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SURVEY TERMINOLOGY EXPLAINED

What does 5.7 ft NAVD88 mean for a seawall?

5.7 ft NAVD88 is an elevation referenced to a survey datum. It does not mean the wall must stand 5.7 feet above your yard, today’s waterline, or the bottom of the canal.

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Published by Miami Beach Seawall

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Elevation is measured from a datum, not from the yardAn illustrative wall cap sits above a yard and changing waterlines. An arrow runs from an illustrative NAVD88 reference to the cap, showing that surveyed elevation differs from visible wall height.Yard level variesSurveyed cap elevationWater level changesNAVD88 referenceElevation from datum
Concept only, not to scale or an engineering design. Scroll sideways on small screens. Reference lines are illustrative. A surveyor must establish the actual elevations and datum for the property.

A shared reference makes elevations comparable

NAVD88 means North American Vertical Datum of 1988. It is a reference for surveyed elevations. A cap elevation and a yard elevation can be compared when the measurements use the appropriate common reference. The visible distance between the yard and cap is a different measurement from the cap’s elevation above that datum.

A changing waterline is not the survey reference

Tides and weather change the water you see. A tape measurement from that surface does not establish the surveyed cap elevation. Likewise, an elevation marked in a different datum cannot be substituted without a qualified professional establishing the appropriate relationship. This guide supplies no generic NAVD88-to-NGVD29 conversion.

Ask for the measurement and its context

  • Which survey or as-built record shows the seawall, and when was it measured?
  • What vertical datum and units are used?
  • Which parts of the cap or wall were measured, and are there gaps in the surveyed scope?
  • What existing and proposed elevations are relevant to design and City review?
  • Does the project need updated measurements or an engineer’s assessment as well as a survey?

Keep the measurement separate from the code trigger

The consolidated code requires at least 5.7 ft NAVD88 for new seawalls and existing walls requiring substantial improvements. It defines substantial seawall improvements at $500 or more per linear foot; that is a regulatory threshold, not a market quote. Narrower existing-wall provisions and limited maintenance exceptions need project-specific review. Not every lower wall is automatically illegal, and there is no universal November 30 retrofit deadline.

A number alone does not establish safety or compliance

A City map can help frame questions, but it does not replace a site-specific survey or engineering evaluation. Neither a compliant-looking height nor an owner measurement establishes structural condition. Keep any City notice with the records so the actual response and work deadlines are considered.

Planning information only, not an inspection, engineering or legal advice, compliance determination, or quote. Confirm project requirements with the City and qualified professionals.

KEEP YOUR PLAN MOVINGPrepare the right questions before requesting proposals