On 12 August 1948, 6.25 inches (160 mm) of rain fell in the area, the total for the week being 10.5 inches (265 mm). Rain falling on the Lammermuir Hills surged into the Eye Water towards Reston, and the channel could not accommodate all of the water. The flood water then backed up the tunnel and flowed to sea in the opposite direction, towards Cockburnspath. The tunnel was flooded to within of the crown of the portal.