USING HISTORIC AND MODERN DATA TO ASSESS MISSISSIPPI RIVER LEVEE FAILURES

A Geographic Information System (GIS) database has been constructed for the Mississippi River between St. Louis, MO and Memphis, TN to identify potential causal mechanisms contributing to historic levee failures. DEM data is being used, in conjunction with surficial geologic maps and borehole logs, to map landforms, fluvial stratigraphic, and geomorphic relationships (e.g., abandoned channels, initiation and inflection points of meander bends, highly permeable strata, etc.) impacting levee failure. An existing river engineering database is being used to identify levee construction irregularities or discontinuities (e.g., high-angle junctions segments, repaired levees, scour holes). This database includes historical levee failures that were employed to identify locations that have been subjected to multiple levee failures. Utilization of land-cover data from historic maps in our database was used to identify the riparian corridor between the river channel and levees for five time steps (1888, 1908, 1948, 1960, 1998). The width, type, and location of the riparian corridor allows us to evaluate its impact on past levee failures.

For this investigation, modern levee elevations also are being assessed locally between St. Louis and Cairo, IL using dual-frequency GPS equipment (post-processed kinematic surveys accurate to <10cm). There is anecdotal evidence of levee heightening without permits in the study area. We are currently comparing the measured current elevations with the reported design elevations to determine whether these levees have settled (e.g., degradation of organic-rich soils, excessive loading of soils due to enlarged levee bases) or if they have been illegally raised above the design flood specifications. To date, the surveying and analysis has been completed for 6 out of the 15 levee districts between St. Louis and Cairo, IL. The elevations of the levees within the surveyed districts meet or exceed their protection level and were found to exceed their proposed grade by as much as two meters locally. However, there is no evidence for district-wide raising of levees to exceed their official protection level.