Title: How springs split; theoretical predictions and field observations of bifurcation angles

Author (Talk): Hansjoerg Seybold, EAPS

Abstract:

A pictorial view of the interplay between geometry of channel networks and ground water flow was proposed by Dunne several decades ago. But how does the ground water flow shape the channel network? This question still remains unsolved. Here we shed some light on how channels bifurcate in response to a surrounding ground water field. Assuming that the channel grows in the direction of the maximal water influx into the tip, theory of Laplacian growth can be applied predicting a characteristic opening angle of 2pi/5 (72 degrees). To test the theory we analyze a huge channel network north of Bristol, FL formed by ground water seepage. The measurements derived from the topography data yield a mean opening angle of 72 degrees plus-minus 5, confirming the predicted value strikingly. This strong agreement between theoretical predictions and observations suggests, that the assumption of growth in the direction of the flux is reasonable. Furthermore it leads to the conclusion that that the channel extension at the spring does not depend on the complex fluvial hydrodynamics and sediment transport inside the stream.