Sediment Spill – Monitoring and Control
WODCON XXIII - Dredging is changing - The Practice. The Science. The Business.
F. Staudt, S.E. Kristensen, S.L. Niemann, A. van der Weck, T. Tuinhof, B. Schlenz
"Sediment spill in the marine environment is the main pressure for generating impact on marine flora and fauna: sedimentation and light reduction caused by increased turbidity can lead to biomass reduction and affect the food chain. The construction of the new Fehmarnbelt Tunnel between Fehmarn (Germany) and Lolland (Denmark) is a large coastal infrastructure project. The Project consists of an Immersed Tunnel which is lowered into a dredged trench on the seabed. With a variety of spill-giving activities, the Project includes a comprehensive spill monitoring program to control sediment spill from the marine Dredging and Land Reclamation Works. A very detailed spill allowance approach sets the conditions for the sediment amounts spilled to the marine environment. The spill budget for the Project is based on a realistic plan for spill amounts from a) the various types of spill-giving activities in the project, b) the spill distribution in geographical areas of the project and c) time. For different geographical areas and time periods (monthly, seasonally, annually, entire construction period), the spill budget defines the sediment spill amounts that are not to be exceeded. The Project is set up as a 'Design and Build', meaning that the contractor has the overall responsibility for the design and construction of the Project according to the Owner's requirement. The control of sediment spill is based on the principle that the one who is in control of the dredging activities has the responsibility for staying within the spill limits. The Contractor (FBC, Fehmarn Belt Contractors I/S) who is carrying out the Works is therefore responsible for compliance with the spill budget, the associated monitoring activities and related documentation. The Project Owner (Femern A/S) has to ensure that the contractors fulfil their responsibilities and that this process is communicated to the authorities. The Owner has set up an environmental construction inspection (ECI) to monitor and document the Contractors' efforts and communicate with authorities and stakeholders as well as construction site management. In Germany, this is covered by the so-called Umweltbaubegleitung (UBB), which in recent years is a condition for the approval of large construction projects. The spill requirements set up is based on the good experiences gained during the construction of the Øresund Fixed Link between Sweden and Denmark. However the Fehmarnbelt Tunnel is the first major marine infrastructure project in Germany that has to adhere to these requirements. As part of the ECI, DHI's tasks are 1) to ensure the spill compliance documentation is based on solid and defendable methodologies, and 2) to ensure transparent communication between stakeholders about the status of spill monitoring and of the spill compliance as well as addressing unforeseen sediment spill events. This approach minimizes potential risks for the Project (e.g. delays or claims). The first step of the ECI tasks was a review of the Contractor's plans for fulfilling their obligation for spill compliance, i.e. their plans for construction and spill monitoring methods, ensuring that the Contractor's methods are according to good practice. Tracking the spill compliance in a project of this size requires continuous book keeping of both the sediment spill that has already occurred (hindcast) and the spill that is expected in the remaining, future activities (forecast). The Contractor has set up a system to control and manage compliance with the allowed sediment spill amounts during the complete duration of the Project. Before the start of construction, the expected sediment spill has been forecasted using"
Keywords: Dredging, Sediment Spill, Monitoring