FLOOD01169

• County: Statewide
• Community: State of Colorado
• Stream Name: All
• Title: Design Guidelines and Criteria Channels and Hydraulic Structures on Sandy Soil
• Date: 6/1/1981
• Prepared For: UDFCD
• Prepared By: Simons Li & Associates Inc.
• Floodplain - Doc Type: Educational/Technical/Reference Information

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a primary factor in sedimentation study, but the size distribution of the

sediment that forms the bed and banks of a stream is of great importance.

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A size classification embracing and expanding the Wentworth scale, which

has been recommended by the Subcommittee on Sediment Terminology of the Com-

mittee on Dynamics of Streams of the American Geophysical Union, contains

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six consecutive size classes; boulders, cobbles, gravel, sand, silt, and

clay (Table 2-1).

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2.3.2.l Boulders

The boulder class has been of little interest when considering sediment

transport problems. In this range, size measurement of a single particle is

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a relatively simple matter. Conversely, it is a difficult problem to establish

the size distribution of a bed of boulders due to the large volume of the

sample required and the size of the particles. Here, indirect methods are

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commonly used, such as photographing the material through a grid.

2.3.2.2 Cobbles and Gravel

These two classes play an important role in prohlems of local scour and

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resistance to flow and to a lesser extent considering bed-load transport.

Size of particles in this range may be determined by direct measurement of

either the volume or one or more diameters of typical particles (usually with

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conversion of results to the normal diameter), or by passing the material

through sieves of the proper mesh size.

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2.3.2.3 Sand

The sand class is very important considering sediment transport. Sand

sizes are almost invariahly determined by sieving or by the visual accumu-

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lation tube.

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