Understanding Water Level Elevation vs Water Depth

The real-time water level data displayed on the Flooding Along Sheltered Shorelines Project page are referenced to the NAVD88 datum (North American Vertical Datum of 1988). This means the values represent water level elevation relative to a fixed reference point, not the actual depth of the water at a given location.

Please note that this differs in both location and datum from tide predictions. NOAA tide forecasts are typically based on MLLW (Mean Lower Low Water) as their reference point and are generated for a specific location. Because NAVD88 and MLLW use different vertical benchmarks, the water levels shown here will not directly match standard tide predictions. Additionally, since the two locations may experience different hydrodynamic forces, the timing of water level changes may also differ.

Since water level impacts vary by location, we encourage users to take time to observe and understand how the plotted values relate to their specific site conditions. By doing so, you can better interpret the data for your needs, whether for navigation, flooding awareness, or ecological observations.