Just in time for the Industry-Rice Earth Science Symposium 2018, the newest iteration of the reduced complexity coastal barrier model was summarized as a poster presentation. Be sure to click on the image to the right to download a high resolution jpeg image of the poster!
For AGU Fall Meeting 2017 in New Orleans, I gave a talk on the application of a simple morphodynamic model to forward model the response of coastal barriers (islands and peninsulas) to spatially variable sea-level rise over centuries. Within the model, coastal barrier geomorphology is simplified to a suite of characteristic scales and surface processes are simplified to parameterized expressions that characterize geomorphic responses to relative sea level rise. The abstract for this presentation is in an earlier post (Getting ready for AGU 2017), and a PDF of the presentation is available here (opens in a new window)!
Exploring the morphodynamic response of coastal barriers to sea-level rise along the Texas Gulf Coast
1 Rice University
2 Montclair State University
The Texas portion of the Gulf Coast spans nearly 600 kilometers and is chiefly composed of barrier islands and peninsulas that shelter numerous landward communities from damaging storm surge and waves. Presently, this coastal barrier system is evolving at an unprecedented rate, as sediment that comprises these protective barriers is being depleted while sea-level rise is accelerating, reducing the resilience of coastal communities. To help explain the morphodynamic response of Texas’ coastal barrier system to anticipated accelerated sea-level rise, a reduced complexity morphodynamic model is constructed from a combination of extant models of barrier morphodynamics, alongshore sediment transport, and time-variable ravinement depth. The model is initialized using a simplified geometric depiction of the barrier system morphology obtained from regional bathymetric and topographic surveys, and sediment composition from best-available subsurface geodatabases. Simulation timesteps capture the morphodynamic response of coastal barriers to accelerated sea-level rise by tracking the motion of key geomorphic boundaries within the barrier system: ravinement depth, shoreline, and bay line. The motion of these boundaries is calculated via parameterized expressions of alongshore, cross-shore, and barrier over-wash sediment transport that represent the time-integrated effect of short-term coastal processes, such as day-to-day waves and storms, and longer-term processes such as sea-level rise, dynamic barrier morphology, and barrier sediment composition. Model results are comparable with historical records and geological interpretations of regional coastal change sampled over a broad range of time and spatial scales.
Time and location: Tuesday, 12 December 2017 14:10 – 14:25 New Orleans Ernest N. Morial Convention Center – 353-355
Please check out the innovative work presented by Ben Cardenas, which uses a surface model for aeolian dune topography, with newly developed routines that allow for aeolian dune climb, and preservation of dune stratification:
Coupling Aeolian Stratigraphic Architecture to Paleo-Boundary Conditions: The Scour-Fill Dominated Jurassic Page Sandstone
1 The University of Texas at Austin
2 Rice University
The stratigraphic architecture of aeolian sandstones is thought to encode signals originating from both autogenic dune behavior and allogenic boundary conditions within which the dune field evolves. Mapping of outcrop-scale bounding surfaces and sets of cross-strata between these surfaces for the Jurassic Page Sandstone near Page, AZ, USA, demonstrates that dune autogenic behavior manifested in variable dune scour depth, whereas the dominant boundary conditions were antecedent topography and water-table elevation. At the study area, the Page Sandstone is ~ 60 m thick and is separated from the underlying Navajo Sandstone by the J-2 regional unconformity, which shows meters of relief. Filling J-2 depressions are thin, climbing sets of cross-strata. In contrast, the overlying Page consists of packages of one to a few, meter-scale sets of cross-strata between the outcrop-scale bounding surfaces. These surfaces, marked by polygonal fractures and local overlying sabkha deposits, are regional in scale and correlated to high stands of the adjacent Carmel sea. Over the km-scale outcrop, the surfaces show erosional relief and packages of cross-strata are locally truncated. Notably absent within these cross-strata packages are early dune-field accumulations, interdune deposits, and apparent dune-climbing. These strata are interpreted to represent a scour-fill architecture created by migrating large dunes within a mature dry aeolian sand sea, in which early phases of dune-field construction have been cannibalized and dune fill of the deepest scours is recorded. At low angles of climb, set thickness is dominated by the component of scour-depth variation over the component resulting from the angle of climb. After filling of J-2 depressions, the Page consists of scour-fill accumulations formed during low stands. Carmel transgressions limited sediment availability, causing deflation to the water table and development of the regional bounding surfaces. Each subsequent fall of the water table with Carmel regressions renewed sediment availability, including local breaching of the resistant surfaces and cannibalization of Page accumulations. The Page record exists because of preservation associated with Carmel transgressions and subsidence, without which the Page would be represented by an erosional surface.
Time and location: Wednesday, 13 December 2017 13:40 – 18:00 New Orleans Ernest N. Morial Convention Center – Poster Hall D-F
The morphodynamic depth of closure, signifies the depth at which fluid motion is unable to move sediment, and morphological change ceases. A very timely contribution from Ortiz et al (2016) expresses depth of closure as a function of both wave climate and a time scale of interest. At IRESS 2017, I presented a quick first-pass applying Ortiz’s model and adopting their workflow for application to the Texas coast using Army Corps of Engineers’ WIS hindcast information and the Coastal Relief Model from NOAA. Although Ortiz’ model does not do well to describe the rather tranquil wave climate of the Texas coast, the results show that fair weather wave base is typically above 4 m water depth, and may increase in depth slightly from the Upper Texas coast to the Lower Texas coast. These predictions crudely agree with depth profiles of morphological change estimated by differencing sequential shoreface profiles obtained by Texas A&M University Corpus Christi which are available from their Coastal Habitat Restoration GIS website. Click on the picture of the poster to download a PDF copy.
 Ortiz, A. C., and A. D. Ashton (2016), Exploring shoreface dynamics and a mechanistic explanation for a morphodynamic depth of closure, J. Geophys. Res. Earth Surf.,121,442–464, doi:10.1002/2015JF003699. (PDF link)