The Subsurface Architecture (SA) Integrated Project (IP) underwent a fundamental restructuring during 2006-2007. We decided to focus the whole SA IP effort on developing methods for predicting delta evolution in support of sustainable delta restoration, with a particular emphasis on integrating predictive models with information from subsurface and experimental studies of delta lobe development, channel network self-organization, and ecogeomorphology. Building on the "surface to subsurface" SA IP theme, we are developing methods to use subsurface records to understand how the delta maintained itself naturally (ie, before human influence) during the Quaternary, with the aim of using these natural self-maintenance processes to guide the design of a sustainable delta-restoration program.

This year, the SA IP has identified 10 projects:

Project SA01 Current sediment budget and subsidence distribution in Mississippi Delta
Plans: NCED graduate student Jeff Nittrouer and colleague Meade Allison of Tulane University collected the first set of suspended sediment profiles for the lower Mississippi River using a P-63 suspended sediment sampler system. We are now in position to start defining the fraction and sand sizes moving as bedload vs suspended load and defining floc concentrations over the range of river discharge to quantify the spatial and temporal variability of bed-material transport in the Mississippi River from Baton Rouge to the river mouth.

Of particular importance is determining the structure of the concentration profiles for suspended sand as a function of river discharge. Improving our understanding of sand transport in the lower river is important to reducing the uncertainty associated with the quantity of sediment available for possible Mississippi Delta restoration projects.

Sub-bottom profiles for the river between Baton Rouge (roughly) and Venice, LA, will be carried out to determine the thickness of the Holocene sand deposit on the channel bed. An understanding of where sediment is being naturally sequestered within the lower river system is also necessary in order to refine our understanding of potential amounts of sediment available for restoration projects.

Project SA02 Behavior and deposition of cohesive sediment
Plans: During the coming year, we will investigate the extent to which traditional sediment-flux equations can be applied to the transport of cohesive sediment, accounting for their effective (flocculated) diameter and density. This work will begin with planned field work at Wax Lake Delta (WLD) in May, 2007, to establish the state of transport of the fine sediment load.

Project SA03 Vegetation-sedimentation interaction in island and marsh development and maintenance
Plans: We are working with National Center for Earth-surface Dynamics (NCED) Principal Investigator (PI) Efi Foufoula-Georgiou, synthesis Postdoctoral Research Associate Doug Jerolmack, and others to explore theoretical models for the aggregation of initial isolated vegetated areas. We will also investigate the feasibility and affect of using the alfalfa methods on our experimental deltas. We have also worked with collaborators at the US Department of the Interior, Bureau of Reclamation (USBR), the National Institute of Water and Atmospheric Research (NIWA), New Zealand, and NCED PI Peter Wilcock on applications of this work to the Stream Resotration (SR) IP, given that revegetating and devegetating channels and bars are often central issues in stream restoration. This year, we will work with PIs Robert Twilley and Mary Power to try to incorporate more realistic ecological effects in this effort.

Project SA04 Reconstructing delta dynamics from seismic records
Plans: Research emphasis this year will be on analysis of the seismic data we have to define the roles of small- and large-scale normal faulting in controlling delta-top subsidence. We will also be seeking additional data for analysis.

Project SA05 Reconstructing delta dynamics from cores and other records
Plans: We are hard at work putting together a new initiative to support an expanded program in the Mississippi Delta. If successful, this initiative will fund the coring work required for this sub-project. Our next task within the existing NCED framework is to characterize the porosity state for the uppermost kilometer of strata between the Breton Sound area through well log analysis combined with direct detection via seismic inversion.

Project SA06 Modeling land building; integration with Louisiana State University’s CLEAR project
Plans: Successive measurements of water and sediment discharge in the primary passes of the WLD, and associated changes in channel bottom and bank topography, will be undertaken this year. It is expected that considerable spatial and temporal variability in sedimentation will exist within the distributary network. These variations will be compared to those already studied in the aggrading Niobrara River, NE. Measurements will be used to refine the evolving numerical models of land construction beginning with the current numerical model and models being developed with Louisiana State University’s Coastal Louisiana Ecosystem Assessment and Restoration (CLEAR) project.

Project SA07 Self-organization of distributary systems including elevation statistics
Plans: We will investigate statistics of length (channel, edge, shoreline) and area on the delta top with the aim of estimating specific habitat parameters for fish as a delta lobe evolves and increases in size. The initial focus will be experiments, calibrated with field data from WLD, and then numerical models. We also expect to make major headway on developing methods for quantifying space-time statistics of active, evolving distributary systems with the eventual goal of forecasting distribution of elevation, grain size, and rate of deposition.

Project SA08 Upscaling short-term rates and small-scale geometries
Plans: We will work on methodology for upscaling laboratory delta data to natural scales for use in numerical models. This will be coupled to physical theory to predict spatial distribution of deposition rate as a function of time scale.

Project SA09 Coastal system response to rising relative sea level
Plans: The next step is to use a combination of experiments and model refinements to move from 1D to 2D prediction, including the response of the distributary pattern to sea-level rise. Eventually, these predictions will be compared with the reconstructed history of the response of the Mississippi Delta to Holocence sea-level rise, but this is three to four years off.

Project SA10 Social tradeoffs in Mississippi Delta restoration
Plans: Our initial tentative focus will be on integrating several broad classes of predictive economic models into predictive models of landscape change, such as Louisiana State University’s CLEAR model. We will also consider conflicts between marsh restoration, business and society, and apply risk and uncertainty analyses. We stress, however, that it is not realistic to expect our present, modest, social-science effort to address these issues in depth. Thus, a major emphasis in our plan to develop and secure additional funding for a larger Mississippi Delta restoration initiative will be to add more social scientists to the group.