[1] Methodologies are presented to (1) evaluate the effect of acoustic Doppler current profiler (ADCP) motion on velocity measurements, (2) assess the stationarity of velocity time series, and (3) ensure that a sample record is of sufficient length for measurements taken with an ADCP at a fixed location in a natural river. ADCP motion occurring on the timescale of an ensemble is investigated by comparing single-ping and multiping measurements obtained at the same location under the same flow conditions. Large-scale motion occurring over the course of the entire measurement is studied by first examining a set of indicators to determine if motion may have resulted in the ADCP measuring in regions of different flow characteristics and then dividing the record into segments representing the potentially different regions for comparison. If boat motion is significant, the ADCP record is edited accordingly. Stationarity is assessed using statistical trend tests with guidance provided for selecting parameters based on instrument physics and flow conditions. Mean streamwise and spanwise velocity profiles can be calculated after confirming the reliability of a measurement. A set of criteria are presented to evaluate the appropriateness of an assumption of the law of the wall for streamwise velocity profiles. The methodology is demonstrated using 67 fixed-vessel measurements obtained at two sites on the lower Roanoke River for two discharges. The results indicate that an appropriate procedure was used for securing the ADCP in the channel and that the sample records were sufficient to provide both accurate measurements of mean quantities and assess the stationarity of velocity.

The logarithmic law of the wall is commonly used to determine the shear stress applied to the river bed by the flow field. The shear stress calculation requires a velocity profile at the location of interest-data that can be obtained with a boat-mounted acoustic Doppler current profiler (ADCP). ADCP survey procedures use either a fixed-vessel (FV) or moving-vessel (MV) with each providing different spatial and temporal resolution. MV procedures require significantly less field effort but the data lack the temporal resolution of FV measurements. This fact has motivated investigators to seek MV procedures and analysis techniques that provide equivalent results to FV measurements. This study compares results of the two survey procedures for depth-averaged quantities (velocity and flow direction), mean velocity profiles, shear velocity and equivalent sand grain roughness. Mean velocity profiles are produced by time averaging for the FV measurements and spatial averaging for the MV measurements. Shear velocity and equivalent sand grain roughness are determined using simple linear regression applied to the logarithmic law of the wall. These procedures are demonstrated using data obtained during bankfull flow on the lower Roanoke River, North Carolina, USA. The results indicate comparable estimates of depth-averaged quantities from both survey procedures. Estimates of the mean velocity profiles were found to be more variable. The agreement for shear velocity and equivalent sand grain roughness was generally poor indicating that further work is necessary to produce comparable results with MV survey procedures.

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Abstract. A variety of hydraulic and ecological processes in rivers depend in part on the grain size distribution of the riverbed. For this reason it is important to accurately sample the bed to determine the grain size distribution. To describe the accuracy of riverbed sediment samples, techniques based on the multinomial distribution are presented. These techniques allow confidence intervals to be calculated for grid, areal, and volume samples. Additionally, sample sizes can be estimated to achieve a desired accuracy for the three sample types. A transformation is necessary when considering areal and volume samples. This is because neither of these two sample types is well conditioned for statistical analysis. The transformation is based on the results of a previously performed grid sample. The transformation then estimates either an areal or volume sample size that is necessary to match the accuracy of the grid sample. This procedure is useful when obtaining a hybrid distribution from grid and areal samples. Having areal and grid sample results of known accuracy allows confidence intervals to be placed on the final hybrid distribution. A series of laboratory experiments is used to illustrate the various techniques. Comparisons are also made with techniques presented in the literature.