The relationship of soils containing liquefaction features and redoximorphic features to perched seasonal water tables in the Lower Mississippi River Valley

Abstract Liquefaction features occur when saturated granular particles are transformed into a fluid state due to the passage of earthquake shear waves. Since the liquefaction features are so numerous and sand conducts water rapidly, our hypothesis for the Lower Mississippi study area was that liquefaction features have improved soil drainage and that redoximorphic features (RMFs) in the soils are relict. Shallow and deep piezometer data indicate that perched seasonal water tables are present and that free-water levels generally agree with RMFs at sites 1 and 2. At site 3 free-water was observed on one date at >128 cm depth whereas RMFs occur here at >110 cm. The disagreement between the occurrence of free-water and RMF at site 3 suggests some of the RMFs are relict. According to a groundwater model, net groundwater movement from pre-development until 1982 was from aquifers to the rivers, but the net flow of groundwater is now from the rivers to the aquifer. At site 3 lowering of the regional aquifer rather than the liquefaction features may be responsible for the difference between the depth of RMFs and the occurrence of free-water.