# USD-49 depth-integrating sampler

This article is a summary of sub-section 5.6.2.6 of the Manual Sediment Transport Measurements in Rivers, Estuaries and Coastal Seas[1]. This article describes how the suspended load can be measured with a USD-49 sampler. This sampler is, just as the Collapsible-Bag depth-integrating sampler an example of a depth-integrating sampler.

## Introduction

Figure 1: USD-49 sampler
Figure 2: Transit rate curve

The USD-49 is a depth integrating sampler. The sampler is lowered at a uniform rate from the water surface to the streambed, instantly reversed, and then raised again to the water surface. The sampler continues to take its sample throughout the time of submergence. At least one sample should be taken at each vertical selected in the cross-section of the stream. A clean bottle is used for each sample. The USD-49 sampler has a cast bronze streamlined body in which a round or square pint-bottle sample container is enclosed. The head of the sampler is hinged to permit access to the sample container (see Figure 1). The head of the sampler is drilled and tapped to receive the ¼-inch, 3/16-inch or 1/8-inch intake nozzle which points into the current for collecting the sample. The transit rate depends on the mean velocity in the vertical, the water depth and the nozzle diameter, as shown in Figure 2. The USD-49 is suitable for depth [integration of streams less than about 5 m in which the velocities do not exceed 2 m/s. The sampler is manufactured by Rickly Hydrological company.

## Determination of the suspended sediment transport

The depth-averaged concentration can be determined as

$c\,=G\,/V\,$

in which: $G$= dry mass of sediment (mg), $V$= volume of water sample (l).

The depth-integrated suspended sediment transport (in kg/m/s) can be determined as:

$S = \large\frac{Gh}{FT}$ or as $S = c\,u\,h\, = \large\frac{G}{V}\normalsize u\,h$

in which: $G$= dry mass of sediment (mg), $V$= volume of sediment sample, including pores (m3),$h$= depth of sampled zone (m), $u$= depth-averaged velocity (m/s), $F$= area of nozzle (m2), $T$= sampling period (s).

The sampler cannot sample down to the stream bed surface. When the sampler touches the bed, the distance between the sample nozzle and the bed is about 0.1 m (see Figure 1). Thus, the depth of the sampled zone is about equal to the water depth minus 0.1 m. Another problem is the short sampling period at each specific point in the vertical. As a result concentration fluctuations are not averaged out and repeat samples are necessary.