FLOOD10307

• County: Statewide
• Basin: Statewide
• Title: Guidelines for Determining Flood Hazards on Alluvial Fans
• Date: 2/23/2000
• Prepared By: FEMA
• Floodplain - Doc Type: Educational/Technical/Reference Information

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20

02/23/00

suspended load is comprised of all of the material carried in suspension. The second system of
classification divides the sediment load into wash load and bed-material load. The wash load is
made of very fine materials, clay and silt, rarely found in the bed. The wash load does not depend
on the carrying capacity of the stream but on the amount supplied by the watershed. The bed-
material load is comprised of all of the material found in the bed. Some of it will move very close
to the bottom, but some may be found in suspension.

Quantification of sediment transport is fraught with uncertainty because of the complexity of the
phenomenon and its inherent spatial and temporal variability. Existing mathematical representations
have relied heavily on experimental results. The available sediment transport formulas have been
grouped according to the approach used to derive them. Three major approaches have been used:
shear stress, power, and parametric. Formulas can also be grouped according to the component of
the total load they attempt to quantifY: bed load, suspended load, or bed-material load. Table 2
summarizes the more commonly used formulas; however, it is not intended to be a complete listing.