It is now widely accepted that a properly managed beach can provide an effective form of sea defence that is in many respects superior to traditional hard engineering solutions. Developing these schemes is not straightforward and requires a detailed analysis of the various interacting processes that affect beach morphology. This inevitably involves the use of mathematical models to simulate coastal processes, and predict the response of beach several years into the future. It is only by using such approaches can conclusions be drawn as to whether a technique such as beach renourishment represents a suitable coastal defence option at a given site. With this widespread reliance on mathematical modelling techniques for coastal engineering it is important that we understand how effective they are. Forecasting of other complex processes in the fields of meteorology and economics are notoriously inaccurate in all but the short term. Accordingly this paper considers the modelling techniques that were used to design a beach management scheme for Seaford on the south coast of England in 1985.