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Oil Spill Boom Strategy for Local Authorities Facing Coastal and Harbor Pollutions: A Survey of the European Research Project ISDAMP+

The Charente-Maritime department engineering school, EIGSI, the TU Lisbon engineering school, IST, and Falmouth harbour were partners of the ISDAMP+ project. We present a modeling tool forecasting the hydrodynamic conditions and the structural behavior of floating barriers for the decision aid of local authorities and harbor masters in marine pollution containment. To improve and validate our models, we carried out four experiments in the harbors of Lisbon, Falmouth, Rochefort and La Rochelle. Using model results remains difficult for local responders, however simplification could cause operational issues for numerical models. Sharing experiences and best practices is essential for further progress.

1.1. Introduction

This chapter is dedicated to maritime pollution preparedness, particularly the practice of floating barriers being a core tool to contain oils on the sea surface.

This chapter is split in to five parts. This first one presents the context and project partnership, the second the hydrodynamic model, the third the barrier model, the fourth the coupling between the fluid and solid mechanics and the fifth gives details about the four experiments performed in situ.

1.1.1. Challenge

We must consider local responses to oil spills through a specific decision aid system. A solely global scale approach appears to be insufficient. A local entity often knows the characteristics of its space very well because it regularly carries out actions there.

The problem addressed is to gather the available data and models efficiently, for example, data regarding the geolocation of pollution, marine currents and the floating barrier behavior. To manage the data, we developed two software tools, named MOHID and BARRIER. To assess the results of these tools, we performed four experiments during the project.

The participating states' policies which are addressed are the marine pollution preparedness area in relation to two topics:

• - increasing the preparedness for the coastal consequences of marine pollution accidents [ALV 15];
• - using and developing e-learning tools [MAL 19] for spreading knowledge about civil protection and marine pollution.

Our tools could potentially be broadened for other scopes of civil protection, such as coastal flooding.

1.1.2. Problem

The following figure illustrates a common question about the best placement of a floating barrier. The answer depends on available mooring possibilities, water current intensities and pollution location and drifting patterns. This barrier device, often called a "boom" and sometimes a "fence" or "curtain", is a mechanical response to contain or deviate floating oils during their entrainment by sea current flow [AMI 09]. The benefit of this device is to concentrate the pollutant and allow for on-sea recovery. Consequently, shoreline pollution is reduced.

Figure 1.1. Boom possibilities along a quay in terms of mooring placements, pollution location and current intensities, which themselves are modeled or measured by a buoy

1.1.3. Project partners

This chapter examines an action named ISDAMP+, implemented from 2012 to 2015 in three European countries - France, Portugal, and the United Kingdom - with the European Commission Civil Protection and Humanitarian Aid Office DG ECHO. The project partners are:

• - EIGSI: one of the oldest French engineering schools. It establisted Ecole Violet in 1901 in Paris, then in La Rochelle in 1991, and a foreign campus opened in Casablanca, Morocco, in 2005.
• - IST: the engineering school of the Technical University of Lisbon, Portugal. It is the largest and the oldest Portuguese engineering school. The MARETEC team specializes in the numerical modeling of aquatic ecosystems, with special emphasis on the hydrodynamics of coastal zones.
• - Action Modulers: a spin-off of IST. Its research and development department has worked continuously on the development of the MOHID Water Modeling System and the graphical user interface of MOHID, MOHID Studio.
• - Falmouth Harbour Commissioners (FHC), including the Carrick Roads, Cornwall, United Kingdom: a statutory harbor authority, reputed to be the third largest natural harbor in the world. It has practical experience and expertise in oil pollution response. It plans and prepares responses to potential future maritime pollution incidents.

1.2. Coastal hydrodynamic model

This model forecasts ocean parameters and sea-state to estimate the location of oil booms if an oil spill occurs. A hydrodynamic module is the core of the MOHID Water modeling system [BRA 04]. We consider the three-dimensional Navier-Stokes equations under the Boussinesq and hydrostatic approximations [FRI 06]. We adapt the three dimensions of the model with a superposition of two-dimensional surfaces. On each of these parallel sigma layer surfaces (sigma vertical levels) along the water depth, we solve the Saint-Venant equations [AUD 05].

MOHID Studio is a graphical user interface for the MOHID Water modeling system. MOHID Studio enables users to edit data files, create and launch MOHID simulations and analyze model results. MOHID and MOHID Studio can run on desktop computers.

METEO-FRANCE and METEO-GALICIA provide publicly available meteorological data, shown on fine resolution meshes or grids. An operational hydrodynamic model was necessary. We apply the Automatic Running Tool (ART) used at the MARETEC lab. This software tool permits automatic simulations of specific data on the MOHID solver. Not long after, we deemed it necessary to run the atmospheric model Weather Research and Forecasting (WRF), using ART.

Since 2004, MARETEC lab (IST) has implemented an operational wave forecasting system for the North Atlantic and Portuguese coasts, based on the WAVEWATCH III model (version 2.22). The ISDAMP+ project allows setting up such a system for Portuguese and South West French coasts, in order to contain oil leak pollution. We deliver wave data to ensure appropriate conditions and the best locations for floating barrier deployment during emergencies.

We implemented the MOHID hydrodynamic model for the La Rochelle region, France [ASC 15], in 2014. The coastal hydrodynamic depends on the flows of the rivers and estuaries of the Sèvre-Niortaise, the Charente, the Seudre and the Gironde [RAY 15]. The unstructured grid resolutions range from approximatively 50 km in the Bay of Biscay grid, to 400-200 m in the La Rochelle Bay fine local grid. A downscaling approach complies with a multigrid scheme. The imbedded mesh grids have successively finer resolutions. It allows for a proper representation of ocean dynamics and wave propagation. The calibration and validation of model results use open data registered by buoys, stations and cruise campaigns. Bathymetry, global ocean circulation and principal tidal constituents give the boundary conditions and an initial state of the fluid velocity and water depth.

1.3. Boom structural analysis model

EIGSI has produced a software named BARRIER, which provides a decision support system for oil spill boom placement. These depend especially on water current. A map displays the current data and results. Software options permit two kinds of booms, air inflated float curtains and solid foam flotation barriers or fences. The numerical method implemented in BARRIER follows a multigrid and multimodel scheme. It proposes four kinds of mesh. Each of them considers a mechanical model with a low or high refinement of the boom geometry. The model names are BAR0D, BAR1D, BAR2D and BAR3D. They assimilate a strained boom geometry as a straight line, a catenary curve, a 2D curvilinear finite-element domain, named cable, and a 3D tensile finite-element surface, named membrane, respectively.

The displacement u and tension T of a 2D cable domain define the function (u,T)(U), written in terms of free-surface velocity U. This one with the water depth h solves the Saint-Venant equations associated with the sea surface layer.

The first operational test cases reveal that BAR0D and BAR1D give a restricted prediction of the boom geometry and containment efficiency [GON 14]. However, the lack of indication on boom tension T, upsets the decision aid for mooring definition. Another outcome of BAR0D or BAR1D is a boom initial position for the non-linear iterative solvers included in BAR2D and BAR3D. The results given by BAR2D are valuable when it comes to proposing a boom deployed geometry in a given environment. BAR2D needs only to moderate the computational cost. Updating the contingency plan is fast and simple.

From the ISDAMP+ point of view, the Rochefort and La Rochelle Chef de Baie experiment computations only use BAR1D and BAR2D results. The BAR3D model is more consistent with a research activity. Its interface with the convergence of the iterative solver remains difficult to handle for end-users. The Departmental Directorate of Territories and the Sea (DDTM, Direction Departementale des Territoires et de la Mer) of Charente-Maritime recommends that these models need to request minimal filling of inputs, variables, parameters, results and outputs. The model should thus become operational.

A useful BAR3D output is a stress map of...