Assessing wave conditions in a Norwegian fjord

Abstract

The focus of this thesis is to obtain an estimate of the significant wave height together with the corresponding peak period for the proposed bridge locations at Bjørnafjord. The task was conducted by modelling and calculations done in SWAN software. The methodology for transforming the NORA10 hindcast data into the design wave conditions for the 10-2 and 10-4 probability of exceedance was introduced for an offshore location. Furthermore a short description for the methods of transforming the metocean conditions to the fjord position were presented. The theory on the different wave generation and dissipation mechanisms present in the coastal waters was described. The description introduced the influence of those physical phenomena on the wave spectrum. The implementation of the dissipation mechanisms in SWAN was described with respect to the models produced for this thesis. As an introduction to modelling in the SWAN, the test case model analysis based on the master thesis by Engbretsen (2012) was performed. Furthermore a series of simplified idealized models was prepared. The models are reflecting the real bathymetry features found in the Bjørnafjord and are the basis for the analysis of the fjord. The cases were modelled to consider the influence of the bottom topography on the wave field. A number of sensitivity studies was executed to investigate the influence of the different coastal effects on the total sea characteristics. Finally the Bjørnafjord wave model was created. Real bathymetry data was modelled based on the maps acquired from Kystverket. The inputs in regard to the wind and incoming wave conditions were based on the reports by SINTEFF - Stefanakos (2015) and NORCONSULT - Lothe (2015). A number of cases with different environmental conditions was analysed. Sensitivity study in regard to the dominating dissipation mechanisms was conducted. The obtained results were compared with the analyses done in the source reports of Stefanakos and Lothe.