Spatial and short-term sediment budget dynamics of a mountain torrent

Johnson, R.M (2006) 'Spatial and short-term sediment budget dynamics of a mountain torrent.' NGU Rapport, 069. p. 47. ISSN 0800-3416

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Detailed quantification of sediment transport in mountain stream catchments is rare. Where measurements have been made these are generally related to a few high-magnitude events or have been averaged over longer periods of time. Here we describe a high-resolution record of coarse sediment supply, storage, and flux from a mountain torrent (Iron Crag) in the English Lake District. This is a small, steep catchment (area 2.4 ha, mean slope of 0.273 m m-1) with a morphology consisting of multiple hillslope sediment sources, a main bedrock step-pool channel with gorge sections, and a basal fan. The sediment budget period runs between April 2002 and April 2003, and focuses on the catchment gully head. The site was visited approximately every two weeks, to collect data on sediment dynamics (hillslope traps, channel cross sections, and channel weir trap) and hydrometerological conditions (rainfall, temperature, evaporation, runoff, and channel discharge). The sediment budget model shows supply-limited and transport-limited sediment flux scenarios. It demonstrates coarse yield from the channel (6.1t), is dominated by episodic pulses separated by periods of relative inactivity. A thunderstorm in July 2002 accounts for 55% (3.4t) of measured output. Corresponding upstream observations and measurements of channel change highlight significant scour of the channel down to bedrock. Hillslope sediment supply is less sensitive, with the July 2002 event accounting for 8.6% of annual hillslope transfer (4.95t) to the channel zone. Conditions of transport limited sediment delivery occur in response to local hydro-meteorological events. Significant factors include the intensity-duration of rainfall, seasonal variations in runoff response, and whether channel discharge is complicated by freezing and snowmelt conditions. Channel sediment supply and exhaustion are especially important to understanding catchment sediment yield. Furthermore, as annual hillslope supply, and channel yield are of similar quantity, it appears there is a near balanced evacuation of sediment from the gully head.

Item Type: Article

NGU Report 2006.069. Fourth ESF SEDIFLUX Science Meeting & First Workshoip of IAG/AIG SEDIBUD

Keywords: Sediment budget, Iron Crag, English Lake District
Subjects: G Geography. Anthropology. Recreation > GB Physical geography
Divisions: School of Sciences
Date Deposited: 23 Mar 2015 21:36
Last Modified: 15 Aug 2021 09:39
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