To be submitted soon!
Abstract: A reduced complexity model aeolian dune stratification model is developed and applied to explore the role of dune morphodynamics in the creation of synthetic sections of aeolian stratigraphy and shredding of environmental signals originating from three sets of environmental forcing: 1) steady transport capacity, 2) steady bed aggradation and variable transport capacity, and 3) steady transport capacity and bed aggradation. In each scenario, the forward motion of initial, highly disorganized dunes generates a significant record exclusively containing autogenic signals that arise from early dune growth, deformation, and merger. However, continued dune growth scours deeply, and shreds all records of early dunes. Afterward, dunes self-organize into groups of dunes. Forward motion of dune groups create, truncate, and amalgamate sets and co-sets of cross-strata, quickly forming a second, significantly more robust stratigraphic record, which preserves a comingling of signals sourced from ongoing autogenic processes and each scenario’s specific set of environmental forcings. Although the importance of self-organization on modeled aeolian stratification is clear in the few presented scenarios, self-organization maybe throttled via variability within environmental forcings. Therefore, additional work is warranted as this numerical experiment only begins to sample possible sets of environmental forcing, boundary conditions, and initial conditions, geomorphic responses, and consequential preservation.
Here’s a sneak peak of the simulations:
The videos below so the co-evolution of dune topography and stratigraphy for three different model scenarios. In each video, bedform stratigraphy is vertically exaggerated 100x. Additionally, bedform topography is reduced 20x. η* and x* are non-dimensional vertical and horizontal scales, respectively. η* represents the fraction of equilibrium dune height, and similarly, x* represents the number of equilibrium dune wavelengths. Enjoy!
1) Steady transport capacity
2) Steady bed aggradation and time-varying transport capacity
3) Steady bed aggradation and transport capacity
Members of the Coastal Sedimentology Group (myself included!) preformed physical demonstrations of processes responsible for sea level rise and how higher sea levels threaten coastal communities for World Oceans Day at the Houston Museum of Natural Science. A big thanks to Dr. Lauren Simkins, Lindsay Portho, and Tian Dong for making our time at the museum a success! Thanks to Dr. Simkins for developing an informative pamphlet which can be downloaded via this link. More information surrounding this event is available on the Rice University webspage and through a “News Fix” video made possible by CW 39.
My role in this collaborative effort was to design and construct a two dimensional wave tank with a highly exaggerated profile of coastal relief, dynamic sea level control and a paddle wave maker to demonstrate how rising sea level allows storm waves and even fair weather waves to over-top protective barrier islands and threaten coastal communities. The wave tank was constructed using many opensource hardware and software tools. Please send me a quick note if you would like plans or help constructing your own wave tank; otherwise check this blog again, as I intend to do a write-up on how to build, wire, and program the wave tank. It was a lot of fun to construct! A big thanks to the Shell Center for Sustainability for funds to purchase components to build the tank.
Aeolian dune topography arises from a highly non-linear interaction between sediment transport, topography, and boundary shear stress. To explore the growth of aeolian dunes under a variety of boundary conditions, a new surface model for aeolian bedform topography is adapted from a surface model of subaqueous bedform topography (Jerolmack and Mohrig, 2005). The resulting modeling framework approximates the dynamic motions of aeolian bedform topography driven by bedform field boundary conditions; namely, different distributions of sediment transport direction and investigating bedform growth with and without the constraint of a fixed sediment source area (modeled as a fixed elevation boundary). The rates at which modeled aeolian bedforms grow and morphologically mature are found to be highly sensitive to the chosen boundary conditions. Click on the image of the manuscript header to visit the journal’s website and read more about this study.
The videos below show four permutations of two boundary conditions: uni- and bi-modal distributions of sediment transport direction are used to grow bedform topography with and without the constraint of a sediment source area. In these videos hot colors indicate higher topography and cooler colors indicate lower topography.
Uni-modal distribution of sediment transport direction with periodic boundaries
Uni-modal distribution of sediment transport moving sediment from a fixed source
Bi-modal distribution of sediment transport direction with periodic boundaries
Bi-modally distributed sediment transport moving sediment from a fixed source
The aeolian bedform surface model code is malleable and readily modified for exploratory study of bedform topography that inherits morphological traits from aeolian bedform field boundary conditions. A version of the source code for these simulations is available from MATGEO. However, a newer version of this software will be made available via a public repository on GitHub, shortly.
 Jerolmack DJ, Mohrig D (2005) A unified model for subaqueous bed form dynamics. Water Resour Res 41(12):W12421. doi:10.1029/2005WR004329 (PDF link)
A pool-riffle-pool sequence is a nearly ubiquitous element of stream bed morphology. The variabiltiy in bed elevation is thought to allow surface water to infiltrate through the stream bed the head of a riffle and upwell back to the stream at the tail of the riffle in a pool-riffle-pool (PRP) sequence, thus driving a surface water-ground water interaction termed hyporheic exchange. Because infiltrating surface water transports heat from daily heating and cooling; Heat tracing within the streambed sediments is a potentially useful method to characterize hyporheic exchange. For this purpose, temperature was monitored within a PRP sequence for several days at Jaramillo Creek in the Valles Caldera National Preserve. Temperature in the hyporheic zone below the pool-riffle-pool sequence reflected the diel temperature change in Jaramillo Creek but not uniformly. The observed thermal pattern exhibited deeper penetration of thermal oscillations below the head pool and shallower penetration below the tail pool. Play the video below to watch diel cycles of temperature change in sediments below a pool-riffle-pool sequence:
To learn more about one-dimensional analytical heat transport (tracing) models that can use such temperature information to estimate the exchange of water between streams and their associated aquifers, check out the manuscript by clicking on the image at the top of this blog post.