Skip Links

USGS - science for a changing world

Woods Hole Coastal and Marine Science Center

Woods Hole Coastal and Marine Science Center > Coastal Model Applications and Field Measurements > Research Components > Field Measurements and Model Applications

Coastal Model Applications and Field Measurements coastal ocean processes,open source coastal ocean models, oceanography, ocean modeling, sediment transport

Field Measurements and Model Applications

Several components of this project are applications to evaluate the model against critical field measurements or to test new model components. Data from field measurements is described in our publications and available in our databases.

Impact of Model Resolution

Numerical models sometimes require high resolution to get accurate results. Comparison of model results at various resolutions with measurements made by collaborators at WHOI revealed an average circulation pattern on the inner shelf south of Martha’s Vineyard that was generated by tidal forcing, and only resolved in the high-resolution model. The loss of model skill with decreasing resolution was attributed to insufficient representation of the bathymetric gradients (Ganju et al., 2011).

Color maps of water depths and model grids

Bathymetry of the New England inner shelf and south shore of Martha’s Vineyard with model grids. From Ganju et al., 2011.

Evaluation of Modeled Bottom Roughness near Martha’s Vineyard Coastal Observatory

Bottom roughness is an important parameter that modifies the current velocity in coastal ocean models. Methods for specifying bottom roughness in models range from very simple specifications of constant, uniform values to complicated nested that base roughness on ripple geometry which, in turn, is governed by sediment type and wave-current combined bottom stresses. We tested several roughness formulations in the COAWST modeling system simulation of flow near MVCO, and compared the results with measurements made by the USGS and collaborators during the ONR Ripples Directed Research Initiative. We found that the more complicated formulations, which incorporated empirical ripple roughness estimates, do not improve our modeling skill (Ganju and Sherwood, 2010).

Pair of gray-scale maps with arrows

Comparison of observed near-bed velocities and modeled near-bed velocities using several bottom-roughness formulations. Velocity vectors are overlaid on map of backscatter from the sea floor showing regions with coarse sand (light color) and fine sand (dark colors). White lines are bathymetry contours. Mean velocities were averaged over entire period (top panel), flood and ebb velocities were determined from dominant alongshore flow direction, and separately averaged for flood- and ebb-oriented flows with speeds >5 cm/s after removing mean velocities (bottom panel). Note change in arrow scale between two panels. From Ganju and Sherwood, 2010.

Floc Model Dynamics near MVCO

We are using data from our OASIS profiling arm measurements to evaluate the recent implementation of floc dynamics in our sediment-transport model (CSTMS). The OASIS data includes measurements by both optical and acoustic instruments, which respond very differently to different types of suspended sediment. Acoustic backscatter sensors respond well to solid, high-density particles like sand, whereas optical sensors are sensitive to larger, density particles like flocs. Idealized model runs for waves, currents, and bottom sediments that resemble measurements at MVCO produce flocs and resuspend bottom sands in a realistic manner.

Orange shaded plots of instrument response.   Floc Model:  Acoustic Response

Modeled response of optical sensors (left) and acoustic sensors (right) to floc population and resuspension of sand in idealized MVCO conditions. The model simulates tidal variation of the floc population and resuspension of sand during a wave event between hours 60 and 80, and highlights the differences the two sensors. In both plots, the top panel shows normalized response to simulated floc population, the middle panel shows normalized response to resuspended fine sand, and the bottom panel showed combined response to the suspended particle field.

Using particle tracking to assess estuarine residence time

Estuarine water quality is strongly related to circulation and residence time. Particle tracking is one method to evaluate how long a parcel of water may remain within an estuary. We used the COAWST model and the LTRANS particle-tracking model to assess the influence of tides, remote forcing, and winds on residence time in Barnegat Bay, New Jersey. We found that tides are relatively inefficient at flushing the northern bay, where water quality is poorest (Defne and Ganju, 2014).

Barnegat Bay residence times in days for (a) scenario T, only tidal forcing; (b) scenario TB, combined offshore hydrodynamic forcing; (c) scenario TBR, streamflow with combined hydrodynamic forcing; and (d) scenario TBRM, full suite with meteorological forcing

Barnegat Bay residence times in days for (a) scenario T, only tidal forcing; (b) scenario TB, combined offshore hydrodynamic forcing; (c) scenario TBR, streamflow with combined hydrodynamic forcing; and (d) scenario TBRM, full suite with meteorological forcing

Scenarios of seagrass change with coupled hydrodynamic-optical models

Estuarine eutrophication due to nitrogen loading has led to numerous ecological changes, including loss of seagrass beds. One potential cause of these losses is a reduction in light availability due to increased attenuation by phytoplankton. Future sea level rise will also tend to reduce light penetration and modify seagrass habitat. We integrated a spectral irradiance model into a biogeochemical model coupled to COAWST, with an offline link to a bio-optical seagrass model. We assessed potential seagrass habitat in a eutrophic estuary under future nitrogen loading and sea-level rise scenarios, focusing on West Falmouth Harbor, a shallow estuary located on Cape Cod. Scenarios of future nitrate reduction and sea-level rise suggest an improvement in light climate in the landward basin with a 75% reduction in nitrate loading. This coupled model may be useful to assess habitat availability changes due to eutrophication and sediment resuspension and fully considers spatial variability on the tidal timescale.

Relative seagrass biomass in West Falmouth Harbor, MA, under current and potential future nitrogen loading scenarios.

Relative seagrass biomass in West Falmouth Harbor, MA, under current and potential future nitrogen loading scenarios. Seagrass biomass increases in western (seaward) portions of the harbor while eastern (landward) areas see new colonization by seagrass.

Accessibility FOIA Privacy Policies and Notices

USA.gov logo U.S. Department of the Interior | U.S. Geological Survey
URL: http://woodshole.er.usgs.gov/project-pages//project-pages/coastal_model/research-themes/applications.html
Page Contact Information: Feedback
Page Last Modified: (GW)