nourishments and shoreline changes uninterrupted coast egmond-bergen (the netherlands)
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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. - PowerPoint PPT PresentationTRANSCRIPT
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 0.2x106 m3
Data set
Morphology: 48 monthly intertidal bathymetries (IBMapper)
t range : June 1999 - April 2003
y range: -680 m to +680 m
z range: 0/-0.4 m NAP to + 0.9 m NAP
► +0.2 m NAP contour (Mean Tide Level)
► Beach width (0m to +0.9m contour)
Hydrodyn.: 3-hourly observations of:
► Hrms, Tpeak, angle of incidence (θ0) (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
218
cos( )sn rms gE gH c
The data (1)M
on
thly
In
tert
idal
Bath
ym
etr
ies
(aft
er:
Caljou
w /
Nip
ius) Egmond station
‘Jan van Speyk’
June 1999-
August 2001
Egmond station‘Jan van Speyk’
October 2001-
April 2003
Mon
thly
In
tert
idal
Bath
ym
etr
ies
The data (2)
The data (3)Mean : 57 m 57 m 0 mSt.dev. : 29 m 16 m 25 mVariance : 838 m2 211 m2 (25%) 627 m2 (75%)
Results EOF analysis
Variance explained by EOF1: 83.1%
= beach nourishment
Example: MTL position (+0.2m contour)
Reconstructed MTL positionbased 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 2942
June 1999
September 1999
March 2000D
istance from R
SP H
eight (m)
9 June 1999
20 December 1999
5 October 1999
15 March 2000
5 September 2001
11 September 2001
77 hours NNW-storm (315-330)
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 O
ctob
er 2
000
24 N
ovem
ber
200
0124 hours S
W-storm
SW
-storm (30 hours)
NW
-storm (25
hours)
Dec
embe
r 20
00
1214
16
29 December 2001
22 February 2002South 96 hoursNorth 13 hours
24 February 2002North 38 hours
28 February 2002South 25 hoursWest 19 hours