Drainage installations will be built around the fixed link's land installations, to ensure that water quickly drains away and is cleaned as far as possible of contaminants from railways lines or roads. Water falling on the bridge or running into the tunnel will also be drained to the sea or a watercourse.

Where does pollution come from?
Water from roads can contain various substances that are harmful to the water environment. These harmful substances may come, for example, from spillage, exhaust fumes from vehicles, tyre abrasion, asphalt and, not least, from salt and grit used on the roads.

The concentrations depend on traffic intensity and the type and quantity of the spilt substances. The season also plays a part. If frost has persisted continuously for a long time or if it has been a long time since the latest precipitation, concentrations will be higher. Frequent rain or heavy rain will tend to dilute the concentration.

From carriageways to watercourses
Surface water on motorways is normally collected in precipitation drains along the sides of the road. From there, the water is led to rainwater basins where contaminants are allowed to settle. From the settling tanks, the water passes at a controlled speed on to an oil separator, before the decontaminated water enters nearby watercourses. The outlet from the basins can be closed off, if environmentally hazardous substances are spilt during an accident on the motorway.

On low-lying access ramps the road and railway may need to be protected from flooding. This is achieved using drain pipes, ditches and pumps to remove the water.

Combating weeds and icy roads
Heavy plant growth can make track areas unstable and present a risk to train traffic. For the sake of traffic safety, railway tracks should therefore be kept free of vegetation on a regular basis. The vegetation control will be carried out with due respect for the surrounding environment because chemical substances can be harmful to lakes and watercourses. Therefore, only approved chemical substances will be used, and the authorities keep a close eye on which substances are used and how they are used. Plant growth will also be controlled along roads.

In winter, asphalted areas are salted to reduce the effects of icy conditions. Melted, salty water can be diluted in the tanks, but the salt is not removed. Surface treatment against ice can be limited by spraying roads with salt water instead of solid salt and by obtaining accurate weather forecasts so salting is only carried out when necessary.

Water running across a railway or road can cause minor landslides and hence affect the stability of the railway track or road. We are therefore planning how drainage is to be managed around roads and railways.