Source? The link provided by asdf downthread indicates a margin more like six feet, and preparedness for two feet more:

...missing from these reports (and from the original release) was the elevation of the plant itself, which turns out to be -- surprise! -- 1,004 feet. According to NRC Senior Public Affairs Officer Victor Dricks, the river yesterday was at 1,005.7 feet and is expected to crest at 1,006.4 feet. By then, the plant will be standing in more than two feet of water; luckily, the eight-foot-tall Aqua Dams should keep the water at bay. And the river is still well below the worst-imaginable scenario that OPPD is required to prepare for: a flood reaching 1,014 feet above sea level.