The Impacts of Dams on the Hydrologic Regime

The earliest remains of obstructs that archaeologists have unearthed find back to around 5000 A.D.They were constructed as part of a domestic wet supply governing body for the ancient town of Jawa in Jordan. everyplace the contiguous few millennia, the building of dams for pee retention spread by dint ofout the Mediterranean, the oculus East, Southern Asia, China, and Central America. Later, as technologies increased and industrialization took hold in Europe, dam mechanisms advanced to incorporate watermills. With the approaching of the water turbine in 1832 and developments in electrical engineering, the first hydro indi thronet plant began barragening in Wisconsin in 1882 (IRN n. pag.). Over the next few decades, speckle structural engineering techniques improved, dams multiplied in size, strength, and numbers worldwide.Today, although the construction of new dams is halting ( albeit with less(prenominal) vigor in underdeveloped countries) (de Villiers 146 Pielou 206), they are still being built around the b altogetherock for a multitude 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, there are adverse effects and concerns that arise from manipulating the environment in such an un congenital manner. wallops of Dams on the Hydrologic RegimeDams are ultimately created as a water germ. This impounding of water impedes the circulation of a river and subsequently changes the hydrology and bionomics of the river system and its contiguous environments.Behind a dam, the rise in water level submerges the let downscape often displacing people and engorging culturally valuable ruins. Furthermore, biodiversity of the expanse is constrained by the destruction of vegetation and loss or quenching of wildlife ( military unit et al. 887-895). In essence, both the aquatic and land-based ecosystems are damaged by the advent of a dam (Pielou 209).Upstream of the barricade, the once flowing water that housed the riverine habitat functions still, type O depleted, deepens into darkness, temperature stratified, and susceptible to enhanced evaporation which adjusts the entire hydrologic cycle (e.g., Pielou 207, 210 sea Planet n. pag. Leopold 157). Moreover, drowned vegetation in the stagnant water is subject to depravation and may thereby pollute the atmosphere and reservoir with methane and carbon dioxide (Leopold 158 Pielou 208).an some other(prenominal) change in the water chemistry that alters many river-based systems is the inclusion of punishing metals (and minerals) such as methyl mercury due to reactions between the reservoir bed and the standing water (Pielou 114, 207). If undetected, these toxins may bioaccumulate by moving through the trophic levels of the food web, eventually reachi ng humans.Aside from the changes in the chemical constituencies of the water, a dam allow also physically augment the river by modifying the shape of the channel. This is primarily due to the retention of depositorys behind the dam wall. pee that was once entrained with silts has the increased erosive power to degrade the riverbanks downriver while upstream, the affirmation process is shallowing and narrowing the river reaches (e.g., Moffat 1116 Pielou 210). These alterations in channel shape can also shift the elevation of the groundwater table and can amplify the sourness 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 depositations, 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). I n addition to the above celebrated 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.). look for species, nevertheless, are not simply affected by the decreased deposition that occurs below a dam. These, and other aquatic based biota competent to the natural pulsations of seasonal flooding, can be strained by the economy of stream flow afforded by a dam (Pielou 145 Leopold 156). Furthermore, chair the flow may actually retard the entire regime of the river by delaying spring break-up (Pielou 212).Apart from the precipitous effects on the hydrologic cycle and river-based ecosystems gum olibanum far noted, there are an extensive number of further reasons to reach a dam. Briefly, a few of these are (Ocean Planet n. pag. Pielou 208-09 Trout Unlimited 17 Leopold 156)x the restoration of anadromous fish migration and subsequent reliant fisheriesx ameliorate conditions as sociated with damming which promote epidemics such as bilharzia and milariax damming has accelerate 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 renovate the river and groundwater qualityYet 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 alter with silt, wear-and-tear has conn its toll, or the dam has become obsolete, the benefit of removal may outweigh the cost of maintaining dam operation (PCFFA n. pag.).Consequences Associated with Dam Removal A Case Study 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), 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). contempt their continued success as a viable resource for Bonneville Power Administration (Meyer n. pag.), the existence and utilization of the Elwha and Glines Canyon dams causes detrimental besetment for the ecosystem and indispensable anadromous fish populations of the Elwha River basin (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 writing table of the Interior to appropriate the two dams (e.g., Winter n. pag.). Measures to remove the dams ordain be undertaken as sanctioned from the Environmental Impact Assessment (EIS) that followed in 1995.Fig. 1. stage of the Elwha River, Clallam County, Olympic Peninsula, Washington.(Olympic National Park n. pag.)In an effort to remove the dams in a safe, environmentally sound and cost effective manner (U.S. Dept. of the Interior, Apr. 1996, n. pag.), sundry(a) procedural alternatives are being considered prior to the implementation of the scheduled 2004 deconstruction. down the stairs the River corrosion alternative, which is the proposed action, the Elwha and Glines Canyon dams would be incrementally removed in succession over a two year cessation 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) 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 million cubelike 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 three-d yards of fine-grained alluvium (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 greater than 0.075 mm in diameter) lead 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 pass 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 will be the uncreated regulation on the rate of sediment withdrawal and will partly effect the resulting term of biological and physical impacts felt on downstream reaches of the Elwha River (U.S. Dept. of the Inter ior, Aug. 1996, n. pag.).An increase of alluvium transport will renew the natural sediment distribution 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 shoot 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 blood line 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 dissolved solids flow through the system. Furthermore, water temperatures, dissolved oxygen concentrations, and pH levels will be affected for the interim of d am 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 underlying 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 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. all the same in the long term, runs will improve with the staged delayed of dam destruction, fisheries management (including the supplementation fish stocks through hatchery intervention), unrestricted passage up the full stretch 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 finis paragraph seems akward) Moreover, apart from the obvious economic profits of salmon run restoration, the heightened decomposition of d.o.a. fish after spawning will significantly meliorate 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 distance of the Elwha Basin. In the future wildlife will be drawn to the decaying remains of dead fish and their young 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 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 unpredictable 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 Interior, Apr. 1996, n. pag.).This Elwha River case watch 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.