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Charted Bridge Clearances
Vertical bridge clearances on charts are referenced to Mean High Water in tidal areas. Therefore if the existing height of tide is below MHW, there will be greater clearance. If the existing height of tide is greater than MHW, there will be less clearance. The USCG provides bridge clearance information to NOAA.
This is a graphic of a bridge and different heights of water level.Nautical chart showing a bridge with a horizontal clearance of 104 feet and vertical clearance of 49 feet.
 
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