I saw a great idea for dealing with straw bale construction for outbuildings in flood prone areas last time I was in California. It was a strawbale noise reduction wall near a main highway. Since flooding was a problem They just starting using the strawbales after laying a foundation made of gabions (see http://en.wikipedia.org/wiki/Gabion). This way flood water could just flow right under the wall leaving the strawbales high and dry. I saw this technique used at the Solar Living Center in Hopland.