Hydrology Essay Research Paper IntroductionThe earliest remains

Hydrology Essay, Research Paper

Introduction

The earliest remains of dams that archaeologists have unearthed date back to around 5000 A.D.They were constructed as part of a domestic water supply system for the ancient town of Jawa in Jordan. Over the next few millennia, the building of dams for water retention spread throughout the Mediterranean, the Middle 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 advent of the water turbine in 1832 and developments in electrical engineering, the first 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 construction of new dams is halting ( albeit with less vigor in underdeveloped countries) (de Villiers 146; Pielou 206), they are still being built around the globe 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 unnatural manner.

Impacts of Dams on the Hydrologic Regime

Dams 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 contiguous environments.

Behind a dam, the rise in water level submerges the landscape; often displacing people and engorging culturally valuable ruins. Furthermore, biodiversity of the region is constrained by the destruction of vegetation and loss or extinction of wildlife (Power 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 becomes still, oxygen depleted, deepens into darkness, temperature stratified, and susceptible 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 may thereby pollute the atmosphere and reservoir with methane and carbon dioxide (Leopold 158; Pielou 208).

Another 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 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 reaching humans.

Aside from the changes in the chemical constituencies of the water, a dam will also physically augment the river by modifying the shape of the channel. This is primarily due to the retention of sediments behind the dam wall. Water that was once entrained with silts has the increased erosive power to degrade the riverbanks downstream while upstream, the deposition 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 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 flooding, can be strained by the regulation 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).

Why Remove a Dam.

Apart 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 restoration of anadromous fish migration and subsequent reliant fisheries

x ameliorate conditions associated with damming which promote epidemics such as bilharzia and milaria

x damming has accelerated the rate of earth s rotation, displaced the axis of the earth, changed the shape of earth s magnetic field, increased the occurrence of seismic events, and influenced sea level changes

x dam removal has been shown to improve recreation, tourism, and aesthetics to the associated riverside communities

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