River Current Measurement Using Coherent Microwave Radar: Toward Gaging Unstable Streams

For several years, the Applied Physics Laboratory of the University of Washington has been working with the US Geological Survey to monitor surface currents in various rivers in western Washington State using coherent, continuous-wave (CW) and pulsed microwave systems. The results have demonstrated the feasibility of monitoring horizontal profiles of surface current velocity for use in making non-contact river discharge measurements. Using an X-band pulsed Doppler radar, called RiverRad, from the river bank, we have demonstrated that discharge can be determined from surface velocity measurements on streams with unchanging beds. These measurements were made with the radar antennas directed nearly perpendicular to the flow. The results compare well with standard USGS discharge measurements and with those made by other more conventional instruments. In addition, two arrays of K-band CW microwave sensors, called Riverscat, have been mounted on bridges over the Cowlitz and Nooksack Rivers in a configuration where the antennas are directed along the flow. Intermittent data have now been collected at these sites for several years. The results of these measurements show that the surface velocity of rivers is a function of the depth of the river both at the site and at downstream controls. We indicate here how time series of surface velocity and stage may be used to infer depths of unstable rivers.