The main scientific objectives of this research proposal can be summarised in the question why certain sandy coasts are dynamically stable and others are not. The following tools will be used to search for the answer:•Literature study•Building of a framework to model sediment transport in the near shore zone•Incorporation of the influence of complex spectra in the formulation of sediment transport influenced by currents and waves•	Synergy of understanding of the physical processes (theoretical basis), numerical and physical modelling•	Qualitative confrontation with available in situ measurementsSince we are convinced that the planned research activities are of international value, not only in terms of scientific merits but also from the point of view of sustainable coastal development, the following objectives form also part of this proposal:•Collaboration with other research teams in Europe who deal with this topic, for example by participating in experiments in the framework of TMR-LSF•Writing and submitting of a problem oriented and interdisciplinary research proposal to the E.U.•Dissimination of the results through conferences and by publication in international journal

Monbaliu, J.

Verhoeven, R.

Wens, F.

Open Marine Archive

F.W.O.-onderzoeksproject G.0200.01 
Hydrodynamica en sedimenttransport. 
Fundamentele aspecten bij een duurzaam beheer van zandige kusten 
 
 
 
 
 
 
HYDRODYNAMICS AND SEDIMENT TRANSPORT 
 
FUNDAMENTAL ASPECTS RELATED TO 
SUSTAINABLE MANAGEMENT OF 
SANDY COASTS 
 
 
 
 
AIM AND SCOPE OF THE 
RESEARCH PROJECT 
 
 
 
 
 
 
Authors : J. Monbaliu, R. Verhoeven, F. Wens 
Date : January 2001 
Version : 1.01 
 
 
 
 
 
LABORATORIUM voor 
HYDRAULICA 
K.U.LEUVEN 
 
 
 
LABORATORIUM voor 
HYDRAULICA 
UNIVERSITEIT GENT 
 
 
 
WATERBOUWKUNDIG 
LABORATORIUM 
BORGERHOUT 
 
 
Aim of the research project 
 
To protect the hinterland against the attacks from storm surges and waves, an explicit 
coastal defence is necessary.  The associated measures can basically be split-up in so-
called ‘hard’ and ‘soft’ methods, referring respectively to dikes, groynes, breakwaters,… 
and dynamic systems such as sand suppletion and floating geotextiles.  More and more 
coastal authorities, also in Belgium, seem to prefer the soft coastal defence systems.  The 
current success of beach renourishment techniques as a coastal defence alternative can be 
attributed both to the added ecological value and to the recreational beach potential. 
 
Ideally sandy beaches form a system where erosion and accretion are in a dynamic 
equilibrium.  Unfortunately, this dynamic equilibrium is not absolute and structural 
erosion is a threat to the coastal area.  As a result beach maintenance is mandatory.  
Depending on the rate of maintenance, both in terms of volume and in terms of 
frequency, the socio-economic and the ecological impact can be considerable.  Therefore, 
to develop a sustainable beach management of a sandy coast it is crucial to know and 
understand the different factors which play a role as well as their mutual interaction, see 
e.g. (De Vriend et al., 1993).  Only fundamental knowledge of the physical processes will 
lead to a better insight.  The dynamic coastal processes are not yet well understood.  It is 
not so clear why certain areas are dynamically stable and others are not.  A critical zone 
is the near-shore, a region where wave impact and tidal flows are equally important for 
the resulting sediment mobility.  The processes in the near-shore zone form the subject of 
this study.  The best route for fundamental research is to find a way to combine process 
theories, numerical simulation, physical experiments in laboratory conditions, and field 
campaigns.  In most studies, synergy of these four components does not exist or is at least 
very incomplete. 
 
The present study first of all wants to combine the theoretical study of physical processes, 
numerical modelling and laboratory experiments.  Each of the partners in this project has 
considerable experience in at least one of the above aspects.  Mutual collaboration will 
confront, combine and supplement the available knowledge.  A detailed comparison with 
a field campaign as a last step in the synergy of the four components, does not form part 
of this project.  However, the existence of field registrations on a macro-scale provides us 
with an opportunity to make a qualitative interpretation.  For a dedicated field campaign 
of high quality, extensive preparation, and incorporation in an interdisciplinary and 
international framework is needed.  The work proposed in this research project gives us 
excellent preparation tools. 
 
 1
Scope of the research project 
 
Theoretical study 
 
A basic understanding of the relevant physical processes starts with a detailed survey and 
study of the available literature.  Starting from a general overview of coastal sediment 
dynamics, a detailed analysis of the hydrodynamics associated with the combination of 
currents and waves and the resulting sediment transport will be worked out.  Standard 
references, e.g. (Soulsby, 1997), together with recent European and other international 
research work (COAST3D, SEDMOC, INDIA, SandyDuck, S.T.O.R.M.,…) will lead to 
a better understanding and problem identification in near-shore sediment processes.  Also 
numerical work, e.g. (Trouw et al., 2000), and physical experiments, e.g. in the 
framework of the European TMR-LSF (Training and Mobility of Researchers – Access to 
Large-Scale Facilities Programme), will need to be studied. 
 
Experimental modelling 
 
Basically, physical experiments validate and analyse detailed sediment transport 
characteristics under controlled hydrodynamic conditions.  Indeed, the complex 
interaction between waves, tidal flow and mobile sediments in the near-shore zone, forces 
the researcher to use idealized situations where the hydrodynamics may not be 100 
percent realistic, but where they are controllable on the one side and reproducable on the 
other.  Therefore, it is proposed to use the laboratory facilities of Flanders Hydraulics in 
Borgerhout.  Their infrastructure is equipped with a wave basin.  The wave generator is 
capable of producing the theoretical JONSWAP and Pierson-Moskowitz spectra and with 
the double pumping system it is possible to generate lateral flow (currents) and vertical 
water level variations (tide).  The combination of these three components in the 
hydrodynamic load scheme makes the experiments quite unique - in comparison with e.g. 
the experiments in the framework of the SAFE-project, LIW-Braunschweig, Prof. H. 
Oumeraci and Prof. H.H. Dette (Dette et al., 1999).  An explicit extension of the wave 
generation system to be able to generate more complex spectral forms of random waves 
is considered part of this project.  The global target of this experimental part of the study 
is to record both in detail the wave field and the flow distribution together with the 
resulting sediment concentration (by using e.g. the ADV-velocity probe and OPCON-
turbidity sensor) and the global cross-section evolution.  Registration of the time 
evolution of the global cross-section is performed with a computer controlled scanning 
system, ensuring an accurate and detailed topographic survey of the resulting sea bottom.  
A so-called scale series of experiments will be executed on the same prototype but with 
different hydrodynamic and morphological scales in order to validate and understand the 
basic physical processes.  A qualitative verification of this global cross-sectional 
evolution will be done by comparing the results of these laboratory experiments with 
available field registrations for a representative suppletion profile for the Belgian East 
 2
coast.  This qualitative validation on macro-scale should help to interprete the physical 
processes on micro-scale in the corresponding physical experiments. 
 
Numerical modelling 
 
When doing numerical modelling, one has modelling of the details of the individual 
processes and modelling of the global effects of these processes.  Ideally one should be 
able to quantify the long-term global effects by integrating the detailed processes over 
time.  In practice this is impossible both because of insufficient computing power and 
because of insufficient knowledge of the detailed processes.  A better understanding of 
the detailed physics however, should allow improving the parametrisation of the global 
effects.  For example, to incorporate the effect of waves on sediment transport one 
typically assumes that shear stresses due to waves and due to currents can be calculated 
separately and then superimposed.  Moreover, for the estimation of the shear stresses 
under waves one assumes that the full wave spectrum can be represented by two 
numbers, the wave height and some characteristic period, for example the peak period, 
see e.g. (Monbaliu et al., 1999).  This assumption is quite often inadequate, especially in 
near shore zones where wave spectra are frequently more complex.  An improved 
parametrisation of the effect of the spectral distribution of wave energy on sediment 
transport, forms the first objective in the numerical modelling part of this study.   
 
For the numerical modelling, a variety of models is needed: 
• Hydrodynamic models (2D/3D 
• Wave models 
• In the frequency domain (spectral wave models; adequate for fairly large areas) 
• In the time domain (shallow water models such as Boussinesq-models; only 
suited for relatively small areas) 
• Sediment transport models 
 
A second objective of the modelling exercise is therefore to create a framework to 
quantify sediment transport in the near-shore zone.  The idea is to have a double action: 
how does one zoom in on a detail of a coastal zone and how does one zoom out.  This 
framework will be tested in a realistic setting of a part of the Belgian coastal zone.   
 
In this study we want to use commercially available software where possible, 
supplemented by public domain and own developments where needed. 
 
Concerning commercial software, our first choice is the TELEMAC-system.  This 
software package contains 2D- and 3D-hydrodynamic models, sediment transport models 
and a Boussinesq model.  It is a powerful package and for research purposes it is 
available at very low cost.  The spectral wave models WAM and SWAN will supplement 
this system.  The K.U.Leuven research team has considerable experience with these last 
two models.  The TELEMAC-system does not contain a package for beach profile 
modelling.  Danish Hydraulic Institute and Delft Hydraulics offer such models.  At this 
moment however, we do not consider these models essential for the tasks in this study. 
 3
Synergy of the theoretical basis and the physical and numerical modelling 
 
It is well known that both physical and numerical models have limitations.  More and 
more numerical models are seen as the tools to study applications in coastal areas.  
Nevertheless physical modelling is important and will remain to be.  The physical 
phenomena are sometimes badly understood or too complicated to work them out 
numerically.  Also the computing power needed for some problems is so large, that it is 
impossible to carry out calculations within a reasonable amount of time. 
 
Synergy of the different aspects offers a good alternative (Schäffer, 1999).  Synergy can 
play in two ways.  Numerical models can be used efficiently to generate good boundary 
conditions for physical model studies (zooming in).  Physical models can be studied in 
more detail and in controlled circumstances in the lab.  These experiments can also be 
modelled numerically.  The intercomparison provides better insight (important for 
zooming out).  The laboratory experiments will therefore concentrate on providing 
understanding of the behaviour of non-cohesive sediments under currents and waves 
representative for a complex spectrum (cf. objective 1 in the numerical modelling part). 
 
The planned confrontation with the available terrain measurements has considerable 
added value.  In situ measurements at the Belgian coast (both bathymetric surveys and 
wave data) have been archived over a long period.  The richness they contain can be used 
to trigger an interdisciplinary and international research project. 
 
Summary 
 
The main scientific objectives of this research proposal can be summarised in the 
question why certain sandy coasts are dynamically stable and others are not.  The 
following tools will be used to search for the answer: 
• Literature study 
• Building of a framework to model sediment transport in the near shore zone 
• Incorporation of the influence of complex spectra in the formulation of sediment 
transport influenced by currents and waves 
• Synergy of understanding of the physical processes (theoretical basis), numerical and 
physical modelling 
• Qualitative confrontation with available in situ measurements 
 
Since we are convinced that the planned research activities are of international value, not 
only in terms of scientific merits but also from the point of view of sustainable coastal 
development, the following objectives form also part of this proposal: 
• Collaboration with other research teams in Europe who deal with this topic, for 
example by participating in experiments in the framework of TMR-LSF 
• Writing and submitting of a problem oriented and interdisciplinary research proposal 
to the E.U. 
• Dissimination of the results through conferences and by publication in international 
journals 
 4
References 
 
 1.  De Vriend,H.J., Capobienco,M., Chesher,T., de Swart,H.E., Latteux,B., and Stive,M.J.F., 1993. 
Approaches to long-term modelling of coastal morphology: a review. Coastal Engineering, 21: 225-269. 
 2.  Dette,H.H., Larson,M., Murphy,J., Newe,J., Peters,K., Reniers,A., and Steetzel,H. Application of 
prototype flume tests for beach nourishment assessment.  1999. SAFE-project Report.  
Ref Type: Report 
 3.  Monbaliu,J., Hargreaves,J.C., Carretero,J.C., Gerritsen,H., and Flather,R., 1999. Wave modelling in 
the PROMISE project. Coastal Engineering, 37: 379-407. 
 4.  Schäffer,H.A. On hybrid modelling in coastal and ocean engineering.  1999. Proc. HYDRALAB-
workshop Experimental research and synergy effects with mathematical models, Hannover.  
Ref Type: Conference Proceeding 
 5.  Soulsby,R.L., 1997. Dynamics of marine sands - A manual for practical applications. Thomas Telford 
Services Ltd., London. 
 6.  Trouw,K., Williams,J.J., and Rose,C.P., 2000. Modelling sand resuspension by waves over a rippled 
bed. Estuarine, Coastal and Shelf Sciences, 50: 143-151. 
 
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Hydrodynamics and sediment transport. Fundamental aspects related to sustainable management of sandy coasts: aim and scope of the research project

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