ABSTRACT

gravel crusher

gravel crusher

Sand and gravel are widely used throughout the U.S. construction industry, but their extraction can significantly affect the physical, chemical, and biological characteristics of mined streams. Fisheries biologists often find themselves involved in the complex environmental and regulatory issues related to instream sand and gravel mining. This paper provides an overview of information presented in a symposium held at the 1997 midyear meeting of the Southern Division of the American Fisheries Society in San Antonio, Texas, to discuss environmental issues and regulatory procedures related to instream mining. Conclusions from the symposium suggest that complex physicochemical and biotic responses to disturbance such as channel incision and alteration of riparian vegetation ultimately determine the effects of instream mining. An understanding of geo-morphic processes can provide insight into the effects of mining operations on stream function, and multidisciplinary empirical studies are needed to determine the relative effects of mining versus other natural and human-induced stream alterations. Mining regulations often result in a confusing regulatory process complicated, for example, by the role of the U.S. Army Corps of Engineers, which has undergone numerous changes and remains unclear. Dialogue among scientists, miners, and regulators can provide an important first step toward developing a plan that integrates biology and politics to protect aquatic resources.

Sand and gravel are essential components of construction materials and are in almost all construction projects, including buildings, roads, bridges, and airports. The importance of these materials has resulted in aggressive mining of sources to meet needs of new construction as well as rehabilitation of aging infrastructures. Abundant deposits of sand and gravel can be found throughout most of the United States, particularly associated with rivers and streams. Approximately 10%-20% of the sand and gravel mined in 1974 was dredged from streams (Newport and Moyer 1974). However, sand and gravel extraction can significantly alter the physical, chemical, and biological characteristics of mined streams (Nelson 1993).

As with many aquatic resource issues, fisheries biologists are called on to provide information about the potential ecological effects of in-stream sand and gravel mining. Instream mining issues are often characterized by insufficient scientific information and a complex regulatory process that heavily influence the outcome of resource-related decisions and regulations. A better understanding of the status of existing scientific information and an overview of the regulatory process are needed to ensure the biological integrity of streams.

In 1997 the Warmwater Streams and Environmental Concerns committees sponsored a symposium on this topic at the midyear meeting of the Southern Division of the American Fisheries Society in San Antonio, Texas. This paper is an overview of the presentations and comments from the symposium. Our objective is to describe some of the complex issues that fisheries biologists need to consider regarding sand and gravel mining, including supply of and demand for sand and gravel, environmental effects of mining, the regulatory process, and recovery and remediation.

Supply of and demand for sand and gravel

Transport and deposition of eroded bedrock and surficial materials create sand and gravel deposits. In this paper, gravel is considered to be water-transported particles ranging from 0.48 cm-7.62 cm in diameter; thus, crushed stone is excluded. Because water is the principal agent of distribution for sand and gravel, these deposits occur in or near rivers and streams or in historic stream courses. Potential mining sites are typically chosen based on the natural supply of sand and gravel material, intended use of the product, quality of the product needed, transportation costs, land ownership, and land use.

Demand for sand and gravel relates to the increasing need for construction materials, which accounts for approximately 96% of the total amount of mined sand and gravel (Langer 1988). The remaining 4% is used for foundry operations, glass manufacturing, abrasives, and filtration beds in water treatment facilities (Langer 1988). Of the sand and gravel used in construction, approximately 43% is used for residential and nonresidential buildings (Langer 1988). The National Sand and Gravel Association reported that almost 91,000 kg of aggregate material (sand, gravel, and crushed stone combined) are needed to construct a 6-room house, and approximately 14 million kg of aggregate are needed to construct a school or hospital (Langer 1988).

Although these values are rough approximations, they give some indication of the volume of material used in building construction. Almost 24% of the sand and gravel used in construction is used for building roads. Langer (1988) reported that close to 59 million kg of aggregate are needed to construct 1.6 km of a typical 4-lane interstate highway. In 1990 almost 4,200 companies produced 830 billion kg of sand and gravel from 5,700 operations (Langer and Glanzman 1993). Approximately 63% of the total sand and gravel operations in 1990 were relatively small, e.g., each producing less than 90 million kg.

Not all instream sand and gravel deposits are suitable for commercial use; particle size, shape, hardness, chemical composition, and intended use are considered in determining the suitability of individual deposits. For example, commercial use requires sand and gravel that are chemically inert and able to resist weathering and mechanical breakdown. Instream gravel is particularly desirable because the prolonged transport in water eliminates weak materials by abrasion and attrition, leaving durable, rounded, well-sorted gravel (Kondolf 1997). As a result, instream gravel is typically suitable for producing high-grade concrete (Barksdale 1991).

Kondolf (1997) noted that sand and gravel in reservoir sediments are largely unexploited sources of building materials. Sand and gravel are mined commercially from reservoirs in California, Taiwan, and Israel. Such sediments can be desirable sources of sand and gravel in that they are sorted by size through deposition. An additional benefit to commercial use of reservoir sediments is the partial mitigation of losses in reservoir capacity from sedimentation.

In addition to the distribution, abundance, and quality of sand and gravel, transportation is an important economic factor. Transportation from the area of supply to the area of demand represents the most significant factor in the total cost of sand and gravel mining. Thus, sand and gravel mining typically occurs within 50 km-80 km of the site where demand is the greatest, often near or on transportation routes to reduce costs (Kondolf 1997).

Sand and gravel are mined commercially in every state in the United States (Langer and Glanzman 1993). Mining of sand and gravel occurs in two major forms—(1) in-stream dredging of a streambed and (2) land mining, which includes floodplain excavations that often involve a connecting outlet to a stream.

During instream mining, sand and gravel deposits are excavated from the streambed by various methods—dragline, bulldozer, front-end loader, shovel, or dredge—and are processed at either an on-site barge or upland location. Processing typically includes screening and grading sand and gravel in wash water (usually stream water), and discharging the wash water into settling pits before releasing it back into the stream or returning the wash water directly to the stream. Processed sand and gravel are sometimes stockpiled along the stream channel for transport to areas of demand.

An understanding of the distribution, abundance, and quality of in-stream sand and gravel resources can provide valuable information for evaluating environmental and economic tradeoffs in dealing with in-stream mining issues. The U.S. Geological Survey’s (USGS) Front Range Infrastructure Resources Project is an example of an integrated effort to develop information for improved resource management (USGS 1997). This project addresses problems with sustaining availability of infrastructure resources (natural aggregate, water, and energy) in rapidly growing areas along the Front Range (Colorado) urban corridor. Principal objectives of the project are to develop information, define tools, and demonstrate ways to (1) enable evaluation of the region’s infrastructure resources, (2) determine the region’s projected needs for infrastructure resources, (3) identify issues that may affect availability of resources, and (4) provide decision makers with tools to evaluate alternatives leading to sustained access to infrastructure resources (W. Langer, USGS, Denver, pers. comm.).

Environmental effects of instream sand and gravel mining

Sand and gravel extraction can result in a number of physical, chemical, and biological effects on mined streams. Sand and gravel mining can change the geomorphic structure of streams (Sandecki 1989; Kondolf 1994), often resulting in channel degradation and erosion from mining operations located either in or adjacent to a stream. Instream mining typically alters channel geometry, including local changes in stream gradient and width-to-depth ratios. Point-bar mining increases gradient by effectively straightening the stream during floods. Thalweg relocation can occur when flooding connects the stream to floodplain mines. Local channel scouring and erosion can occur as a result of increased water velocity and decreased sediment load associated with mined areas. For example, in-stream mining on the Russian River in California during the 1950s and 1960s caused channel incision in excess of 3 m-6 m throughout a distance of 11 km (Kondolf 1997). As a result, the formerly wide river channel is now incised, straighter, and unable to support the diversity of successional stages of vegetation typically associated with an actively migrating river.

Where mining activities are numerous and concentrated, an upstream progression of channel degradation and erosion can occur—-a process referred to as headcutting. Headcuts induced by sand and gravel mining can cause dramatic changes in a streambank and channel that may affect instream flow, water chemistry and temperature, bank stability, available cover, and siltation. Channel erosion from headcuts can cause loss of upstream property values; reduce recreational, fishing, and wildlife values; and contribute to the extirpation and extinction of stream fauna (Hartfield 1993). Sand and gravel mining has been identified as the causative factor in headcutting on the Amite, Bogue Chitto, and Tangipahoa rivers in Mississippi and Louisiana, and on the Buttahatchee and East Fork Tombig-bee rivers in Mississippi (Hartfield 1993). Headcutting more than 1 km upstream from an instream mine has been documented in Cache Creek, California (Kondolf 1997).

The combined processes of channel incision and headcutting also can undermine bridge piers and other structures. Channel incision caused by instream gravel mining on the San Luis Rey River in California exposed aqueducts, gas pipelines, and footings of highway bridges (Kondolf 1997).

Sedimentation and increased turbidity also can accrue from mining activities, wash-water discharge, and storm runoff from active or abandoned mining sites. Gravel mining in Blackwood Creek, California, increased the stream’s suspended sediment loads four-fold (Kondolf 1997). Turbidity is generally greatest at mining and wash-water discharge points and decreases with distance downstream. Forshage and Carter (1973) found that settleable solids were deposited within 1.6 km of a gravel-dredging operation on the Brazos River, Texas. Nelson (1993) suggested that evaluations of instream mining effects include measurements of sediment loads and turbidity levels taken at the points of mining and wash-water discharges.

Little is known about changes in chemistry as a result of instream sand and gravel mining. Changes may be primarily local and subtle (Nelson 1993). Forshage and Carter (1973) found no significant differences in dissolved oxygen, acidity, specific conductance, chlorides, or hardness between a dredge site and an upstream reference area on the Brazos River in Texas. Martin and Hess (1986) found that dissolved oxygen, temperature, acidity, and total hardness were similar in dredged and reference areas in the Chattahoochee River, Georgia. However, decreases in dissolved oxygen (Martin and Hess 1986) and increases in temperature (Webb and Casey 1961) have been reported downstream from dredging activity.

Mining-induced changes to the geomorphic structure of the stream can significantly affect fish habitat and abundance. Instream mining can reduce the occurrence of coarse, woody debris in a channel, an important habitat for fish and invertebrates. In the Brazos River, gravel-dredging operations were associated with habitat changes and reduced abundance of sport fishes [spotted bass (Micro-pterus punctulatus); largemouth bass (M. salmoides); and bluegill (Lepomis macrochirus)] and benthic macroinver-tebrates (Forshage and Carter 1973).

Gravel mining on floodplains in Alaska produced severe channel alterations, apparently resulting in the elimination of or a reduction in fish populations (Wood ward-Clyde Consultants 1980). However, Nelson (1993) reported no major differences in fish species composition, diversity, relative abundance, or biomass in a comparison of dredged and nondredged control areas in the Tennessee and Cumberland rivers in Tennessee.

Effects of mining on fish communities also may vary among and within streams. Fish densities in Uphapee, Line, Cubahatchee, and Mulberry creeks in Alabama were similar among sites affected by mining and sites upstream of mining activity, although Cubahatchee Creek had higher densities at the reference site (S. Peyton, Auburn University, pers. comm.). Comparisons of fish species composition at mined and unmined sites indicated low similarity in Uphapee, Line, and Cubahatchee creeks. At mined sites, relative abundance of cyprinids [(skygazer shiner (Notropis uranoscopis); blacktail shiner, (Cyprinella venusta); and speckled chub {Macrhybopsis aestivalis)] increased, while relative abundance of percids [(speckled darter (Etheostoma stigmaeum); greenbreast darter (E.juli-ae); rock darter (E. rupestre); and blackbanded darter (Percina nigrofasci-ata)] decreased.

Sedimentation and increased turbidity as a result of mining can have varying effects on fishes. Newport and Moyer (1974) reported that although fish species differ in their ability to tolerate suspended sediments, most could survive short-term exposure to greater than 1,000 ppm. The authors also reported that exposing fishes to concentrations less than 25 ppm caused no harm to a fishery, and chronic exposure to concentrations of 25 ppm-100 ppm would generally be tolerated. High turbidity and sediment loads may favor nonsight feeders such as catfish, whereas sight feeders such as trout and bass may be harmed (Newport and Moyer 1974). The U.S. Environmental Protection Agency (EPA)(1976) considered turbidity of up to 50 Nephelometric Turbidity Units (NTU) to be satisfactory for aquatic biota in streams, but levels greater than 200 NTU were considered detrimental to biological productivity. Based on information in Newport and Moyer (1974) and the EPA (1976), Nelson (1993) suggested that suspended sediment concentrations greater than 50 ppm and/or turbidities above 50 NTU would likely harm fisheries.

Categories: Mining Knowledge Tags: , , ,

Products Quick Links