Reston and Fairfax County floodplain study shows developers are understating flood risks

The flooding along the Potomac River in Reston and Fairfax County occurred not because of the weather, but because of development on steep hilltops and low areas. Both the Federal Emergency Management Agency and the Environmental Protection Agency have warned the public for years that there are too many homes on the plains and too little developed land, especially at the edge of low-lying floodplains. Yet planners in Fairfax County and the Washington metropolitan area continue to pour new development into those places with the mistaken belief that more land means less risk.

Not true, in Fairfax, at least. The map below shows how many homes are in floodplains in Fairfax County. You can see that there are considerable parcels of land in excess of the flooding threshold.

That data, combined with other data, have led the county to conclude that much of the development along the Potomac River is not justified, particularly as the area thins out as a result of redevelopment. That is good news. The type of development and pattern of development should be re-examined to see if it can be upgraded. As the map on the left shows, some of the current and projected development in floodplains includes not just homes but commercial developments in and around town centers. Meanwhile, the town center at Reston is being developed on a significant farm above the flood level. This disturbing pattern points to a strong need for a clear demarcation between development that is truly in floodplains and that is not, to delineation lines for the highest and lowest flood levels along any given property, to better coordination between FEMA and the Metro system on potential flood elevations, and a clear set of actions if the map does not show well under the new criteria.

As Metro continues to study and work to identify areas where station height areas could be lowered to protect users in high-flooded areas, this type of information is extremely valuable. In addition, obtaining that information on developments in floodplains is critical for the planning process and could potentially produce better flood protection for those who need it.

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