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

• Rill and sheet erosion

• Gully erosion• Bed and bank

erosion• Suspended material

transport• Bed material

transport• Wash load transport

Rill erosion progressing to gullies

Australian Dept. of Environment

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