Dams provide benefits like water regulation and power generation but also have negative environmental impacts. They block sediment flow and change water quality, quantity, and temperature downstream. This disrupts the local river ecology and harms fish. Over 40,000 large dams have been constructed worldwide, altering circulation systems. Specific impacts include erosion, siltation of reservoirs, salinization of irrigation water, and disruption of natural cycles that aquatic plants and animals depend on. While dams provide irrigation and flood control, they also submerge land and wildlife habitats.

2.  A dam is an artificial barrier usually
constructed across a stream channel to
impound water.
 Timber, rock, concrete, earth, steel or a
combination of these materials may be used
to build the dam.
Function of a Dam
 Dams provide a means of regulating
downstream surface water flows over
space and time by altering the natural
spatial and temporal distributions of
stream flows .

3.  The construction of large dams completely change the relationship of
water and land, destroying the existing ecosystem balance, which in many
cases, has taken thousands of years to create
 Around 40,000 large dams which abstract the World’s rivers
 Completing changing their circulation system
 Dams alter aquatic ecology and river hydrology upstream and
downstream, affecting water quality, quantity and breeding grounds.

4. Impact of Dams

5.  One of the first problems with dams is the erosion of land.
 Dams hold back the sediment load normally found in a river flow
causing deprivation of sediment in downstream.
 In order to make up for the sediments, the downstream water erodes its
channels and banks
 A major example of soil erosion problems is the Aswan Dam.

6.  larger sediments in water entering a reservoir are deposited and steadily
raising the level of the upper reaches of the reservoir.
 Siltation is the outcome of silt being deposited at the bottom of the
reservoir, which inevitably reduces the utility of the dam

7.  The arid and semi-arid areas are incapable of handling large amounts of
water brought by irrigation.
 Irrigation water has more saline content and adds more salt to the system
leading to the increase of salinisation.
 Changes in the salt regime can affect the entire ecosystem and disrupt
breeding of fishes.
 Large areas on the river banks are likely to be affected by an increased
quality of salt after dam construction.
 In total, over 32,000 hectares of land have been submerged by the Sardar
Sarovar Dam, 13,000 of which is forest land and 11,000 hectares of
agricultural land.

8.  Downstream of the dam the flow rate in the river will depend on the
amount of the compensation flow.
 Water volume is considerably reduced during the dry season.
 Due to decreased water discharges, water temperature will rise in daytime
and decline sharply at night.
 Rooted plants will grow in the riverbed due to the decrease in water
volume.
 Fish such as snow trout, catfish and loaches may be pulled into the intakes
and get killed. Even riverine fish adapted to fast current may be lost. Fish
food organisms will be highly affected by reduced flow rates and new
species will invade areas with a slow current

9. Sardar Sarvor Dam Project

10.  Irrigation: The Dam Project will provide irrigation facilities to 17.93 lac
ha. of land.
 Drinking Water Supply: A special allocation of0.86 MAF of water has
been made to provide drinking water to 135 urban centers and 8215
villages
 Power: Two power houses viz. River bed power house and canal head
power house with an installed capacity of 1200 MW and 250 MW
respectively.
 Flood Protection: It will also provide flood protection to riverine reaches
measuring 30,000 ha.
 Wild Life: to develop wild life sanctuaries viz. "Shoolpaneshewar wild life
sanctuary" on left Bank, Wild Ass Sanctuary in little Rann of Kachchh etc.

11.  The impoundment of water behind a dam causes the velocity of the water
to drop. Sediment carried by the river is dropped in the still water at the
head of the lake. Below the dam, the river water flows from the clear water
directly behind the dam. Because the river no longer carries any sediment,
the erosive potential of the river is increased.
 Erosion of the channel and banks of the river below the dam will ensue.
Even further downstream, sediment deprivation affects shoreline processes
and biological productivity of coastal regions.
a. The Ecology: The plant and animal communities that inhabit the river and
river margins have evolved to adapt peculiar pattern. Dams disrupt this
ecology.

12. b. Armoring the Riverbed: dam is allowed to release water from its
reservoir only once in awhile this leads to scouring and armoring of the
riverbed.
c. Starving the River: - Dams hold back not only sediment, but also debris.
The life of organisms downstream depends on the river with debris. It
hiding places for all sizes of animals and surfaces for phytoplankton and
microorganisms to grow.
d. Changing Temperatures: From the dam the below water is released
which is cold in temperature. Many macro invertebrates depend on a
regular cycle of temperatures throughout the year.
e. Stopping Fish Migration
f. Impacts of the dam on the catchment: The construction of a dam itself
can contribute to the degradation of its catchment.

13. g. Impacts of mining and quarrying for construction materials such
extraction aggravating dust pollution, disturbing wildlife and destroying
vegetation.
h. Interrupting Natural Cycles The first effect of a dam is to alter the
pattern of disturbances that the plants and animals of a river have evolved
for
i. Others:
◦ Waterlogging and salinity
◦ Impacts on human health
◦ Wildlife losses
◦ Submergence of forests

14. Thank you