Coastal cliff behaviour: Observations on the relationship between beach levels and recession rates

Beaches dissipate wave energy and regulate the frequency that the cliff foot is subject to wave attack. The relationship between beach levels and cliff recession rates has been established for Pleistocene soft rock cliffs along the North Norfolk and Suffolk coasts, UK. The results suggest that over a decadal timescale, there is a non-linear increase in the average recession rate as the beach profile area above High Water Mark (HWM) decreases. Small changes in beach level can result in significant differences in the recession rates. The impact of a unit change in beach level on the recession rate depends on the initial beach level. On a year-by-year basis, it is possible to divide the beach level and recession relationship into a series of zones with characteristic types of behaviour. At low beach levels there is high to extremely high recession with considerable variability, whereas at high beach levels there is almost zero recession with limited variability. It is concluded that historical recession rates are the product of both the past forcing events and changes in cliff–beach state. Extrapolation of historical rates can be extremely unreliable unless it is supported by an understanding of the dynamic behaviour of the cliff–beach system and the energy inputs over the observation period.