Storm-hit Dawlish: Where could a second rail line run?

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The winter weather has severely damaged the South West's rail network and it is now almost eight weeks since a train from the rest of England reached Newton Abbot, Plymouth or Cornwall.

http://www.bbc.co.uk/news/uk-england-26521168

First there were repairs to the Whiteball tunnel, between Taunton and Tiverton, and then storms in February destroyed the main line at Dawlish in Devon.
The Whiteball tunnel has opened again and the Dawlish line should reopen in early April.
But at the same time as mending the track, Network Rail has been looking at three options for a possible secondary route into the South West.
They all involve going back to old railway maps or reinstating former lines.