Recognize first that the term ...

Recognize first that the term "floodplain" does not mean much unless you attach a probability to it. So when you are talking about the best use of a floodplain it may be quite different if you are talking about the 50-year floodplain or the 500-year floodplain. The less the probability and hence risk of inundation, the more likely that part of it can be developed. In the U.S. we typically restrict development within the 100-year floodplain. For planning purposes, areas that flood regularly can be used as park land for recreational purposes, particularly day use (picnic areas, hiking or running paths, wildlife observation). Some jurisdictions are a bit more aggressive and cite amphitheaters for outdoor musical listening and so forth. See what the City of Dallas is proposing for the Trinity River corridor (http://www.trinityrivercorridor.com). If a portion of the floodplain is a wetlands, it is best left that way, since wetlands provide valuable functions for water storage, as well as settling basins that help improve water quality and provide habitat for wildlife.