¶ … Damns on Wildlife and the Environment
Background to Dams and Levees - One of the issues resulting from civilization and urbanization is that most of the places humans chose to locate, for reasons of convenience, agriculture, transportation, and economic independence, have been near water. Dams provide hydroelectric power, help control floods, and make rivers navigable. Levees are quite similar to dams in their purpose, although they are primarily build to restrict water in times of high flow -- and for the majority of time are not under water. Per capita, floods are the most destructive and frequent of Mother Nature's natural disasters. In the last 50-60 years, in fact, the number and severity of flooding has worsened globally. Several reasons have contributed to this: global warming and worsening of storm activity; the deforestation and paving of natural watersheds; and more people living and working on known flood-plains. However, many scholars and engineers believe that it is not just the external conditions that are causing more flooding problems, but the very nature of the dam and levee method of flood control. When engineering projects reduce the capacity of river channels, block nature drainage, and increase the speed of floodwater, flood damage becomes greater. Additionally, the "hard path" flood control based on a working levee system often ruins the ecological health of rivers and estuaries (McCully, 2007).
Environmental Impact Issues- Despite the basic hydrological cycle, or the recirculation of moisture from ground to air and back, many areas of the world are overdeveloped and face an extreme shortage of potable water. The environmental impact of dams and reservoirs is increasingly receiving more attention as the global demand for water and energy increases, and the number and size of reservoir and damn projects increase. In general, the damming of a river creates some sort of a reservoir of water upstream from the dam. The dam project has four major environmental impact issues: upstream impacts, downstream impacts, effects beyond the reservoir, and then global or macro impacts.
Upstream Impacts- are due to the back flush of water that flows from the area of construction to the surrounding environment, flooding the natural habitats and creating a larger surface area than before the dam, and thus more evaporation. To date, scientists estimate some alarming statistics: over 400,000 km of the earth have been flooded dur to damming, and a loss of up to 2.1 meters of water to evaporation in some climates (Graham-Rowe, 2005). The initial filling of the reservoir floods the plant material already existing, leading to decomposition and rotting, which releases large amounts of carbon into the atmosphere. Because much of this rotted material exists at the lower or non-oxygenated bottom of the reservoir, there is little oxygen flowing, resulting in the over-production of dissolved methane (Marmulla, 2001).
Fragmentation of river ecosystems -- A dam also acts as a barrier between upstream and downstream movement of many migratory river animals and their spawning areas (e.g. trout and salmon). This threatens to reduce the species populations, and usually fish ladders are used to mitigate this. Even using this, or transporting fish via barge, wildlife often has difficulty migrating through or around a dam which, with the permanent altering of the wetlands surrounding the river, further disrupts eco systems. Dams may reduce the floodplains below, helping human populations, but the areas surrounding riverbanks are particularly rich in bio-diversity, which is also reduced. Many endemic species will not survive the environmental consequences, and new species are often likely to adopt the altered habitat, thus throwing off even more the indigenous eco-system (Maser, 2009).
Reservoir Sedimentation -- Rivers typically carry several different types of sediment down their riverbanks. This allows for a rich and diverse formation of river deltas, alluvial fans, braided rivers, riverbanks, oxbow lakes, and coastal shores. When a dam is constructed, it blocks the flow of sediment downstream, which leads to rather serious erosion of depositional environments, and increased sediment build-up in the reservoir. Eventually, most reservoirs develop a reduced water-storage capacity due to this build-up; which in turn results in a decrease in hydroelectric power, water for irrigation, and if left untouched, the eventual expiration of the dam and river (Morris and Fan, 1998).
Downstream Impacts - Placing a barrier where there was none creates havoc both upstream and downstream. As might be expected, the water that flows into the dam is not the same as the water...
In many ways, the Vietnam War represented the height of Cold War tensions in much the same way that the decade was giving way to an inevitable breaking point in environmental negligence. Though the years which would follow would see a gradual intensification of environmental protection laws, these have by and large been nullified by the impact of that for which Abbey offers the most criticism. With both Vietnam
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