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LETTER OF THE DAY - Damn those dam ideas

Published:Monday | January 10, 2011 | 12:00 AM

THE EDITOR, Sir:

In response to the letter 'Dams needed', published Friday, January 7, I would urge this letter writer and the country, in general, to genuinely consider first what dams are and what they do. They impact! The environmental impacts of reservoirs and dams are coming under ever-increasing scrutiny as world demand for water and energy increases and the number and size of reservoirs increases.

The upstream impacts are as follows:

1. The damming of a river creates a reservoir upstream from the dam. The reservoir waters spill out into the surrounding environments, flooding the natural habitats that existed before the dam's construction, killing all that was there. The decaying plant matter itself settles at the non-oxygenated bottom of the reservoir, and the decomposition - unmitigated by a flow pattern that would oxygenate the water - produces and eventually releases dissolved methane.

2. A dam also acts as a barrier between the upstream and downstream movement of migratory river life, such as fish. Dams block their migration upstream to spawning areas, threatening to decrease reproduction numbers and reduce the species' population. Dams change a key ecosystem to which all surrounding ecosystems have adapted. Dam construction nearly always reduces wildlife diversity, for better or for worse. It also results in the loss of habitat of many living organisms.

3. The construction of a dam blocks the flow of sediment downstream, leading to downstream erosion of these sedimentary depositional environment, and increased sediment build-up in the reservoir. While the rate of sedimentation varies for each dam and each river, eventually all reservoirs develop a reduced water-storage capacity because of the exchange of storage space for sediment.

Impact below dam

As all dams result in reduced sediment load downstream, a dammed river is said to be 'hungry' for sediment because the rate of deposition of sediment is greatly reduced as there is less to deposit. But the rate of erosion remains nearly constant, the water flow eats away at the river shores and riverbed, threatening shoreline ecosystems, deepening the riverbed, and narrowing the river over time.

While reservoirs are helpful to humans, they can also be harmful as well. One negative effect is that the reservoirs can become breeding grounds for disease vectors. This holds true especially in tropical areas like Jamaica, where mosquitoes and snails - which are vectors for schistosomiasis - can take advantage of this slow-flowing water.

Reservoirs may contribute to changes in Earth's climate. Warm-climate reservoirs generate methane, a greenhouse gas, when the reservoirs are stratified, in which the bottom layers lack oxygen, leading to degradation of biomass through anaerobic processes.

So, as is evidenced by my argument, damming Jamaica is not an easy solution!

I am, etc.,

YANNICK PESSOA

yannickpessoa@yahoo.com

Montego Bay