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New information on the sediment-related effects of sea disposal

The effects of sea disposal on the marine environment are usually clearly visible during the disposal work. The observation of long-term effects is more difficult. Moreover, only a limited amount of research information is available on these effects.

The objective of the sediment study, conducted in connection with the further excavation of the Uusikaupunki sea route, is to gain new information on these long-term effects.

“Concrete research data on sea disposal is required in order to implement sea disposal projects in as smart a manner as possible, while also considering their environmental aspects,” says Tiina Vaittinen from Sito. Dredging of the seabed is typically a precondition for the maintenance of sea routes and ports on the Finnish coast due to, for instance, the sedimentation of the dry solid transported by the water, increased vessel sizes, and uplift, particularly in the Gulf of Bothnia.   “The dredging mass generated must be disposed of, which may cause adverse environmental effects,” Vaittinen continues.

Sea disposal is a mass disposal method often used in marine dredging projects, even though the first option is to utilise the dredged mass in port structures, for instance. However, the utilisation of dredging mass is not always possible due to the weak geotechnical properties of the mass, or other similar reasons.   Other alternative disposal methods are typically significantly more expensive than sea disposal.

The goal of the research project is to generate information for impact assessment

“Launched in May 2014, the research project aims to assess the level of dry solid load caused by sea disposal, compared with background conditions, while also analysing the applicability of the used research methods such as sediment collectors in observing the effects of sea disposal,” Tiina Vaittinen says. The research applies to clean sediment masses. The objective is to generate information to support impact assessment at disposal sites and the determination of the terms of reference for disposal sites, while also providing additional information on cost-efficient research methods for route project permit applications and implementation.

The study utilises sediment collectors installed in the seabed, continuous water quality and flow measurements, depth data available for the area, and previous studies. Sedimentation, water quality and flow measurements have been conducted in three one-month-long research periods, the latest of which commenced at the end of April 2015. By comparing the results of these research periods, the researchers aim to analyse potential changes caused by sea disposal in the amount and quality of sediment in the research area. To support the interpretation of the results, the researchers use control stations located outside the impact zone of the disposal site but in similar areas as the actual research stations.

The project research report will be published in the autumn of 2015 as part of a series of publications by the Finnish Transport Agency. The project is a public R&D project of the Finnish Transport Agency.