Frequently Asked Questions
What does Flood Levels monitor?
Flood Levels™ is a municipal flood-monitoring system. Emergency managers use it to watch coastal surge and inland flooding across a community from one dashboard — tide stations and land-based flood gauges together.
Are the readings and forecasts accurate?
Flood Levels stations report live water levels from gauges in the field. Forecasts use the same techniques that NOAA uses and are typically more accurate than NOAA predictions at subordinate stations.
Stations are typically located where NOAA does not have harmonic stations or does not provide public forecasts.
Why do observed and predicted values sometimes differ?
Wind, residual surge, and ice can push water away from the predicted tide or river level.
Wind speed and direction can force water higher or lower. Wind-driven higher levels are often called storm surge and can cause flooding.
If a bay freezes in winter, ice can hold observed levels consistently below the prediction.
How far from a station are readings valid?
Water levels are local. A reading at one gauge does not describe a whole town.
A narrow inlet can produce very different levels inside a bay than on the ocean side. Nearby basins can differ because of inlet size, depth, and shape. Along a long, narrow waterway, levels also change from one end to the other.
What datums can I display?
Stations can show water levels relative to ground, MLLW, or NAVD88.
MLLW (Mean Lower Low Water) is the long-term average of the daily lowest tide. It is the zero level by definition for that datum. Other common tidal datums include MLW, MHHW, MHW, and MSL.
For NOAA tidal-datum definitions, see NOAA datum options.
What do the color-coded flood stages mean?
Stations on the map use color-coded flood stages so responders can see which areas are approaching or exceeding action levels. Open a station for the current reading, the chart, and any configured alert thresholds.
How do I view a station's water-level chart?
- Open the station from the map or station list
- Click the Flood Chart tab (tide stations label this Tide Chart)
How do I subscribe to flood alerts?
- Open the station page
- Click the Alerts tab
- Follow the prompts to subscribe to public alerts or to manage thresholds if your account allows it