In the InVEST sample data after the first 16x5 data packets (REI_VX, REI_PCTX, WavP_X, WavPPCTX, V10PCT_X), there are still the following 11 columns.
Only the variables described in the User Guide are required for the model to run. Those other 11 columns are not used by the model.
What physical considerations does WWIII use to calculate the wave power (and related WavP_X)?
I’m not completely certain. I think the WWIII model is based on observed wind and wave measurements at buoys. The wave power that the invest model calculates at each shore point is defined by equation 20 in the User Guide. Coastal Vulnerability Model — InVEST documentation