[DollarGuru]

How does a dam like Hoover effect the flow rate of water down stream after filling the dam?

My assumption was that after the dam is filled the flow rate can be regulated very close to pre dam levels of at least 95% flow rate factoring in any losses due to evaporation.

[beerandt]

Because that's literally what it was designed to do. Absorb the floodwaters and release them slowly.

All the water being siphoned out to supply Vegas and irrigation comes from somewhere. And doesn't make it downstream. Plus all the water retained by Urban build out (ponds, vegetation, pools) that normally would flow straight into a river and head downstream.

Over burden pressure from the lake forces water into the ground. The temperature of the water in the lake rises, causing chemical changes and making evaporation downstream more likely. Sediment drops out of the water column, allowing light to penetrate deeper than it normally would.

All of that is before you even get into the flow rate variance. Because winter floods don't "flush out" the canyon, there are problems with sedimentation downstream, which causes water to slow and evaporate more...

And this is just hydrology/hydraulics, before you touch any of the biological / ecological aspects.

It gets complicated, quickly.

Even if you assume it's only 5% evaporation reduction and exclude what's pumped out, there are at least what? 15-20 major dams that feed the Colorado? Even if you assume 3% times 15 dams, that's almost half the flow of the river, before you even pump anything out.