Positive and negative impacts of dams on the environment
Answers
The environmental consequences of large dams are numerous and varied, and includes direct impacts to the biological, chemical and physical properties of rivers and riparian (or "stream-side") environments.
The dam wall itself blocks fish migrations, which in some cases and with some species completely separate spawning habitats from rearing habitats. The dam also traps sediments, which are critical for maintaining physical processes and habitats downstream of the dam (include the maintenance of productive deltas, barrier islands, fertile floodplains and coastal wetlands).
Another significant and obvious impact is the transformation upstream of the dam from a free-flowing river ecosystem to an artificial slack-water reservoir habitat. Changes in temperature, chemical composition, dissolved oxygen levels and the physical properties of a reservoir are often not suitable to the aquatic plants and animals that evolved with a given river system. Indeed, reservoirs often host non-native and invasive species (e.g. snails, algae, predatory fish) that further undermine the river's natural communities of plants and animals.
The alteration of a river's flow and sediment transport downstream of a dam often causes the greatest sustained environmental impacts. Life in and around a river evolves and is conditioned on the timing and quantities of river flow. Disrupted and altered water flows can be as severe as completely de-watering river reaches and the life they contain. Yet even subtle changes in the quantity and timing of water flows impact aquatic and riparian life, which can unravel the ecological web of a river system.
A dam also holds back sediments that would naturally replenish downstream ecosystems. When a river is deprived of its sediment load, it seeks to recapture it by eroding the downstream river bed and banks (which can undermine bridges and other riverbank structures, as well as riverside woodlands). Riverbeds downstream of dams are typically eroded by several meters within the decade of first closing a dam; the damage can extend for tens or even hundreds of kilometers below a dam.
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Answer:
A dam is a building constructed across a river or stream to retain water. Over the years, many materials have been utilised to construct dams. Ancient dam builders made use of raw resources like clay or stone. Today's dam builders frequently use concrete. Reservoirs—artificial lakes built by man-made dams—are created.
Explanation:
Large dams have a wide range of negative environmental effects, including direct effects on the biological, chemical, and physical characteristics of rivers and riparian (or "stream-side") habitats.
Fish migrations, which in some circumstances and with some species totally separate spawning grounds from rearing habitats, are obstructed by the dam wall itself. Additionally, the dam captures sediments that are essential for preserving physical processes and habitats downstream of the dam (including the maintenance of productive deltas, barrier islands, fertile floodplains, and coastal wetlands).
Upstream of the dam, where there had previously been a free-flowing river ecology, there is now an artificial slack-water reservoir habitat, which has major and evident effects. Changes in temperature, chemical make-up, dissolved oxygen levels, and physical characteristics of a reservoir are frequently unsuitable for aquatic life that has developed alongside a certain river system. Indeed, reservoirs frequently support invasive and non-native species (such as snails, algae, and predatory fish), which further jeopardize the natural plant and animal ecosystems along the river.
The most significant long-term environmental effects are frequently brought on by changes to a river's flow and sediment transport downstream of a dam. The timing and volume of a river's flow affect how life develops in and around it. Water flows that are disrupted or altered can cause just as much damage as entirely drying up river sections and the life that lives there. However, even little variations in water flow quantity and timing have an impact on aquatic and riparian species, which can disrupt the biological interdependence of a river system.
A dam also prevents the natural replenishment of downstream ecosystems by sediments. When a river's sediment load is taken away, it tries to get it back by eroding the banks and riverbed downstream (which can undermine bridges and other riverbank structures, as well as riverside woodlands). Within ten years of a dam's initial closure, riverbeds downstream often erode by several meters; the harm might reach tens or even hundreds of kilometers below a dam.
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