Comparative evaluation of selected continuum and discrete-fracture models: Emphasis on dispersivity calculations for application to fractured geologic media, creston study area, eastern Washington

A quantitative comparison of dispersivity calculated from a discrete-fracture model and an analytical solution for fractured rock is made. The calculated transverse dispersivity from an analytical solution to the dispersion equation is compared to that from a discrete-fracture model for four cases involving two sets of parallel, planar, continuous fractures intersecting at various angles. Anisotropy is used in one of the cases. Results of the comparison indicated that the functional relationships of transverse dispersivity were preserved by both models when the angle of the hydraulic gradient changed with respect to the two fracture sets, the spacing between fractures changed, the angle between fracture sets changed, or the hydraulic properties of one of the fracture sets changes. The magnitude of the calculated transverse dispersivity using the discrete-fracture model was within 10% of that calculated using the analytical solution after the scale effects of the fracture system were taken into account. The results demonstrate that dispersivity calculated by a discrete-fracture model agrees well with theory. Scale effects of transverse dispersivity indicated that a relatively constant value was reached after particles had traveled about 10 times the fracture spacing of the most widely spaced fracture family. 41 refs., 21 figs., 2 tabs.