Flow and Transport Parameters for Colonnade Networks

Numerical simulations are conducted to obtain asymptotic estimates of equivalent continuum hydraulic conductivity, porosity and macrodispersivity for discrete colonnade network models of fractured basalts. For colonnades with lognormally distributed apertures and a column diameter of 1 m, the equivalent hydraulic conductivities and porosities for single realizations are directionally dependent at smaller length scales but show little directional dependence for networks that are in excess of 20 times the column diameter. The length scale requirements for directionally isotropic macrodispersivities are much more stringent than those for hydraulic conductivity and porosity; macrodispersivities are directionally dependent at length scales of up to 30 times the column diameter. The computed asymptotic and preasymptotic macrodispersivities are compared with available stochastic solutions; the ensemble-based numerical data are in excellent agreement with Dagan (1984, 1988) and Gelhar and Axness (1983) solutions. However, for individual realizations, nonergodic behavior is clearly apparent in the near-source, evolving region of transport and the numerical data are quite variable between realizations.