Impacts of Dam Construction on River Ecosystems

Presented By:
Sangit Banik (16ID60R15)
1st Yr. M.Tech, RCGSIDM

RCGSIDM, IIT Kharagpur Pallavi & Sangit 2
• Dam project is regarded as one of the most critical factors contributing to
changes of river ecosystem. Eco-environmental impact may arise during
all project phases, i.e. construction, river impoundment, and dam operation.
• The flow manipulations result in physical, chemical, and biological changes
to the ecosystems of upstream backwaters, the reservoir body and
surroundings, and downstream.
• The reservoir waters spill out into the surrounding environment, flooding
the natural habitats that existed before the dam’s construction.
• Up to the present, over 4,00,000 km2 of the earth have been flooded due
to damming.
RCGSIDM, IIT Kharagpur Sangit Banik (16ID60R15) 2
Dam-Introduction

• To study the effects of dam construction to the river ecosystem.
• To formulate dam running scheme that benefits eco-environment.
• To review a case-study: Farakka Barrage.
Objective

• Water Supply for Domestic and Industrial Use.
• Meeting the Agriculture Demand for Food Supply.
• Flood Control.
• Recreation.
• Hydropower Generation.
• Inland Navigation.
Positive Effects of Dam Construction

• Flow Influences
 Dam acts as a barrier between the upstream and down-stream habitat of
migratory river animals .
 Dams block their migration upstream to spawning areas, threatening to
decrease reproduction numbers and reduce the species population.
 Dams hold back sediments that would replenish down stream ecosystems
naturally.
 The running river may become still pond, and change to the lake
condition.
Negatives Effect of Dam on River Ecosystem

• Flooded Area Reduced
 The areas surrounding riverbanks are of a particularly rich bio-diversity,
supported by the natural flooding of a dam-free river.
 Compared with reservoir’s sub-merged areas, the flooded areas are
useable soil because it is only little periodical time overpass water on the
flooded areas.
 Floods bring nutrition and species as a supplement repeatedly.
 Without flooding and a healthy riparian zone, this debris will be scarce.

• Species Change
 Many aquatic animals coordinate their reproductive cycles with annual
flood seasons.
For example, a fish on a certain river may only reproduce during April of
every year so that its offspring will have abundant food and places to hide.
If the flood never comes because a dam holds the river back, the offspring
may be produced during a time when they cannot possibly survive.
 Vegetation, too, depends upon these regular cycles of flood. Dams are built
to stop flooding, so that people can build houses in the floodplains. As a
result, riparian vegetation changes forever.
An example of this may be found in Southwest United States where
enormous floodplains of cottonwood and marsh have been replaced by dry,
barren areas of tamarisk and grass.

• Sediment Deposition Problem
 A dammed river is said to be “hungry” for sediment. Because the rate of
deposition of sediment is greatly reduced, the water flow eats away at the
river shores and riverbed, threatening shoreline ecosystems, deepening the
riverbed, and narrowing the river over time.
 Erosion reduced riverbed and affected river-bank and riparian bank, which
is the habitat of many organisms.
 The eroded channel could create a lower water table level in the affected
area.
 Dams are engineered to withstand the force of a certain number of tons of
water - however large the reservoir will be. They are not engineered to
withstand the additional force of tons of wet sediment pressing on their
backsides.

 All reservoirs develop a reduced water-storage capacity due to the
exchange of storage space for sediment.
 Diminished storage capacity results in decreased ability to produce
hydroelectric power, reduced availability of water for irrigation, and if
left unaddressed, may eventually result in the expiration of the dam and
river.
 The initial filling of a reservoir floods the existing plant material, leading to
the death and decomposition of the carbon-rich plants and trees.
 The decaying plant matter itself settles to the non-oxygenated bottom of
the stagnant reservoir, and the decomposition produces and eventually
releases dissolved methane.

• Effects on Human
 The artificial lakes created by dams become breeding grounds of disease.
This holds true especially in tropical areas where mosquitoes, which are
vectors for malaria, and snails, which are vectors for schistosomiasis.
 The amount of bio-mass converted to methane results in power generation
that pollutes 3.5 times more than an oil-fired power plant would for the
same generation capacity.
 The construction of large dam has resulted in the displacement or
resettlement of many million people across the world which causes loss of
over million people’s homes, the loss of many valuable archaeological
and cultural sites, as well as significant ecological change.

• Drawing Flood Regulation Scheme That Benefits the Eco-
Environment and Managing Flooded Areas
 Releasing water designedly, thus achieving the need of preventing flood,
subtracting the negative effects caused by dam construction and satisfying
the people’s product and living need in upstream and downstream
 Using the traditional and modern river basin synthesis development
concept.
 Strict management on the sub-areas for the different frequent flooded area
should be practiced.
 We need to ascertain the relationship between flooded area’s product,
function, attribute, and inundation, which can quantify the inundation
amount to maintain ecosystem.
Dam Running Scheme That Benefits Eco-Environment

• Building Hydraulic Engineering That Benefits Ecological
Protection
 In fishway’s design, the fish living behaviour, posture character and hydraulic
buildings should be considered.
 We can set sound fitting on the fishway, which can lead the migrated fishes
move swiftly upstream or lower reaches.
 Manual propagate to the spawning migration.
• Enhancing the Water Pollution Treatment of the Upriver
 Treatment to the upriver environment pollution has a far-reaching
significance to protect whole river system’s water resource.
 We still need to cut off the contamination concentration in the river to avert
accumulating, depositing and concentrating of deposits.
Dam Running Scheme That Benefits Eco-Environment

The Farakka Barrage: Impact on Bangladesh
• In 1974 India built a barrage on the Ganges at Farakka in order to divert water
for its own use .
• The water is diverted to
the Hooghly River via a
26-mile long feeder canal.
• The unilateral and
disproportionate diversion of the Ganges caused a dangerous reduction in
the amount of sediment and water flow of the Ganges in Bangladesh.
• Now Bangladesh's delta receives less sediment and inadequate water flow for
navigation and irrigation during the summer months.
• Groundwater also dropped below the level of existing pumping capacity
• Such conditions lead to significant decreases in food production and
curtailment of industrial activities
Case Study: Farakka Barrage-Problems

• As a result of a lack of adequate freshwater inflow, the coastal rivers
experienced saltwater intrusion 100 miles farther inland than normal
during the summer months, affecting drinking water in these areas.
• The reduction in sediment supply has curtailed delta growth and has led to
increased coastal erosion.
• At the present time the rates of sediment accumulation in the coastal areas
are not sufficient to keep pace with the rate of relative sea level rise in the
Bay of Bengal.
• This reduction in carrying capacity due to river bed aggradations has
increased the frequency of severe floods over the last decade, causing
enormous property damage and loss of life.
• If the amount of sediment influx in the coastal areas is further reduced then
a relative sea level rise in the Bay of Bengal by 1 meter will severely curtail
the delta growth, resulting submergence of about one-third of Bangladesh.
Case Study: Farakka Barrage-Problems

• India has suggested building of 3 dams on Brahmaputra in Assam and
excavation of a 209-mile link canal through which 100,000 cusec of water
would be diverted from the Brahmaputra to the Ganges during the summer
months.
• Building of the more canal and dams on the Brahmaputra will make
Bangladesh more dependent on India for its share of water.
• Diversion of water from the Brahmaputra will jeopardize irrigation,
navigation, and other components of ecosystem in the Brahmaputra valley.
Besides, about 20,000 acres of lands will be lost in Bangladesh to the canal.
• Bangladesh is suggesting for an alternate artificial canal connecting the
Ganges and Barhmaputra between Sirajganj and Bheramara in Kushtia
district would serve the same purpose for Bangladesh as the 209- mile link
canal proposed by India. The length of the proposed Sirajganj-Bheramara link
canal would only be 60 miles.
Case Study: Farakka Barrage-Solutions

• The Government of Bangladesh proposes to augment the Ganges flow by
building of numerous storage reservoirs in India, Bhutan, and Nepal to
store water during rainy seasons which can be released in summer months.
• The potential for electric power that can be generated from such project is
huge.
• A better physical control of the supply, accumulation, and dispersal of
sediment and water can ensure growth of the delta.
• Annual dredging of rivers and dispersion of the dredged sediments on
the flood plains and delta plains will increase the water carrying capacity
of the rivers, and reduce flooding propensity.
• Re-excavation and re-occupation of abandoned distributaries of the
major rivers would re-establish the already disrupted equilibrium of the
hydrodynamic system due to upstream diversion of the Ganges.
• An integrated management plan for both surface and groundwater is
necessary for Bangladesh to reduce the economic hardship that is being
caused by the diversion of the Ganges.
Case Study: Farakka Barrage-Solutions

• Dam construction, like a coin, has its two sides. How to exploit favourable
conditions and avoid unfavourable ones is the business of dam architects,
dam constructors and dam managers.
• We should study the disadvantages caused by dam engineering, and
demonstrate the feasibility of dam construction project
• Moreover, we should promote the beneficial aspects and subtract the
negative effects caused by dam construction.
• Then we can make new engineering projects to be facilitated in society’s
sustainable development and accelerate the harmonious coexist between
nature and human being.
• The degradation of river ecosystems, as a consequence of river regulation,
can have profound economic and social implications. In the past failure
to take into account the cost of these consequences has resulted in the
benefits of many dams being overstated.
Conclusion

The Real Debate
• Whether dams are useful or detrimental???
• Whether they improve our environment as a
whole and man’s well-being or whether they
spoil it???
Future Scope for Research

Chen, S., Chen, B. and Su, M. (2010). The cumulative effects of dam project on river ecosystem based on multi-scale
ecological network analysis. Procedia Environmental Sciences, 5, 12-17.
Collier, M., Webb, R. H. and Schmidt, J. C. Dams and rivers: a primer on the downstream effects of dams, US Geological
Survey Circular 1126, Arizona, 1996.
Dwivedi, V. K., Gupta, S. K., and Pandey, S. N. (2010). A study of environmental impact due to construction and operation of
dam. National Conference of Eco friendly Manufacturing and Sustainable Development, 31.
Lin, Q. (2011). Influence of dams on river ecosystem and its countermeasures. Journal of Water Resources and Protection, 3,
60-66. doi:10.4236/jwarp.2011.31007
McCartney, M.P., Sullivan, C. and Acreman, M.C. Ecosystem Impact of large dam. Report prepared for IUCN / UNEP /
WCD.
Mia, M.Y., Hossain, M.U., Hossain, M.S. and Farzana, S. Impact assessment of Farakka barrage on environmental issues at
Bheramara U pazila, Bangladesh. Bangladesh Journal of Fisheries Research , 13(1), 2009, 89-93.
References

Impacts of Dam Construction on River Ecosystems

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