COLLABORATIVE RESEARCH: Smart Sediment Grains and the Incipient Motion of Coastal Heterogeneous Sediments

University Of New Hampshire, Durham NH

Investigators

Abstract

Foster/Chou 0933409/0933694 NOAA estimates that the large local, state, and federal financial investments in nourishment projects to maintain existing beaches is returned ten-fold through tourism dollars alone. As sea level rises and population demands on our shorelines increase, some experts predict the socioeconomic and ecological pressures on the beaches and coastal planners will also rise. These projects are generally successful at temporarily restoring the beach width, however re-nourished sediment more quickly erodes as it has different characteristics than the "native" sediment. The PIs will develop and experimental program for these studies. Theories for the motion of sediment largely neglect any unsteady contributions from the passing waves or more local turbulent disturbance. The existing applied engineering models based on such principles have relatively low skill when predicting the onshore transport of sediment in moderate wave climates (e.g small wave periods of 3-5 s and wave heights of roughly 1 m) with weak mean flows where beaches rebuild and could significantly benefit from an improved understanding of nearshore sediment dynamics. The hypothesis the PI's seek to test is that in wave-driven coastal environments where the flow regime is unsteady and the sediment characteristics can be heterogenous, the incipient motion of a sediment bed results from a combination of the shear stress gradient and the horizontal pressure gradient. The PIs will test this hypothesis by developing a new wireless Lagrangian sensor, the Smart Sediment Grain. The specific objectives for this project are to develop a theoretical formulation for the incipient motion of sediment in response to random free surface gravity waves, extending Sleath's 1999 formulation; develop a Smart Sediment Grain (SSG) to measure the three-dimensional acceleration of individual motes (or grains); and finally observe the motion and transport of heterogeneous sediments (both natural and smart particles) through a comprehensive full-scale laboratory observation. Full-scale observations will be performed at the Ven Te Chow Laboratory at the University of Illinois (UIUC). Observations will be obtained for a range of natural grain classes (0.2 < d50 < 20.0 mm) and also for a range of lighter particles that will allow for a range of the full parameter space relevant to coastal environments. This effort represents a synergistic collaboration between a wireless technology expert and a sediment transport scientist. This effort is transformative in its application of state-of-the-art MEMs technology to resolve longstanding fundamental questions regarding the motion of intermittently mobile sediment beds exposed to free surface gravity waves. There exist wide-ranging broader impacts of this effort that include increasing the participation of underrepresented groups, transitioning high technology to society, entraining k-12 students into science and engineering, and increasing the predictive skill of coastal management models. This project will provide support for the Ph.D. studies of a minority female student. The PIs will participate in outreach programs at the Joan and James Leitzel Center at UNH and through Girls Inc, Eureka! Ongoing collaborations with TUDelft will provide an opportunity to model the successful Dutch methods for transitioning scientific findings to the larger engineering community.