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Technical

Site / environmental surveys

A site survey documents the environmental conditions at a surveyed site. The environmental conditions evaluated include the local wind conditions, water currents, waves, risk of icing, bathymetry and bed sediments.

Geir Håvard Espnes
Department manager for Technical
Geir Håvard Espnes

The site / environmental survey should be carried out before the fish farm installation is deployed at the site since the report forms the basis for the load calculations of the floating fish-farm installation and its moorings.  

If a site is to be further developed or extended, an update of the current survey is required, where the desired expansion area is thus included in the survey.

Typically, site surveys are written based on 1 month’s measured current data and modelled waves. Alternatively, the surveys can be based one year’s measurements of both currents and waves at the site. Åkerblå performs both extreme-value analysis and long-term statistics on the measured data for use in the site surveys, through the use of programs developed in-house.

The 10- and 50-year return periods for local currents and waves are calculated from the evaluation of the environmental conditions, using expert assessment of the area’s meteorology, oceanographic conditions and bathymetric conditions.

Site currents are additionally described in terms of some of the current components comprising the measured current.  These components include tidal contribution, wind-driven flows, seasonal influences, wind set-up, coastal current influences, spring floods and flows due to melted ice.

Wave conditions are characterized according the wind-generated waves, swell waves that have propagated in to the site, combined sea-state, ship-generated waves, wave reflection, the effect of several wave trains and wave-current interaction.

Åkerblå uses the SWAN model for calculation of the wave conditions. Åkerblå does not use the fetch – length method as it’s considered to be unsuitable for the determination of wave conditions along the Norwegian coastline.  Wind-generated waves, swell and the combined sea-state are well described by modelling the wave conditions using the SWAN model.

Wind data, used in the various calculations, is provided by the Norwegian Meteorological Institute.  Åkerblå performs both extreme-value analysis and long-term statistics on this data for use in the site surveys.

Åkerblå also performs site surveys with alternative objectives, for example, outflow from underwater discharge pipes, the laying of water cables for the municipality or electrical plants, small boat harbours and large port structures.