Here’s a report from Cally Carswell writing for The High Country News. Click through and read the whole article, here’s an excerpt:
If the San Juan River were a freeway, Glen Canyon Dam would be a 50-car pile-up. It forces the river to back up and spread out for dozens of miles. As the river morphs into Lake Powell, the sand in its current settles out. A rock overhang at Grand Gulch where boaters once lounged is now buried more than 30 feet deep.
Before the dam killed the current, the San Juan carried all of this silt to the Colorado, which spit much of it through the Grand Canyon, replenishing hundreds of sandbars. These expansive blonde beaches, which form in eddies, are river runners’ favorite campsites, and they provide backwater habitat for fish. But today, about 95 percent of the sediment that once washed through the canyon sits at the bottom of Lake Powell, and the sandbars have shrunk: The Colorado erodes them, but doesn’t build them back up.
This is one of the problems the 1992 Grand Canyon Protection Act was supposed to correct. It directed federal officials to figure out how to manage the dam in a way that did less harm and even protected the national park’s assets. In addition to threatened sandbars, three of eight fish species native to the Grand Canyon have disappeared since the dam went up, and two are endangered.
But can altering dam operations really help the river when the dam itself imperils it? Scientists have explored this question since 1992, and their research informs the Bureau of Reclamation’s draft management plan for the dam’s next 20 years, released earlier this year. Conservationists are optimistic that it will yield improvements downstream, but only small ones. “You’re really just trying to make the best of a bad deal,” says Utah State University watershed sciences professor Jack Schmidt…
But there might be other ways to help fish, Kennedy says. Chub spawn almost exclusively in the toasty Little Colorado, then move into nearby parts of the mainstem Colorado, where their growth is inhibited by chilly water. The water does warm as the river twists further from the dam, but though it should be good habitat, few chub live in these downstream reaches.
Scientists think that could be because there aren’t enough bugs to eat there. Aquatic insects lay their eggs at river’s edge, and when the water level drops, as it does daily when water releases fluctuate with hydropower demand, the stranded eggs shrivel and die.
The plan proposes to eliminate flow fluctuations on spring and summer weekends, when electricity demand isn’t quite as high, in hopes of keeping eggs wet and boosting insect numbers. More food might help chub populations colonize and prosper in the river’s lower reaches.