Twice-daily observations over a fixed range were made covering three consecutive sets of spring tides. Some dune population dimensions (e.g. mean wavelength) show a long-lasting (at least weeks) alteration during the most vigorous springs, but a short-lived (tides or days only) change over the weaker ones. Other properties (e.g. mean height) experience merely short-lived alterations. The changes seem to be linked to the creation during spring tides of new dunes of an initially small size (minor dunes), which introduces new matured dunes into the populations if there is sufficient subsequent sediment transport, and to the limited ability of individual dunes to respond to changing hydraulic conditions during their life-spans. The dunes are active during only a very small proportion of each spring-neap cycle, but the bank is permanently covered by them, and cross-stratification caused by dune movement is the only internal structure. Without a knowledge of the history and dynamics of the dune populations, the quality of the environment at Lifeboat Station Bank cannot be satisfactorily assessed from the sedimentary products.