Question

In a 1978 monograph on late-nineteenth-century agricultural hydrology in the lower Mississippi basin, environmental historian Sarah Mercer investigated the structural failures of early earthen levees constructed by private agrarian consortiums. Mercer noted that while contemporary engineers attributed levee breaches exclusively to seasonal flood volumes exceeding historical averages, sedimentological analysis reveals that structural integrity was primarily compromised by the systematic removal of riparian hardwood forests. Root systems of species such as Quercus nigra had previously stabilized alluvial soils; their clearing for cotton cultivation increased sub-surface seepage by upwards of forty percent. Furthermore, Mercer documented that private consortiums frequently relied on uncompacted clay fill rather than the clay-silt mixtures mandated by regional civil engineering guidelines of the 1880s, thereby creating localized structural voids susceptible to piping failure under modest hydraulic pressure.

Based on the passage, which of the following statements regarding late-nineteenth-century levees in the lower Mississippi basin are explicitly supported? Select all that apply.