Dams


A dam is a barrier that stops or restricts the flow of water  or underground streams. Reservoirs created by dams not only suppress floods but also provide water for activities such as irrigation, human consumption, industrial use, aquaculture, and navigability.

USES OF DAMS:
  • Generally, water is stored and used by the people. Water is also stored for irrigation purpose. 
  • Dams can prevent floods in forest.
  • Dams are necessary for irrigation.
  • Dams are necessary for hydro-electric power generation.
  • Dams are necessary for fishing.
  • Dams facilitate tourism. 
  • Dams facilitate inter basin water transferences.
  • Dams facilitate regional and inter regional water – resource schemes. 
  • Recharge of water is the main factor for the stable water
The impact of Dam
a) The construction of large dams involves key expenditure.
b) The loss will be more, when the electricity produced in the large dams distributed to many places.
c) Due to heavy siltation in the large dams, there is a rapid reduction in water capacity.
d) The life time of Tehri Dam is estimated 100 years, but it might be within 30-40 years. 
e) The dams are constructed by destroying the environment and many organisms. For Eg. The Silent Valley Project in Kerala has destroyed very old Flora and Fauna.
f) Soil erosion due to Kali river project in Karnataka produces Waste Land
g) Construction of dams requires cutting of trees, which affects the climate.
h) The people around the areas have to be evacuated.
i) The stagnation of water causes diseases like malaria and brain fever.
j) The cultivatable lands near the dam are affected by stagnation of water. 
k) Dams increase the ground water which dilutes calcium and the people are affected by Floralysis.
l) Dams are responsible for earthquakes

DAM BUILDING ON ENVIRONMENT AND ITS EFFECT
  • Flooding and the destruction of surrounding habitat
Dammed rivers create a reservoir upstream from the dam, which spills out into the surrounding environments and floods ecosystems and habitats that once existed there. Such flooding can kill or displace many different organisms, including plants, wildlife, and humans.
  • Dams produce green house gases 
The flooding of surrounding habitat around dams kills trees and other plant life that then decomposes and releases large amounts of carbon into the atmosphere.
Because the river is no longer flowing freely, the water becomes stagnant and the bottom of the reservoir becomes depleted of oxygen.
This lack of oxygen creates a situation where methane (a very potent greenhouse gas) is produced from the decomposition of the plant materials at the bottom of the reservoir that eventually gets released into the atmosphere, contributing to global climate change.
  • Sediment builds up behind the dam 
Because a dammed river no longer flows freely, the sediment that would have otherwise been deposited naturally downstream begins to build up behind the dam, forming new riverbanks, river deltas, alluvial fans, braided rivers, oxbow lakes, levees and coastal shores. These changes in sedimentation can lead to dramatic alterations in plant life and animal life and how they are distributed.
  •  Downstream sediment erosion
 Due to the restrictions in the sediment flow above a dam, the lack of sediment that would have once flowed downstream ultimately leads to a deficiency in sediment load, and therefore, leads to an increase in downstream erosion. 
This lack of sediment load causes the riverbed to deepen and narrow over time, a compromised water table, the homogenization of the river’s flow, reduced wildlife support, and a reduction in sediment that reaches coasts and deltas.
  • Negative impacts on local fish populations
Typically, local fish species will not be adapted to the new environment that is present after a dam is built and do not survive, leading to the destroy of local populations.
Many factors impact their survival, including the blockage of migration routes, a disconnection from the river’s flood plain, changes in a river’s flow, changes in temperature, turbidity, dissolved oxygen, and changes in local plant life.
The construction of dams is one of the major factors that is cont r ibuting to the loss of freshwater fish species worldwide.
  • Production of methyl mercury
The stagnant water in reservoirs creates a situation where the decomposition of organic matter from decaying plants can transform inorganic mercury into methylmercury.
Unfortunately, methyl mercury tends to bio- accumulate and cause toxic effects in humans and wildlife that eat the fish in reservoirs


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