New model ranks hazardous wrecks

There are hundreds of shipwrecks along the Swedish coast that can be described as a ticking environmental bomb. The wrecks contain up to 15 000 tonnes of bunker fuel liable to leak into the sea. But how do we know which wrecks that have to be taken care of? That has Hanna Landquist, the Department of Shipping and Marine Technology, Chalmers, focused her research on.

Each wreck has its unique risks and problems. They have different damage, are on different exposed locations, can have different kinds of hazardous substances.  It is estimated that remediation of one single wreck could cost USD 1‐100 million and it is therefore not economically feasible to remediate every sunken shipwreck. Therefore, Hanna Landquists research is important, she has developed the method VRAKA (the Swedish word for wrecking) where the wrecks environmental hazard can be evaluated in order to facilitate prioritisation of wrecks and identification of how available resources can be used most efficiently.

- There was a feasibility study back in 2007 that got the ball rolling, so it was exciting when it became research money available to invest more in VRAKA, Hanna Landquist says.

The aim of VRAKA is to get an overall picture of the risks of sunken ships. The model consists of three parts, first an estimate of how big the risk is that oil will leak from the wreck, then a consequence assessment and ultimately a risk evaluation. For example, the model looks at the deterioration of a ship, if the seabed is stable, if diving occurs, shipping traffic in the area and more.
23 different experts have been involved in efforts to develop the points that are important for a risk assessment of a sunken vessel. A total of eight different activities has been identified that may affect the breakdown of a ship and the probability and extent of the damage the specific hazardous activities can lead to are assumed to be dependent on a number of site‐specific and wreck‐specific indicators, for example hull thickness, water salinity and depth.

After the risk has been estimated, next step in VRAKA is an impact assessment. The expected volume of oil and potentially hazardous cargo discharged, distance to shore and the environmental values ​​that may be affected. With the help of the risk estimation, it is possible to compare different wrecks with each other to see where action is most needed. It is also possible to compare an area of ​​several wreck with another area, and possibly reduce the cost of remediation by coordinating operations.

To determine which wrecks that need to be taken care of is one way to use the VRAKA, but another option might be to reduce the frequency of a hazardous activity. With the help of VRAKA it is possible, for example, to find out what reduced trawling in an area would mean for the risk of the break down and discharge of oil from a wreck.
VRAKA has been realised in the form of an Excel‐based tool. Hanna Landquist doctoral thesis is focused on shipwrecks located in Scandinavian waters that contain oil, but a wider geographical scope and expansion to other substances are possible future developments.

- The Swedish Agency for Marine and Water Management is responsible for the wreck issue in Sweden. They have begun work to prioritize their efforts and I hope that VRAKA will be able to assist in this work, Hanna Landquist says.

Text: Andreas Kron

Facts: 

Hazardous activities affecting wrecks

  • Construction work
  • Deterioration
  • Diving
  • Military activity
  • Shipping traffic
  • Storms/Extreme weather
  • Trawling
  • Unstable seabed

Site‐specific and wreck‐specific indicators:

  • Average bottom water oxygen concentration
  • Average bottom water salinity
  • Average bottom water temperature
  • Average bottom water current speed
  • Average hull thickness
  • Seabed character
  • Ship use
  • Time since sinking
  • Water depth
  • Wreck position on seabed