Multi-year evolution of a nourished beach

preliminary results

Kathelijne WijnbergStefan Aarninkhof

Objective

• Monitor a nourished beach with Argus video remote sensing technology in terms of one or more CSI’s defined in the Coastview project

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

Data set: 43 monthly intertidal bathymetries (IBMapper)

t range : Jun. 1999 to Dec. 2002

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)

Mon

thly

In

tert

idal

Bath

ym

etr

ies

(aft

er:

Caljou

w /

Nip

ius)

Egmond station‘Jan van Speyk’

June 1999-

August 2001

Approach to 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)

The dataMean : 60 m 60 m 0 m

St.dev. : 29 m 12 m 26 m

Variance : 844 m2 149 m2 (18%) 695 m2 (82%)

Results EOF analysis

Explained variance

1 84.3% (84.3%)

2 4.9% (89.2%)

3 3.3% (92.4%)

4 2.3% (94.7%)

nourishment

Recon

str

ucte

d M

TL d

ata

Conclusions

At Egmond beach :

• Position of the shoreline (MTL) largely (82%) 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 84% of spatial pattern variance) within ~ 4 months

Future work

• Expand analysis to beach width and/or volumes

• Analyse morphological evolution in relation to hydrodynamic conditions (H, T, wave direction, water level), for prediction purposes.