Too many Kubotas
Veteran Member
In my case I'm not sure a "floor" would do any good.Those old brick arc systems used a flat mortared or poured brick floor, and then a self supporting arc "roof". I wouldn't do it without a "floor"
That ditch has had large amounts of water in it once in 15 years, a result of me screwing up with a smaller irrigation ditch some 200 feet away.
Normally it only deals with rain (small watershed) and snow melt. The latter mostly because I pile a lot of snow in it's "intake area".