Here in the American Southwest, water is king and the scarcity of this commodity is written into the DNA of every living creature. Pack rats process so much water out of their urine that their pee comes out thick as molasses. This enables them to get by on next to no water at all and they obtain most of it from what they eat. They are the ultimate southwestern creatures who laugh at the monthly periods of no rain that we oftentimes experience here.
The pack rats' viscous pee has an unintended consequence - it cements together all of the material inside their nest. This is composed of pieces of dried out cactus, pine needles, juniper berries, Rolex watches, etc. Pack rats only travel about 100 meters away from the nest to obtain all of this material. So even if we couldn't see beyond the nest, if we were a crippled pack rat so to speak, we would know what is growing within 100 meters just by examining the material found within the nest. (Where's that damn Rolex tree?).
It's so dry here that the vegetation held in these cemented nests can last tens of thousands of years in an protected cave. This is how geologists are able to reconstruct what the Ice Age Southwest looked like 15,000, 20,000, even 50,000 years ago. No person was present here to write about or otherwise record what was growing at that time. But the pack rats were recording it for us (by collecting whatever was growing within 100 meters of that ancient nest). What a beautiful science!
Along comes a creature with a big brain and voila! - water storage. Water storage has been the real growth engine for cities in the southwest and without it, Phoenix, San Diego, Los Angeles, and Las Vegas would still be towns of about 75,000 people. Water storage is the Miracle-Gro for Southwestern cities.
But water storage on sediment rich rivers like the Colorado has long term consequences. These consequences were not even considered (if at all recognized) when we decided to tame the Colorado River for water storage in the 1920's. Think about it - the idea to build dams on the Colorado River was hatched before we knew that the Milky Way was not the only galaxy in the universe, and long before we knew that the continents drifted over the surface of the earth.
My point is that the cumulative human knowledge that we possessed when we decided to tame the Colorado was miniscule compared to what we see and know now. Our knowledge of the natural world has increased many times over and our large brains might allow us to reevaluate the decision to dam this river (if political interests weren't so strong). Don't get me wrong - the short term benefits of these dams is still viable and has actually allowed southwestern cities to laugh at the current 12 year drought. Lawns are still green in Arizona and cement driveways are still being washed in southern California.
But what will happen to the Colorado River as all of its sediment continues to pile up behind the dams? Perhaps only a geologist could even begin to frame such a question (although environmentalists were the first to question the rationality of these dams but for other reasons). Only a geologist could think that the 700-year maximum life expectancy of Glen Canyon Dam (with other estimates as low as 250 years) will be here before we know it. Perhaps only a geologist can envision the mess that will be created on a regional scale as these dams fill with sediment. When the sediment absolutely fills the storage body, what will the river water do? What will those cities do for water?
When I bring this topic up with most people, they become noticeably indifferent - it's just too far off in the future for most people. (Our brains also retain a lot of wiring from the Pleistocene that "keep us in the moment"). But the era of tearing down dams has begun already. If you want to see a vision of the future for our southwestern dams (admittedly hundreds of years in the future but reality nonetheless) watch this video of the Condit Dam in Washington state being breached and drained of its sediment.
The future is here now. And what you watch here in this excellent video will happen on the Colorado River one day. This is the ultimate fate of Glen Canyon Dam, Hoover Dam, and every dam ever built on any river. This is the beginning of the end.
You can watch the video here.