Application of Unibest to model White Lagoon Beach Enhancement

Application of Unibest to model White Lagoon Beach Enhancement

De Bruijn, F.A.
Erdbrink, C.D.

Verhagen, H.J. (mentor)
Stive, M.J.F. (mentor)

Civil Engineering and Geosciences

Hydraulic Engineering

2005-06-01

The objective of this study is to test the use and applicability of the Unibest CL+ and TC models for the White Lagoon case. The White Lagoon is a small bay near Balchik, Bulgaria, that is characterised by two T-groynes and a rocky bottom nearshore. A local hotel would like the present beach to be enlarged to accommodate for more guests. In addition, due to bad circulation algae and seaweeds flourish in the tourist season. Different data are available, including results from a bathymetric survey, wind data, offshore wave data, sediment sieve curves and some preliminary research. Relevant physical processes are identified, such as wave transformation due to decreasing water depth and wave-induced currents and sediment transport. It is expected that different wave conditions cause widely varying processes. Due to limited breaker depth under normal wave conditions, there will be no longshore sediment transport offshore from the groynes, whereas under storm conditions, longshore transport is expected offshore from the groynes and cross-shore transport from the zone between the groynes to the offshore zone. Unibest CL+ is a single line coastline model that assumes an invariant bottom profile. Unibest CL+ is therefore incapable of modelling cross-shore dynamics, for which Unibest TC is used. For a number of reasons, it is not possible to model the entire area in Unibest CL+ and as a result the model area is limited to the area between the groynes, where diffracted waves are used as wave input. Unibest TC is used to model cross-shore dynamics for a profile between the groynes. Many problems have been encountered when applying the models. The most important problem is the lack of good calibration data. Furthermore it is expected that both models, which have been designed for sandy coasts, are very limited in their applicability to the rocky coast with little available sand at White Lagoon. It is recommended for the follow-up of this study that better calibration data is collected by measuring wave properties throughout the surf zone, with according bottom changes. In addition, more accurate wave scenarios are needed, especially for the CL+ model, either from measurements or a number of SWAN runs.

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(c) 2005 The Author(s)