Transcript DES601 - Hour 21

Basic Hydraulics:
Solids Transport
What is sediment?
• Matter that settles to the bottom of a liquid
• Matter transported by water or wind
• May be particles that are derived from rocks,
biological materials, or chemical precipitates
• Highway sediments may be a mix of materials,
including pavement dust, natural soils, vehicle rust
particles, tire dust particles.
Soil erosion (scour)
• Caused by impact and
dislodgment of
individual soil particles
by rain drop impact.
• Caused by flow of water
over soil surfaces.
• Caused by movement of
water in channel
systems.
Erosion and transport mechanisms
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Rill and sheet erosion
Gully erosion
Bed and bank erosion
Suspended material
transport
• Bed material transport
• Wash load transport
Australian Dept. of Environment
Rill erosion progressing to gullies
Suspended material transport
• Channels
accumulate
sediment from
sheet/rill and gully
erosion
• Lighter sediment
carried as
suspended
material
• Heavier materials
settle to bottom,
added to material
eroded from banks
and bed
Bed material transport
• Stream bed load is part of total sediment load that
moves along bottom of channel
• Sediment particles roll, bounce, or slide along
bottom
• When stream has ability to re-suspend, some of
particles will move
• When it loses ability to carry particles in
suspension, they will drop out again
• Depends on local stream velocity and settling
velocity of individual particles
Wash material transport
• Material that tends to flow through a reach without
significant interaction with the bed
• Material is usually coarse sand, smaller in size
Solids transport – bed & suspended
load
• El Paso District
Solids transport – bed & suspended
load
• Terrell County
Solids transport – debris
• Also have bouyant solids (debris) in the flow