CBBT - Chesapeake Bay Bridge Tunnel

Sensor Observation

The red line shows the observed water level over the past 30 days.

Predicted Astronomic (m30) Tide

The blue line shows the Tidewatch Charts prediction for astronomical tide at this sensor location. This incorporates two factors:

1. The expected daily change in water level produced by known gravitational interactions between the Earth, moon, and sun on the amplitude, phase, and frequency of the tides; these can be predicted years in advance.
2. A plus or minus "m30" value, which is a 30-day running mean of the actual water level observed at a tidal station. m30 represents a time-local departure from mean sea level due to seasonal variations in winds and currents, decadal fluctuations in sea level, and the long-term sea-level trend relative to land.

Residual

The green line is the residual difference between the predicted astronomical tide and the observed water level over the past 30 days. Values are positive when observed values exceed predicted values, and negative when observed values fall below predicted values.

MLLW (Tidal Datum)

Observed and predicted water level values are displayed in feet and referenced to the tidal elevation benchmark Mean Lower Low Water (MLLW). This datum represents the water elevations relative to the lower of the two low tides observed daily at this semidiurnal tide monitoring site.