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Sand mining and its impact

Sand is a naturally occurring granular material composed of finely divided rock and mineral particles. River sand has the ability to replenish itself. The composition of sand is highly variable, depending on the local rock sources and conditions, but the most common constituent of sand in inland continental settings and non-tropical coastal settings is silica (silicon dioxide, or SiO2), usually in the form of quartz which because of its chemical inertness and considerable hardness, is the most common mineral resistant to weathering.

Sand is an important economic resource and also a source of silica for making sodium silicate, a chemical compound used for manufacture of both common and optical glasses. Sand is an ingredient in plaster and concrete and is added to clays to reduce shrinkage and cracking in the manufacture of bricks. Sand in the river channel and floodplains constitutes an important raw material in the construction industry and has a variety of uses in this sector. River sand is used along with cement, gravel, water and steel for making reinforced concrete. Along with cement and water, it is used as mortar for joint filling and plastering.

The economic aspects of sands are not confined to its value as raw material and its various uses. Sand production, movement and deposition are of great concern to the engineering geologist and to the geomorphologist, especially those concerned with river basin management, shore erosion and harbour development.

Besides its economic importance, sand also constitutes an important abiotic component in aquatic ecosystems like rivers. It provides suitable substrate for many benthic organisms. It is an unavoidable component for psammophilic fishes as it provides breeding, spawning, feeding and hiding grounds. Inter-beds of sand within floodplain deposits act as aquifer systems storing large quantities of ground water. In addition to this, sand acts as an efficient filter for various pollutants and thus maintains the quality of water in rivers and other aquatic ecosystems. In earlier days, mining of sand did not create any problem to river ecosystem as the quantity of mining was well within the replenishment limits. However, increase in population and the rise in economic and industrial developments during the past few decades have aggravated mining of river sand many folds higher than natural replenishments which really made a host of damages to river ecosystems in the world.

Sand Mining and impact on environment

Sand Mining is an activity referring to the process of the actual removal of sand from the foreshore including rivers, streams and lakes. Sand is mined from beaches and inland dunes and dredged from ocean beds and river beds. A related process is the mining of mineral sands, such as mineral deposits like diamond, gold and silver. These minerals typically occur combined with ordinary sand. The sand is dug up, the valuable minerals are separated in water by using their different density, and the remaining ordinary sand is re-deposited.

Excessive in-stream sand-and-gravel mining causes the degradation of rivers. In-stream mining lowers the stream bottom, which may lead to bank erosion. Depletion of sand in the streambed and along coastal areas causes the deepening of rivers and estuaries, and the enlargement of river mouths and coastal inlets. It may also lead to saline-water intrusion from the nearby sea. The effect of mining is compounded by the effect of sea level rise. Any volume of sand exported from streambeds and coastal areas is a loss to the system. It is also a threat to bridges, river banks and nearby structures. Sand mining also affects the adjoining groundwater system and the uses that local people make of the river.

In-stream sand mining results in the destruction of aquatic and riparian habitat through large changes in the channel morphology. Impacts include bed degradation, bed coarsening, lowered water tables near the streambed, and channel instability. These physical impacts cause degradation of riparian and aquatic biota and may lead to the undermining of bridges and other structures. Continued extraction may also cause the entire streambed to degrade to the depth of excavation. Sand mining generates extra vehicle traffic, which negatively impairs the environment. Where access roads cross riparian areas, the local environment may be impacted.

In-stream mining can have other costly effects such as many hectares of fertile streamside land are lost annually, as well as valuable timber resources and wildlife habitats in the riparian areas. Degraded stream habitats result in loss of fisheries productivity, biodiversity, and recreational potential. Severely degraded channels may lower land and aesthetic values.

Further all species require specific habitat conditions to ensure long-term survival. Native species in streams are uniquely adapted to the habitat conditions that existed before humans began large-scale alterations. These have caused major habitat disruptions that favored some species over others and caused overall declines in biological diversity and productivity. In most streams and rivers, habitat quality is strongly linked to the stability of channel bed and banks. Unstable stream channels are inhospitable to most aquatic species.

Factors that increase or decrease sediment supplies often destabilize bed and banks and result in dramatic channel readjustments. For example, human activities that accelerate stream bank erosion, such as riparian forest clearing or in-stream mining, cause stream banks to become net sources of sediment that often have severe consequences for aquatic species. Anthropogenic activities that artificially lower stream bed elevation cause bed instabilities that result in a net release of sediment in the local vicinity. Unstable sediments simplify and, therefore, degrade stream habitats for many aquatic species. Few species benefit from these effects.

The most important effects of in-stream sand mining on aquatic habitats are bed degradation and sedimentation, which can have substantial negative effects on aquatic life. The stability of sand-bed and gravel-bed streams depends on a delicate balance between stream-flow, sediment supplied from the watershed, and channel form. Mining-induced changes in sediment supply and channel form disrupt channel and habitat development processes. Furthermore, movement of unstable substrates results in downstream sedimentation of habitats. The affected distance depends on the intensity of mining, particles sizes, stream flows, and channel morphology.

The complete removal of vegetation and destruction of the soil profile destroys habitat both above and below the ground as well as within the aquatic ecosystem, resulting in the reduction in faunal populations.

Also, Channel widening shallows the streambed, producing braided flow or subsurface inter-gravel flow in riffle areas, hindering movement of fishes between pools. Channel reaches become more uniformly shallow as deep pools fill with gravel and other sediments, reducing habitat complexity, riffle-pool structure, and numbers of large predatory fishes. 

Apart from it, sand mining transforms the riverbeds into large and deep pits; as a result, the groundwater table drops leaving the drinking water wells on the embankments of these rivers dry. Bed degradation from in-stream mining lowers the elevation of stream flow and the floodplain water table which in turn can eliminate water table-dependent woody vegetation in riparian areas, and decrease wetted periods in riparian wetlands. For locations close to the sea, saline water may intrude into the fresh water body. 

In-stream sand mining activities will have an impact upon the river's water quality. Impacts include increased short-term turbidity at the mining site due to resuspension of sediment, sedimentation due to stockpiling and dumping of excess mining materials and organic particulate matter, and oil spills or leakage from excavation machinery and transportation vehicles.

Increased riverbed and bank erosion increases suspended solids in the water at the excavation site and downstream.
Suspended solids may adversely affect water users and aquatic ecosystems. The impact is particularly significant if water users downstream of the site are abstracting water for domestic use. Suspended solids can significantly increase water treatment costs.

Example:

Illegal sand mining is posing the biggest threat to the last of the wild and breeding ghariyals left. Found in maximum strength in National Chambal Sanctuary running across three states- UP, MP and Rajasthan, ghariyals are losing out to human interference.

Mining of sand banks is destructive for ghariyal population as sand banks are essential for nesting and basking:

Ghariyals lay their eggs under sand beds, but illegal sand mining destroys their nests. The complaint submitted to NGT reads, ‘Sand is extracted for construction works. Local inhabitants are cultivating river banks immediately adjacent to the river and this is causing considerable disturbance to the natural habitat of ghariyals. Villagers residing along the river are flattening ravines present in the sanctuary for farming.’

The 425 km stretch of the Chambal River was declared a protected area in 1979. The river originates from Kota in Rajasthan, runs through sandy ravines and ends at Bhare in Etawah, where it merges with the Yamuna. UP has 150 km of the river sanctuary running along Bah (Agra) and Etawah.

Ghariyals are the major wildlife attractions of the sanctuary: Illegal fishing is another threat to ghariyals as they get entangled in fishing nets and drown. Many a time, ghariyals injured by fishing hooks starve to death as they can neither hunt nor eat.

According to the 2012-13 census, UP stretch of the sanctuary had 785 ghariyals which is a remarkable increase. There were 307 ghariyals in 2008-09 and the number rose to 674 in 2011-12.

• Ghariyals were found historically in India, Pakistan, Nepal, Bangladesh, Bhutan and Myanmar
• Apart from small population in Nepal, maximum wild population exists in three Indian rivers - Son, Geruwa and Chambal
• Chambal sanctuary is a tri-state protected area running along MP, UP and Rajasthan
• UP stretch of the sanctuary has 785 ghariyals as per 2012-13 census
 

By Manoj K Jha

Part 1 of 2 article series

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