"Mean higher high tide" is the daily highest water level averaged over a complete tidal cycle of 18.6 years.
(Mean higher high tide; is; the daily highest water level averaged over a complete tidal cycle of 18.6 years) (the daily highest water level; averaged; over a complete tidal cycle of 18.6 years)
Mean higher high tide the daily highest water level
is averaged
the daily highest water level averaged over a complete tidal cycle of 18.6 years
over a complete tidal cycle of 18.6 years