The project group consists of a PhD student and supervisors. Responsibles: Hanne Vidgren (HiN), Aud Helland (Rambøll Norge), Elisabeth Roman (HiN)
Objectives
Behaviour of capping material in the water column, cap placement
In-situ sediment properties and significance of cohesiveness in dredging and disposal actions
Description of sediment for modelling purposes (sensitivity of models)
Background
In Norway contaminated marine sediments are a national concern raising a need for cost effective methods to reduce risk from the sediments. Remedial methods mainly in used today consist of monitored natural attenuation, dredging, and in situ capping (covering with clean isolating material). Various technical challenges are still involved into handling of large amounts of sediments with varying properties during the operations. The focus of this work package is to strengthen knowledge within physical and technical aspects on the sediments behaviour during the operations. Computer simulations have opportunity to be one of the most cost-effective approaches to investigate sediment behaviour during open water disposals or dredging operations. Anyway, accurate description of the (in-situ) sediments properties (e.g. description of cohesive dredged sediments) are needed for reliable modelling results.
The work package consists of a PhD project taking part to 2-3 dredging and capping projects occurring during the period both in the Southern and Northern coast of Norway. The main difference between these areas is better availability to the coarse capping material in the North. Anyway, the results of the study are applicable regardless of the location.
Sand cap placement as an open water release
Capping is an attractive method to isolate and immobilize polluted sediments in-situ in certain settings. 40 cm thick sand cap was used on the deep contained aqueous disposal (CAD) site at Malmøykalven (Oslofjord). The site was now used as a case study about the constructability of a sand cap utilizing the field data collected during the operations (from the years 2008-2010). Conventional dredging equipment is often used to place the cap as a surface release. Especially on the deep sites the method questions concerning the ability to accurately place sediments in a targeted area as well as the manage loss of the material. Successful implementation of capping technology requires an understanding of the capping material fate released to the water.
An instantaneous release of sediments into a fluid are widely studied and modelled since it occurs in many engineering applications. STFATE and MDFATE models were now utilized here to describe cap placement, material losses and variability in cap thickness. Better understanding of the cap layer formation obtained by model simulations enables to evaluate efficiency of the split hull barge to place the cap accurately.
In-situ properties of sediments and significance of cohesion, description of the sediment in the transport models
Importance of cohesion / clumping during dredging and disposal
Spatial distribution of the sediments in the estuary / Estimating the volumes of cohesive sediments
Description of the sediments in the sediment transport modelling
Testing the different variables in the modelling (sensitivity of models)
Dredging activities are carried out in coastal areas in order to maintain navigable depths and/or to remove the contaminated sediments. Dredging activities and disposal of dredged material to the open water requires understanding on behaviour of sand-mud mixtures. Dredged masses may include solid blocks or clods of very dense cohesive material. The proportion of them depends primarily on the properties of the sediment and how those have been affected during the dredging operation. Sediment properties are important for predicting / modelling consequences of dredging and disposal works in marine environment. Sediment that remains in suspension during the dredging and disposal introduces additional environmental concerns such as increased turbidity, which can adversely affect aquatic vegetation, fauna, and overall water quality. Therefore accurate predictions the suspended solids levels in the water column have great importance for environmental impact assessment and operation planning.
This study concentrates especially on the importance of cohesiveness of muddy sediments as dredged and released back to the water. Laboratory settling tests are carried out for large estuary area with varying sediments properties. Target is to study the importance of in situ properties for sediment behaviour and estimate sediment erosion when disposed to open water site. Increase understanding of sediment properties and behaviour should lead to the better estimations about the effect of operations for suspended solids concentrations.
Co-operation with WP 3 – Sediment remediation methods – waste management
Developing tools for choosing the remediation method
Comparison of remediation methods applicable with the same harbour area
Significance of sediment properties for overall success of the remediation
Publications
–https://site.uit.no/ewma/wp-content/uploads/sites/61/2012/10/1-Poster-A1-Vidgren-Pedersen1.pdf
Articles
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Related links
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In the Press
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