Hudson's equation

Hudson's Equation, also known as Hudson's Formula, is an equation used by coastal engineers to calculate the minimum size of riprap (rock armour) required to provide satisfactory stability characteristics for rubble structures under attack from storm wave conditions.

The equation was developed by the United States Army Corps of Engineers, Waterways Experiment Station (WES), following extensive investigations by Hudson (1953, 1959, 1961a, 1961b).^{[citation needed]}

Equation

The equation itself is:

$W =\frac{\ w_r H^3}{K_D(S_r-1)^3\cot\theta}$

where:

• W is the design weight of the riprap armour
• w_r is the unit weight of the armour
• H is the design wave height
• K_D is a dimensionless stability coefficient, calculated for different kinds of armour by laboratory experiment
• S_r is the specific gravity of the armour, relative to the water at the structure i.e. S_r = (w_r / w_w)
• θ is the angle of revetment with the horizontal

See also

• Breakwater (structure)
• Coastal erosion
• Coastal management
• Riprap

References

• US Army Corps of Engineers (1984). "Shore Protection Manual." Vol. II.