Hs is significant wave height for that region. In the gulf of mexico, this tends to be around Hmax/1.8 = Hs. Where Hmax is your maximum wave height.
If you actually have wave data, Hs is just the average of the highest third of your waves.
I have never used equation 3.35 and am not really...
In the United States, my understanding is that oil spills are tracked as amounts of spills per volume so it'd be # of spills per barrels.
Does anyone know how Asia tracks their oil spills?
Many Thanks,
Lee Tran