TidalBoundaryClassification In England and Wales this is the mean level of all the high tides, in Scotland this is the mean level of the spring high tides. In places where there is no Foreshore (eg. vertical cliffs), the TidalBoundary is classified as High Water Mark. High Water Mark In England and Wales this is the mean level of all the low tides, in Scotland this is the mean level of the spring low tides. When there is Foreshore, this defines the lower limit of Foreshore. Low Water Mark