Summary
There is a growing concern over sediment-related issues in coastal areas, such as beach erosion and harbour accretion. Numerical (process-based and empirical) models are increasingly used to evaluate sediment fluxes, in order to analyse trends and to predict the effect of human interventions. However, the quantification of these sand fluxes often involves errors of over 100% for current-driven transport, and much higher for wave-driven transport. Quantifying these errors and understanding their sources is therefore vital for the quality and credibility of many coastal engineering studies.

SATUrN will verify the following hypothesis: in engineering applications, the errors in the evaluation of sediment fluxes are, to a large extent, determined by errors in the inputs. The latter include errors from other models (e.g., velocities computed by a hydrodynamic model), model approximations (e.g., spatially constant sediment characteristics), lack of data (e.g., sediment diameters based on limited data), etc.

The various sources of uncertainty will first be investigated individually, in order to sort out the key parameters that control the errors. Since the strong non-linearity of sand transport formulae precludes analytical approaches, Monte-Carlo simulations will be performed to analyze the error propagation from the parameters to the sediment fluxes. Simulations with an integrated modelling system for littoral processes will be also performed to define the model parameters that have a major influence in the variability of longshore sediment transport results. These results will provide useful insight on the limits of predictability of sediment transport formulae and a quantification of the errors introduced in the evaluation of sediment fluxes by inaccuracies in input parameters. The implications in coastal engineering studies of the uncertainty in the sediment transport results will be evaluated, by extending the theoretical analyses to two contrasting case studies: a small coastal lagoon and a beach with rocky outcrops.

Objectives
The major goals of the SATUrN are:

• to determine the key parameters that control sediment transport accuracy;
• to determine if the combined effect of errors in this key parameters can lead to error amplification;
• to understand the consequences of the errors in sediment fluxes in long-term simulations of coastal evolution.

The objective will be achieved through the applications of empirical sediment transport formulae for the case of tidally-driven transport and a nearshore sediment transport model for wave-driven applications. The implications of these errors will be assessed in case studies.
Activity

• Task 1: Sediment transport due to tides and other low frequency flows: terminated
• Task 2: Sediment transport due to short waves: terminated
• Task 3: Engineering applications: ongoing

Selected Results


Publications

• Oliveira, M.A., Freire, P., Andrade, C. Influence of sediment grain size in littoral transport evaluation. Recursos Hídricos (submitted in October 2006).
• Pinto, L., A.B. Fortunato e P. Freire, (2006). Sensitivity Analysis of Non-cohesive Sediment Transport Formulae, Continental Shelf Research, 26/15: 1826-1839.
• Fortunato, A.B. (2006) - Accuracy of sediment flux computations in tidally-driven simulations, Journal of Waterways, Ports, Coastal and Ocean Engineering, em impressão.
• Pinto, L.; A.B. Fortunato; P. Freire (2005) - Sensitivity analysis of sediment transport formulae, Book of Abstracts of the 9th International Conference Estuarine and Coastal Modeling, 82.

Team
LNEC: André Fortunato, Lígia Pinto, Paula Freire, Anabela Oliveira

Other Projects

• Beach morphodynamics
• Dynamics of estuaries and lagoons
• EMERA - Morfodynamic Study of Ria de Aveiro Inlet
• BERNA - Beach evolution in areas of restricted fetch: experimental and numerical analysis