What do official depth numbers mean?
NOAA's Coast Pilot explains that depth is measured from chart datum to the bottom, and that NOAA charts in tidal waters use mean lower low water as chart datum. It distinguishes the controlling depth, the least known depth of a channel from hydrographic surveys, from the project depth, the planned dredging depth, which may not reflect surveyed conditions. Channels shoal, especially along their edges. The Army Corps of Engineers posts its latest hydrographic surveys at navigation.usace.army.mil/Survey/Hydro/.
Figures for side waterways can be old. The October 2026 Coast Pilot still reports a 1983 controlling depth of 12 feet for Seminole River in Fort Lauderdale, and it notes that depths alongside wharves are usually reported by owners and not verified by government surveys.[1][2]
How do you check depth for a specific property?
Plan the check during your inspection period so you can act on the results.
- Hire a licensed surveyor or marine contractor to measure depths at the dock face, along the canal and at the canal mouth, referenced to a stated datum such as mean low water.
- Ask for the date and tide stage of the measurements.
- Compare the low-water depth with your boat's draft plus a margin.
- Look at the whole route: a deep slip does not help if the canal entrance has shoaled.
- Ask the city or county whether the canal is publicly maintained and whether dredging is planned.
- Request prior dock or seawall permit drawings; Broward County's general license for work in tidal canals requires mean high water, mean low water and bottom elevations, so earlier plans may contain depth data.[3]
Can a shallow canal be dredged?
Dredging requires approvals. Under Broward County's April 2025 technical bulletin, the streamlined Environmental Resource General License covers only one-time dredging of 20 cubic yards or less of sediment from isolated lakes or ponds and residential canals with no seagrasses; larger projects need a regular Environmental Resource License. Federal rules also require Department of the Army permits under Section 10 for work in or affecting navigable waters. Ask the agencies or a licensed marine contractor before counting on dredging.[3][4]
Key takeaways
- NOAA chart depths use mean lower low water, and a channel's project depth is not a guarantee of actual depth.
- The federal project depth of the Intracoastal from Fort Pierce to Miami is 10 feet, but side canals are a separate question.
- A recent, datum-referenced depth survey of the dock, canal and canal mouth is a dependable way to verify depth.
- Dredging a canal requires county, state and federal approvals, so do not assume it can be fixed quickly.
Sources
- [1]NOAA Office of Coast Survey — U.S. Coast Pilot 4, Chapter 1: General Information
- [2]NOAA Office of Coast Survey — U.S. Coast Pilot 4, Chapter 12: Intracoastal Waterway
- [3]Broward County Resilient Environment Department — Technical Bulletin: Docks, Seawalls and Bulkheads (Environmental Resource General License)
- [4]eCFR — 33 CFR Part 322, Permits for structures or work in navigable waters
Reviewed October 11, 2026. General real-estate information for Florida, not legal, tax, lending or insurance advice. Laws, rates and deadlines change — confirm property-specific facts with the agency cited, a Florida real-estate attorney, CPA or licensed insurance agent.