The 1996 Flood:
What Came, What Went, What Came and Went
Tracking a Dynamic System

It’s no secret that one of the goals of the late March Habitat/Beach Building Flow is to redeposit the Canyon’s beaches. But that’s only part of the story. The overreaching objective of this experiment is to restore the dynamic disturbance to our river system, to bring into balance the processes that shaped the river corridor and all of the flora and fauna that evolved in concert with it. We want to restore the lost deposition processes to the river.

What goes up, must come down.

Any river system not constrained by sheer rock walls settles into a dynamic equilibrium. That state depends on the pattern, range, and magnitude of the river’s flows and the amount of sediment available to work with. In our case, dam operations determine the flows and, at least in Marble Canyon, the Paria River determines the sediment available. The beaches are one of the physical indicators of that equilibrium state. For any set of flows the processes of erosion and deposition will balance one another over time. Therefore, when we increase the amount of sand above the water, one of the natural and anticipated results is erosion.

A Dynamic Process

“Dynamic” implies change, and change we should expect. The only way to protect the beneficial deposition of the 45,000 cfs would be to maintain releases at that level—that wouldn’t help the camping much. When the water drops, we can expect large and noticeable erosion initially, until equilibrium is approached. Erosion itself isn’t the concern, its understanding how it’s happening and where it’s going that’s important. That’s where we can help.

More up than down

As the system adjusts to the lower post-flood levels, cut banks will form; in some places large sections of beach will quickly return to the river. The rate of cutting will decrease with time leaving more beaches and sand. The long-term goal is to find the most effective flows that will deposit sand and then maintain those deposits. (Unfortunately, due to high lake level and high snow-pack this spring, we are anticipating flows of close to 20,000 all summer. In turn, we expect greater erosion that we would have had with a lower, more typical summer. C’est la vie)This dynamic system must be monitored closely over the next few months and we’ve got to be there to watch it and take note.

So what happened?

Over the next several months Grand Canyon River Guides will be collecting the guides’ observations of what happened during and after the March Beach/Habitat Building Flow. Your short term observations are important, but equally as valuable are your repeated observations throughout the season. Is a beach missing in August that you camped on in July? Did a beach that calved in in April rebuild at a lower level in June?
GCRG has come up with several questions; researchers have added more. Use these questions to get an idea of what sort of observations we’re looking for. There are a lot more questions that we haven’t thought of. Ask them. Answer them. Please.
You can use this 4-page tear-out form to send in data or just sent in notes. The important thing is to write it down and get it to us. And that you continue to note further changes over time and send that in as well. Exact location of the beach is critical information of course; so is the date and approximate river level.

Thanks-

Tom Moody

Sand and Beaches

· Where was significant sand deposited where there was none before?

· Were some of the beaches restored that had suffered from recent side-canyon flash-floods? Where? Which ones weren't?

· Where did sand start eroding immediately?

· Why is it eroding (wave action, river flow, eddy flow, motor wake, foot traffic, other) ?

· Did you see any significant events (massive calving...)? When and where? What seemed to be causing it?

· Where are there stable, non-eroding beaches?

· What beaches or sites were removed or severely eroded as a result of the flood?

· Were new beaches more steep or less steep than before the flood? Did the slope change over time?

· Are there any perched beaches where there were none before? (High beaches with an abrupt drop to the river)

· What observations can you make about the process of beach building and erosion?

Habitats

· Where have you noticed new backwaters (long, finger-shaped fjords of water that reach around in and behind beaches), loss of old backwaters or changes in the shape of backwaters? (Especially around the Little Colorado) · Have you noticed significant deposition of sand or loss of vegetation in marsh habitat?

· Did you notice significant removal or change in beach vegetation?

· Did some areas of new sand colonize with plants while others didn't? Where?

· Did cottonwood trees that moved into the river corridor since '91 survive? Where and where not?

· Have you had better or worse luck fishing at your favorite spots? Any other fish observations of note?

· Did you notice tributary mouths being filled in? Scoured?

Rapids

· Did you see changes in any of the rapids? (especially those that have changed since the last high water in '86--Lava, Crystal, Bedrock, 24-mile, others...)

· Specifically, what changed?(Shape, run, rocks, difficulty...) Be specific.

· Did you encounter any water related problems during the flood? Well?

· What benefits did you see from the flood flow?

· What problems did the flood flow cause?

· Do you think the flood flow was a good idea, or bad? Why?

· What do you think would have made it work better?

Send your observations to: Flood Survey, GCRG, P.O. Box 1934, Flagstaff, AZ 86002