| Popis: |
A major environmental and economic problem currently faces the New Orleans area, in southeastern Louisiana, stemming from salinization of freshwater aquifers that are important resources for the community. Major pumping of these aquifers has altered the potentiometric flow, allowing saltier bodies of water to flow into the region. The impact of pumping wells on encroachment of saltwater and the time as well as the route for saltwater to travel from the current saltwater-freshwater interface to pumping centers is not well constrained. Water planners need additional information to make decisions about future management of groundwater resources. The most effective way to analyze pumping effects on groundwater is to build a computer simulated flow model. However, such a model is reliable only if the permeability pathways and structures through which the water moves are well understood, which necessitates a clear picture of the subsurface geology. The lithology and structure of the New Orleans subsurface is controlled by the fluvial/deltaic environment that has characterized southeastern Louisiana during the Pleistocene and Holocene periods. The Mississippi River and associated deltas have migrated throughout southern Louisiana over geologic time. The river channels and deltaic lobes that migrate back and forth likely do not return to the exact same spatial coordinates upon return to southeastern Louisiana, creating complications in defining stratigraphic features. Therefore, a geologic model was produced using well log correlation to characterize both lateral continuity and thickness of lithologic units. The geologic model and associated cross sections highlight proposed locations of geologic units only when the units are clearly indicated in geophysical logs. Results reveal a highly heterogeneous subsurface, where units are discontinuous at scales of 1000 ft (300 m), highlighting the significant lack of available geophysical logs to create an accurate geologic model. Therefore, many plausible realizations of the subsurface architecture are possible, and variability of factors used for lithologic correlation can create large differences in the numerical modeling of saltwater encroachment, demonstrating a need to explore new stochastic methods of correlation in complex environments such as the New Orleans area. |
