Hi,
I have followed this discussion with some interest, and I am surprised at the answer as well. German runways in Denmark had a distinctive slope from the centerline to both sides (crown ?) and there was a gutter along the entire length of the runway. This was connected to a very effective drainage system, at Aalb-West even augmented with pumps (which incidentally are still hard at work). But I can offer no alternate explanation to wooden planks on top of a concrete runway.
I for one would also welcome a book on German airfields in Norway, but if I remember correctly concrete is not one of your favorite topics Kjetil
.
bregds
SES