Long-term UHF RiverSonde river velocity observations at Castle Rock, Washington and Threemile Slough, California

Long-term, non-contact river velocity measurements have been made using a UHF RiverSonde system for several months at each of two locations having quite different flow characteristics. Observations were made on the Cowlitz River at Castle Rock, Washington from October 2003 to June 2004, where the unidirectional flow of the river ranged from about 1.0 to 3.5 m/s. The radar velocity was highly correlated with the stage height which was continually measured by the U. S. Geological Survey. The profile of the along-channel velocity across the water channel also compared favorably with in-situ measurements performed by the Survey. The RiverSonde was moved to Threemile Slough, in central California, in September 2004 and has been operating there for several months. At Threemile Slough, which connects the Sacramento and San Joaquin Rivers, the flow is dominated by tidal effects and reverses direction four times per day, with a maximum speed of about 0.8 m/s in each direction. Water level and water velocity are continually measured by the Survey at the Threemile Slough site, with velocity recorded every 15 minutes from measurements made by an ultrasonic velocity meter (UVM). Over a period of several months, the radar and UVM velocity measurements have been highly correlated, with a coefficient of determination R² of 0.976.