ADVANCES IN THE USE OF NON-LITHIC MEDIA AND CLOSE RANGE PHOTOGRAMMETRY IN PHYSICAL MODELING OF FLUVIAL PROCESS

Small-scale physical modeling of fluvial processes presents challenges that have greatly limited its scientific utility. Over the last few years we have developed practical solutions to a few critical problems, including particle density scaling, morphology measurement, and visualization. Unique advances developed in our lab include color coded by size (CCS) thermoset plastic modeling media coupled with close range photogrammetry (CRP) to measure both morphology and surface particle size. We have also investigated the use of water-soluble polymers to address the critical problem of media cohesion.

CCS media offers powerful advantages for teaching and research. Surface deposits and mode of deposition are easily seen and recorded. Transient processes such as pulses of sediment released by cantilever bank failure are easily observed. The distinctive colors allow recording and analysis using digital video and still photography. With academic discounts, a complete CCS system can be bought for about US$3,200. CRP offers exciting measurement capabilities for physical modeling whether or not used in conjunction with CCS media. Using software and off the shelf cameras, this method has theoretical resolution of 1mm over areas of a few square meters. CRP offers many advantages over laser scanning, including high resolution full-color image overlays, much lower cost, ease of use, and instantaneous image acquisition. Ongoing research addresses the challenge of sub water surface measurements using CRP and use of multi-camera setups for high frame rate measurement of rapidly changing morphology.

Use of thermoset plastic CCS media remains limited by high cost (about US$40 per kg) and difficulties in manufacturing, which is done by grinding recycled material. The material is available only in a very narrow range of particle densities averaging 1.5 gcm^-1. We are developing a modeling media made from a combination of acrylic (with a low density of 1.1 gcm^-1) and high-density minerals that add both color and variable particle density. This combination could yield relatively low cost particles of various sizes, shapes, colors, and densities that could be made through extrusion rather than grinding.