Sand is a naturally occurring granular material composed of finely divided rock and mineral particles. River sand has the ability to replenish itself.
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. lt 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.
Impacts of sand mining can be broadly classified into three categories:
• Physical: The large-scale extraction of streambed materials, mining and dredging below the existing streambed, and the alteration of channel-bed form and shape leads to several impacts such as erosion of channel bed and banks, increase in channel slope, and change in channel morphology. These impacts may cause:
(1) the undercutting and collapse of river banks,
(2) the loss of adjacent land and/or structures,
(3) upstream erosion as a result of an increase in channel slope and changes in flow velocity, and
(4) downstream erosion due to increased carrying capacity of the stream, downstream changes in patterns of deposition, and changes in channel bed and habitat type.
• Water Quality: Mining and dredging activities, poorly planned stockpiling and uncontrolled dumping of overburden, and chemical/fuel spills will cause reduced water quality for downstream users, increased cost for downstream water treatment plants and poisoning of aquatic life.
• Ecological: Mining which leads to the removal of channel substrate, resuspension of streambed sediment, clearance of vegetation, and stockpiling on the streambed, will have ecological impacts. These impacts may have an effect on the direct loss of stream reserve habitat, disturbances of species attached to streambed deposits, reduced light penetration, reduced primary production, and reduced feeding opportunities.