Free-of-Obstruction Requirements for Buildings Located in Coastal High Hazard Areas in accordance with the National Flood Insurance Program [open pdf - 9MB]
"Protecting buildings that are constructed in special flood hazard areas (SFHAs) from dam¬age caused by flood forces is an important objective of the National Flood Insurance Program (NFIP). [...]. Coastal waves and flooding can exert strong hydrodynamic forces on any building element that is exposed to the waves or flow of water. Therefore, foundations that offer minimal resistance to waves and floodwaters passing beneath elevated buildings (e.g., pile and column foundations) are required in Coastal High Hazard Areas (Zones V, VE, and V1 -V30). Standard foundations such as solid masonry or concrete or wood-frame walls will generally obstruct flow and be at risk of damage from high-velocity flood forces. In addition, these sol¬id foundations and other obstructions may cause wave runup or reflection, or divert floodwaters, into the elevated portion of the building or into adjacent buildings. Use of structural fill to support buildings in V zones is prohibited because fill will be subject to erosion during a flood event. In either case, the result is generally structural damage to, or catastrophic failure of, the affected buildings [...]. This Technical Bulletin provides specific guidance concerning the NFIP's free-of-obstruction requirement in V zones, as well as the general requirement for construction that will minimize flood damage potential, as it applies to V zone construction."
Technical Bulletin 5
Federal Emergency Management Agency: http://www.fema.gov/