The ballast supports the tracks and provides drainage
Days after the flood waters hit Cornwall, we're still discovering new areas of destruction.
The Bodmin and Wenford Steam Railway faces a bill of tens of thousands of pounds to repair flood damage to its line.
Hundreds of tonnes of ballast were washed away on Wednesday morning last week.
Part of the track will be closed for up to four months.
Richard Jones looks at the damage caused by the floods
The railway's general manager, Richard Jones, said much of the damage was believed to be a result of water flowing off an overhead road bridge.
The rails themselves and the underlying sleepers were intact, but the other damage was sufficient to halt services.
He said: "The ballast has a valuable role supporting the line and providing drainage.
"It is certainly the most amount of structural damage that the line has experienced in 20 years."
Mr Jones said he was hopeful the complete line would reopen during the first quarter of 2011.
He added that the railway's Santa by Steam special trains in December would still run.
Public transport railway lines have also been affected by the floods last Wednesday, which saw water up to 6ft deep in places across the county.
The Newquay to Par branch line was closed by mudslides on the track near Luxulyan.
It is not expected to reopen until mid-December, Network Rail said.