Coco Giovanni

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Coco
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Giovanni
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  • Article
    The role of tides in beach cusp development
    (American Geophysical Union, 2004-04-10) Coco, Giovanni ; Burnet, Tom K. ; Werner, B. T. ; Elgar, Steve
    Field measurements of morphology and swash flow during three episodes of beach cusp development indicate that tides modulate the height and cross-shore position of beach cusps. During rising tide, beach cusp height decreases as embayments accrete more than horns and the cross-shore extent of beach cusps decreases. During falling tide, beach cusp height increases as embayments erode more than horns and cross-shore extent increases. A numerical model for beach cusp formation based on self-organization, extended to include the effects of morphological smoothing seaward of the swash front and infiltration into the beach, reproduces the observed spacing, position, and tidal modulation. During rising tide, water particles simulating swash infiltrate, preferentially in embayments, causing enhanced deposition. During falling tide, exfiltration of water particles combined with diversion of swash from horns causes enhanced erosion in embayments. Smoothing of beach morphology in the swash zone seaward of the swash front and in the shallow surf zone accounts for most of the observed tidal modulation, even in the absence of infiltration and exfiltration. Despite the qualitative, and in some cases quantitative, agreement of the model and measurements, the model fails to reproduce observed large deviations of horn orientation from shore normal, some aspects of beach cusp shape, and deviations from the basic tidal modulation, possibly because of the simplified parameterization of cross-shore sediment transport and the neglect of the effects of sea surface gradients on flow.
  • Article
    Sorted bed forms as self-organized patterns : 2. Complex forcing scenarios
    (American Geophysical Union, 2007-08-14) Coco, Giovanni ; Murray, A. Brad ; Green, Malcolm O. ; Thieler, E. Robert ; Hume, T. M.
    We employ a numerical model to study the development of sorted bed forms under a variety of hydrodynamic and sedimentary conditions. Results indicate that increased variability in wave height decreases the growth rate of the features and can potentially give rise to complicated, a priori unpredictable, behavior. This happens because the system responds to a change in wave characteristics by attempting to self-organize into a patterned seabed of different geometry and spacing. The new wavelength might not have enough time to emerge before a new change in wave characteristics occurs, leading to less regular seabed configurations. The new seabed configuration is also highly dependent on the preexisting morphology, which further limits the possibility of predicting future behavior. For the same reasons, variability in the mean current magnitude and direction slows down the growth of features and causes patterns to develop that differ from classical sorted bed forms. Spatial variability in grain size distribution and different types of net sediment aggradation/degradation can also result in the development of sorted bed forms characterized by a less regular shape. Numerical simulations qualitatively agree with observed geometry (spacing and height) of sorted bed forms. Also in agreement with observations is that at shallower depths, sorted bed forms are more likely to be affected by changes in the forcing conditions, which might also explain why, in shallow waters, sorted bed forms are described as ephemeral features. Finally, simulations indicate that the different sorted bed form shapes and patterns observed in the field might not necessarily be related to diverse physical mechanisms. Instead, variations in sorted bed form characteristics may result from variations in local hydrodynamic and/or sedimentary conditions.
  • Article
    Effects of density-driven flows on the long-term morphodynamic evolution of funnel-shaped estuaries
    (The Authors, 2018-10-13) Olabarrieta, Maitane ; Geyer, W. Rockwell ; Coco, Giovanni ; Friedrichs, Carl T. ; Cao, Zhendong
    Subtidal flows driven by density gradients affect the tide‐averaged sediment transport in estuaries and, therefore, can influence their long‐term morphodynamic evolution. The three‐dimensional Coupled Ocean‐Atmosphere‐Wave‐Sediment Transport modeling system is applied to numerically analyze the effects of baroclinicity and Earth's rotation on the long‐term morphodynamic evolution of idealized funnel‐shaped estuaries. The morphodynamic evolution in all the analyzed cases reproduced structures identified in many tide‐dominated estuaries: a meandering region in the fluvial‐tidal transition zone, a tidal maximum area close to the head, and a turbidity maxima region in the brackish zone. As the morphology of the estuaries evolved, the tidal propagation (including its asymmetry), the salinity gradient, and the strength of subtidal flows changed, which reflects the strong bathymetric control of these systems. The comparison with barotropic simulations showed that the three‐dimensional structure of the flow (induced by density gradients) has leading order effects on the morphodynamic evolution. Density gradient‐driven subtidal flows (1) promote near‐bed flood dominance and, consequently, the import of sediment into the estuary, (2) accelerate the morphodynamic evolution of the upper/middle estuary, (3) promote a more concave shape of the upper estuary and reduce the ebb‐tidal delta volume, and (4) produce an asymmetric bathymetry and inhibit the formation of alternate bars that would form under barotropic conditions. This latter effect is the consequence of the combined effect of Earth's rotation and baroclinicity.
  • Article
    Field observations of swash zone infragravity motions and beach cusp evolution
    (American Geophysical Union, 2005-02-22) Ciriano, Yolanda ; Coco, Giovanni ; Bryan, K. R. ; Elgar, Steve
    Fluid flows consistent with low-mode edge waves were evident in video observations of swash motions during a field experiment in which beach cusps developed on an initially smooth beach. As beach cusps grew, energy lying along low-mode dispersion curves increased. The most energetic edge-wave propagation direction changed from upcoast to downcoast as the orientation of the cusp horns rotated. These observations suggest a coupling between morphodynamics and hydrodynamics, and are evidence that beach cusp evolution might control low-mode edge wave dynamics.