The Impacts of Dams on the Hydrologic Regime

The earliest remains of blocks that archaeologists consider un cosmosed date back to nigh 5000 A.D.They were constructed as part of a domestic peeing system supply organisation for the ancient town of Jawa in Jordan. Over the next fewer millennia, the create of obstructs for water retention spread without the Mediterranean, the Middle East, Southern Asia, China, and key America. Later, as technologies increase and industrialization took hold in Europe, dkm mechanisms in advance(p) to incorporate wa callills. With the advent of the water turbine in 1832 and developments in electrical engineering, the starting hydropower plant began running in Wisconsin in 1882 (IRN n. pag.). Over the next few decades, while structural engineering techniques improved, dams multiplied in size, strength, and numbers worldwide.Today, although the whirl of new dams is halting ( albeit with less vigor in underdeveloped countries) (de Villiers 146 Pielou 206), they argon still being built arou nd the globe for a throng of social and economical reasons flood control, hydroelectric power production, river navigation, irrigation, human consumption, industrial use, emergency water reservation, tourism, and flat-water recreation (e.g., NPDP n. pag. Trout Unlimited 11). For all the benefits that dams provide, however, at that place ar ill effects and concerns that arise from manipulating the environment in such an stirred manner.Impacts of Dams on the Hydrologic RegimeDams are ultimately created as a water reservoir. This impounding of water impedes the circulation of a river and subsequently changes the hydrology and ecology of the river system and its abutting environments.Behind a dam, the rise in water level submerges the decorate often displacing people and engorging culturally valuable ruins. Furthermore, biodiversity of the region is constrained by the destruction of botany and freeing or extinction of wildlife (Power et al. 887-895). In essence, two the aqu atic and land-based ecosystems are damaged by the advent of a dam (Pielou 209).Upstream of the barricade, the once full stoping water that housed the riverine habitat becomes still, oxygen depleted, deepens into darkness, temperature stratified, and vulnerable to enhanced evaporation which adjusts the entire hydrologic cycle (e.g., Pielou 207, 210 Ocean Planet n. pag. Leopold 157). Moreover, drowned vegetation in the stagnant water is subject to rotting and whitethorn thereby pollute the atmosphere and reservoir with methane and carbon dioxide (Leopold 158 Pielou 208).A nonher change in the water chemistry that alters many river-based systems is the inclusion of heavy metals (and minerals) such as methyl mercury due to re achievements between the reservoir bed and the rest water (Pielou 114, 207). If undetected, these toxins may bioaccumulate by moving through the trophic levels of the nutriment web, finally reaching humans.Aside from the changes in the chemical constituencies of the water, a dam impart also physically augment the river by modifying the shape of the channel. This is mainly due to the retention of sediments behind the dam wall. Water that was once entrained with silts has the increase erosive power to degrade the riverbanks downstream while upstream, the deposition dish up is shallowing and narrowing the river reaches (e.g., Moffat 1116 Pielou 210). These alterations in channel shape can also swag the elevation of the groundwater table and can amplify the severity of the floods that the dams may have been built to prevent (de Villiers 155-56 PCFFA n. pag.).The silting process, though, can have other effects on riverine environments. With the deprivation of sediments, valuable nutrients are withheld from the floodplains and the delta of the river. Ultimately, agricultural land suffers from fertility loss and coastlines recede (e.g., DRIIA n. pag. Pielou 212). In addition to the above noted deterioration of wetland environs, major fish spawning and nursing grounds are harmed by the lack of continual silt and gravel replenishment (e.g., Chambers n. pag.).Fish species, nevertheless, are not simply affected by the decreased deposition that occurs below a dam. These, and other aquatic based biota adapted to the natural pulsations of seasonal worker flooding, can be strained by the regulation of stream full point afforded by a dam (Pielou 145 Leopold 156). Furthermore, moderating the flow may actually retard the entire regime of the river by delaying spring break-up (Pielou 212). obscure(predicate) from the precipitous effects on the hydrologic cycle and river-based ecosystems thus far noted, there are an extensive number of further reasons to remove a dam. Briefly, a few of these are (Ocean Planet n. pag. Pielou 208-09 Trout Unlimited 17 Leopold 156)x the overhaul of anadromous fish migration and subsequent reliant fisheriesx ameliorate conditions associated with damming which advertize epidemics such as bilharzia and milariax damming has accelerated the rate of earths rotation, displaced the axis of the earth, changed the shape of earths magnetic field, increased the occurrence of seismic events, and influenced sea level changesx dam remotion has been shown to improve recreation, tourism, and aesthetics to the associated riverside communitiesx amend the river and groundwater quality thus far for all of the reasons that a dam may be removed, it is often economic and, in part, safety purposes that prompts the decommissioning of a dam. Whether the reservoir has filled with silt, wear-and-tear has taken its toll, or the dam has become obsolete, the benefit of removal may outweigh the make up of maintaining dam operation (PCFFA n. pag.).Consequences Associated with Dam Removal A Case require of the Elwha RiverEarly in the 20th century, two hydroelectric dams were built on the Elwha River within the Olympic Peninsula of Washington State. The Elwha Dam, the first to be constructed (1910), create d the Lake Aldwell reservoir 4.9 miles from the tattle of the Elwha river fig. 1. Respectively, 8.5 miles upstream, Lake Mills is contained by the Glines canyon Dam (1926). Despite their continued winner as a viable resource for Bonneville Power Administration (Meyer n. pag.), the world and utilization of the Elwha and Glines Canyon dams causes detrimental besetment for the ecosystem and native anadromous fish populations of the Elwha River bathroom (U.S. Dept. of the Interior, 1995, n. pag.). Thus, per restitution stipulations, the 1992 Elwha River Ecosystem and Fisheries Restoration Act (the Elwha Act) authorized the Secretary of the Interior to admit the two dams (e.g., Winter n. pag.). Measures to remove the dams exit be undertaken as approved from the Environmental Impact Assessment (EIS) that followed in 1995.Fig. 1. Map of the Elwha River, Clallam County, Olympic Peninsula, Washington.(Olympic home(a) Park n. pag.)In an effort to remove the dams in a safe, environmental ly sound and cost effective manner (U.S. Dept. of the Interior, Apr. 1996, n. pag.), various procedural resources are being considered prior to the implementation of the scheduled 2004 deconstruction. Under the River Erosion resource, which is the proposed action, the Elwha and Glines Canyon dams would be incrementally removed in succession over a two year period with the controlled regulation of natural sediment erosion (e.g., U.S. Dept. of the Interior, Aug. 1996, n. pag.). A dredge and slurry system, a further method of sediment disposal, is an action alternative that has also been analyzed by the Environmental Impact Statement (EIS) aggroup (e.g., U.S. Dept. of the Interior, Apr. 1996, n. pag.).Between the inauguration of the Elwha River dams and 1994, it is estimated that 17.7 million cubic yards of sediments has become trapped in the Lake Aldwell and Lake Mills reservoirs (U.S. Dept. of the Interior, Aug. 1996, n. pag.). Of that total deposition, some 4.8 to 5.6 million cub ic yards of fine-grained flood (silts and clays less than 0.075 m in diameter) and 1.2 to 2.6 million cubic yards of coarse grained sediments (sands, gravels, and cobbles great than 0.075 mm in diameter) provide be reintroduced into the Elwha River system through the proposed action (U.S. Dept. of the Interior, Apr. 1996, n. pag. U.S. Dept. of the Interior, Aug. 1996, n. pag.).In comparison, approximately 6.9 million cubic yards of the fine-grained sediments stand to be directly pumped via a pipeline into the Strait of Juan de Fuca if the dredge and Slurry alternative is undertaken (U.S. Dept. of the Interior, Aug. 1996, n. pag.). Incremental removal of the dams forget be the primary regulation on the rate of sediment withdrawal and will partially effect the resulting term of biological and physical impacts felt on downstream reaches of the Elwha River (U.S. Dept. of the Interior, Aug. 1996, n. pag.).An increase of alluvial sediment transport will renew the natural sediment dist ribution and hydrological flow patterns to their pre-dam character while new channels and wetland habitats will be created in the freshly drained areas (Foster Wheeler 17). Aggradation of stream load materials will be most prominent in the low-lying and less circulating shoals, including a revitalization of the Ediz Hook fig. 1 and estuarine beaches (U.S. Dept. of the Interior, Aug. 1996, n. pag.). In response to these raised river beds, water elevations are expected to rise, thereby threatening the resources that fall within the 100-year floodplain (U.S. Dept. of the Interior, Apr. 1996, n. pag.).Surface water quality is likely to be hampered for two to 6 years after dam abstraction as turbidity, suspended sediments and dissolve solids flow through the system. Furthermore, water temperatures, dissolved oxygen concentrations, and pH levels will be affected for the interim of dam removal (U.S. Dept. of the Interior, Apr. 1996, n. pag.). Turbidity, in turn, will be the chief cause of groundwater contamination by infiltration into be foundations or well and septic systems (removal (U.S. Dept. of the Interior, Apr. 1996, n. pag.).The implementation of either the Proposed Action or Dredge and Slurry alternatives will also impact the native anadromous (indigenious?) and resident physician populations on the Elwha River. The high sediment regimes, especially those of the River Erosion Alternative (the proposed action), will encumber the migrating fish over the deconstruction process.However in the yen term, runs will improve with the staged delayed of dam destruction, fisheries management (including the add-on fish stocks through hatchery intervention), unrestricted passage up the full spread out of the Elwha River, and the formation of quality spawning grounds and rearing habitats from the released sediments (U.S. Dept. of the Interior, Aug. 1996, n. pag.). (steph, this last paragraph seems ak shield) Moreover, apart from the obvious economic profits of salmon run restoration, the heightened decomposition of short fish after spawning will significantly enrich nutrients cycling through the riparian area (Munn et al. n. pag.).Magnified numbers of anadromous fish will, too, eventually increase the biotic diversity down the length of the Elwha Basin. In the incoming wildlife will be drawn to the decaying remains of dead fish and their five-year-old even though the immediate disturbances during the removal period may ward off certain animals (U.S. Dept. of the Interior, Apr. 1996, n. pag.). Vegetation and marine organisms will benefit from the circulation of total remains those primarily adapted to sandy substrates will flourish after the initial strain of post-dam sediment conditions (Winter, 2000, n. pag. U.S. Dept. of the Interior, Aug. 1996, n. pag.).Prospective temporary consequences to the environment will also include air, traffic, and noise pollution in conjunction with dam destruction and debris conveyance (U.S. Dept. of the Inter ior, Apr. 1996, n. pag.).This Elwha River case study exemplifies the foremost probable impacts on the hydrologic cycle and the environmental ecosystems which it encompasses. Successful removal of a dam can, in the end, rehabilitate a region to its natural state. Recovery, however, is not without adverse consequences to the existing regimes and full restoration may take many years.