USE OF THERMOPLASTIC SAND IN PHYSICAL MODELS OF FLUVIAL SYSTEMS

Physical models of fluvial systems are powerful educational tools. They offer hands-on lab experience, effectively demonstrate fluvial processes by compressing both temporal and spatial scales, and demonstrate phenomena that cannot be directly observed in the field. Movable bed models (MBMs), or “stream tables” have a long history in geoscience education but remain relatively rare and underused. This is in part due to the use of quartz sand as a modeling media. Thermoplastics, which have a lower particle density of about 1.5 g cm^-2 (versus ~2.6 g cm^-2 for quartz sand), offer greatly improved hydraulic similitude. The material’s angularity and brighter colors also improve its performance over that of sand in small MBMs. Used as an industrial abrasive and made from recycled stock, ground thermoplastics (such as melamine) have become widely available in the last decade and can be bought for less than US$4.5 per kilogram. The material is available in a variety of sizes, enabling experiments and demonstrations with varied particle size distributions. Though color can be specified to some degree, current recycling/manufacturing processes are configured solely to produces abrasives, making production of the material in pure colors difficult. Recent research addressing hydraulic similitude in small MBMs has suggested models have limited predictive capability at extreme (1:10,000 and less) scaling ratios. Though further work is needed to assess research capabilities, thermoplastic media clearly offers improved performance and educational potential for these models.