Sediment Sampling in Sand-bed Rivers - VLIZ › imisdocs › publications › 34 › 253234.pdf · •Importance of sediment data in rivers •General principles and some criticisms

Sediment Sampling in Sand-bed Rivers

Jean J. Peters, Brussels, Belgium Consulting engineer Prof. VUB & UCL

Methods & Instruments

Content • Importance of sediment data in rivers • General principles and some criticisms • Development of sediment measuring devices • Measurement in sand-bed rivers with Delft

Bottle and BTMA: experiences and how to have the feed-back from the practitioners to manufacturers

• Conclusions and recommendations

Why to get sediment data?

• We do not have yet sufficient understanding of sediment transport processes, especially in morphologically dynamic sand-bed rivers

• Worldwide, there is a pressing need for solving engineering questions (modelling?)

• Modelling requires, besides good input data, also the best possible understanding of the processes




About principles

• The traditionally accepted theories about sediment transport distinguish only between bed load and suspended load, though adding sometimes “saltation”

• Most research in sediment transport was organised with artificial sediment, single diameter and uniform specific weight

• Sediment transport in rivers is much more complicated …

Sediment transport modes (ISO)

About principles

• Suspended sediment transport is usually determined by multiplying a measured sediment concentration with the local velocity (of the flow), which is not really the determination of the transport rate

• Bed load transport is seldom measured, because its measurement is said to be too difficult and too uncertain




Development of sediment devices

• Direct measurement requires sampling • Sediment samplers were developed mainly

during the first half of the 20th century • Indirect measurement of sand transport has

not been quite successful, yet (ADCP ?) • The demand for samplers is very limited

and manufacturing is often by official organisations (FISP, Nanjing Automation)




Delft Bottle & BTMA

• Samplers designed in The Netherlands for studying sand and gravel transport in Dutch rivers having limited depths and velocities

• Shape and efficiency of samplers were studied in laboratory (Delft and Zurich)

• Design changed by successive manufacturers for manufacturing reasons, not because of feed-back by users

Delft Bottle suspended mode

• The design of the body remained almost the same; however the technology for making the body has been adapted

• The original suspension mode was modified

Delft Bottle suspended mode • Original design of

Delft Bottle, used in Congo river (sampler procured in 1959, photo from 1971)

• Next slide is the present design, taken over by Eijkelkamp from Van Essen so that same body can be used on a frame

Delft Bottle suspended mode

Delft Bottle mounted on frame • The design was

completely modified, especially the system to fix the bottle to the frame

• For different reasons, the nozzle elevation above the river bed may be wrong, inducing large errors

Delft Bottle mounted on frame • The picture (Bangladesh,

1994, Brahmapoutra River) shows the small front plates on which the sampler rests on the bottom, instead of the “skis” from the original design

• The sampler on frame has become much taller, requiring larger davits

Bedload Transport Meter Arnhem • The design of this

bedload sampler was modified, some changes were improvements, other not

• The sampler is much more secure than the Helley-Smith which was derived from it (see slide further)

Bedload Transport Meter Arnhem • Original design, 1971,

Congo River; although the sampler was not conceived for very large streams, it could be used successfully in water depths of up to 30 meters and velocities of more than 2 m/s

• The frame was loaded with lead strips

Bedload Transport Meter Arnhem

Bedload Transport Meter Arnhem

Bedload Meter Helley-Smith

Experiences with DG & BTMA Jamuna river - Bahadurabad 28/05/94

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Sediment transport rate (m³/m.day)

Elev

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bed

(cm

)

Vert 1Vert 2Vert 3Vert 4

Experiences with DG & BTMA Jamuna river - Bahadurabad 28/05/94

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Sediment particle size D50(µm)

Elev

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(cm

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Vert 1Vert 2Vert 3Vert 4

Experiences with DG & BTMA Jamuna river - Vertical 3

0

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Sand transport rate (m3/m.day)

Elev

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0100200300400500600700800900

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Sediment particle size (µm)

Elev

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D35D50D65


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Sediment particle size (µm)

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D35D50D65

Collapsing bag sampler






Conclusions & Recommendations • Direct sampling can be done with traditional

instruments such as Delft Bottle and BTMA • Direct sampling is needed to measure both the

transport rate and the sediment size distribution in the water column, especially near the bed

• More data are needed to check the existing theories about sediment transport processes and combing direct and indirect measurement may help tremendously

Conclusions & Recommendations • There is a need for closer collaboration between

the users and the manufacturers of equipment • Manufacturers need to give the correct and

detailed information about the instruments and their use

• Organisations such as IAHR and WMO can help the users by organising comparison between different instruments and by editing manuals and guidelines that must be specific to the various river environments

Documents

Sediment Sampling in Sand-bed Rivers - VLIZ › imisdocs › publications › 34 › 253234.pdf · •Importance of sediment data in rivers •General principles and some criticisms