Observations on the movement of coarse gravel using implanted motion-sensing radio transmitters

Motion-sensing radio transmitters were implanted in cobbles (72-92 mm diameter) and placed in a stream in southwest Idaho for 43 days during a snowmelt period. The radios transmit different pulse rates depending on whether the rocks are at rest or in motion. Every 30 s, a datalogger samples the receiver and records the pulse rate of the transmitters. Such information can be used to assess numerous properties of particle transport that are beyond the capabilities of conventional tracking methods. Conclusions include: (i) rocks are more likely to move on rising hydrograph limbs than on failing hydrograph limbs; (ii) the average Shields' parameter is 0·046; (iii) rocks move only a fraction of the time between initial and final motion during an event; (iv) the distributions of motion and rest periods are best modeled by gamma functions rather than exponential, but the distributions approach exponential as the tails are trimmed.