Surrogate Monitoring of Sediment Transport using Hydrophones along the San Joaquin River and Tributaries
Traditional methods for measuring coarse bedload sediment transport by discrete physical sampling tend to be labor intensive and expensive (Gray and others, 2010). As such, bedload samples often are collected too infrequently to capture the temporal variability inherent in transport rates, which can vary significantly, sometimes by a factor of ten or more, over time periods of several minutes to hours for a given discharge (Gomez and others, 1989).
Physical bedload sampling, as well as bedload transport formulae, have much larger uncertainty at low bedload transport rates (Gomez and others, 1989, Batalla 1997). For river restoration programs, such as the San Joaquin River Restoration Program, accurate estimates of bedload transport, often at low transport rates, are necessary but the limitations of physical sampling and bedload formulae make it difficult to obtain accurate estimates.
Surrogate measurement techniques, which use indirect methods for estimating bedload sediment transport, have demonstrated an ability to augment discrete physical sampling programs and have value as independent measures of bedload mobilization (Gray and others, 2010). The use of hydrophones to detect the sound generated by cobble- and gravel-sized particles moving along the riverbed (for example, Barton and others, 2010, Marineau and others, 2012) is one such type of surrogate technology. Hydrophones are relatively inexpensive, can operate nearly continuously, and may be deployed remotely (Gray and others, 2010). Hydrophones may be used to quantify bedload transport rates at high temporal resolution (e.g. seconds to hours) with calibration using physical bedload samples (for example, Barton and others, 2008) or they may be used as stand-alone measurements to detect the threshold of mobilization and cessation of coarse bed material movement.
The objective of this study is to evaluate the use of hydrophone stations for estimating coarse bedload sediment transport dynamics at high temporal resolutions (e.g. hourly or finer) on the mainstem San Joaquin River downstream of Friant Dam for water years 2015-17. Three separate types of installations will be evaluated: four stereo hydrophone installations and one 'Quadraphone' (double stereo) installation co-located at existing bedload sampling locations for measuring coarse bedload transport rates, and five stereo hydrophone installations located at riffle sites for estimating thresholds of coarse bedload mobilization and cessation. Each type of hydrophone installation will be evaluated for its accuracy in estimating coarse bedload transport rates and bed mobilization using data collected by other studies funded by the SJRRP. In particular, the hydrophone data will be evaluated for the ability to 'tune' the hydrophone response to the relative low rates and low bedload grain sizes present on the San Joaquin River.
Traditional methods for measuring coarse bedload sediment transport by discrete physical sampling tend to be labor intensive and expensive (Gray and others, 2010). As such, bedload samples often are collected too infrequently to capture the temporal variability inherent in transport rates, which can vary significantly, sometimes by a factor of ten or more, over time periods of several minutes to hours for a given discharge (Gomez and others, 1989).
Physical bedload sampling, as well as bedload transport formulae, have much larger uncertainty at low bedload transport rates (Gomez and others, 1989, Batalla 1997). For river restoration programs, such as the San Joaquin River Restoration Program, accurate estimates of bedload transport, often at low transport rates, are necessary but the limitations of physical sampling and bedload formulae make it difficult to obtain accurate estimates.
Surrogate measurement techniques, which use indirect methods for estimating bedload sediment transport, have demonstrated an ability to augment discrete physical sampling programs and have value as independent measures of bedload mobilization (Gray and others, 2010). The use of hydrophones to detect the sound generated by cobble- and gravel-sized particles moving along the riverbed (for example, Barton and others, 2010, Marineau and others, 2012) is one such type of surrogate technology. Hydrophones are relatively inexpensive, can operate nearly continuously, and may be deployed remotely (Gray and others, 2010). Hydrophones may be used to quantify bedload transport rates at high temporal resolution (e.g. seconds to hours) with calibration using physical bedload samples (for example, Barton and others, 2008) or they may be used as stand-alone measurements to detect the threshold of mobilization and cessation of coarse bed material movement.
The objective of this study is to evaluate the use of hydrophone stations for estimating coarse bedload sediment transport dynamics at high temporal resolutions (e.g. hourly or finer) on the mainstem San Joaquin River downstream of Friant Dam for water years 2015-17. Three separate types of installations will be evaluated: four stereo hydrophone installations and one 'Quadraphone' (double stereo) installation co-located at existing bedload sampling locations for measuring coarse bedload transport rates, and five stereo hydrophone installations located at riffle sites for estimating thresholds of coarse bedload mobilization and cessation. Each type of hydrophone installation will be evaluated for its accuracy in estimating coarse bedload transport rates and bed mobilization using data collected by other studies funded by the SJRRP. In particular, the hydrophone data will be evaluated for the ability to 'tune' the hydrophone response to the relative low rates and low bedload grain sizes present on the San Joaquin River.