Sediment and Morphodynamics of Shoreface Nourishments Along the North-Holland Coast
Sediment and morphodynamics of shoreface nourishments along the North-Holland coast
Ben de Sonneville Ad van der Spek
33rd International Conference on Coastal Engineering 2nd of July, 2012 (Santander, Spain) Introduction (I)
• Since 1990, the Dutch coastal policy is to fight structural erosion by nourishing sand • Initially, sand nourishments were placed on the beach • At some locations, their lifetime was relatively short • Since 1999, part of the City of Egmond aan Zee on North-Holland coast (Kustfoto, 2005) nourishments were applied on the shoreface • This method is more economic and easier to apply
1/16 Introduction (II)
• General behaviour of shoreface nourishments > reshaping into bar with trough on landward side > interruption of autonomous bar behaviour > in this period of interruption, assumed to Lee effect (Van Duin, 2004) contribute to coastal profile by lee and feeder effect • Factors controlling lifetime of nourishments not well understood
Feeder effect (Van Duin, 2004)
2/16 Research objectives
• Research objective: > to investigate and compare the evolution and lifetime of five large shoreface nourishments along the North-Holland coast…
… in order to get a better understanding of the factors controlling their lifetime
• Research questions: > how do shoreface nourishments evolve and interact with adjacent coast? > what are the governing factors influencing the lifetime?
3/16 Study area
Marsdiep inlet
Camperduin (2002) Km 20 Bergen (2005) Camperduin Netherlands Km 30 Egmond (2004) Bergen
Km 40 Egmond aan Zee
Km 50 IJmuiden
The Netherlands (Google Earth) North-Holland coast (Google Earth)
4/16 Methodology
• Focus on five large shoreface nourishments (>1.5x106m3) • Consider large extent of coast (>40km) • De-curve bathymetry to improve visualization of morphology • Analysis of autonomous behaviour of shoreface • Analysis of shoreface nourishments • Consider factors possibly influencing lifetime of nourishments
5/16 Overview of nourishments
Site RSP location Year Volume [million m3] Type Egmond 37-39km 1999 0.88 shoreface nourishment Egmond 37-39km 1999 0.21 beach nourishment Bergen aan Zee 32-34km 1999 0.21 beach nourishment Egmond 38-39km 2000 0.21 beach nourishment Bergen aan Zee 32-33km 2000 0.23 beach nourishment Bergen aan Zee 32-34km 2000 0.99 shoreface nourishment Bergen 28-30km 2001 0.51 beach nourishment Petten 18-20km 2002 0.50 beach nourishment Camperduin 26-30km 2002 1.97 shoreface nourishment Petten 19-21km 2003 0.23 beach nourishment Camperduin 25-26km 2003 0.36 beach nourishment Egmond aan Zee 36-40km 2004 1.80 shoreface nourishment Petten 20-21km 2004 0.13 beach nourishment Camperduin 25-26km 2004 0.22 beach nourishment Egmond 37-39km 2005 0.49 beach nourishment Castricum 46-48km 2005 0.52 beach nourishment Bergen 31-36km 2005 1.50 shoreface nourishment Bergen 32-34km 2005 0.30 beach nourishment Pettemer Zeewering15-30km 2009 5.70 shoreface nourishment Source: Rijkswaterstaat
6/16 Improving visualisation of bathymetry
7/16 Autonomous behaviour of study area
1980 1985 1990 1995
8/16 Behaviour of shoreface nourishments (I)
1996 1998 2003 2000 2002
II II
I I
9/16 Behaviour of shoreface nourishments (II)
2004 2006 2008 2010
III III III
II V IV/V IV/V I IV
10/16 Observations (summarized)
• Lifetime of shoreface nourishments differed considerably • The small and isolated nourishments at Bergen/Egmond disappeared within two or three years. • The Camperduin nourishment merged with pre-existing outer bar, gained sediment and interrupted the autonomous behaviour for about 6 years. • The large nourishments at Egmond/Bergen interconnected and remained much more stable than the first ones, interrupting the offshore migration for over 6 years.
11/16 Factors possibly contributing to lifetime (I)
• External forcing > mainly storms • Sediment properties > grain size • Water depth • Size (or length) • Location
NW storm at IJmuiden on 18/03/ 2007 (stormfoto.nl)
12/16 Factors possibly contributing to lifetime (II)
• Storm conditions at Bergen/Egmond 2000-2003
2000-2003 2004-2007
Hs;mean;storm>3m 3.32m 3.33m
Dirmean;storm>3m 282º 291º
Nostorm>3m 13 21
2004-2007 > storm intensity comparable > more storms in ‘stable period’ ĺ no explanation for different lifetime
• Sediment properties > grain sizes comparable to surrounding area ĺ no explanation for different lifetime 13/16 Factors possibly contributing to lifetime (III)
• Water depth > comparable (~8m) ĺ no explanation for different lifetime
• Size (or length) > larger length ĺ longer lifetime • Location (or ability to connect) > able to connect ĺ longer lifetime
14/16 Conclusions
• Lifetime of shoreface nourishments differed considerably • No apparent differences observed in external forcing, sediment properties, water depth • Size (or actually length) appears to influence lifetime • Ability to connect to surrounding bars appears to affect the lifetime
15/16 Further research…
• How much does coastal profile benefit from a longer nourishment lifetime? • Is the coastal profile actually restored? • What are the contributions of feeder and lee-effects? • Where does the sand go?
• A sediment budget analysis will help to better understand the sand-transport mechanisms and pathways
16/16 Thank you for your attention!
B. de Sonneville, A. van der Spek (2012) Sediment and morphodynamics of shoreface nourishments along the North-Holland coast 33rd International Conference on Coastal Engineering, Santander, 2nd of July 2012.
For more information contact [email protected]