Laboratory and in situ analysis of samples
This article is a summary of chapter 8 of the Manual Sediment Transport Measurements in Rivers, Estuaries and Coastal Seas[1]. This article describes how measurement samples can be analysed in situ or in a laboratory. Sample analysis usually consists of determining the following parameters: sediment concentration, sediment composition, sediment density, and chemical analysis. Samples for chemical or bioassay analysis should be immediately chilled and stored at 4oC after collection.
Contents
Sediment concentration
The two most commonly used methods are evaporation and filtration. The filtration method may be somewhat faster for samples of small concentrations. However, large concentrations tend to clog the filter material (silt concentrations > 100 mg/l).
Bed material composition
Preparation of samples prior to analysis is of the utmost importance if accurate and reproducible results are to be obtained. Samples containing clay minerals or organic material are very liable to cracking on drying and care should always be taken to avoid samples drying out prior to analysis. However, when samples may have dried out naturally when collected on a mudflat or a riverbank, then the aggregates should be broken down (hydrogen peroxide treatment).
Organic materials ranging from macroscopic plant and coal to microscopic colloidal humus does affect average specific weight and greatly affects the particle size and/or fall velocity, if present in sufficient quantities. Quantitative determination of organic material, usually is recommended if the sample consists of 10% or more of organic material. Complete removal of organic material is necessary for all samples to be analyzed for particle size or fall velocity when other than native water is used because the organic material may bind together the sediment particles.
Samples having a size range from pebbles or cobbles down to fine sands will require hand separation of the largest particles. If possible, the size-distribution of the large particles (cobbles) should be determined in-situ by manual measurement of the nominal diameter or by means of photographic methods.
Suspended sediment composition
The physical analysis of suspended sediment samples should be focussed on the determination of the particle fall velocity distribution because this latter parameter is of essential importance in sedimentation studies. Therefore, the sedimentation methods (settling tests) must be preferred above the other methods such as sieving or the Coulter counter. These latter two methods may be used to check the results of the sedimentation tests.
See also
Summaries of the manual
- Manual Sediment Transport Measurements in Rivers, Estuaries and Coastal Seas
- Chapter 1: Introduction, problems and approaches in sediment transport measurements
- Chapter 2: Definitions, processes and models in morphology
- Chapter 3: Principles, statistics and errors of measuring sediment transport
- Chapter 4: Computation of sediment transport and presentation of results
- Chapter 5: Measuring instruments for sediment transport
- Chapter 6: Measuring instruments for particle size and fall velocity
- Chapter 7: Measuring instruments for bed material sampling
- Chapter 9: In situ measurement of wet bulk density
- Chapter 10: Instruments for bed level detection
- Chapter 11: Argus video
- Chapter 12: Measuring instruments for fluid velocity, pressure and wave height
References
- ↑ Rijn, L. C. van (1986). Manual sediment transport measurements. Delft, The Netherlands: Delft Hydraulics Laboratory
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Please note that others may also have edited the contents of this article.
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