This year, the Subsurface Architecture (SA) Integrated Project (IP) has undergone a major transformation; bringing this about has been a major focus of the SA team this year. This section summarizes SA research including that conducted under the previous version of the Strategic and Implementation Plan (SIP).

A new study of the construction of leveed channels and overbank surfaces by depositional turbidity currents linked measurements of submarine levees and stratigraphy from the offshore Borneo with a laboratory experiment that resolves the processes controlling submarine levee growth. We found that levee taper rapidly increased during early levee growth then transitioned to a slower taper growth rate at a channel relief exceeding approximately 30 m. Results from laboratory experiments indicate that the degree of channel confinement and vertical structure of the sediment concentration profile are the most important parameters controlling levee growth. Using these observations, we developed a levee growth model based on an advection-settling scheme coupled to a sediment concentration profile described by the Rouse profile. We identified a reasonable set of flow conditions that produced a levee taper growth history similar to observations. The measurements and associated model of the morphodynamics of levee growth in aggrading channel settings can also be applied to terrestrial levee dynamics.

The main eXperimental EarthScapes facility (XES) activity this year was completion of a long-planned experiment on interaction of multiple sediment sources in an asymmetrically subsiding basin modeled after the Rio Grande rift. This work contributes to the SA IP via its theme on tectonic steering of channel systems. The experiment had four sediment/water sources: two on the footwall side, one on the hanging-wall side, and one axial. Thus far, the main finding has been that the relative sizes of the domains controlled by the four sediment sources is almost entirely controlled by the ratio of sediment supply to subsidence; water supply does not seem to play a major role. In a sense, the boundaries between the transverse and axial domains can be thought of analogous to a shoreline with strong alongshore transport.

In addition, we carried out a series of experiments with colleagues at ExxonMobil to demonstrate that a new cohesive sediment simulant mix they have developed can indeed capture the spatial structure of fine-grained deltas like the Mississippi Delta. The shoreline of such fine-grained deltas is much more irregular than for the noncohesive case, which we believe will influence the distribution of biota sensitive to the total length of the land-water interface. To help clarify the distribution of habitat types, we developed what we believe is the first quantitatively based method to distinguish channel edges from true shoreline. We also developed prototype cellular channel-avulsion models that we have implemented in various forms (ie, different sediment transport dynamics, including or excluding backwater effects) to determine their affects on delta dynamics.

Finally, we have been working intensively, with input from the National Science Foundation (NSF), on a new initiative in delta restoration that will extend the SA IP to a larger group of colleagues.