Grand Canyon gets a rebuild

[richardm]

Could mean almost anything that headline - but as it turns out they're flooding the Grand Canyon (http://news.bbc.co.uk/1/hi/world/americas/4033323.stm) with millions of gallons of water, to release hundreds of thousands of tonnes of sediment back into the canyon to help various species survive. 1,161 cubic metres of water per second at one point. I'd like to see that.

http://newsimg.bbc.co.uk/media/images/40553000/jpg/_40553475_water_b203_ap.jpg

Mind you, I can't help but wonder what effect that flow rate will have on the unfortunate creatures, let alone the estimated million tonnes of sediment that's going to be joining them shortly.

[thatguywhojuggles]

perhaps this is actually some attempt of the creationists to prove something...

[richardm]

Originally posted by thatguywhojuggles
perhaps this is actually some attempt of the creationists to prove something...

:D Actually I did consider the reverse - if they can release all that water so quickly and not substantially erode the canyon and make it bigger, does that not count as strong evidence that it could not have been formed by "the" flood?

[Soapy Sam]

Did you know the gorge of the Spean at Roy Bridge may have been cut in a couple of days?

[richardm]

Originally posted by Soapy Sam
Did you know the gorge of the Spean at Roy Bridge may have been cut in a couple of days?

No! How did that happen?

I mean, yes, obviously "Lots of water came down it" :D But why? How? What? When? Etc... Sounds like an interesting fact to shock and stun visitors with.

[patnray]

Originally posted by richardm
Mind you, I can't help but wonder what effect that flow rate will have on the unfortunate creatures, let alone the estimated million tonnes of sediment that's going to be joining them shortly.

Before the dam was built the river experienced periodic flooding events. The problem is that the dam prevents these natural events. Over 90% of the original sediments have now washed away. Also, as I understand it, this technique has been used in other settings. This is a test trial. There is a team of scientists on the river to monitor the process.

[thatguywhojuggles]

http://newsimg.bbc.co.uk/media/images/40553000/jpg/_40553529_chub_203_usgov.jpg

What a crazy looking fish. It looks like a fat fish swallowing a skinny one!

[pupdog]

They had an experimental release a year or so ago. There was a writeup about the results in Geotimes or somewhere.

[neutrino_cannon]

'round these parts, all who insult the humpback chub, razorback sucker or Colorado squawfish are quickly and effectively chastised with a spanking!

[Eos of the Eons]

Is that a threat or a promise :D

[richardm]

Originally posted by patnray
Before the dam was built the river experienced periodic flooding events. The problem is that the dam prevents these natural events. Over 90% of the original sediments have now washed away. Also, as I understand it, this technique has been used in other settings. This is a test trial. There is a team of scientists on the river to monitor the process.

Yep, understood. I would still have thought that that amount of sediment arriving so suddenly would have a pretty dramatic effect on water turbidity, which would in the short term at least be a damaging to the creatures living in the water.

I suppose they know what they're doing,

[Correa Neto]

The lifecycle of many fish species are adjusted to periodical floodings of river margins, that creates environments well-suited for their offspring (I mean small baby fish, not the band). A simliar mcehanism is valid for the extra sediment input.

All rivers with dams suffer from these problems. The "artificial floods" may help solve just part of the problem. Sediment load, however, is reduced, and will not be restored. So, for example, if the riverine ecosystem is adjusted say, to a new organic matter and minerals-rich mud layer do be deposited each year, surely the fertility at the river´s margins will decrease. Conditions may change also at the river´s delta and surrounding shoreline, due to the decrease in sediment input.

[neutrino_cannon]

This reminds me of how farming worked in ancient Egypt. Periodic flooding from the Nile was necessary to keep the farmlands fertile.

[Correa Neto]

Precisely.

As a couple of sidenotes, some stuff I remember reading somewhere (yep, that was a refference to quite vague sources, I admit, since my memory is prone to failure):

(1) Specialists are concerned about the dams in rivers around the Mediterranean. Reductions in freshwater input from the rivers may cause its salinity to increase. Also, a reduction in sediment load may cause changes in the quantity of nutrients dispersed in the water and in its turbidity.

(2) The reduced sediment load is creating problems at the Nile´s delta, since subsidence created by a fault is no longer being compensated by deposition. So, the phreatic level (water table) "raises" and the freshwater layer over the salty water is getting thinner or absent at several places, with obivous problems.

[Hydrogen Cyanide]

Originally posted by richardm
No! How did that happen?

I mean, yes, obviously "Lots of water came down it" :D But why? How? What? When? Etc... Sounds like an interesting fact to shock and stun visitors with.

There are cases where water dammed up during the ice age was released "suddenly". It is one explanation for the topography of "scablands" in our neck of the woods:
http://vulcan.wr.usgs.gov/Glossary/Glaciers/IceSheets/description_lake_missoula.html

And this one has pictures:
http://www.fs.fed.us/r6/columbia/missoula.htm

(oddly enough, I kept getting hits on creationist sites for this... though I have seen the exhibit in the nearby Burke Museum, and have visited Dry Falls -- which is where I learned of this really big flood)