The erosion of a nourished beach may be conveniently described as the sum of the linear coastal retreat and a surcharge which decreases exponentially in time. Application of this model to data from eight nourishment projects in north-western Europe has shown on average only 52% of nourished volume becomes a permanent part of the coastal volume. Allowing for an initial loss of some 10%, the results obtained indicate that in practice computed nourishment volumes should be multiplied with a factor of about 2.2, somewhat higher than in previous recommendations.