Sediment dynamics and sub-recent sediment budget of the braided sandur system at Sandane, Erdalen (Nordfjord, western Norway)

Transcription

1 Sediment dynamics and sub-recent sediment budget of the braided sandur system at Sandane, Erdalen (Nordfjord, western Norway) A.A. Beylich (1,2), L. Hansen (1), S. Liermann (3), D. Gintz (3), K. Laute (3), G. Vatne (2), O. Fredin (1), V. Burki (1,4) and I. Berthling (2) (1) Geological Survey of Norway, Quaternary Geology and Climate group, Trondheim (2) Norwegian University of Science and Technology, Department of Geography, Trondheim, Norway (3) Martin-Luther-University of Halle-Wittenberg, Institute of Geosciences, Halle (Saale), Germany (4) University of Zurich - Irchel, Department of Geography, Switzerland Third SEDIBUD Workshop, Boulder, September 9-13, 2008

2 Study area Source: NGU Trondheim

3 Erdalen (Photo: O. Fredin)

4 Braided sandur system at Sandane, Erdalen - viewing direction west / northwest (Photo: S. Liermann)

5 Aims and objectives The detection of different zones with negative, positive or balanced sub-recent (following the Little Ice Age advance) sediment budget within the braided sandur system The identification of sediment sources upstream of Sandane and at the slope systems to both sides of the braided sandur system The analysis of the sub-recent (following the Little Ice Age advance) sediment budget of the entire Sandane system

6 The Erdalen catchment is instrumented with an automatic weather station which provides continuous data on: wind speed and direction air temperature precipitation snow cover thickness ground temperature radiation Photos: T. Lopez, K. Laute Further 4 stationary gauging stations are installed at the outlets of the different sub-catchments and the entire upper Erdalen catchment continuous year-round monitoring of runoff, fluvial suspended sediment and solute transport

7 mm Mean air temperature, precipitation and discharge per day (2005 / 2006) Tageswerte Air Lufttemperatur temperature ( C) ( ) Tageswerte Precipitation Niederschlag (mm/d) and (mm/d) Discharge und Abfluss (mm/d) (mm/d) ( ( ) ) - -Niederschlag precipitation - - discharge Abfluss air temperature - Lufttemperatur Tag Day C Day Tag

8 Mean air temperature, precipitation and discharge per day (2006 / 2007) Tageswerte Precipitation Niederschlag (mm/d) (mm/d) and Discharge und Abfluss (mm/d) (mm/d) ( ( ) ) - -Niederschlag precipitation - - discharge Abfluss mm Tageswerte Air Lufttemperatur temperature ( C) ( C) ( ) - - air Lufttemperatur temperature Day Tag C Tag Day

9 Research methods Geomorphologic mapping Dendrochronology Granulometric / morphometric analyses Shock sensors 14 C dating of flood deposits Biofilm analysis

10 Geomorphological map of the braided sandur system Author: Susan Liermann Sources: Digital topographic map Nordfjord/Erdalen; NGU, Trondheim Aerial photograph Erdalen ; NGU, Trondheim Orthophoto Erdalen; NGU, Trondheim

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12 Granulometric / morphometric analyses The particle size decreases with the increasing length of the streams as a result of the main factors of sediment-transport (discharge, flow velocity, slope etc.) and the effect of downstream-fining Comparison of the selected test stretches Legend Lake Forest Channel Test stretches Contour line Author: S. Liermann Cumulative frequency (%) Overview of the seven selected test stretches and cumulative frequency distribution Particel size classes (mm)

13 Shape analysis: Sneed and Folk triangular diagrams and frequency distribution of two selected test stretches frequency distribution 30 stretch Vesledalen c : a b : a percent C CP CB CE P B E VP VB VE (a - b) / (a - c) Sneed and Folk classes frequency distribution 30 stretch Stordalen c : a b : a percent C CP CB CE P B E VP VB VE (a - b) / (a - c) Sneed and Folk classes

14 Determination of the particle roundness and flatness of two selected test reaches by using a visual 6-by-6 roundness matrix sphericity - flatness sphericity - flatness roundness - angularity roundness - angularity stretch Vesledalen stretch Stordalen

15 14 C dating of flood deposits At 6 profiles samples were taken for 14 C datings of the flood deposits in the lower part of Sandane Furthermore samples for grain size distribution and loss on ignition were taken at 12 profiles Regarding dendrochronology samples were collected from the predominant species alnus incana Photos: K. Laute

16 Author: K. Laute Source: Orthophoto Erdalen; NGU, Trondheim

17 Shock sensors Photos: G. Vatne

18 1000 9,0 900 Timeserie-june-sensor3 8, , ,0 Acceleration (ms -2 ) ,0 4,0 Discharge (m³s -1 ) 300 3, , , : : : : : : : : : : :20 0,0

19 Biofilm analysis Photo: A.A. Beylich Photo: D. Gintz

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21 Conclusions The upper part of Sandane is characterised by a negative sub-recent sediment balance, with erosion of coarse sediments from the Little Ice Age advance and downcutting of channels (small width/depth ratio) In comparison, the lower part of Sandane has a balanced to slightly positive sub-recent sediment budget with formation of younger flood sediments and more stable channels Present-day coupling of slope and fluvial systems is limited and only a rather small amount of material is directly transported from the slopes into the braided sandur Apart from flood deposits, material is only temporally stored in channels in the lower part of Sandane before export during peak-runoff Altogether, the sub-recent sediment budget of Sandane, following the Little Ice Age advance, appears to be slightly negative and fluvial sediment transport is supply-limited