Spontaneous channelization in permeable ground: theory, experiment, and observation
|NORBERT SCHORGHOFER a1, BILL JENSEN a2a3, ARSHAD KUDROLLI a2 and DANIEL H. ROTHMAN a1|
a1 Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
a2 Department of Physics, Clark University, Worcester, MA 01610, USA
a3 Department of Physics, University of Massachusetts, Boston, MA 02125, USA
Landscapes that are rhythmically dissected by natural drainage channels exist in various geologic and climatic settings. Such landscapes are characterized by a length-scale for the lateral spacing between channels. We observe a small-scale version of this process in the form of beach rills and reproduce channelization in a table-top seepage experiment. On the beach as well as in the experiments, channels are spontaneously incised by surface flow, but once initiated, they grow due to water emerging from underground. Field observation and experiment suggest the process can be described in terms of flow through a homogeneous porous medium with a freely shaped water table. According to this theory, small deformations of the underground water table amplify the flux into the channel and lead to further growth, a phenomenon we call ‘Wentworth instability’. Piracy of groundwater can occur over distances much larger than the channel width. Channel spacing coarsens with time, until channels reach their maximum length.
(Received June 2 2003)
(Revised September 24 2003)