by Karin Almlöf
Three studies in Sweden have shown that ship traffic through sensitive areas causes erosion. The Swedish Transport Authority, Maritime Authority and Harbour of Stockholm have all released reports focusing on damages to shoreline and beaches in the Furusund fairway.
From standing on a beach or cape along this archipelago, wave energy from passing ships is highly visible: water is sucked out as the ship approaches and returns with great force after it has passed.
The study “Erosionsskador i Furusundsleden 2000-2013” by Lars Granath points out that powerful high energy water movement along shallow beaches created by the bigger ships pressure-waves as the problem.
The study shows that the damages in sensitive areas along the route Furusundsleden to and from Stockholm has clearly increased in the last couple of years. This increase is probably due to a higher volume of ship traffic with larger displacement at high speed. It is a combination of volume, shape and speed.
One solution to the coastline erosion problem is to reduce the speed when passing through the most sensitive areas and allow a higher speed in more open water areas. A future possibility could be individual fitted speed-limits, Granath suggests.
What’s up with the timetable?
Big vessels are caught speeding in the fairway and traffic on the Åbo-route are allowed due to their timetables to pass sensitive areas in 12 knots instead of in 10 knots.
A picture of M/S Viking Grace leaving Stockholm, a vessel on the Åbo-route said to have a particularly high wave pressure (Lars Granath).
Granath states in his study that to demand ships to decrease their speed on the Åbo route will be difficult to do without compensating measures. A major change of the system as a whole is needed, for example the 24-hour base for a cruise or a change of the rule that ships have to port in Åland to stay tax-free. He also points out that there are sensitive areas in the archipelago of Åland and in the Finnish archipelago as well.
This phenomenon of adhering to tight timetables also occurs on a smaller scale. Passenger ferries in the Stockholm archipelago operate on a timetable set by the government-founded “Waxholmsbolaget“ for example. The timetables are set so strinctly that the vessels have to run close to maximum speed, leaving no space for speed reduction when passing close to shore or approaching or leaving the quay.
It’s possible that consequences of increasing ship traffic extend further than the shorelines, local quays and facilities. If bays, beaches and other areas particularly with reed are affected and disturbed, this may affect the biodiversity of the entire archipelago. This biotope functions as nurseries for many organisms and is an important piece of the base of the biodiversity in the archipelago, Granath says.
The fuel consumption, stress to the crew, equipment wear and smaller margins for errors are other important pieces of a well-coordinated traffic. A well-managed timetable will reduce costs for both the environment and the shipowner.
- Karin Almlöf