Observing Multi-Scale Ocean Dynamics off Rough Rocky Coastlines: Obstacle-Scale Pressure and Velocity Sensor Array

Rosmans objectives are to use field observations to study the physics of coastal ocean dynamical processes important to Navy operat ions, in particular, to develop accurate representations of rocky shoreline processes that have first order effects on nearshore wav e and current conditions but are not typically resolved in coastal models. About 75% of the world coastlines are rocky, limiting Nav al accessibility. In contrast to well-studied sandy shores, rocky shores have complex three-dimensional geometries at scales of cm t o 100s m, are often exposed to strong waves, and relatively little is known about their wave and circulation dynamics. Rocky shore o cean dynamics are inherently multi-scale. Multi-scale bottom variability (or roughness) has strong effects on wave processes such as scattering, reflection, nonlinear energy transfers, and dissipation that are dramatically different than on sandy beaches. Rocky sh ore wave processes also strongly affect water-column turbulence and wave-driven currents. The accuracy of existing models developed for low-sloped beaches for predicting wave propagation, circulation and turbulence on rocky shores is unknown, as is what new physi cs must be included to make accurate predictions. Dissipation associated with interactions of waves with bottom features of a range of sizes is of first order importance, but existing bottom friction parameterizations do not explicitly account for these processes , limiting predictive capability. This DURIP proposal is associated with a MURI Program, ONR Topic 3: Littoral ocean dynamics off of rocky coasts and shorelines submission by a PI team led by MacMahan (NPS), which proposes field experiments on representative rocky shores, and modeling of wave, circulation, and turbulence processes. We propose to develop an Obstacle-Scale Pressure and Velocity Sensor Array to coherently measure how wave properties are altered and energy is dissipated as waves propagate over bottom features of different sizes and shapes over an area up to 20 m x 20 m. The PI, graduate students and post-doctoral researchers will utilize this system in research, publications, and presentations. The array requested in this proposal includes: Synchronized pressure sens ors. A set of 18 RBR Coda pressure sensors connected to three RBR Maestro multi-channel data loggers. These sensors will coherently measure the pressure field around bottom features as waves propagate over and enable us to calculate forces exerted on water by obs tacles: Synchronized velocity sensors. Six Nortek Vector acoustic Doppler velocimeters and one Nortek Signature 1000 acoustic Dopple r current profiler. These instruments will be used in conjunction with ADV/ADCPs requested in a companion DURIP proposal (Wilson), a nd instruments owned by the PI and collaborators in a synchronized array, enabling us to measure wave orbital motion and turbulence around obstacles as waves propagate past; and A set of microcomputers in an underwater housing at the measurement site to synchroni ze measurements from all sensors in the array.