Erosion and Accretion Patterns along the Danish Shores

Transcription

1 Department of Geosciences and Natural Resource Management rosion and Accretion Patterns along the Danish Shores Aart Kroon Danish Coasts and Climate Adaptation (COADAPT) Climate Change and Coastal Adaptation 30 October 2012, GUS Copenhagen

2 Contents Introduction Character of the Danish shores rosion and accretion patterns Responsible coastal processes Climate change and changes along the coasts

3 Introduction Relevance of the study Coadapt erosion and flooding of shores Climate change: changes in forcing changes in waves and waterlevels What do we have now? process characteristics special attention to extreme events What about the character of the Danish shores? quaternary geology geomorphology sediment sources and sinks centennial and decadal changes along the Danish shores???

4

5 Present-time isostatic uplift rates (mm year -1 ) of Denmark (Hansen et al., 2011)

6 North Sea Geomorphology of Denmark Kattegat 3 Wadden Sea Baltic Sea Sted og dato Dias 6 Sources of sediment (GUS, Geodatabase)

7 Height above sea level North Sea Kattegat Wadden Sea Baltic Sea Risk for flooding (KMS, 2010)

8 Height above sea level onshore Lyø offshore (Google arth, 2012) Coastal classification (Dyrholm Hansen, 2012)

9 rosion and accretion rates Data source: Topographic maps HMB/LMB Scanned paper map sheets K10 Vector dataset Survey dates Map-sheet polygon feature attributes Map sheets Orthorectified & georeferenced raster Digitize shoreline Shoreline Polyline Split by map-sheet polygons Spatial join Shoreline feature class HMB/LMB Survey dates as attributes Shoreline feature class K10 Survey dates as attributes Shoreline acquisition in ArcGIS HMB: Høje Målebordsblade, LMB: Lave Målebordsblade, K10: Kort10 (Kabuth et al., submitted)

10 Shoreline change computation in ArcGIS / DSAS Digital Shoreline Analysis System (USGS) (Kabuth et al., submitted)

11 12 0'0" 10 0'0" 8 0'0" 57 0'0"N 56 0'0"N 55 0'0"N Shoreline movement rate [m/yr] km 15 0'0" 55 0'0"N Danish Coasts and Climate Adaptation (Kabuth et al., submitted) rosion and accretion rates along the Danish shores

12 SHORLIN CHANGS - ORDR OF MAGNITUD SHORLIN CLASS BHAVIOR Alongshore extension [m] Cross-shore range [m] xamples of shoreline-change rate (99 th percentile)[m/yr] Straightening coast Adjacent accretion and erosion m/yr, m/yr (Vigsø bight) +1.8 m/yr, -2.0 m/yr (Jammer bight) Distal accretion, longitudinal and/or latitudinal m/yr (Feddet spit) m/yr (Korevlerne barrier spits) Spit, barrier spit Proximal erosion m/yr (Krageø) Proximal stability or accretion (barrier spits) ca. +2 m/yr (Korevlerne) Pivoting spit point (mature spits) m/yr, -6.3 m/yr (Skagens Odde) Marsh Accretion ,, confined by bay extent or barrier +2.8 m/yr (Ølsemagle Revle lagoon) Marine dominated estuaries Accretion (shoreline straightening) m/yr (Tudeå) Land reclamation Accretion 10 3, confined by dam 10 3, confined by dam m/yr (Lumby Kvissel bay closure) m/yr (Amager territorial waters) Upstream accretion ,, confined by jetty length +1.5 m/yr (Hanstholm) Harbour Upstream erosion m/yr (Gilleleje) Downstream erosion m/yr (Frederikshavn) Coastal protection Upstream accretion ,, confined by groin length or breakwater position +0.5 m/yr (Lisleje) Downstream erosion m/yr (Lisleje) Beach parks Accretion 10 3 Unconfined Not computed (Kabuth et al., submitted)

13 rosion and accretion patterns Remarks first erosion-accretion map of DK with a high spatial resolution observed patterns are in line with expectations (verified at several locations with detailed studies) Critical remarks resolution in time is limited no distinction between natural processes and man-made interventions no direct coupling to coastal processes

14 Coastal a site Waves Wave energy flux (longshore/cross-shore); Ω parameter NORTH 15% 10% WST 5% SOUTH AST Hs[m] xtreme events xtreme water levels wave overtopping Tides (spring) tidal range

15 Spit on the eastern shore of Sjælland Shoreline movement rate (m/yr) Coastline 1891 Coastline 2002 none ± Præstø Fjord Feddet km

16 Spit on the eastern shore Shoreline movement rate (m/yr) Coastline 1891 Coastline 2002 Præstø Fjord none ± WST NORTH NORTH 20% 20% 15% 10% 5% AST Hs[m] SOUTH SOUTH (Modelled wave data , DHI-DMI) Rørvig Feddet km (xtreme sea level statistics; DCA, 2007)

17 Spit on the eastern shore Abundant sediment in the system cliff erosion in the north shallow waters around the fjord entrance Sources are not protected by construction works Beach ridge plain is building up during the Holocene xtreme event: only once observed with overwashes (1872; Clemmensen et al., in prep.)

18 Barrier island on the southern shore of Sjælland Danish Coasts and Climate Adaptation

19 Barrier island on the southern shore ± Holsteinborg Nor Basnæs Nor Glænø Shoreline movement rate (m/yr) none Coastline 1891 Coastline km rosion of a former glacial bluff? (KMS, 1989)

20 Barrier island on the southern shore Inlet dynamics (After Brøndum, 1972 in Westh, 2012)

21 Barrier island on the southern shore (Westh, 2012)

22 Barrier island on the southern shore ± Holsteinborg Nor Basnæs Nor Glænø NORTH 15% Shoreline movement rate (m/yr) none Coastline 1891 Coastline km WST 5% SOUTH 10% AST Hs[m] (Modelled wave data , DHI-DMI) Korsør (xtreme sea level statistics; DCA, 2007)

23 Concluding remarks Inlet closing: longshore wave-driven fluxes; Inlet breaching: extreme water levels and onshore storms (Photos Sune Westh, 2012) xtreme event: water level +120 cm over DVR90, 6 January 2012 Flooding, but no breaching nor erosion Last 20 years, under 30% of high waters with eroding waves What is the joint probability? Time series are too short! Climate change, change in the joint probability distribution?

24 Thanks for your attention! (Photo Mette Bendixen, 17 February 2011)