Environmentalists and residents in flood-ravaged southern Fairfax County communities have begun to raise new concerns over the details of popular but uncertain flood protections.

The neighborhoods of Belle View and New Alexandria were inundated during Hurricane Isabel in 2003 and in March learned that the area meets the federal criteria for $12.7 million worth of protections, including a lengthy flood wall that would run parallel to the George Washington Parkway. The communities were largely pleased with the news.