TucuruÃ, Brazil’s second largest dam has many times the GHG emissions of a natural gas plant of the same capacity — though there is fierce argument over whether that output substantially exceeds what a natural watercourse would produce. (The emissions are due to methane from trapped organic matter in the dam.)
There is now a proposal to tap that methane to run gas turbines and produce electricity, reducing the emissions many times, since CO2 from burning the methane has a much lower impact than the methane itself. It would also close to double the electrical output from the dam. This seems very close to an acknowledgment that critics of methane from dams are correct. Outside of estuaries, I don’t know many natural water courses that might be tapped in such a way. I have to admit that it is an ingenious solution to the problems of dams as methane sources.
How complete a solution is another question: I’d be curious to know what percent of methane production they are proposing to capture. They don’t have to capture all of it to reduce greenhouse impact to zero — some of the methane would produced anyway, though how much is under dispute. At any rate, I’d be curious see estimates of net methane production minus the dam, compared to net methane production with the dam plus methane capture and burning.
Methane capture won’t undo any of other damage dams often do, of course, but it may be a solution to the problem of dams as net greenhouse emitters.