ABSTRACT: Modeling of initiation and propagation of single conduits and networks.

CGRG Bibliography of Canadian Geomorphology
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Abstract

Most dissolutional conduits develop along fissures (bedding planes, joints, or faults) in which the initial opening differs considerably from place to place, i.e. they are anisotropic. The propagation of conduits between input and output points in an anisotropic fissure was studied systematically with three types of hardware models: - Electric-current analogs, and - Sandbox analogs--both to investigate flowfield geometry. - Artificial fissures cast in plaster of paris, with random anisotropic elements on their surfaces. A first series of experiments studied the case of a single input to the fissure. The earliest protoconduits were observed to extend in a radial (Darcian) array, but one principal and several secondary tubes quickly extended down the hydraulic gradient, robbing competitors of their flow. This mode of propagation was tested with a resistor-network computer model using 100 by 100 nodes, Weyl's (1958) equation for dissolution and transport with parameters appropriate for plaster, and three choices of opening-isotropic, anisotropic but homogeneous, and heterogeneous. The computer model results closely matched those of the hardware models. In a second and third series of plaster hardware experiments, these cases were explored: - Multiple inputs to the fissure in one rank. - Multiple inputs in multiple ranks. In the competition between inputs, some principal tubes in near ranks first "breakthrough" to the output boundary. This reorients the flowfields of failed nearby competitors, which then extend to join the principal via their closest secondaries. The process extends outward and to the rear, linking up all inputs in a "cascading system.".

Bibliography of Canadian Geomorphology