Phenomena

Surge Flows

Sandy beaches can be a great place to play with neat flows. In a recent video, Frank Howarth describes playing with beach rivers on the Oregon coast and observing a surge flow there. Under the right conditions, a current flowing over sand will build up sand ripples large enough that they form miniature dams in the flow. This traps additional water, which eventually collapses the sand ripples, releasing a surge of water. The surge tends to smooth out the sand and cause the ripple-making process to start over. It’s a fairly unusual phenomenon, but it’s one known to happen seasonally in a few specific places, like at Medano Creek in Colorado’s Great Sand Dunes National Park. There the snowmelt-fed creek surges during the late spring and early summer, releasing a fresh wave every 20 seconds or so. (Image credit: F. Howarth, source; h/t to Sebastian E.)

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