6. Which of
the following is/are the possible consequence/s of heavy sand mining in
riverbeds?
1. Decreased salinity in the river
2. Pollution of groundwater
3. Lowering of the water-table
Select the correct answer using the code given below:
(a) 1 only
(b) 2 and 3 only
(c) 1 and 3 only
(d) 1, 2 and 3
Ans: (b) 2 and 3 only
Explanation:-
Sand is vital for sustenance of rivers.
Sand mining has several impacts on the river environment. Sand mining disturbs and completely removes
the habitat from the mined zones. It leads to changes in its channel form,
physical habitats and food webs – the river‘s ecosystem. It also increases the
velocity of flow in river which destroy flow-regime eventually erodes the river
banks.
• Channel widening causes shallowing of the streambed, producing braided
flow or subsurface intergravel flow in riffle areas, hindering movement of
fishes between pools.
• Riverbed becomes dry due to exposure to solar radiation decrease the
surface and groundwater.
• Depletion of
sand in the
streambed causes the
deepening of rivers
and estuaries, and
the enlargement of river mouths and coastal inlets. It leads to
saline-water intrusion.
• Removal of vegetation and destruction of the soil profile destroys
habitat above and below the ground and faunal population decrease.
Sand Mining and impact on environment
Sand Mining is an activity that refers 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.