Floods have caused a wall to collapse on the West Coast Mainline at Caldew Maltings, near Carlisle.
A pylon carrying overhead cables has also become unstable.
All rail services north of Carlisle are currently suspended because of flooding.
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The "terrified" victim was forced to hand over her bag and phone, as the men held a knife to her face.
Anthony Davidson had the blade of a Stanley knife in his pocket, when he was arrested in grounds of the nursery and infant school.
The news could have major implications for the Moorside development in Cumbria.