Hs is the design significant wave height at the toe of the structure (m)
Δ is the dimensionless relative buoyant density of rock, i.e. (ρr / ρw - 1) = around 1.58 for granite in sea water
ρr and ρw are the densities of rock and (sea)water (-)
Dn50 is the nominal median diameter of armour blocks = (W50/ρr)1/3 (m)
KD is a dimensionless stability coefficient, deduced from laboratory experiments for different kinds of armour blocks and for very small damage (a few blocks removed from the armour layer) (-):
KD = around 3 for natural quarry rock
KD = around 10 for artificial interlocking concrete blocks
θ is the angle of revetment with the horizontal