Sand and Gravel Resources
Sand and gravel accumulates along shorelines and on continental shelf regions where waves and currents winnow away finer clay fractions allowing coarser sediments to accumulate (Figure 17.3). After petroleum, in economic terms, extraction of sand and gravel from the seabed is the next largest marine physical resource. Sand and gravel are increasingly being mined from continental shelf regions as sources on land in crowded coastal regions are being depleted or operations are restricted do to changes in land use. Sand and gravel are added to cement used in building foundations and is used in all forms of construction, including artificial island and levees (Figure 17.4).
|Figure 17.3. Gravel deposit on South Carlsbad Beach, CA||Figure 17.4. Artificial islands in Dubai, United Arab Emirates|
Sand is mined from offshore areas and pumped in slurry form to replenish beaches that loose sand to beach erosion. Offshore sand and gravel mining operations are expensive, but the impact is as visually obvious as land-base operations, but benthic communities can be impacted by offshore dredging activities.
Offshore dredging is currently used to replenish beach sand in San Diego County. It is the source of sand for artificial beaches like Miami Beach, Florida and massive coastal construction projects in many places including Dubai, Saudi Arabia, and the construction of artificial islands in the South China Sea.