What is the datum for vertical clearances?

The datum for vertical clearances is Mean High Water (MHW). This reference point is used in maritime contexts to determine the vertical clearance for structures such as bridges and piers over navigable waters. MHW represents the average of all the high water heights observed over a significant period of time, typically 19 years, which allows for a consistent benchmark that reflects customary conditions for marine navigation.

Using MHW as the datum for vertical clearances is particularly important because it helps ensure that vessels can safely navigate under structures without running aground due to low water levels. This consideration is critical for maritime safety and is often mandated in engineering and regulatory practices. Understanding this concept allows professionals in planning and scheduling to design infrastructure that accommodates the needs of navigation while considering historical data trends and climate impacts.