FBW 2

Update
I recalculated the results of my previous post, but instead of using a fixed value for the depth (SWL), I used as input for the threshold an instantaneous depth, where the modulation was given by the low frequency signal from the gage record. This signal had a low amplitude (O(5 cm)), and the resuls did not differ that much from the ones posted previoulsy. This can be seen in the first plot of today, where the time evolving signal is shown as a dashed line, and the constant threshold as a dotted line.

New Bussiness

After looking carefully to the events that showed a wave height larger than the threshold at offshore gage in Run 25, I noticed that many of them turned into active breakers within 5 m of the gage. This behavior can be seen in the following figure (Run 26 instead)



Note that there is a good visual correlation between the wave heights exceeding the threshold and waves breaking within 5 m down the tank. The exception are the 3 large waves near t=175 s, which didn't break at all.

That seemed to suggest that the breaking criterion was working well to determine the onset of breaking. Hence, I pursued the idea used by David Huntley, in the sense that if I know the offshore wave condition, the bathymetry and the location of the breaking point, the classical depth limited model should allow us to compute the breaker height. All that is needed then is a suitable formulation of gamma.

Hence, I found the location of the onset of breaking for each of the waves I identified using the FBW code. That gave me a specific point in space and time, which could be correlated with the (fixed) bathymetry at that location, and with gamma (from Nairn, 1990), I could get the wave height.

It turned out that since this gamma value is fixed for a given wave condition,
this procedure yields that the wave height profile is a scaled version of the bathymetric profile, as shown in the following figure:



where a poor agreement is observed. According to Ruessink et al, (2003), this should not be surprising because gamma was found to be a function of kh, rather than h alone.