|The Colorado River flows along a stretch near Moab known as the "Daily"|
Work done by Dr. Victor Baker at the University of Arizona, uncovered deposits of silt and driftwood located high up the bank along a stretch of river known as the "Moab daily," about 8 miles upstream from town. Here they found evidence for 44 large floods occurring in the last 2,000+ years. These were not merely high water year floods, but were exceptionally large floods, that likely resulted from rain on snow events. Of the 44 floods detected, 34 of them exceeded the accepted 100-year-flood level and a whopping 26 of them dwarfed 500-year-floods. Two massive paleofloods were higher than scenarios that engineers and planners now use to prepare for flood disasters. The discharge for these floods is estimated at over 300,000 cubic feet per second (cfs). To compare, the largest estimated modern flood at Lee's Ferry, Arizona was in 1884 and is estimated to have crested at 125,000 cfs.
Baker said that Glen Canyon Dam is ill prepared to handle floods such as these, should they occur today."It’s not something theoretical,” said Noam Greenbaum of the University of Haifa in Israel, the lead author of the study. “What we are actually documenting are the natural floods.
|Amid placid days of drought, risks of massive floods may loom for the Colorado River|
As a geologist, I naturally tend to look at both sides of an argument before leaning one way or the other. I understand for example, that these dams have allowed our southwestern culture to thrive. Yet, is it a good thing that 35 million people are dependent on a river that fluctuates between scorching drought and (now) humungous floods? The dams have clearly done what we wanted them to do. But at the same time, our knowledge of the rivers' inherent nature was virtually non-existent at the time the dams were conceived and built. Do we need to rethink dams on the Colorado River?
One observation I cannot escape is that the dams are piling up sediment for which there is no obvious, easy or inexpensive solution. In the long-term, dams on sediment rich rivers is a really bad idea. I don't know how you can continue to have 35 million people (and increasing), dependent on a system of water delivery that was conceived in the hydrologic 'dark ages.' To me, it doesn't make sense and I know that the detriments of the dams will only come into clearer focus as our science and technology reveal the wild character of the river.
“Nature is variable,” Baker said in the LA Times article. "The Southwest has suffered in the wake of recent droughts, but the long-term history of the region suggests that can change quickly. Ignoring Mother Nature is not too smart,” Baker concluded.
Greenbaum points to the uncertainty of the future and hopes to seek out more long-term flood records along the river. “During the last 2,000 years, the climate changed a lot. It was maybe sometimes wetter, different periods were dryer,” he said. None of this was really known in 1922 when the Colorado River Compact was ceremoniously signed in Santa Fe.
Sharlot Hall, forever the First Lady of Arizona said it best in 1906 i the last stanza of her incredibly prescient poem, "Song of the Colorado":
O ye that would hedge and bind me —
remembering whence I came!
I, that was, and was mighty,
ere your race had breath or name!
Play with your dreams in the sunshine —
delve and toil and plot —
Yet I keep the way of my will to the sea,
when ye and your race are not!
Sharlot Hall, 1906
How did she know? As they say, may you live in interesting times!