Search Results

You are looking at 1 - 3 of 3 items for

  • Author or Editor: C. Brock Woodson x
  • Refine by Access: All Content x
Clear All Modify Search
C. Brock Woodson

Abstract

Cross-shelf exchange resulting from wind- and wave-driven flows across the inner shelf has been the focus of a considerable body of work. This contribution extends recent analyses to the central California coastline using 5-yr of moored current observations. Acoustic Doppler Current Profiler (ADCP) data from stations across the Monterey Bay (two in the northern bay and one in the southern bay), in water depths of ~20 m, showed net offshore transport throughout the year. For the northern bay sites, cross-shelf exchange was dominated by Ekman transport driven by along-shelf diurnal sea breezes during the upwelling season. Intense stratification in the northern bay leads to very shallow observed Ekman layers (~5–8 m), and consequently no overlap between bottom and surface Ekman layers within a few hundred meters of the coast. The total transport is less than predicted by theory consistent with models of shallow-water Ekman transport. The observed transport (~42% of full Ekman transport) is shown to be caused by the influence of a positive vorticity that effectively increases the Coriolis parameter. Wave-driven return flow estimated from an offshore buoy was strongly correlated with observed transport during nonupwelling conditions for the northern, outer bay site, but not for the two inner bay sites (northern and southern). In the southern bay, winds and waves have a significantly reduced effect on the cross-shelf exchange. Internal tidal bores are believed to contribute most of the observed cross-shelf exchange in this region.

Full access
Ryan J. Moniz, Derek A. Fong, C. Brock Woodson, Susan K. Willis, Mark T. Stacey, and Stephen G. Monismith

Abstract

Autonomous underwater vehicle measurements are used to quantify lateral dispersion of a continuously released Rhodamine WT dye plume within the stratified interior of shelf waters in northern Monterey Bay, California. The along-shelf evolution of the plume’s cross-shelf (lateral) width provides evidence for scale-dependent dispersion following the 4/3 law, as previously observed in both surface and bottom layers. The lateral dispersion coefficient is observed to grow to 0.5 m2 s−1 at a distance of 700 m downstream of the dye source. The role of shear and associated intermittent turbulent mixing within the stratified interior is investigated as a driving mechanism for lateral dispersion. Using measurements of time-varying temperature and horizontal velocities, both an analytical shear-flow dispersion model and a particle-tracking model generate estimates of the lateral dispersion that agree with the field-measured 4/3 law of dispersion, without explicit appeal to any assumed turbulence structure.

Full access
Justin S. Rogers, Samantha A. Maticka, Ved Chirayath, C. Brock Woodson, Juan J. Alonso, and Stephen G. Monismith

Abstract

Flow over complex terrain causes stress on the bottom leading to drag, turbulence, and formation of a boundary layer. But despite the importance of the hydrodynamic roughness scale z 0 in predicting flows and mixing, little is known about its connection to complex terrain. To address this gap, we conducted extensive field observations of flows and finescale measurements of bathymetry using fluid-lensing techniques over a shallow coral reef on Ofu, American Samoa. We developed a validated centimeter-scale nonhydrostatic hydrodynamic model of the reef, and the results for drag compare well with the observations. The total drag is caused by pressure differences creating form drag and is only a function of relative depth and spatially averaged streamwise slope, consistent with scaling for kδ-type roughness, where k is the roughness height and δ is the boundary layer thickness. We approximate the complex reef surface as a superposition of wavy bedforms and present a simple method for predicting z 0 from the spatial root-mean-square of depth and streamwise slope of the bathymetric surface and a linear coefficient a 1, similar to results from other studies on wavy bedforms. While the local velocity profiles vary widely, the horizontal average is consistent with a log-layer approximation. The model grid resolution required to accurately compute the form drag is O(10–50) times the dominant horizontal hydrodynamic scale, which is determined by a peak in the spectra of the streamwise slope. The approach taken in this study is likely applicable to other complex terrains and could be explored for other settings.

Full access