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While the natural gas industry and cows get a bad reputation for emitting methane — a greenhouse gas that scientists say contributes to global warming — a form of renewable energy touted as a green alternative might actually be producing more of this potent gas than previous thought.

Hydroelectric power and reservoirs, which were thought to account for about 20 percent of all man-made methane emissions, could be producing even more, according to the blog Climate Central.

The U.S. Environmental Protection Agency considers methane to be the second most abundant greenhouse gas from human activities in the U.S. There are natural sources and sinks of methane as well. Though its “lifetime” is shorter than that of carbon dioxide, another greenhouse gas, methane has a 20 times greater impact on climate change than CO2 per pound, the EPA says.

Subjectivist wrote:Interesting new hit piece against hydroelectricity, more at link.

While the natural gas industry and cows get a bad reputation for emitting methane — a greenhouse gas that scientists say contributes to global warming — a form of renewable energy touted as a green alternative might actually be producing more of this potent gas than previous thought.

Hydroelectric power and reservoirs, which were thought to account for about 20 percent of all man-made methane emissions, could be producing even more, according to the blog Climate Central.

The U.S. Environmental Protection Agency considers methane to be the second most abundant greenhouse gas from human activities in the U.S. There are natural sources and sinks of methane as well. Though its “lifetime” is shorter than that of carbon dioxide, another greenhouse gas, methane has a 20 times greater impact on climate change than CO2 per pound, the EPA says.

http://www.theblaze.com/stories/2014/10 ... y-thought/

Subjectivist wrote:Interesting new hit piece against hydroelectricity, more at link.

Loki wrote:

Subjectivist wrote:Interesting new hit piece against hydroelectricity, more at link.

It's hardly a "hit piece," we've known for years that hydroelectric reservoirs and other manmade impoundments emit methane. The rate depends in part on age and latitude. There are plenty of scientific articles on the subject.

Hydro-Québec Production a obtenu l'autorisation de construire un complexe hydroélectrique de 1 550 MW sur la rivière Romaine, au nord de la municipalité de Havre-Saint-Pierre, sur la Côte-Nord. Composé de quatre centrales alimentées par des réservoirs, le complexe de la Romaine offrira une production annuelle moyenne de 8 TWh. Une route permanente de 150 km reliera la route 138 à la zone d'implantation des ouvrages.

http://www.hydroquebec.com/romaine/projet/index.html

As of 2007, there were more than 600 hydroelectric projects operating in Brazil with a total capacity of more than 73,000 MW, according to the Ministry of Mines and Energy. And Brazil is home to the second largest hydroelectric facility in the world in terms of installed capacity: 14,000 MW Itaipu on the Parana River on the border between Brazil and Paraguay. The first unit began operating at Itaipu in May 1984. Hydro development activity in the country is scheduled to continue at a rapid pace, with more than 31,000 MW of new projects scheduled for completion by 2017.

http://www.hydroworld.com/articles/prin ... pment.html

Subjectivist wrote:

Loki wrote:

Subjectivist wrote:Interesting new hit piece against hydroelectricity, more at link.

It's hardly a "hit piece," we've known for years that hydroelectric reservoirs and other manmade impoundments emit methane. The rate depends in part on age and latitude. There are plenty of scientific articles on the subject.

Tomate-toe/Tomaht-toe. Sure there are lots of papers on the topic, but why now and why report it this way?

Climate Central reported that scientists are beginning to think, based on recent research, that reservoirs might be more of a methane source, but they don’t know how much more due to a lack of data.

“[It's] still a big question mark,” John Harrison with Washington State University, Vancouver’s School of the Environment told Climate Central.

With that, he added that he doesn’t think “we really know what the relative greenhouse gas effect of reservoirs is compared to other sources of energy in the U.S.”

“We’re still in the very early days here of understanding how these systems work with respect to greenhouse gas production,” Harrison told Climate Central.

The EPA is beginning a study that will measure the emissions at 25 reservoirs from Indiana to Georgia. Data from this study will allow the agency to better estimate the contribution reservoirs have on methane emissions from man-made sources.

The useful life of a hydroelectric project can be measured by its engineered elements or by its rate of sedimentation. Efficiencies and improvements in design of the power plant and hydraulic elements can almost indefinitely expand the useful engineering life of the equipment; however, sedimentation is an inherent limiting factor of the hydroelectric facility. Moreover, dredging or weir construction can add to the useful life of a project, even though the energy and environmental consequences of dredging may outweigh the benefits of such an undertaking. The fundamental rate of sedimentation of dams varies widely, but useful lives of twenty to 100 years represent the majority of plant expectations.[1] Correspondingly many of the world's major hydro plants are well along in their life cycle.
http://www.eoearth.org/view/article/153619/

From 1993, when the Manwan Dam started to store water, to 2003 ... The reservoir capacity loss caused by the annual sediment trapped is ... equivalent to 21.5-22.8% of the total storage capacity of the Manwan reservoir.
https://www.zotero.org/start_library/it ... y/36QHM9H4

Professor K. Mahmood of George Washington University in Washington, DC, "roughly estimated" for a 1987 World Bank study that around 50 cubic kilometres of sediment – nearly one per cent of global reservoir storage capacity – is trapped behind the world’s dams every year. In total, calculated Mahmood, by 1986 around 1,100 cubic kilometres of sediment had accumulated in the world’s reservoirs, consuming almost one–fifth of global storage capacity.

The rate of reservoir sedimentation depends mainly on the size of a reservoir relative to the amount of sediment flowing into it: a small reservoir on an extremely muddy river will rapidly lose capacity; a large reservoir on a very clear river may take centuries to lose an appreciable amount of storage. Large reservoirs in the US lose storage capacity at an average rate of around 0.2 per cent per year, with regional variations ranging from 0.5 per cent per year in the Pacific states to just 0.1 per cent in reservoirs in the northeast. Major reservoirs in China lose capacity at an annual rate of 2.3 per cent.
...
In fact, time and again dam planners have made hugely overoptimistic predictions that reservoirs will fill much more slowly than they actually do. Chixoy is one of a number of very expensive hydrodams built in Central America during the 1970s and 1980s with loans from the World Bank and Inter–American Development Bank despite the very high and accelerating rates of erosion in their watersheds. These dams are now rapidly filling with sediment, leaving small, impoverished countries like Guatemala, Honduras and Costa Rica with huge debts and in desperate need of building new power plants to reduce their dependence on their white–elephant dams. A team from the US Army Corps of Engineers concluded in 1993 that sedimentation could reduce the life of the 135 MW Cerron Grande Dam in El Salvador to 30 years – compared to the pre–construction prediction of 350 years.

In India, government statistics on eleven of the country’s reservoirs with capacities greater than one cubic kilometre show that all are filling with sediment faster than expected, with increases over assumed rates ranging from 130 per cent (Bhakra) to 1,650 per cent (Nizamsagar in Andhra Pradesh). A 1990 World Bank paper on watershed development concluded that in India, "erosion and [reservoir] sedimentation are not only severe and costly, but accelerating. It is now obvious that the original project estimates of expected sedimentation rates were faulty, based on too few reliable data over too short a period."

Most modern dams are designed so that they can afford to lose some storage capacity without their performance being impaired – the part of a reservoir known as "dead storage" which lies beneath the elevation of the dam’s lowest outlet. However sediments do not build up evenly along a horizontal plane, so that some "live storage" is usually lost long before the dead storage is filled. At Tarbela Reservoir in Pakistan, for example, 12 per cent of the live storage had been lost by 1992 (after 18 years of operation) while 55 per cent of the dead storage was still empty of sediment.
http://www.internationalrivers.org/sedi ... -with-dams

More than 60 percent of the sediment delivered to the world's oceans in the prehuman world originated from erosion in mountainous areas with elevations greater than 3 km above sea level.
...
Other analyses suggest that inland reservoirs today hold about 100 billion metric tons of sediment. Most of that material, with a carbon content of 1 to 3 percent, is sequestered behind dams that have been constructed in the past 50 years, says Syvitski. That carbon-rich matter, now locked away, is unavailable to nourish coastal ecosystems.
http://www.phschool.com/science/science ... aters.html

He noted that Fresno Reservoir on the Milk River in northern Montana has lost about one-third of its water storage capacity since it was built in the 1930s. Bighorn Reservoir has lost only 4 to 5 percent, he said.
http://billingsgazette.com/lifestyles/r ... a4df6.html

Tanada wrote:KM your very first citation admits that weir's or dredging cures sedimentation, which is something I have been saying on PO.com for almost ten years. Thanks for your support.

the energy and environmental consequences of dredging may outweigh the benefits

Tanada wrote:The two most sensible things to do are to reclaim the soil because it tends to have high fertility.

Tanada wrote: Failing that dumping it down stream of the dam restores a balance to the ecosystem interrupted by the impoundment of the sediment behind the dam structure.

Tanada wrote:The two most sensible things to do are to reclaim the soil because it tends to have high fertility. Failing that dumping it down stream of the dam restores a balance to the ecosystem interrupted by the impoundment of the sediment behind the dam structure.