Tennessee Department of Transport: Smartmap
The Tennessee Department of Transport's Smartmap uses Google Maps to show weather-related road conditions, construction/incidents, camera images and message signs for the state.
If you zoom in on Nashville and select the 'Road Condition' option you can view the currently flooded roads and Nashville road closures.
Tennessean.com - Flooding Incidents Map
Nashville newspaper the Tennessean.com has created a Google Map to show incidents of the Nashville flood. The map shows the locations of shelters, missing person reports, fatalities and public transit cancellations.
Staff of the Tennessean.com are working to keep the map up-to-date.
NOAA: Advanced Hydrologic Prediction Service
You can view near real-time data for the Cumberland River in Nashville with the National Weather Service's Advanced Hydrologic Prediction Service. At the time of writing the NOAA shows the river level at nearly 51 feet (the major flood stage is from 45ft) and a flood warning is in place.
The site includes a Google Map showing the location of the gauge reading. If you click on the 'upstream gauge' or 'downstream gauge' links you can navigate to other gauge measurements of the river.