The suspended load of a flow of

fluid In physics, a fluid is a liquid, gas, or other material that may continuously motion, move and Deformation (physics), deform (''flow'') under an applied shear stress, or external force. They have zero shear modulus, or, in simpler terms, are M ...

, such as a

river A river is a natural stream of fresh water that flows on land or inside Subterranean river, caves towards another body of water at a lower elevation, such as an ocean, lake, or another river. A river may run dry before reaching the end of ...

, is the portion of its

sediment Sediment is a solid material that is transported to a new location where it is deposited. It occurs naturally and, through the processes of weathering and erosion, is broken down and subsequently sediment transport, transported by the action of ...

uplifted by the fluid's flow in the process of

sediment transport Sediment transport is the movement of solid particles (sediment), typically due to a combination of gravity acting on the sediment, and the movement of the fluid in which the sediment is entrained. Sediment transport occurs in natural systems wh ...

ation. It is kept suspended by the fluid's

turbulence In fluid dynamics, turbulence or turbulent flow is fluid motion characterized by chaotic changes in pressure and flow velocity. It is in contrast to laminar flow, which occurs when a fluid flows in parallel layers with no disruption between ...

. The suspended load generally consists of smaller particles, like

clay Clay is a type of fine-grained natural soil material containing clay minerals (hydrous aluminium phyllosilicates, e.g. kaolinite, ). Most pure clay minerals are white or light-coloured, but natural clays show a variety of colours from impuriti ...

silt Silt is granular material of a size between sand and clay and composed mostly of broken grains of quartz. Silt may occur as a soil (often mixed with sand or clay) or as sediment mixed in suspension (chemistry), suspension with water. Silt usually ...

, and fine

sand Sand is a granular material composed of finely divided mineral particles. Sand has various compositions but is usually defined by its grain size. Sand grains are smaller than gravel and coarser than silt. Sand can also refer to a textural ...

s''.''

Sediment transportation

The suspended load is one of the three layers of the

fluvial A river is a natural stream of fresh water that flows on land or inside caves towards another body of water at a lower elevation, such as an ocean, lake, or another river. A river may run dry before reaching the end of its course if it ru ...

ation system. The

bed load The term bed load or bedload describes particles in a flowing fluid (usually water) that are transported along the stream bed. Bed load is complementary to suspended load and wash load. Bed load moves by rolling, sliding, and/or Saltation (geolo ...

consists of the larger sediment which is transported by saltation, rolling, and dragging on the riverbed. The suspended load is the middle layer that consists of the smaller sediment that's suspended. The wash load is uppermost layer which consist of the smallest sediment that can be seen with the naked eye; however, the wash load gets easily mixed with suspended load during transportation due to the very similar process. The wash load never touches the bed even outside of a current.

Composition

The boundary between

and suspended load is not straightforward because whether a particle is in suspension or not depends on the flow velocity – it is easy to imagine a particle moving between bed load, part-suspension and full suspension in a fluid with variable flow. Suspended load generally consists of fine sand, silt and clay size particles although larger particles (coarser sands) may be carried in the lower water column in more intense flows.

Suspended load vs suspended sediment

''Suspended load'' and ''suspended sediment'' are very similar, but are not the same. Suspended Sediment contains

uplifted in

Fluvial A river is a natural stream of fresh water that flows on land or inside caves towards another body of water at a lower elevation, such as an ocean, lake, or another river. A river may run dry before reaching the end of its course if it ru ...

zones, but unlike suspended load no turbulence is required to keep it uplifted. Suspended loads required the Velocity to keep the sediment transporting above the bed. With low velocity the sediment will deposit.

Velocity

The suspended load is carried within the lower to middle part of the water column and moves at a large fraction of the mean flow velocity of the stream, with a Rouse number between 0.8 and 1.2. The rates within the Rouse number reveal how at which the sediment will transport at the current velocity. It is the ratio of the fall velocity and uplift velocity on a grain.

Diagrams

Suspended load is often visualised using two diagrams. The Hjulström curve uses velocity and sediment size to compare the rate of erosion, transportation, and deposition. While the diagram shows the rate, one flaw about the Hjulström Diagram is that it doesn't show the depth of the creek giving an estimated rate. The second diagram used is the Shields Diagram. The Shields Diagram (based on the Shields formula) uses the critical shear stress and

Reynolds number In fluid dynamics, the Reynolds number () is a dimensionless quantity that helps predict fluid flow patterns in different situations by measuring the ratio between Inertia, inertial and viscous forces. At low Reynolds numbers, flows tend to ...

to estimate transportation rate. The Shields Diagram is considered a more precise chart to estimate suspended load.

Measuring suspended load

Shear stress

To find the stream power for sediment transportation,

shear stress Shear stress (often denoted by , Greek alphabet, Greek: tau) is the component of stress (physics), stress coplanar with a material cross section. It arises from the shear force, the component of force vector parallel to the material cross secti ...

helps determine the force required to allow sediment transportation.

\tau= Pw.g.d.s

Critical shear stress

The point at which the sediment is transported within a stream

\tau = \tau . g. (p-p)d50

Suspended load transport rate

q=w.h.c . (a/h)^z-(a/h))/((1-a/h)Z . (1.2-Z))