Grand Canyon flood experiment restores beaches

• Feds increased Glen Canyon Dam release to 42%2C300 cfs for 24 hours in November
• New sandbars provide haven for fish%2C vegetation and campsites for rafters
• Researchers uncertain whether new sandbars will quickly erode away

Scientists studying last fall's experimental flood of the Grand Canyon say it did what it was supposed to do: build sandbars.

Or, at least it built more sandbars than it eroded and generated new Colorado River campsites and fish habitats.

But the question is for how long.

"We'll just have to see," Grand Canyon Monitoring and Research Center Chief Jack Schmidt told participants in an annual canyon work-group session Wednesday. The real results will come over the next year or so, when researchers will know what remains of the newly built sandbars.

Over a 24-hour period in November, the U.S. Bureau of Reclamation cranked Glen Canyon Dam's release from 8,000 cubic feet per second to 42,300 to churn up sand and allow the U.S. Geological Survey and others to track the impact.

Some of the new sandbars and beaches are dramatically larger, nearly doubling, providing rafters a flat overnight perch and young endangered humpback chubs a warm backwater shelter from the pulsing river. The sand washed up by the flood also is meant to provide a wind-borne source of cover for uphill archaeological sites and a purchase for vegetation.

But it's unclear whether the benefits to these and other Grand Canyon National Park resources can withstand longer-term dam releases that fluctuate to meet hydropower or downstream water needs, and a shrinking sand source. After the previous three experiments that started in 1996, the buildup in many parts of the canyon has been on a downward trend as the river swept residual sand to Lake Mead.

Glen Canyon Dam blocks most of the sediment carried downstream by the Colorado River. Among the few remaining sources of sand is the Paria River, which flows into the Colorado about 15 miles below the dam and dumps, on average, about a tenth of the sand that the undammed river used to wash into the Canyon. The flood experiments are meant to find out how to make the best use of it.

Schmidt's staff has reviewed snapshots from remote digital cameras that showed more than half of the monitored sandbars and beaches — 18 — grew substantially after the November flood receded. Twelve sites showed no change and three eroded substantially.

"Every time we do a flood, it builds sandbars," said Paul Grams, a U.S. Geological Survey research hydrologist. "We know the floods build the bars, and they tend to erode in the six months to a year following the floods."

The Canyon's chub numbers have grown threefold, to 12,000 over the past two decades, biologists at this week's meetings estimated, perhaps aided more by warmer water spilling from a low reservoir.

Some river advocates have argued that only frequent artificial floods can approach pre-dam conditions — a possibility that the U.S. Interior Department set up by stripping environmental red tape from experimental releases for the next decade.

But others want more drastic action.

"It's not working," said John Weisheit, conservation director for Living Rivers, a non-profit organization dedicated to Colorado River conservation. The dam blocks too much sand, and the government should either breach the dam, transport sand around it or give up, he said.

"I would hope that this country could solve the health of Grand Canyon National Park," he said.

The Bureau of Reclamation has estimated it would cost more than $100 million to build a pipeline around the dam to deliver about the same amount of sand that the Paria dumps in the Canyon. Schmidt and his staff advised river managers this week that there's a chance that sand depletion could at some point wipe out gains from these floods — but not yet.

Most of the targeted sandbars in Marble Canyon — the highest stretch of the park affected by the flood — grew in the November flood. But the results downstream were mixed, and USGS scientists said it was because prolonged high flows last year to move water from Lake Powell to Lake Mead washed away sand.

The Colorado River Energy Distributors Association estimates that its cooperative members from Arizona to Wyoming lost about $1.4 million in power generation as water bypassed turbines during the release. It's unclear whether the canyon got "the bang for the buck," association Executive Director Leslie James said. Each flood introduces new results and variables.

"The more you experiment," she said, "the less you know."

Next fall is the soonest the government could plan another flood, if monsoon rains wash sufficient sediment down the Paria.