Expert: Ted Barnhill (Principal, Design45 LLC) - 2/23/2010

Question
I am a writer and the ending of the story I'm working on happens inside a high-end northwest contemporary oceanfront home built on a bluff on the Oregon Coast.  I'm wondering what kind of damage a ferocious coastal storm could do to this type of house that would cause the characters to have to leave - ie. fear of mudslide, foundation damage,???  I need them to leave the house, but return to it later.  Since it is a million dollar plus property, I'm wondering what could realistically happen to a well-built house in this type of situation?

Answer
Charlotte,
I love Oregon, having lived there for a few years in my twenties.  The coast is stunning - a great setting for your story.

Mudslides do occur on steep slopes in Oregon, but are most threatening to homes in valleys or gorges, probably not a rocky beachfront bluff.  The two most likely threats I see are direct damage from waves/storm surges, and windblown trees.

Strong storms raise the water level and cause enormous waves, which are bigger than ever in recent years. See http://www.surfrider.org/stateofthebeach/05-sr/state.asp?zone=WC&state=or&cat=be for a brief explanation, including:

"A major increase in maximum ocean wave heights off the Pacific Northwest in recent decades has forced scientists to re-evaluate how high a “100-year event” might be, and the new findings raise special concerns for flooding, coastal erosion and structural damage. The new assessment concludes that the highest waves may be as much as 46 feet, up from estimates of only 33 feet that were made as recently as 1996, and a 40 percent increase. December and January are the months such waves are most likely to occur, although summer waves are also significantly higher."

Homes are routinely constructed to withstand 100-year events, so if those events are worse than ever, it is likely that pier footings and retaining walls could be undercut by high waves, causing partial collapse of homes, especially modern designs with large cantilevers (overhangs) at a cliff edge.

The other likely threat is from large falling trees.  Old douglasfirs reaching hundreds of feet high (and weighing 50,000 lbs or more) are plentiful in Oregon, and it is a natural part of their lifecycle to blow down in storms.  You can imagine the damage caused by a grove or even a single tree coming down in a 100mph storm.

I hope this helps with your story.  Best of luck.

Ted Barnhill
Design 45 LLC