GS01 - Chickahominy River

Sensor Observation (dashed line = forecast)

The solid red line shows the observed water level (observed water level data from the Virginia Institute of Marine Science). The solid red line shows the water levels observed by the sensor over the past 24 hours; the dashed red line shows the Tidewatch Charts water level forecast for the next 36 hours.

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 (dashed line = forecast)

The green line is the residual difference between the predicted astronomical tide and the observed water level. Values are positive when observed values exceed predicted values, and negative when observed values fall below predicted values. The solid green line shows the residual observed over the past 24 hours; the dashed green line shows our forecast for the residual over the next 36 hours.

NAVD (Geodetic Datum)

Observed and predicted water-level values are displayed in feet and referenced to the elevation benchmark North American Vertical Datum of 1988 (NAVD88). This is the datum in which house and roadway elevations are typically referenced.