Toward a general calibration of the Swiss plate geophone system for fractional bedload transport

[摘要] Substantial uncertainties in bedload transport predictions insteep streams have encouraged intensive efforts towards the development ofsurrogate monitoring technologies. One such system, the Swiss plate geophone(SPG), has been deployed and calibrated in numerous steep channels, mainlyin the Alps. Calibration relationships linking the signal recorded by theSPG system to the intensity and characteristics of transported bedload canvary substantially between different monitoring stations, likely due tosite-specific factors such as flow velocity and bed roughness. Furthermore,recent flume experiments on the SPG system have shown that site-specificcalibration relationships can be biased by elastic waves resulting fromimpacts occurring outside the plate boundaries. Motivated by thesefindings, we present a hybrid calibration procedure derived from flumeexperiments and an extensive dataset of 308 direct field measurements atfour different SPG monitoring stations. Our main goal is to investigate thefeasibility of a general, site-independent calibration procedure forinferring fractional bedload transport from the SPG signal. First, we useflume experiments to show that sediment size classes can be distinguishedmore accurately using a combination of vibrational frequency and amplitudeinformation than by using amplitude information alone. Second, we apply thisamplitude–frequency method to field measurements to derive generalcalibration coefficients for 10 different grain-size fractions. Theamplitude–frequency method results in more homogeneous signal responsesacross all sites and significantly improves the accuracy of fractionalsediment flux and grain-size estimates. We attribute the remainingsite-to-site discrepancies to large differences in flow velocity and discussfurther factors that may influence the accuracy of these bedload estimates.

[学科分类] 土壤学