The fence on the coastline was actually built by the production design department to a length of 30 meters. Most of close ups and middle length shots were shot in front of this real fence, while in wide shots it was extended digitally. Every six hours the fence had to be dismounted because of the incoming flood.
In reality between shown coastline and village center, there was a distance of more than 600 kilometers. The movie-makers tried to bound together these locations with a handful of CGI-Compositings, that show both places in the same image - but had to rely on the imagination of the audience while cutting the rest of the transitions hard together.
During production there was shot a lot more of military footage, but was deleted in editing to focus the story on the protagonists.