Great Diurnal Range (Gt)

Great Diurnal Range (Gt) is the height difference between Mean Higher High Water and Mean Lower Low Water at a station, the standard measure of tidal range in US tidal datum work. It captures the full daily excursion including the diurnal inequality, so in mixed and diurnal regimes Gt exceeds the mean range computed from MHW minus MLW. NOAA tabulates Gt with the other datums from the 19-year epoch. The value sizes tide windows, lock and berth depth limits, and the vertical reach a vessel must allow over a tidal cycle.