Meeting Abstract

35.5  Sunday, Jan. 5 09:00  Characterizing wave impact forces in the field JENSEN, MM*; DENNY, MW; Hopkins Marine Station, Stanford University mmjensen@stanford.edu

Wave-swept rocky shores are among the most physically stressful environments on the planet. Hydrodynamic forces produced by breaking waves can damage and dislodge organisms, complicate external fertilization, and ultimately influence the species composition of intertidal communities. However, despite the critical role of hydrodynamics in shaping intertidal communities, what may be the largest forces in the intertidal zone remain poorly understood. Impingement is the sharp, transient force occurring at wave impact, and it is believed to be the largest hydrodynamic force acting on intertidal organisms. This transient force spike is thought to be caused by a brief increase in drag due to higher water velocities at the front of a wave. While impingement has been characterized under experimental conditions, only one study has measured impingement events in the field. Those data showed impingement occurring in less than 1% of waves; however, the measurements lacked the temporal resolution to fully capture and resolve impingement events. To better estimate the frequency of occurrence and forces associated with impingement events, a sensor capable of recording transient force spikes was built and deployed in the rocky intertidal zone at Hopkins Marine Station. High-frequency measurements of wave forces were recorded for multiple sampling periods of several days, and spanned a range of tidal heights, significant wave heights, and seasons. Preliminary data indicate that impingement events appear to occur roughly 40% of the time, regardless of environmental conditions. This suggests that intertidal organisms are exposed to impingement events on a near constant basis, increasing the potential for organism dislodgment and damage.