WASHINGTON – If you live in the town of Occoquan or along the lower Occoquan River in Fairfax and Prince William counties, you will hear a big, whooping siren about 10 a.m. Thursday.
The new siren will be used to warn the town of a catastrophic dam failure at the Occoquan Reservoir, which holds 8.3 billion gallons of drinking water.
Occoquan residents are familiar with storm-related flooding. But Jeanne Bailey, a spokeswoman for Fairfax Water, the dam’s owner, says the sirens would sound only for a major failure of the dam.
“That really, really, unlikely event that the dam should fail with no warning,” says Bailey.
Bailey says the dam, which is more than 60 years old, is in good shape and inspected on a regular basis. It withstood last year’s 5.8-magnitude earthquake without even a crack. But new regulations require the sirens and the test.
“We just want people to be aware of what they sound like, to be aware of what they are,” she says.
The siren was purchased with some federal help, a $25,000 grant in 2010.
Studies show that a catastrophic dam failure would bring water to the town of Occoquan within five to 10 minutes and cover most of its historic district with 10 feet of water within 20 minutes – depending upon pre-existing saturation of the ground, according to Fairfax Water.
Other residential areas downriver also would be flooded.
Residents who live within the impact zone have already received postcards letting them know about the siren tests. You can hear what they sound like here.
This story has been modified in the section describing how much water it would take to flood Occoquan and to reflect that flooding would depend on existing ground saturation.