I was looking for the NOAA "water rise" map which shows the extent of the predicted storm surge, but found this in the process. It's a map of Harris county's live rain gauges and stream level sensors:
http://www.hcoem.org/HCRainfall.aspx
If you hover your mouse over a particular measurement, you'll get a new window where you can check the stream/bayou level.
While this isn't a real-time "surge" measurement, it will be interesting to watch in the hours ahead. A lot of water is getting pushed up towards Houston, to say the least.