The Impacts of Dams on the Hydrologic Regime

The soonest carcass of jams that archaeologists have unearthed date posterior to around 5000 A.D.They were constructed as part of a domestic pissing supply remains for the ancient town of Jawa in Jordan. either over the next few millennia, the building of impedes for piddle remembering spread by dint ofout the Mediterranean, the nub East, Southern Asia, China, and Central America. Later, as technologies subjoin and industrialization took hold in Europe, obstruct mechanisms advanced to incorporate peemills. With the advent of the piddle turbine in 1832 and developments in electrical engineering, the premier(prenominal) hydropower plant began running in Wisconsin in 1882 (IRN n. pag.). Over the next few decades, charm structural engineering techniques improved, dams multiplied in size, strength, and add up worldwide.Today, although the construction of new dams is halting ( albeit with little vigor in developing countries) (de Villiers 146 Pielou 206), they be still being built around the globe for a confluence of social and stintingal reasons flood control, hydroelectric power production, river navigation, irrigation, human consumption, industrial use, collar piss reservation, tourism, and flat-water recreation (e.g., NPDP n. pag. Trout Unlimited 11). For all the benefits that dams provide, however, there be adverse do and c one timerns that arise from manipulating the milieu in such(prenominal) an un innate manner.Impacts of dam ups on the Hydrologic RegimeDams ar ultimately created as a water reservoir. This impounding of water impedes the circulation of a river and after screens changes the hydrology and ecology of the river system and its contiguous environments. back end a dam, the rise in water level submerges the landscape often displacing race and engorging culturally valuable ruins. Furthermore, biodiversity of the region is agonistic by the destruction of vegetation and neediness or extinction of wildlife (Power e t al. 887-895). In essence, some(prenominal) the aquatic and land-based ecosystems be damaged by the advent of a dam (Pielou 209). upriver of the barricade, the once shineing water that housed the riverine home ground fails still, oxygen depleted, deepens into darkness, temperature stratified, and susceptible to enhanced dehydration which adjusts the wide hydrologic rung (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 ampere-second dioxide (Leopold 158 Pielou 208).A nonher change in the water chemistry that alters many river-based systems is the inclusion of difficult metals (and minerals) such as methyl hectogram due to reactions between the reservoir draw back and the standing water (Pielou 114, 207). If undetected, these toxins may bioaccumulate by moving through the trophic levels of the nutrient web, eventu ally reaching humans.Aside from the changes in the chemical constituencies of the water, a dam allow for also physically augment the river by modifying the organize of the channel. This is primarily due to the retention of bank deposits behind the dam wall. Water that was once entrained with silts has the increased erosive power to let down the riverbanks downstream while upstream, the deposition procedure is shallowing and narrowing the river reaches (e.g., Moffat 1116 Pielou 210). These alterations in channel shape fag also shift the aggrandisement of the groundwater table and can amplify the sourness of the floods that the dams may have been built to frustrate (de Villiers 155-56 PCFFA n. pag.).The silting process, though, can have other cause on riverine environments. With the deprivation of bank deposits, valuable nutrients ar withheld from the floodplains and the delta of the river. Ultimately, agricultural land suffers from fertility pass and coastlines recede ( e.g., DRIIA n. pag. Pielou 212). In addition to the in a higher place noted deterioration of wetland environs, major look for spawning and nursing grounds are harmed by the lack of continual silt and get 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 biological science adapted to the inbred pulsations of seasonal flooding, can be gradeed by the ruler of stream flow 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).aside from the precipitous hearts on the hydrologic cycle and river-based ecosystems thus far noted, there are an extensive number of further reasons to need a dam. Briefly, a few of these are (Ocean Planet n. pag. Pielou 208-09 Trout Unlimited 17 Leopold 156)x the amends of anadromous seek migration and resultant reli ant slanteriesx ameliorate conditions associated with damming which crowd 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 riverbank communitiesx amend the river and groundwater quality tho for all of the reasons that a dam may be pull backd, it is often economic and, in part, safety purposes that prompts the decommissioning of a dam. Whether the reservoir has change with silt, wear-and-tear has taken its toll, or the dam has become obsolete, the benefit of removal may outmatch the cost of maintaining dam operation (PCFFA n. pag.).Consequences Associated with Dam Removal A Case athletic field of the Elwha RiverEarly in the 20th century, twain hydroelectric dams were built on the Elwha R iver in spite of appearance the Olympic Peninsula of Washington State. The Elwha Dam, the first to be constructed (1910), created the Lake Aldwell reservoir 4.9 miles from the mouth of the Elwha river fig. 1. Respectively, 8.5 miles upstream, Lake Mills is contained by the Glines Canyon Dam (1926). Despite their keep success as a feasible resource for Bonneville Power Administration (Meyer n. pag.), the earth and utilization of the Elwha and Glines Canyon dams causes detrimental besetment for the ecosystem and native Australian anadromous fish populations of the Elwha River basin (U.S. Dept. of the Interior, 1995, n. pag.). Thus, per remediation stipulations, the 1992 Elwha River Ecosystem and Fisheries Restoration Act (the Elwha Act) authorized the secretarial assistant of the Interior to appropriate the 2 dams (e.g., spend n. pag.). Measures to remove the dams go away be undertaken as sanctioned from the Environmental Impact opinion (EIS) that followed in 1995.Fig. 1. M ap of the Elwha River, Clallam County, Olympic Peninsula, Washington.(Olympic study Park n. pag.)In an effort to remove the dams in a safe, environmentally depart and cost effective manner (U.S. Dept. of the Interior, Apr. 1996, n. pag.), divers(a) procedural alternatives are being considered foregoing to the implementation of the scheduled 2004 deconstruction. Under the River corrosion alternative, which is the proposed action, the Elwha and Glines Canyon dams would be incrementally removed in succession over a twain year period with the controlled regulation of natural sediment erosion (e.g., U.S. Dept. of the Interior, Aug. 1996, n. pag.). A hale and slurry system, a further method of sediment disposal, is an action alternative that has also been canvas by the Environmental Impact record (EIS) Team (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 billion cubelike yards of sedimen ts 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 one thousand thousand cubic yards of fine-grained alluvial sediment (silts and clays less than 0.075 m in diameter) and 1.2 to 2.6 gazillion cubic yards of coarse grained sediments (sands, gravels, and cobbles greater than 0.075 mm in diameter) give 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 line of reasoning 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 leave alone be the primal regulation on the rate of sediment withdrawal and leave alone partially effect the resu lting term of biological and physical repairs matte on downstream reaches of the Elwha River (U.S. Dept. of the Interior, Aug. 1996, n. pag.).An increase of alluvium transport will renew the natural sediment distribution and hydrological flow patterns to their pre-dam reference point while new channels and wetland habitats will be created in the freshly beat(p) 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 assume 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 six years after dam abstraction as turbidity, suspended sediments and dissolve solids flow through the system . Furthermore, water temperatures, dissolve 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 hirer cause of groundwater contamination by percolation into underlying foundations or well and unhealthful 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 populations on the Elwha River. The high sediment regimes, especially those of the River eroding Alternative (the proposed action), will encumber the migrating fish over the deconstruction process.However in the long term, runs will improve with the arranged delayed of dam destruction, fisheries management (including the accessory fish stocks through hatchery intervention), unrestricted pass up the full stretch of the Elwha River, and the composition o f quality spawning grounds and rearing habitats from the released sediments (U.S. Dept. of the Interior, Aug. 1996, n. pag.). (steph, this move paragraph seems akward) Moreover, apart from the obvious economic profits of salmon run restoration, the heightened putrefaction of dead 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 duration of the Elwha Basin. In the future wildlife will be drawn to the decaying remains of dead fish and their young even though the ready disturbances during the removal period may ward off certain animals (U.S. Dept. of the Interior, Apr. 1996, n. pag.). Vegetation and shipboard soldier organisms will benefit from the circulation of organic 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 preventive pollution in conjunction with dam destruction and debris conveyance (U.S. Dept. of the Interior, Apr. 1996, n. pag.).This Elwha River shell 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.