Rock
Rock may vary from soft marl via weak rocks (for example, sandstone and coral) to hard rocks (such as granite and basalt). Rock may also vary in size from large to small, depending on the dredging equipment used and the type of material. Rock may also result from blasting, cutting, or ripping and is seldom of only one material type. Whether the rock can be used economically depends on its quantity and size. Rock is a valuable construction material and may be used for both terrestrial and aquatic projects. Usually, dredged rock is not contaminated.
Gravel and Sand
Gravel and sand (granular) are generally considered the most valuable materials derived from a dredging project. Gravel and sand are suitable for most engineering uses without processing. Some additional processing (such as freshwater washing) may be needed for certain agricultural or product uses. Granular material can be used for beach nourishment, parks, turtle nesting beaches, bird nesting islands, wetlands restoration and establishment, and many other applications. Granular material is usually not contaminated.
Consolidated Clay
Consolidated clay varies from hard to soft clay and is material obtained from capital dredging. The material may occur as lumps or as a homogeneous mixture of water and clay, depending on the material type and the dredging equipment used. If the water content is high, dredged clay may have to be dewatered before being transported. Possible uses of consolidated clay range from forming industrial products, such as bricks and ceramics, to building erosion control structures, such as dikes and berms. Consolidated clay is not usually contaminated.
Silt/Soft Clay
Silt and soft clay are the most common materials acquired from maintenance dredging in rivers, canals, and ports. These materials are most suitable for agricultural purposes (such as topsoil) and all forms of wildlife habitat development. Depending on national regulations and laws, mildly contaminated silt and soft clay may be used for some engineered uses or product uses such as bricks, tiles, and ceramics. Because of the high water content, silt and soft clay must be dewatered for any product use. Dewatering can require months or years and, depending on the draining process used, can require temporary storage.
Mixture (rock/sand/silt/soft clay)
Capital dredged material usually occurs in layers as deposited from some past hydraulic process and may require the use of different dredging methods. Maintenance dredged material is usually a mixture of materials such as boulders, lumps of clay, gravel, organic matter, and shells, with varying densities. Even though engineered and product uses will be somewhat restricted because of the mixture, mixed material may be used for a wide range of beneficial uses, such as land reclamation, habitat improvement, and landfill capping.
| Dredged Material Sediment Type |
| Examples of Beneficial Use Activities |
Rock |
Gravel & Sand |
Consolidated Clay |
Silt/Soft Clay |
Mixture |
| Engineered Uses |
| Land creation |
x |
x |
x |
x |
x |
| Land improvement |
x |
x |
x |
x |
x |
| Berm creation |
x |
x |
x |
|
x |
| Shore protection |
x |
x |
x |
|
|
| Replacement fill |
x |
x |
|
|
x |
| Beach nourishment |
|
x |
|
|
|
| Capping |
|
x |
x |
|
x |
| Construction materials |
x |
x |
x |
x |
x |
| Aquaculture |
|
|
x |
x |
x |
| Topsoil |
|
|
|
x |
x |
| Wildlife habitats |
x |
x |
x |
x |
x |
| Fisheries improvement |
x |
x |
x |
x |
x |
| Wetland restoration |
|
|
x |
x |
x |
