Nourishments and shoreline changes uninterrupted coast Egmond-Bergen (The Netherlands) Ruud Spanhoff (RIKZ) and Stijn de Keijzer (University of Amsterdam) Kathelijne Wijnberg and Stefan Aarninkhof (WL | delft hydraulics) Coastview meeting, Bologna, Italy, 4/5 March 2004

Nourishments Bergen-Egmond since 1999

Objective Monitor a nourished beach with Argus video remote sensing technology in terms of one or more CSI’s defined in the Coastview project Analyse relation between seasonal wave forcing and beach evolution

Study area Egmond (NL), Argus site: Jan van Speijk lighthouse Beach nourishment: June 30 – July 5, 2000 location: y = 0 – 800 m volume 0.2x10 6 m 3

Data set Morphology: 48 monthly intertidal bathymetries (IBMapper) t range : June April 2003 y range: -680 m to +680 m z range: 0/-0.4 m NAP to m NAP  ►+0.2 m NAP contour (Mean Tide Level) ► Beach width (0m to +0.9m contour) Hydrodyn.: 3-hourly observations of: ► H rms, T peak, angle of incidence (θ 0 ) (YM6, ELD) ► Water level (IJmuiden, Petten)

Methods (1): morphological data analysis Temporal evolution of alongshore-averaged MTL position Temporal evolution of spatial patterns in MTL position set of spatial patterns empirically defined by EOF method (empirical eigenfunctions) For comparison to seasonal wave forcing: linear subsampling to 3-hourly interval Hanning filter, 90 days window width

Methods (2): seasonal wave forcing Cross-shore component of nearshore wave energy flux: evaluated at 6m –NAP depth contour Extract seasonal signal: Hanning filter 90 days window width

The data (1) Monthly Intertidal Bathymetries (after: Caljouw / Nipius) Egmond station ‘Jan van Speyk’ June August 2001

Egmond station ‘Jan van Speyk’ October April 2003 Monthly Intertidal Bathymetries The data (2)

The data (3) Mean :57 m57 m0 m St.dev. :29 m16 m 25 m Variance:838 m m 2 (25%) 627 m 2 (75%)

Results EOF analysis Variance explained by EOF1: 83.1% = beach nourishment Example: MTL position (+0.2m contour)

Reconstructed MTL position based on EOF1 only

Correlation between seasonal wave forcing and alongshore-averaged contour evolution

Correlation between seasonal wave forcing and amplitude evolution EOF 1

Correlation between seasonal wave forcing and beach width evolution

Conclusions At Egmond beach : Position of the shoreline largely (75%) determined by positioning and amplitude of naturally occurring spatial patterns, rather than cross-shore movement of the beach as a whole Beach nourishment incorporated in dominant spatial pattern (explaining 83% of spatial pattern variance) within months Seasonality wave forcing of subordinate importance in observed beach evolution Regarding prediction of beach evolution at seasonal scale we need to assess the relation between bar evolution and beach evolution (e.g. delayed beach response?).

Longshore position June 1999 September 1999 March 2000 Distance from RSP Height (m)

9 June December October March 2000

5 September September hours NNW-storm ( )

Variance explained by EOF1: 83.1% = beach nourishment

December 2003

Conclusions Present case / in general: Local problems (1-2 km, 1-5 years) can only be properly understood/tackled by involving larger scales (tens of kilometers/years) This uninterrupted coast (Egmond-Bergen): 3D features important, also on a decadal timescale Local shallows (spacing 2km) on the breaker bar Interplay between bars and shore

Conclusions (continued) After the shoreface nourishment(s): NW-storms straighten the bar/ SW-storms induce crescentic shapes between the shallows (local shoreline: S-N oriented)

Conclusions (continued) Shoreface/beach nourishment quite satisfactory in terms of CSI’s (4-5 years stead of 2 years) Negative side-effect probably could have been prevented Argus (with its high resolution) helpful : At a local scale, and as a complementary instrument in studies of larger scales In the design of a new nourishment ?

10 October November hours SW-storm

SW-storm (30 hours) NW-storm (25 hours) December

29 December February 2002 South 96 hours North 13 hours 24 February 2002 North 38 hours 28 February 2002 South 25 hours West 19 hours