Recent scientific studies have shown that previously ignored carbon and methane emissions from reservoirs are a significant source of greenhouse gases, and these emissions are not just limited to the first few years of vegetation potentially drowning after a new reservoir is formed, emissions being significant for periods of 20yrs and beyond.
The BHA recognises the essential role that the science must play in the feasibility and carbon analysis of projects involving the formation of new reservoirs. It is important that projects that do not significantly contribute to the overall lowering of greenhouse gas emissions are not incorrectly considered as viable.
Too often a lack of knowledge and understanding of the positives and negatives of large dam projects have led to polarised debate with individuals either for hydropower or against it. The reality is that the difference between the positives and negatives of large dam hydropower is so vast that both camps can be right and wrong.
For example a new dam of say 150m in height, for example in the fords of Norway, might have a reservoir capacity that is very large from a relatively small surface area and be on a site with a large river flow. Calculations on drowned area and methane emissions show that the emissions are (including consideration of the very high global warming potential of methane, 25 times that of CO2) a very tiny fraction compared with the carbon savings from replacing fossil fuel power generation. However take the same set of calculations to for example the 128m high Kariba Dam on the Zambezi river at the Zimbabwe/Zambia border with its large shallow tropical reservoir, the yearly methane CO2 equivalent emissions come out significantly larger than the carbon savings from the yearly electricity generation.
When it comes to reservoir surface evaporation, another significant issue in some parts of the world, the difference from one project to another can be significant being dependant on surface area and climate/location.
The BHA support projects that provide overall significant benefit and we support every effort on the work that is undertaken to ensure that only environmentally beneficial hydropower projects are built with care for the natural environment through planning, construction and throughout their operation.