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Comment by Gwypaas | Hacker News Reader

Because you're not disrupting a river's flow and natural ecosystem, you only utilize the watershed some more during the initial filling period. After that, it's a closed system separate from the river ecosystem where only evaporation causes leakage.

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That ship has already sailed as most power producing dams have been around for long time. Removing them would destroy the (now natural) ecosystem they have created. Plus dams have way more benefits to us than the extremely clean energy they produce - not just store.

This is the first time I've seen a claim that dams create ecosystems that we should worry about destroying. As far as I know, they disrupt fish and animal migrations, reduce natural carbon sinks, reduce biodiversity, and block sediment from providing nutrients downstream.

Is there any source saying dams create healthy natural ecosystems? A necessary evil I can kind of see, but a net positive for ecosystems? That seems doubtful.

I don’t know. I suspect the bias is towards the pre-dam ecosystem so it might be challenging to rationally compare them.

Certainly an ecosystem will grow up around nearly any situation.

Yup my opinion only. To me water is life and if you let it flow to the ocean where it’s only use is to dilute saltwater you’ve wasted a precious natural resource.

Dams does not save any water except the initial filling. Their inflow and outflow match over a seasonal cycle.

Also, they tend to cost water instead: the larger surface area increases the amount "lost" to evaporation.

Perhaps. I suppose that would depend on size and depth of the reservoir and the makeup of the river. Also without a dam the water would be traveling the river mostly during the cold wet season with little evap. So yeah likely so. But in the end the cost would be lost saltwater. Probably a benefit for those that are worried about sea levels.

Yup that’s simplistically true. The difference though they do allow you to choose when it gets released. Around where I live that allows irrigation of crops during the summer months. That water does not go into the ocean. Also around here many of the municipalities draw water downstream from the dam as well. A portion of that travels through the sewer systems, gets purified then dropped back into the river.

there are many human ecosystems living below the dam though. Removing the dam means removing entire towns downstream in some cases.

That is not, in fact, true. Almost all dams have a river flowing below them, where it always did.

A very few places use all of the inflow for irrigation.

This is not the case, removing dams still can come with huge benefits to the ecosystems those dams disrupted: https://www.mercurynews.com/2019/05/08/four-years-after-cali...

Read the article. Sounds like in that instance it was a good choice to remove the dam and had a good outcome. Well based on the information presented anyhow. Also I’m not sure if the main justification for removal pencils out for me. Yes some fish - 123 so far - were able to reproduce further upstream by 7 miles. What would have happened if the dam was still in place? Breed just below the dam? Do the fish really care where they do the deed or lay their eggs? Can’t believe that would be very true. Heck when I was their age I was pretty happy to do the deed and wasn’t too too awful concerned where it was at either. :D

No. First off, most dams silt up, not only not of being use in storing water but also not in creating power. Second, once they silt up, whatever ecosystem there is also destroyed and artificially created ecosystems are never natural and usually are bad for local fish populations. Artificial lakes can also host a number of non-native fish and are not any benefit to the native species that should be living there. Also, dams also block the migration paths of native fish.

Just think of this way, dams have a life span and for the most part, most of them in US have hit the end of their life spans and should be removed. They serve no purpose to anyone.

This is a pretty incomplete understanding of the issue, there are plenty of dams where silting is not an issue at all and will serve their purpose for centuries if properly maintained. There are also dams where silting is a regular problem. A so called 'sediment bypass' is often a feature of these dams, where water is pulled from the base of the dam through a bypass to clear out silting.

It all depends on the natural hydraulic dynamics of the dam - some are better placed than others.

Right. Storing water for 50M+ people and generating enormous quantities of electricity. No use at all.

We are, in fact, demolishing dams at an increasing rate.

Dams very commonly destroy fisheries worth far more than any value the dam can deliver.

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