water waves | Water Calendar

Wake spreading after duck — Wild Duck (Mallard) swimming across a water surface, generating a wake behind it. Small waves can be seen capturing up with the main wake, overtaking it, and then dissolving as they advance ahead and loose their energy. Söderåsen National Park, Sweden.
Photo: Lasse Johansson

Quietly, the duck swims across the water surface, its legs paddling silently underneath. Behind it, a small wake spreads distinctly, disturbing the otherwise completely still water surface. The sun is setting over the little lake – the oblique light causes the ripples to stand out, bringing them to my attention. Here at the outlet, just above a small dam, pieces of pond weed come drifting in an almost invisible current, and the duck hunts for food. Continue reading The wake

Karman vortex street - fully developed — Kármán vortex street, generated by a paddle and captured on paper with dye. The inrolling motion, clockwise at left, counter-clockwise at right, has developed more fully, and the alternating vortexes are clearly discernible. Paddle movement is downwards. From a workshop with Nigel Wells. Archives of Institute of Ecological Technology.

Flip, flap, flip, flap, the tail fin of the trout swishes to and fro, thrusting the fish forward in the still water. Silently it speeds away under the surface. Seemingly without effort it moves, leaving a series of wakes behind. As a contrast, our propeller thrusts water backwards indiscriminately, creating a white foam of turbulent water behind the boat. How can the fish swim so fast and elegant, almost effortlessly? Continue reading The fish and the propeller