I've done cabins and houses along a river, and was required to have nothing electrical below 7' (100 year flood stage) at this point along the side of the river, service laterals are ok, but no pad mount transformers. Homes were built on piers above the flood plain with blowout walls if any below that point. Propane tanks had to be strapped down also. Nothing in the code on it though that I know of. There was no inspecting authority on these, so it was up to the builder to know and comply with the restrictions. Now they will not let you build within 50' of a waterway, and I think there wanting to change it to 100'.