Elsevier

Coastal Engineering

Volume 44, Issue 2, December 2001, Pages 153-190
Coastal Engineering

Review
Scour around coastal structures: a summary of recent research

https://doi.org/10.1016/S0378-3839(01)00024-2Get rights and content

Abstract

This paper summarizes the results of the European Union Marine Science and Technology (EU MAST) III project “Scour Around Coastal Structures” (SCARCOST). The summary is presented under three headings: (1) Introduction; (2) Flow and scour processes with the subheadings: flow and scour processes around vertical cylinders; flow and scour processes at detached breakwaters; flow and scour processes at submerged breakwaters; and the effect of turbulence on sediment transport; and (3) Sediment behaviour close to the structure with the subheadings: field measurement and analysis of wave-induced pore pressures and effective stresses around a bottom seated cylinder; non-linear soil modelling with respect to wave-induced pore pressures and gradients; wave-induced pressures on the bottom for non-linear coastal waves, including also wave kinematics; development of a numerical model (linear soil modelling) to calculate wave-induced pore pressures—the effect of liquefaction on sediment transport; penetration of blocks in non-consolidated fine soil; and cyclic stiffness of loose sand.

The paper also includes a discussion of the role of scale effects in laboratory testing and the applicability of the results obtained in supporting engineering design.

Introduction

When a structure is placed in a marine environment, the presence of the structure will change the flow pattern in its immediate neighbourhood, resulting in one or more of the following phenomena: the contraction of flow; the formation of a horseshoe vortex in front of the structure; the formation of lee-wake vortices (with or without vortex shedding) behind the structure; the generation of turbulence; the occurrence of reflection and diffraction of waves; the occurrence of wave breaking; and the pressure differentials in the soil that may produce “quick” condition/liquefaction allowing material to be carried off by currents. These changes usually cause an increase in the local sediment transport capacity and thus lead to scour.

The scour is a threat to the stability of coastal structures such as piles, breakwaters, seawalls, etc. Such structures are usually exposed to currents, waves, and combined waves and currents. Clearly, scour processes in the marine environment (with waves being the dominating flow effect) are more complex than in steady-current flows such as in rivers. In river hydraulics, a long tradition exists for studying scour around hydraulic structures. Scour at a bridge pier, for example, has been studied most extensively Breusers and Raudkivi, 1991, Melville and Coleman, 2000, simply because it has been realized that this is an important cause of bridge failure. The scour problems in coastal and offshore engineering have not received the same kind of attention. Analysis of failures due to scour has proven that more basic knowledge on scouring needs to be accommodated in the design exercise. To study the potential risk for scour in the vicinity of coastal structures, and to prepare and disseminate practical guidelines, a 3-year research program (1997–2000), Scour Around Coastal Structures (SCARCOST), has been undertaken by a consortium within the framework of MAST (Marine Science and Technology) program of the European Union (EU).

The consortium consisted of nine research institutions from six European countries, namely Department of Hydrodynamics and Water Resources (ISVA), Technical University of Denmark; HR Wallingford (HR), Great Britain; The Foundation for Scientific and Industrial Research at the Norwegian Institute of Technology (SINTEF), Trondheim, Norway; Laboratoire des Ecoulements Geophysiques et Industriels (LEGI) Université Joseph Fourier, Grenoble, France; Department of Civil Engineering, The University of Liverpool (UL), Great Britain; Instituto do Mar (IMAR), University of Coimbra, Portugal; Centre International D'Investigació dels Recursos Costaners (CIIRC-UPC), Barcelona, Spain; Department of Engineering Science, University of Oxford (UOX), Great Britain; and Coastal and Ocean Engineering, Norges Teknisk-Naturvitenskapelige Universitet (NTNU), Trondheim, Norway.

The results of this research program have been published, or are to be published, in various journal and conference papers, in research reports, and in conference abstracts. The purpose of the present paper is to summarize the results of this research program, thereby providing a synthesis of the work, an overview account of the project, combining the separately reported elements of the project into a whole.

The project is divided into two sub-projects. In the first sub-project, attention has been primarily concentrated on the water column with flow processes and the resulting scour. In the second sub-project, processes associated with the sediment have been the major concern. The results from these two sub-projects will be given in the present paper under the following two headings:

  • Flow and scour processes (Section 2), and

  • Sediment behaviour close to the structure and scour (Section 3).

Section snippets

Flow and scour processes

As mentioned in the preceding paragraphs, the focus in this sub-project has been the water column with flow processes and the resulting scour.

An overview of the state-of-the-art on flow and scour processes has been presented in the book by Whitehouse (1998) and in a review paper by Sumer and Fredsøe (1999)*.1 The book by Whitehouse (1998) provides methods and guidelines for the engineer to adopt when assessing

Sediment behaviour close to the structure and scour

The main objective here has been to investigate the effect of wave-induced pore pressures in the bottom sand on the scour around coastal structures, and sand transport in general.

As mentioned in Section 1, the research themes investigated in this sub-project of the research program are: (1) field measurement and analysis of wave-induced pore pressures and effective stresses around a bottom seated cylinder; (2) non-linear soil modelling with respect to wave-induced pore pressures and gradients;

Conclusions regarding flow and scour processes

The main findings from the laboratory work are listed below. (In all cases, the experiments were designed with the most appropriate scaling to study the relevant scour processes. This means that the results will become less relevant to situations where other processes are acting).

1. Scour-depth development around a single pile in linear waves can be predicted as a function of the KC number. The predictions can be extended to non-linear waves provided an appropriate definition of the wave

Acknowledgements

The results reported here represent the work of the entire consortium who have undertaken the European Community funded MAST III research program Scour Around Coastal Structures (SCARCOST), and not just the authors. The other members of the research program undertaken by the consortium include: M. Mory, B. O'Connor, F.J. Seabra-Santos, A. Sanchez-Arcilla, G. Sills, and Ø. Arntsen, and their co-workers A. Roulund, J. Sutherland, J.S. Damgaard, G. Svanø, B. Brørs, P. Larroude, C. Rose, S. Pan, J.

References (85)

  • M.A Biot

    General theory of three-dimensional consolidation

    J. Appl. Phys.

    (1941)
  • H.N.C Breusers et al.

    Scouring

    (1991)
  • Brørs, B., 1999. Prediction of kinematics and pressure in wave breaking at a slope. SCARCOST draft report, September...
  • J Carreiras et al.

    Wave scour around piles

  • T.G Carter et al.

    Mass transport by waves and offshore sand bedforms

    ASCE J. Waterw., Harbors Coastal Eng.

    (1973)
  • A.J Chorin

    Numerical study of slightly viscous flow

    J. Fluid Mech.

    (1973)
  • J.C.C de Ruiter

    The mechanism of sediment transport on bedforms

  • Fergui, O., Sills, G.C., 2000a. Seabed measurements on a model breakwater element. Internal reports: Part 1:...
  • Fergui, O., Sills, G.C., 2000b. Pore pressures in a sand bed subjected to waves in the UK Coastal Research Facility....
  • X Gironella et al.

    Hydrodynamic behaviour of submerged breakwaters. Some remarks based on experimental results

  • Gislason, K., Fredsøe, J., Mayer, S., Sumer, B.M., 2000. The mathematical modelling of the scour in front of the toe of...
  • P Hjorth

    Studies on the nature of local scour

  • G.J.C.M Hoffmans et al.

    Scour Manual

    (1997)
  • J.R.C Hsu et al.

    Wave-induced Soil Response in an unsaturated anisotropic seabed of finite thickness

    Int. J. Numer. Anal. Methods Geomech.

    (1994)
  • J.R.C Hsu et al.

    Short-crested wave-induced soil response in porous seabed of infinite thickness

    Int. J. Numer. Anal. Methods Geomech.

    (1993)
  • S.A Hughes

    Physical Models and Laboratory Techniques in Coastal Engineering

    (1993)
  • S.A Hughes et al.

    Wave-induced scour prediction at vertical walls

  • Ilstad, T., 2000. Non-linear modelling of wave-induced pore pressures in a plane seabed. SINTEF Report STF22 A00605,...
  • I Irie et al.

    Laboratory reproduction of seabed scour in front of breakwaters

  • H Kim et al.

    Modelling wave-induced scouring at a seawall front, Sooyung Yacht Centre, Korea

  • Kuhnen, F., 2000. Scour and scour protection around berm breakwaters. Diploma thesis University of Braunschweig,...
  • Kuhnen, F., Menze, A., 1999. Wave bottom pressures and wave kinematics in the surf zone. Wave forces on a truncated...
  • Ph Larroudé et al.

    Erosion autour de structures côtières

  • Li, M., O'Donnell, C., O'Connor, B.A., 2000. Investigation of the effect of bed seepage on near-bed shear stress and...
  • Lillycrop, W.J., Hughes, S.A., 1993. Scour hole problems experienced by the Corps of Engineers; Data presentation and...
  • Liu, P.L.-F., Lin, P., 1997. A numerical model for Breaking Waves: The Volume of Fluid Method. Research report NO....
  • S Mayer et al.

    A fractional step method for unsteady free-surface flow with applications to non-linear wave dynamics

    Int. J. Numer. Methods Fluids

    (1998)
  • B.W Melville et al.

    Bridge Scour

    (2000)
  • Menze, A., 2000. Stability of multilayer berm breakwaters. Diploma (MSc) thesis, University of Braunschweig, Germany....
  • S.G Millard et al.

    Assessing bridge pier scour by radar

    NDT&E Int., August

    (1998)
  • M Mory et al.

    Scour around pile groups

  • Nicholson, J., O'Connor, B.A., 2000. Effect of enhanced turbulence on suspended transport due to a current and waves....
  • Cited by (0)

    Disclaimer: Every effort has been made to ensure the accuracy of statements made in this paper. However, the paper is a contribution to research generally and it would be imprudent for third parties to rely on it in specific applications without checking its suitability.

    View full text