Direct measurements of sediment response to waves with “Smart Sediment Grains”

Measurements of sediment motion have been primarily limited to indirect observations with acoustic and optical instruments. A micro-electro-mechanical systems device that can measure and record Lagrangian observations of coastal sediments at incipient motion has been developed. These sensors move freely, measure acceleration in the six degrees of freedom and their mobility characteristics are similar to coarse gravel. Experiments conducted in a small oscillating flow tunnel and a large wave flume verified that the sensors detect incipient motion under various hydrodynamic conditions. Analysis of complementary fluid velocity measurements suggest the influence of pressure gradient induced sediment motion.