Difference between revisions of "Measuring instruments for rivers"

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Revision as of 17:11, 1 July 2007

Instruments for rivers

The available instruments (and accuracies involved) for measuring: - bed load transport, - suspended sediment concentrations and transport rates, - particle sizes and fall velocities,

are presented in Tables 1, 2 and 3 below; order of preference is based on the overall sampling accuracy.

Simple mechanical instruments such as the bottle-type, the trap-type and the pump-type samplers are still very attractive because of their robustness and easy handling, particularly when used at isolated field sites. The accuracy of the measured parameters involved can be increased by increasing the number of samples collected. Analysis costs of all samples involved may be critical with respect to the available budget. Optical and acoustic instruments are attractive when large numbers of data have to be collected. As calibration is involved, the accuracy strongly depends on the quality/reliability of the calibration curves. Hence, many calibration samples are required using a pump sampler with the nozzle as close as possible to the optical/acoustic sensor.

A major technological advance for measuring suspended load transport is the in-situ Laser diffraction instrument (LISST). This instrument can measure the particle size distribution and sediment concentration simultaneously. An attractive solution is the LISST-ST, which includes a streamlined body to improve sampling accuracy and is equipped with a pressure sensor and current meter for measuring the sampling height above the bed and the ambient velocity. The velocity data are used to control pump sampling (isokinetic sampling) across the internal Laser arrangement. The velocity and concentration data are used to compute fluxes for up to 32 particle size classes at points, verticals, or in the entire stream cross-section. All data are transmitted via a cable to the survey vessel (on-line measurement). Limitations (related to light penetration) are the maximum concentration ranges of about 150 mg/l for fines (mud/silt) and 500 mg/l for sand particles. Hence, the instrument cannot be used in high-concentration conditions (close to bed; upper flow regime).

Photographs and Figures

Table 1 and 2
Table 3















External links

Selection guidelines for sampling instruments in rivers focusing on the typical mechanical US-instruments are given by the U.S. Geological Survey. This report and many other reports of various typical US-samplers can be downloaded from the FISP-site (http://fisp.wes.army.mil).

These US-samplers are manufactured by Rickly Hydrological Company (http://www.rickly.com]).

The manuals: Field methods for measurement of fluvial sediment (Edwards and Glysson, 1999) and Fluvial sediment concepts (Guy) can be downloaded from USGS-site (http://www.usgs.gov).

References


See also

Other contributions of Leo van Rijn

articles with parts of the manual

other articles


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