Sediment is any particulate matter that can be transported by fluid flow, and which eventually is deposited.

Sediments are most often transported by water (fluvial processes) transported by wind (aeolian processes) and glaciers. Beach sands and river channel deposits are examples of fluvial transport and deposition, though sediment also often settles out of slow-moving or standing water in lakes and oceans. Desert sand dunes and loess are examples of aeolian transport and deposition. Glacial moraine deposits and till are ice transported sediments.

Classification

Sediment can be classified based on its grain size and/or its composition.

Grain size

main: Particle size (grain size)

Sediment size is measured on a log base 2 scale, called the "Phi" scale, which classifies particles by size from "colloid" to "boulder".

Composition

Composition of sediment can be measured in terms of:

• parent rock lithology
• mineral composition
• chemical make-up.

This leads to an ambiguity in which clay can be used as both a size-range and a composition (see clay minerals).

Sediment transport

main: Sediment transport

Sediment is transported based on the strength of the flow that carries it and its on size, volume, density, and shape. Stronger flows will increase the lift and drag on the particle, causing it to rise, while larger or denser particles will be more likely to fall through the flow.

Particle Motion

Rivers and streams carry sediment in their flows. This sediment can be in a variety of locations within the flow, depending on the balance between the upwards velocity on the particle (drag and lift forces), and the settling velocity of the particle. These relationships are given in the following table for the Rouse number, which is a ratio of sediment fall velocity to upwards velocity.

$\backslash textbf\{Rouse\}=\backslash frac\{\backslash text\{Settling\; velocity\}\}\{\backslash text\{Upwards\; velocity\; from\; lift\; and\; drag\}\}=\backslash frac\{w\_s\}\{\backslash kappa\; u\_*\}$

where

• $w\_s$ is the fall velocity
• $\backslash kappa$ is the von Kármán constant
• $u\_*$ is the shear velocity