Breaking waves play an enormous role in structuring communities in the rocky intertidal zones of Monterey Bay. The hydrodynamic stress imparted by waves affects a number of processes, including where species settle, organism dislodgment, predation, and fertilization. Despite the importance of water movement for rocky intertidal communities, the largest forces imparted by waves are still poorly understood.
While the classical (and most frequently studied) hydrodynamic forces -- lift, drag, and buoyancy -- have long been assumed to dominate the intertidal environment, a less well known force, the impingement force, may actually be larger. Impingement is characterized by a sharp, brief force imposed on intertidal organisms at the instant of a wave’s arrival, followed by somewhat steady drag as flow continues past the object. This impingement spike is, on average, twice the magnitude of drag, and is presumably the greatest hydrodynamic force exerted on intertidal plants and animals. Despite its likely ecological importance, impingement was only recently discovered and remains largely unstudied. In particular, the impingement force’s dependence on shape, size, and flexibility of the organism is not known. As part of my research, I am working to determine the factors that affect impingement forces, and to relate them to plant and animal morphology, mechanics, and ecology.
To test which factors affect impingement, I am using plastic models that span a range of biologically relevant sizes, shapes, and flexibilities. I am subjecting these models to controlled, simulated waves, and measuring the force imparted to the object as the wave passes over it. To produce repeatable waves for these laboratory experiments, I am using a gravity-driven "water cannon." This apparatus is used to simulate impinging waves in a controlled manner by filling a large (approximately 30 feet tall) vertical pipe to a set height and opening a valve, releasing a simulated wave.
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Since impingement forces are likely to be the greatest hydrodynamic force imposed on intertidal organisms, they may represent an important selective pressure in the organism's evolution. Understanding the factors that affect impingement events will help to explain how organisms of different shapes and sizes respond to this environmental load, and provide a critical link in successfully modeling the relationships between local rocky intertidal communities and environmental stresses.
Breaking waves play an enormous role in structuring communities in the rocky intertidal zones of Monterey Bay. The hydrodynamic stress imparted by waves affects a number of processes, including where species settle, organism dislodgment, predation, and fertilization. Despite the importance of water movement for rocky intertidal communities, the largest forces imparted by waves are still poorly understood. 