Wave transmission and reflection at low-crested structures: design formulae, oblique wave attack and spectral change

Coastal Engineering 52 (2005) 915 – 929 www.elsevier.com/locate/coastaleng

Wave transmission and reflection at low-crested structures: Design formulae, oblique wave attack and spectral change
Jentsje W. van der Meer a,*, Riccardo Briganti b, Barbara Zanuttigh c,1, Baoxing Wang d
Infram, Geomatics Business Park, PO Box 16, 8316 ZG Marknesse, The Netherlands b DSIC-Universita di Roma Tre, ViaV. Volterra, 62 - 00146 Roma, Italy ` c University of Bologna, DISTART Idraulica, viale del Risorgimento, 2- 40136 Bologna, Italy d UNESCO-IHE, Institute for Water Education, former MSc-student, Westvest 7, 2611 AX Delft, The Netherlands Available online 8 November 2005
a

Abstract A part of the DELOS research focused on wave transformation at low-crested structures, called LCS. This papergives a summary of all results. Wave transmission on rubble mound structures has been subject for more flume tests in the DELOS programme and simultaneously an existing database has been increased extensively by receiving data from other researchers in the world. This new database consists of more than 2300 tests and has been used to come up with the best 2D wave transmission formula for rubble moundLCS, although not necessarily new as existing ones have been evaluated. Oblique wave attack on LCS was a second objective within DELOS. Results were analysed leading to new empirical transmission formulae for smooth LCS and to conclusions on 3D effects for both rubble mound and smooth LCS. The spectral shape changes due to wave transmission and this change has been subject of analysis for all newtest data described above. Although analysis has not been finished completely, former assumptions on spectral change were more or less confirmed. Finally, some analysis was performed on reflection at LCS and a first formula was derived to take into account the effect that wave overtopping or transmission reduces reflection and must be dependent on the crest height of the structure. D 2005 ElsevierB.V. All rights reserved.

1. Introduction Waves coming from deep water may reach a structure after refraction, shoaling and breaking. As soon

* Corresponding author. Tel.: +31 527 242341; fax: +31 527 241119. E-mail addresses: jentsje.vandermeer@infram.nl (J.W. van der Meer), barbara.zanuttigh@mail.ing.unibo.it (B. Zanuttigh). 1 Tel.: +39 051 2093754; fax: +39 051 6448346. 0378-3839/$ - seefront matter D 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.coastaleng.2005.09.005

as waves reach a structure, such as an LCS, a lot of processes start. The waves may break on the structure, overtop it, generate waves behind the structure and reflect from the structure. Another effect may be wave penetration through openings between structures and diffraction around the head ofstructures. Both wave penetration and diffraction do not depend on the fact whether the structure is low-crested or not and, therefore, one is referred to handbooks for these items. The main effect of an LCS is that energy can pass over the crest and generate waves behind the struc-

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J.W. van der Meer et al. / Coastal Engineering 52 (2005) 915–929

ture. The description of this wavetransmission is the main objective in this chapter. As wave reflection decreases for lower structures, also this item will be treated. More in detail the following subjects will be treated: 2D wave transmission at rubble mound LCS 3D effects on rubble mound LCS Spectral change due to wave transmission Wave transmission at smooth and impermeable LCS ! Reflection at LCS ! ! ! !

3. 2D wave transmission atrubble mound LCS Wave transmission and overtopping are the two phenomena that allow wave energy to pass over or through LCS. The other part of the wave energy will be dissipated by wave breaking on and over the structure and some of the energy will be reflected. As these structures are commonly employed in coastal defence interventions, the prediction of the amount of energy transmitted behind...