Wake of the Flood Fractals

By Tom Yulsman | September 25, 2013 12:45 am

A new but ephemeral tributary of Left Hand Creek near Boulder, Colorado catches the sun’s fading light. (Photo: © Tom Yulsman

Since the epic rainfall and subsequent flooding that hit Colorado’s Front Range beginning two weeks ago, I’ve been going back to a couple of places near where I live to document the aftermath of the deluge with my camera.

Among many things, I’ve been struck by how Left Hand Creek, an ordinarily tame stream that pours out onto the plains from the foothills of the Colorado Rockies, jumped its banks and transformed its floodplain for hundreds of yards on either side.

The waters are receding now, in places leaving behind a fractal pattern of rivulets and sediments like the one in the photograph above. Fractals are self-similar patterns, meaning they are similar at different scales.

The pattern in that photograph is repeated at a larger scale in this photograph from the day before:

As the flood waters of Left Hand Creek recede in the wake of Colorado’s deluge, a fractal pattern emerges in the sediments left behind. (Photo: © Tom Yulsman)

And this kind of pattern can be seen at a much larger scale, as in this photograph of a river in New Zealand:

Waimakariri River, Canterbury, New Zealand. (Source: Greg O’Beirne, GFDL/Creative Commons)

The flooding here in Colorado has killed eight people, destroyed more than 1,800 homes, and caused untold misery among the many thousands of people whose homes and businesses were damaged. But in its aftermath, nature is asserting itself in a beautiful way as well. In the days and weeks ahead, I’ll try to keep documenting it.

CATEGORIZED UNDER: Extreme Weather, select, Top Posts, Weather
  • Buddy199

    Fractal patterns are the mathematical foundation of nature, including human nature, where they become obvious when humans act on a mass scale, for instance during asset bubbles. The graphical representation of asset bubbles is nearly identical to that of influenza epidemics (Google it). A “hot” idea (you can get rich quick flipping houses!) spreads through the population in much the same way mathematically as a virus does physically during an epidemic. It is also striking in which the way the photos above bear a resemblance to the anatomy of the circulatory system.

    • Tom Yulsman

      Fabulous! Thank you for these comments.

      On my way home from work today, I’m going back to this very spot, and thanks to your comments, and John’s, I probably won’t be looking at the scene in quite the same way as before. The question is whether it can help change the way I look at the scene photographically. Probably not. But it’s an interesting question to consider.

  • John Zulauf

    The amazing thing about fractals is how deceptively simple the generating mechanism can be — in this case the simple fact that pressure doesn’t change across the boundary layer. As boundary layer processes are self-similar, so are the emergent properties.

    How? The meander starts with any perturbation (even a flow instability) causing the flow direction to change. The transverse pressure gradient exactly (across the direction of flow) balances the inertia of the water changing direction in the free stream (outside the boundary layer). Because pressure doesn’t change across the boundary layer, that same pressure gradient is acting on the slower flow within the boundary layer. This gradient causes transverse flow of the water on the bottom of the channel. That flow transports sediment from the outside of the curve to the inside creating the meander.

    • Tom Yulsman

      Nice! The explanation is almost as beautiful as the phenomenon!

  • Roger Bagula

    Hurst exponents:
    “the Hurst exponent were originally developed in hydrology for the practical matter of determining optimum dam sizing for the Nile river’s volatile rain and drought conditions that had been observed over a long period of time.”



ImaGeo is a visual blog focusing on the intersection of imagery, imagination and Earth. It focuses on spectacular visuals related to the science of our planet, with an emphasis (although not an exclusive one) on the unfolding Anthropocene Epoch.

About Tom Yulsman

Tom Yulsman is Director of the Center for Environmental Journalism and a Professor of Journalism at the University of Colorado, Boulder. He also continues to work as a science and environmental journalist with more than 30 years of experience producing content for major publications. His work has appeared in the New York Times, Washington Post, Audubon, Climate Central, Columbia Journalism Review, Discover, Nieman Reports, and many other publications. He has held a variety of editorial positions over the years, including a stint as editor-in-chief of Earth magazine. Yulsman has written one book: Origins: the Quest for Our Cosmic Roots, published by the Institute of Physics in 2003.


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