UK upland sediment system

Johnson, R.M and Warburton, J (2008) 'Significance of event versus post-event sediment transfer processes in a UK upland sediment system.' NGU Rapport, 2008 (058). ISSN 0800-3416

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Investigations of sediment transfer in upland catchments are rarely conducted over a sustained period of time, consequently a fuller understanding of the changing nature of sediment supply, storage, and yield is often lacking. Recent contemporary sediment budget studies from the Wet Swine Gill headwater catchment in the Lake District, Northern England, UK (a 0.65 km2, first-order tributary), provide evidence of changes in sediment transfer dynamics over the period 2002-2008. The first sediment budget from this catchment in 2002 describes the impact of a hillslope debris slide and channelised debris flow event. The termination of the debris flow in the channel meant that the vast majority of slide failure material (203 plus/minus 36 t) was not transferred to the downstream fluvial system. However, the exposure of hillslope sediments to post-event erosion processes and the creation of an erodible in-channel sediment store has arguably had a more enduring impact. In this regard a second sediment budget (June 2003- January 2004) demonstrates: 1. Channel sediment yield downstream of the in-channel debris slide deposits far exceeds upstream fluvial sediment delivery by two orders of magnitude (4t and 0.02t, respectively). This confirms the event sediment store became a post-event sediment supply. 2. Erosion of sediment from the exposed hillslope slide scar (c. 1.3t) was less than channel erosion. However this was dominated by gully erosion of the slide scar, rather than by erosion of the scar margins (0.35t) and un-gullied scar surface (0.03t). 3. Vegetated hillslope locations with event and post-event sediment deposits yield less sediment than exposed (unvegetated) hillslope locations (0.05-0.6t). 4. Sediment yield from both the hillslope and channel sediment sources is sensitive to high-magnitude, low-frequency trigger events including summer thunderstorms, and winter rainfall/ snow-melt events. Fixed point photography and cross-sectional measurements over the last six-years have shown a continuation of slide scar gully erosion, and recent measurements of the slide scar indicate that the sediment yield from post-event reworking has now exceeded the importance of sediment delivery from the initial event. These results suggest that event and post-event sediment flux in small headwater catchments is more complex than short-term investigations would immediately suggest and; clearly establishes a need for continued, long-term investigation of sediment systems in environmental locations potentially sensitive to the impacts of predicted climate change.

Item Type: Article

Third I.A.G./ A.I.G. SEDIBUD Workshop, Boulder, USA: Sediment fluxes and sediment budgets in changing high-latitude and high-altitude cold environments

Editors: Beylich, A., Lamoureux, S.F., Decaulne A.

Subjects: G Geography. Anthropology. Recreation > GB Physical geography
Divisions: School of Sciences
Date Deposited: 23 Mar 2015 21:57
Last Modified: 15 Aug 2021 09:39
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