L.S. Robertson and F.J. Pierce Department of Crop and Soil Scences Michigan State University Sediment is the solid organic or mineral material in suspension that is transported or moved from its original site on the earth's surface. While sediment usually represents soil material, it can be other material such as a by-product from a manufacturing process. Sediment movement is associated with water, wind, gravity and ice. Only that directly related to soil and water is considered here. Sediment is a product of erosion. The types of erosion that produce sediment include: (l) sheet erosion, (2) rill erosion, (3) gully erosion and (4) stream channel erosion. Erosion is common along roadsides and on both rural and urban construction sites. There is increasing awareness of sedimentation problems because it affects water use in many ways. Suspended solids clog the gills of fish, cover spawning areas and reduce the amount of sunlight available to aquatic plants, therefore adversely affecting fish populations. Recreational uses of water-swimming, boating and fishing-are limited due to the turbidity that sedimentation causes. Interest in sediments is also increasing because people are now aware of how rapidly sediment can accumulate in streams, ditches and culverts. Many are now aware of the shortened economic life of lake property, farm ponds and water reservoirs. Some have had experiences with plugged filters, damaged pumping equipment and sprinkler nozzles. Many are concerned about the decreased quality of their drinking water.

This publication outlines the nature of sediment materials and describes methods useful in controlling sediment accumulation. The Sedimentation Process There are three steps in the sedimentation process. The first is the detachment of materials from the earth's surface. Both rain and sprinkler irrigation water drops can detach solid particles of material from the soil surface. The overland flow of water also represents an important detachment process. The second step is transport of detached soil particles. Water movement-velocity, depth, volume, frequency, duration and turbulence- regulates the extent of detachment and the distance that materials can be transported. The third step is deposition. Sediment is deposited when water velocity decreases to such an extent that it can no longer support the suspended material, or when the water depth decreases to such an extent that particle movement is impossible. Sediment Characteristics Sediment particles vary greatly in size, shape, density and composition. Light-weight organic materials range in size from macroscopic to sub- microscopic colloidal materials. This is also the case with the denser mineral particles. Large-sized mineral particles such as sand and gravel are not likely to be major sediment problems despite the fact that they are relatively uncohesive and are easily detached from the soil body. Soil aggregates of similar size are less dense than single particles of sand and gravel, hut they tend to react in similar ways.