One thing we have learnt this week-dams

Usina_Hidelétrica_do_Passo_RealHydroelectric dams.  They are a good thing right in fighting peak oil and climate change?  Well it depends.  This week there is a fuss over the building of a series of massive hydroelectric dams in Brazil with up to 26GWp capacity.  An astounding figure.  Greenpeace are opposing this and other vast hydro schemes in the Congo.

There are two problems with such dams.  The first is the one we all hear about which is loss of habitat and damage to indigenous tribes.  There seems never to be enough compensation to people displaced in this way by dams and you read of corruption from India to China.

The second problem is one you don’t so often hear about.  That is anaerobic digestion and the release of methane from the reservoirs.  This makes hydroelectric schemes (at least in the tropics) net greenhouse gas emitters.  The sludge at the bottom of the reservoirs contains organic compounds, bacteria and little oxygen.  Aerobic bacteria require oxygen for respiration but anaerobic bugs don’t and will grow quite happily without.  Instead of producing CO2 they produce methane a much more potent greenhouse gas.  In temperate regions of the world the lower water temperatures mean that either the bacteria don’t at all or only very partially so that the schemes are carbon negative overall.

Two questions arise.  Is there any way to stop this in the tropics?  The answer is almost certainly no.  The only exceptions to this might be schemes that do not use reservoirs (which do less of first type of damage) and high altitude schemes where the water is cold.  The second is with rising global temperatures how long before some hydro schemes in temperate regions become a problem?  One final point is that sediment does still exist at the bottom of reservoirs in temperate regions.  These need dredging if they are not to get silted up.  In most dams in this country this is made of peat.  Its now being sold as an environmentally friendly alternative to peat from peat bogs.

Neil

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