Mean High Water

Mean High Water (MHW) is the average of all the high water heights observed over a period of several years. For example, in the United States this period spans 19 years and is referred to as the National Tidal Datum Epoch. Mean High Water (MHW) is the average of all the high water heights observed over a period of several years. For example, in the United States this period spans 19 years and is referred to as the National Tidal Datum Epoch.