Interpolation of Horizontal Transmissivity Anisotropy from Head and Flowpath Observations

Rocks are rarely equally permeable in all directions. Ground water does not flow directly downgradient through anisotropic aquifers, but deviates at an angle determined by the direction and magnitude of the major and minor transmissivities. We show a mathematical model whereby the orientation and ratio of major to minor transmissivities can be estimated by an analysis of the deviation of ground-water flow from the hydraulic gradient. The solution is derived from the construction of transmissivity ellipse where the hydraulic gradient and flow direction are known. An example is given using an ethylene dibromide contaminant plume at Nemo, South Dakota, where the plume has been deflected because of bedrock foliation.