Frequently streams in flood overflow their banks and spread over floor plains which may be many kilometres wide. Because of the amount of water, the nature of the terrain and the status of the road, it is sometimes not economically justifiable to pass all the water under the road. Instead, some of the water is allowed to flow over the roadway at depressed sections known as floodways.
The pavement at floodways must be designed to resist scouring and to withstand the expected traffic loading while inundated. Embankment batters must be protected from scouring.
The types of pavements used include:-
• A good quality crushed rock or soil aggregate base sealed with a 2 or 3 coat sprayed bituminous seal. This type of pavement is used for light traffic and infrequent low velocity inundation.
• Cement, bitumen or lime stabilised crushed rock or soil aggregate with a 2 or 3 coat sprayed bituminous seal.
• Asphalt or Portland cement concrete pavements which are suitable for the more heavily trafficked roads.