Laboratory Measurement of Bedload with an ADCP Rauf Ramooz and Colin D. Rennie Department of Civil Engineering, University of Ottawa, Ottawa, ON, Canada. Abstract Moving bottom bias in acoustic Doppler current profiler (aDcp) bottom tracking has been used by several researchers as an estimate of apparent bedload velocity. However, it remains unknown if the apparent bedload velocity is an unbiased estimate of average bedload particle velocity. This paper presents a controlled laboratory calibration of ADCP apparent bedload velocity, which was performed in the Main Test Channel at the St. Anthony Falls Laboratory (SAFL) as part of the National Center for Earth-Surface Dynamics (NCED) SedT project. The length of the sediment-recirculating mobile bed test section was 20 m. Both sand-bed (d50 = 0.98 mm) and gravel-bed (d50 = 11.06 mm) bedload transport experiments were conducted, with five flow rates tested for each sediment. Bottom track data were collected with both 600 kHz and 1200 kHz Rio Grande ADCPs, and over a range of bottom track pulse lengths from &R20 to &R40. Actual bedload transport rates were measured using 1) conventional samplers, 2) five automatic weigh pans distributed laterally across the channel at the end of the test section, 3) dune tracking by means of eight sonars, and 4) high speed digital videography. In this paper, measured apparent bedload velocity is compared to bedload transport rate from the weigh pans and dune tracking. In addition, the influence of bottom track pulse length and operating frequency on measured bedload velocity is assessed. The results show reasonable correlation between ADCP bedload transport and measured bedload transport rates, with coefficient of determination (r 2 ) ranging from 0.59 to 0.93 with RMSE (root mean square error) ranges from 0.059 m/s to 0.106 m/s for sand bed. For the gravel bed, correlation was found between capture rates and dune tracking with r 2 ranging from 0.52 to 0.97. However, correlations of ADCP apparent bedload velocity and transport rates were lower in gravel bed runs, with r 2 ranging from 0.22 to 0.73. This was probably due to the relatively sporadic nature of gravel bedload transport (Rennie and Villard 2004), but may possibly also have been due to insufficient flow depths for the operation of the ADCP during gravel-bed runs. Introduction Bedload measurements in rivers are required to assess sediment load for the design of structures such as bridges and pipelines, river training works, reservoir silting problems, and assessment of aquatic habitat. Knowledge of bed material transport is essential for understanding river morphology and channel change, which depend on the pattern of sediment transfer along a river reach through local erosion and deposition. Fluvial phenomena, such as river meandering, development of bars and ripples, Published online in 2010 as part of U.S. Geological Survey Scientific Investigations Report 2010-5091. 367