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Comment by hinkley | Hacker News Reader

But we can engineer nature. Beavers did it for tens of thousands of years before we showed up.

There are groups experimenting with reestablishing beavers on tributaries of the Columbia river, with positive results. We really need to be doing these on the upper reaches of the Colorado.

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you can build the largest reservoir in the world, but if water consumption and evaporation exceed precipitation in the watershed you're on borrowed time.

I wonder how beaver activity impacts evaporation rates versus human reservoir-building? Does lots of small ponds (perhaps mostly in wooded areas?) work better than a few massive reservoirs?

Wait, what? You'd need hundreds of thousands of "small ponds" in the woods to approximate a comparison with a human mega reservoir like Lake Mead and associated reservoirs. I don't really understand the comparison.

I think you're underestimating the extent of beaver altered terrain in the west. Estimates are between 60 and 400 million beaver before the fur trade started. We are currently sitting at 6-12 million and there are a number of watersheds where they have to be reintroduced because there are no populations in that area.

I was actually reading the other day about beavers and supposedly as much as 10% of North America was covered in beaver-built reservoirs and ponds. There were a lot of beavers.

Wet forest land cools the air. When humid air hits cold air you get rain. We don’t know the extent to which biological systems create their own rain, but we know it’s greater than zero. Also ground water recharging helps restore the water table, which helps keep the flow rate of the river higher for longer.

So yes, keeping water in the system longer doesn’t magically increase the rate you can draw it down… unless it does.

How much water does generating electric power waste? Or does the system suck everything dry?

Power generation doesn't generally waste water, it just extracts the potential energy from discharges that would've happened anyway.

It does however increase the carbon footprint of the river. Submerging forests to create reservoirs has created huge methane releases that nobody who thinks hydro is green power wants to talk about.

As someone living in the West, we have another reason to dislike dams: loss of salmon breeding grounds.

> loss of salmon breeding grounds.

There are technology available to alleviate this problem. Not easy, but solvable

The angel's share might account for a fair bit, most importantly if people are expecting water downstream. eg 20 kAF yearly at Lake Mojave with expectations in Mexico for the water.

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