Criteria for the transition from a breaking bore to an undular bore

Field data on undular and breaking bores observed in a coastal zone and river estuaries were collected. The existing criteria of distinction of these two regimes of bores, which depend on the ratio between the bore height and unperturbed water depth, are applied to the collected data. It is shown that criterion H/h > 1.5 (where H is bore height measured from the bottom and h is unperturbed depth of reservoir) is sufficient for the rough separation of the bores by their type.