Repair, Evaluation, Maintenance, and Rehabilitation Research Program: The Effects of Vegetation on these Structural Integrity of Sandy Levees.
1991
Gray, Donald H. | MacDonald, Anne | Thomann, Thomas | Blatz, Imogene | Shields, F. D | Jr
The purpose of this study was to investigate the relationship between vegetation and the structural integrity of river levees. A specific objective was to determine the distribution of roots within levee embankments, and how these roots alter properties of levee embankments and affect their resistance to mass wasting, surficial erosion, piping, etc. With this information, engineering criteria can be developed in the future that may allow additional vegetation to remain on levee embankments where sufficient effort can be made for levee inspection. Current Corps of Engineers guidelines for levee maintenance and operation limit vegetation on the embankment to sod-forming grasses 2 to 12 in. in height to provide for structural integrity, visual inspection, and unhindered flood fight access to levees. Root concentrations and distributions were determined using the profile-wall method in which root cross sections were exposed in the vertical wall of an excavated trench. Transects were excavated running both parallel and perpendicular to the crest of the levee through areas dominated by different woody plant species typical of riparian vegetation. Plant roots reinforce the levee soil and increase shear strength in a measureable manner. A shear strength increase or root cohesion can be estimated from the root biomass per unit volume or alternatively from the root area ratio.
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