Often when a plunging breaker impacts on a wall, an air pocket is trapped a
t the wall. This paper extends a pressure-impulse model for wave impact on
a wall to include a simple model of a trapped air pocket. The inclusion of
an air pocket leads to a higher impulse at impact for a given wave as there
is some rebound of the water. The model is shown to compare satisfactorily
with small-scale experimental data performed on a caisson breakwater with
an impermeable berm. The effect of a porous berm on pressure impulse is inv
estigated theoretically in a companion paper.