Ryrie Vorticity Balances

These are the vorticity balances from the Ryrie simulation.
They are taken at the start of the wave group breaking over the bar, in the middle of the wave group breaking, and then a few minutes after the wave forcing ceased. The balance begins with local acceleration vs. wave forcing. Then the effect of bottom friction becomes more relevant (only at the shoreline though?). The velocity may just be too small over the bar for the bottom friction to be entirely relevant. Finally we are balanced by the two acceleration terms (local and advective) as the entire RHS of the vorticity equation is zero. But what makes them die away eventually?