Water depth is the single most operationally consequential physical variable in a marina. It determines which vessels can use which slips, whether a passage is navigable at low tide, when a dredge project becomes urgent, and how your marina's capacity changes across a tidal cycle. Yet most marinas manage depth information through informal knowledge — the dock master knows which areas are shallow, experienced tenants know to wait for the tide — rather than systematic, mapped depth data.
A GIS-based tidal and depth map changes depth from tribal knowledge into documented, searchable, shareable operational data.
Types of Depth Data for Marinas
Bathymetric Survey Data
A bathymetric survey measures water depth at systematic intervals across the marina basin. A professional hydrographic survey company will produce either:
- A point cloud (CSV with latitude, longitude, and depth readings for thousands of points)
- A gridded raster (GeoTIFF where each pixel represents the average depth in a small cell)
- Contour lines (depth contours at regular intervals, like topographic contours on land)
Depths are referenced to a tidal datum — typically Mean Low Water (MLW) in the United States, which represents the average lowest tide level. All navigable depth information should be expressed relative to this datum.
Tidal Correction
A raw echo sounder depth reading during a survey is the actual depth at the moment of measurement. To convert this to a MLW depth (which is what you want for operational planning), you subtract the height of tide at the time of the survey. This tidal correction process requires a simultaneous tide gauge reading during the survey.
Your survey contractor will typically handle this correction and deliver tidal-corrected depths in the final dataset.
NOAA/Hydrographic Office Charts
Existing nautical charts for your area contain official soundings referenced to chart datum. These provide a starting-point depth picture but are often outdated in areas with active shoaling. Import NOAA chart data (available as raster tiles or vector soundings) into Atlas as a reference layer.
Importing Depth Data into Atlas
Point Cloud CSV Import
If your bathymetric survey was delivered as a CSV file with columns for latitude, longitude, and depth:
- Open Atlas and create a new project or open your marina project
- Click Import Layer and select your CSV file
- Map the latitude, longitude, and depth columns to their correct fields
- The data imports as a point layer — one point per depth reading
With thousands of points imported, apply a color ramp based on the depth attribute: dark blue for deepest depths, transitioning to light blue, yellow, and red for critically shallow areas. This immediately visualizes your depth distribution across the marina.
Raster GeoTIFF Import
If your survey was delivered as a GeoTIFF raster:
- Import the file as a raster layer in Atlas
- Apply a depth color ramp to the raster — Atlas supports custom color classification by value range
- The raster displays as a continuous color gradient showing depth variation
Contour Line Import
Depth contour lines (in GeoJSON, shapefile, or KML format) import as a line layer. Apply labels to show the depth value of each contour — typically displayed as negative values (−6.0 ft) or as positive values with a depth label.
Building Tidal Stage Overlays
The depth at any point in the marina changes constantly with the tide. A static depth map shows MLW conditions — the lowest expected depth. But operational planning often needs to know depth at different tidal stages.
Tidal Range Data
Find the mean tidal range for your marina location from NOAA tide tables or equivalent national data. The tidal range — the average difference between mean high water and mean low water — tells you how much depth you have to work with across the tidal cycle.
For example, if a marina has a 4-foot mean tidal range:
- At MLW: depths as surveyed
- At mean tide (mid): MLW depth + 2 feet
- At MHW: MLW depth + 4 feet
Creating Navigable Depth Layers by Tide Stage
In Atlas, create a set of analysis polygons showing navigable areas at different tide stages:
- For each tide stage (MLW, MTL, MHW), calculate the minimum navigable depth
- Draw polygons covering all areas with sufficient depth for vessels of specific drafts
- Style each polygon set with a different color
This produces a set of layers you can toggle: "show me which basin areas a 6-foot draft vessel can navigate at mean low water" — a critical operational question that your depth map can answer visually.
Applying Depth Data to Slip Management
With depth data in Atlas, you can cross-reference against your slip polygon layer:
Minimum Depth per Slip
For each slip polygon, use the depth raster to identify the minimum depth within that slip boundary. Store this as an attribute: "Min Depth MLW = 5.8 ft."
This attribute feeds directly into your slip assignment process — when a 6.5-foot draft vessel requests a slip, you filter your slip inventory by minimum depth greater than 6.5 feet plus a safety margin (typically 1 foot) and see only slips with MLW depth greater than 7.5 feet.
Identifying Slips Requiring Dredging
Filter slips by minimum depth and compare against the vessel draft of the current occupant plus a 1-foot safety margin. Slips where depth has shoaled below the required margin for their occupant are flagged as dredging priorities.
Guest Vessel Pre-Arrival Screening
When a transient vessel requests a berth and provides their draft, you can check the depth map to confirm that the assigned slip and the approach route have sufficient clearance at the expected arrival tide stage. This prevents the embarrassing situation of a vessel running aground in your marina.
Communicating Depth Information to Guests and Tenants
Approach Channel Depth on Your Website
Publish the controlling depth for your approach channel — the minimum depth along the navigable path from open water to your marina — on your website and in your reservation confirmations. Include the tidal datum reference: "Approach channel controlling depth: 6.2 feet MLW. Add tidal correction for your arrival time."
Deep-draft vessel operators planning passages depend on this information. Marinas that publish it clearly attract more transient traffic from the vessels that can use them.
Interactive Depth Map for Guests
Create a guest-facing Atlas embed showing your marina's depth distribution overlaid on the slip layout. Guests can zoom into their assigned slip area and see the depth contours. This builds confidence and reduces pre-arrival anxiety for visiting boaters.
Live Tide Stage Reference
Add a link to the nearest NOAA tide gauge (or equivalent) in the marina guest map — guests can see current tide stage and calculate actual depth at their slip based on the MLW chart depth you've provided.
Updating the Depth Map
Depth maps become less accurate over time as sediment accumulates in a tidal marina. Plan to resurvey:
- Every 5–10 years in low-shoaling environments
- Every 2–5 years in active silting environments
- After any major storm event that may have shifted sediment significantly
- Before any dredging permitting process
When new survey data arrives, import it into Atlas as a new layer with the survey date as a layer attribute. Retain the previous survey data in an archive layer — the comparison between the two surveys is valuable data for sediment accumulation rate calculations and future dredging project planning.
