March 25th, 2011 – Can we predict a tsunami wave height? – Are the models valid?

From: Sheron, Brian
Sent: Friday, March 25, 2011 5:57 PM
To: Kammerer, Annie
Cc: Case, Michael; Richards, Stuart; Hogan, Rosemary; Uhle, Jennifer
Subject: RE: Question

I think what you told me is that we can calculate the open ocean wave height very well. It is when it runs up on the shore, you need to know the near shore topography in detail in order to accurately calculate the runup wave height? If we know the near shore topography, are the models valid?

From: Kammerer, Annie
Sent: Friday, March 25, 2011 5:33 PM
To: Sheron, Brian
Cc: Case, Michael; Richards, Stuart; Hogan, Rosemary; Uhle, Jennifer
Subject: RE: Question

Hi Brian,

Sorry for the delay in getting back to you.

First let me clarify. NOAA’s real time prediction of a tsunami wave have nothing to do with TEPCO’s design basis tsunami. In terns of the real time wave, NOAA hasn’t under predicted anything (8m offshore and 14m runup onshore are consistent quantities).

The best estimate of the wave at daiichi from NOAA was a 8 meters offshore (at the 5 meter bathymetric line-where the water at mean tide is 15 meters deep). This is a calculation performed using what is widely believed to be the best available global model for tsunami. So, that wasn’t either a educated guess or professional judgment, it was a calculation using a well validated modeling tool. However, the numbers do have uncertainly based on the fact that the model does not have the preferired very high resolution bathymetric information in the very near shore area (that’s why NOAA’s calculations can push only to the 5meter bathy line). The NOAA model results were also informed by (and checked against) the recordings on the closest DART buoys, these are actual measurements of wave height and the pressure front in the open ocean.

A tsunami has two phases of response. In the open ocean if is very well behaved and calculations are highly accurate. As it gets close to shore and the shoaling effect begins, the behavior starts to go non-linear and very high resolution bathymetric (an topographic) information is required for a very precise prediction of runup (onto land) at any particular point on the coastline. However, it is well understood that as a tsunami wave comes onshore it grows in size significantly.
Therefore, NOAA’s calculation of 8 meters offshore and TEPCO’s (most recently) announcement of 14 meters onshore are consistent.

My previous comment (before this event) was actually that NOAA’s tsunami warning system models (NOAA, not the USGS) have been extremely well validated over time (with hundreds of real tsunami), and that continues to be the case.

But, again, that is up to water depth where they have the necessary resolution of bathymetric data (and where the nonlinear response begins in earnest). As a result of this fact, there is an effort currently to collect very high resolution data for the entire US pacific coast and to implement it into the NOAA database (currently the resolution of US data is not uniform). This will make US Pacific coast onshore runup predictions highly accurate. As part of the recent UW/NOAA
contract, NOAA will give us a tool (ComMIT) that will provide NRC staff with very accurate run-up predictions in the areas around SONGS and Diablo during future tsunami warnings (it will allow us to do independent PTHA at SONGS and Diablo). We had recently pushed that technology transfer back to slow the burn rate on the UW/NOAA contract (due to budget cuts) but we may find that we need to find the money sooner rather than later so that we can run some analyses.

As noted, TEPCO has recently said the tsunami had a 14meters runup (onshore). However this is the 3 rd time they have provided numbers. I didn’t believe (and didn’t post) their initial 2 postings because they were lower than NOAA’s offshore measurements and calculations (which is inconsistent with basic physics). Also, we knew that it had to at least exceed -the elation of the equipment that was impacted. TEPCO is most likely (in my opinion) getting the measurements from watermarks on the buildings, or something similar. It’s hard for me to believe that their tide gauges survived the tsunami, but one of NOAA’s top experts in tide gauges and offshore measurements is my brother Carl (who, ironically was named after the Carl Kammerer who used to work at the NRC, who was my father’s cousin). I can ask him about the chance of survival of equipment at the site. There are a lot of uncertainties with this, obviously, but 14 meters onshore is believable.

With regard to TEPCO’s design basis tsunami, I have long gone on record as saying that the Japanese should be using PTHA, which would have predicted this water level, instead of the deterministic method that they use. Many of the tsunami specialists in Japan agree, and JNES had come around to that way of thinking due to their new concept of “residual risk”. I think everyone was eagerly awaiting the new JSCE codes that detailed.the PTHA technique to be used in Japan. Also, FYI, developing guidance on PTHA was identified as the #1 priority for the tsunami working group of the IAEA ISSC and NRC, JNES, and NOAA were going to jointly lead the work. We were supposed to have a kick of conference call to start the work the week after the earthquake hit. As we all know, fate intervened.

I hope this answers your questions.
Cheers,
Annie

From: Sheron, Brian
Sent: Thursday, March 24, 2011 8:27 AM
To: Kammerer, Annie
Cc: Case, Michael; Richards, Stuart; Hogan, Rosemary; Uhle, Jennifer
Subject: Question

I am seeing a spectrum of tsunami wave heights that reportedly hit the Fukushima plant. I saw in one of your briefing packages that was a USGS calculation that showed the peak wave height at about 30 feet. I saw some slides from TEPCO yesterday that said the tsunami wave height at the plant was “more than 10 meters”. In
today’s “Nucleonics Week” on page 11 it says “Tepco discovered by checking the walls of Fukushima 1 …. and the nearby Fukushima 2 ….. March 21 that the tsunamis had reached higher than 14 meters (about 46 feet) above sea level….” It then said the design basis for Fukushima 1 &2 was 5.7 and 5.2 meters respectively.

Without any accurate measurements, are we limited to educated guesses and expert judgment?

I think one question we will be asked is how well can we predict a tsunami wave height? I seem to recall you said the USGS calculations (wave height versus time at various locations) were probably pretty good because they had a well validated model. However, it would now appear they significantly under-predicted the wave
height.

Am I missing something?

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