Sand Body Geometry of the Wax Lake Outlet Delta Atchafalaya Bay, Louisiana

TLDR: In this paper, the development history of the Atchafalaya delta is described using stratigraphy, aerial photography and digital terrain model data sets, and the Wax Lake Outlet delta is compared to other Mississippi deltas.

Abstract: Deltas forming in Atchafalaya Bay, L-ouisiana, are the result of delta switching by the Mississippi River. The larger Lower Atchafalaya River delta has been heavily manipulated by dredging for navigation, but the Wax Lake Outlet delta is largely undisturbed and an excellent example of a 'bayhead' delta. Combining stratigraphy, aerial photography and digital terrain model data sets, the developmental history of this delta is presented. The Wax Lake Outlet delta is comprised of a typical upward-coarsening sequence, although its prodelta unit is extremely limited. Its plan-view form is typical of deltas developing in low-energy, unstratified, shallow basins. Early developmental processes were identified by Roberts and van Heerden (1992) Development through the 1980s involved the maturation of distributary channels. From 1989 to 1994, the majority of sediment was retained seaward of the delta proper, due to the efficiency of the distributary’ system. Greatest sand body thicknesses were found on the upstream portions of delta lobes, but not necessarily at points of bifurcation. Estimates of sand body volume range from 129 to 139 x 106 m3. A small area of the Atchafalaya River delta investigated for comparison also contains an upward-coarsening sequence but with upper and lower coarse­ grained bounding units generated by dredging activity. Comparison of the Wax Lake Outlet delta to other Mississippi deltas reveals some similar processes of development despite differences in settings. The Wax Lake Outlet delta has shown a lower rate of infilling compared to subdeltas of the Mississippi River Balize delta due to the relative immaturity of the Atchafalaya. Growth curves based on terrain model data predict an area of 111 knt (at and above 0.0 NGVD) by the year 2000, which falls within the range of values given by the Wells et al. (1982) generic model based on the Mississippi subdeltas.