Offshore water depth and tsunami 1

[buoy]

Can anyone point me to general guidelines on how far offshore you'd have to go for the following to be comparable or less than conditions in a 100-year storm:
(1) Change in water depth due to tsunami
(2) Currents associated with surging / retreating crest
I have found recommendations that boats move offshore to waters deeper than 100m and even 400m, but no technical guidelines.

 

[MikeHalloran]

Just head away from shore, and only turn around when you hear news reports that the tsunami has arrived. If you're far enough offshore, you won't even notice it go under the boat.



Mike Halloran
Pembroke Pines, FL, USA

 

[beej67]

Tsunami height varies according to dozens of factors, so it's very difficult to guess at. Further out you are, the lower the delta. Wave height varies by shore line shape, by approach depth profile, by earthquake intensity, by the way in which the earthquake adjusted the ocean floor profile, etc. It just depends.

Same can be said for storm surge. Surge varies by how low the central pressure of the hurricane is, by whether you're on the leading or trailing side, by the speed with which the storm tracks over land, and also by some of the same geometry factors above, like shore line shape and approach depth profile. The big one for hurricanes is the delta between the central pressure of the storm and the surrounding air, which tends to squeeze surrounding water towards the center of the hurricane.

"100 year storm" is a terrible thing to try and compare to, because the 100 year storm is a measure of rainfall depth over an arbitrarily chosen duration, which is only loosely correlated with the surge. But even if it wasn't, I seriously doubt you find the data to answer your question anywhere, unless it's neck deep in someone's phd thesis.

Go watch some youtube videos. There was a fantastic one of the Indonesian tsunami that I saw a while back taken from a guy on his sailboat, anchored up in a cove. He and his buddies in the anchorage all came above decks to check out what was going on as they swung at anchor, and I remember him filming his anchor rode. Looked to be about a four or five knot current going under his boat. Then he panned the camera shoreward and caught the wave as it hit the village. I can't seem to find it now, but if I do later I'll post a link.

Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East -

http://www.campbellcivil.com

 

[IRstuff]

Since waveheight is a function of slope of the terrain, there cannot be a hard and fast rule of thumb.

Personally, I would be more comfortable with distances on the order of miles rather than hundreds of meters.

TTFN

FAQ731-376
Chinese prisoner wins Nobel Peace Prize

 

[buoy]

Thanks to all. Sounds like a regional tsunami height model is the way to go.

 

[IRstuff]

If you've followed all the tsunami videos from Japan, you can see where some places had intrusions on the order of miles, and others places where the intrusion was tens of miles, due to localized terrain constrictions forcing the water to flow along natural terrain features and riverbeds.

TTFN

FAQ731-376
Chinese prisoner wins Nobel Peace Prize