thumb|Gravel pit in Tullingeåsen, which forms part of [[Uppsalaåsen.]]
A gravel pit is an open-pit mine for the extraction of gravel.
Gravel pits often lie in river valleys where the water table is high, so they may naturally fill with water to form ponds or lakes. Gravel pit lakes are typically nutrient rich and can support thriving ecosystems, but can also present environmental issues such as the release of toxic metals into watersheds from the exposed rock. Old, abandoned gravel pits are normally used either as nature reserves, or as amenity areas for water sports, landfills and walking. In Germany former gravel or sand pits that have filled up with water are known as Baggersee ("power dug lake") and popular for recreational use. In addition, many gravel pits in the United Kingdom have been stocked with freshwater fish such as the common carp to create coarse fishing locations. Gravel pit lakes have also been stocked with carp in Denmark, as well as rainbow trout.
Products
Gravel pits are a main source of aggregates such as gravel and sand, which are extracted then processed extensively to be suitable for various uses. Aggregates are mined to make concrete, be crushed into construction aggregate, and for other industrial mineral uses. Gravel pits are located where there are rich sources of materials suitable to be crushed into aggregate, often at sites of fluvial, glacial, or floodplain geological deposits. Once a pit is dug into the aggregate, it can be lifted out by bulldozers that load it onto a conveyor or dredged out if the pit fills with water. It is then separated by particle size, crushed, and washed in preparation for use. All the layers of the road structure requires naturally occurring aggregates that are extracted from gravel pits or other surface material extraction sites. Beyond the initial construction of paved roads, gravel pits are important for the ongoing maintenance of unpaved roads because the surfaces of unpaved roads must be continually graded and re-surfaced with new loads of aggregate. In remote regions served by isolated unpaved roads, gravel pit operations are often located at strategic intervals every few hundred kilometers along the roadway in conjunction with road maintenance camps to provide the maintenance crews working out of these camps with the necessary materials. For example, along the Dempster Highway that stretches across the isolated northern region of Yukon Territory, Canada, there are several gravel pits in use for road maintenance and several more that have fallen into disuse.
Issues surrounding gravel pits
Environmental impacts
Gravel pits disrupt the natural processes of the landscapes in which they are operating by displacing vegetation, soil, and rock. This in turn re-routes surface water flow changing runoff patterns, which can create further environmental problems for entire watersheds. Environmental impact assessments must be conducted before such projects to mitigate negative affects, and rehabilitation efforts should be undertaken after projects to restore the natural ecosystem. Unfortunately, most old gravel pits have not been rehabilitated after aggregate extraction has ceased, and their potential to be restored to accommodate improved ecosystem function is wasted. There are also concerns that agricultural plants coated in dust from gravel pit operations pose a risk to human health through consumption if the plant contains the dust. Many become informal recreation sites or transition into wetlands, lakes, or ponds as they fill with water, but remediation can help this process and reduce safety hazards they impose in their industrial state. Remediation programs can be undertaken to build abandoned gravel pits into sites of thriving wildlife habitats, parks or farmland, and/or be flooded and stocked for recreational fishing and to create aquatic ecosystems.