Processing of outcrop-based lidar imagery to characterize heterogeneity for groundwater models.

Accurate representation of heterogeneity at varying scales is vital for modeling solute dispersion in groundwater aquifers and petroleum reservoirs. Dispersion, the result of varying velocities in a flow field, is, in part, due to material heterogeneity. In order to represent the influence of heterogeneity at the outcrop scale, a series of terrestrial LIDAR scans at millimeter-scale point spacing were recorded in sediments located in braided stream exposures west of Albuquerque, New Mexico, and outside the Hanford Site in Washington. Scans are projected onto a vertical plane and converted to a high-resolution TIFF image. Using the mean and standard deviation of the ‘‘stacked’’ images, the data are processed through a series of filters to enhance textural information and distinguish between lithologies. The product is converted to a grid with numerical color values for each lithology (e.g., sandstone, gravel). Each lithologic class is assigned reasonable values of hydraulic conductivity. Groundwater flow and transport time are simulated using MODFLOW and MODPATH, respectively. Simulations show that flow and solute transport are focused in the coarser-grained laminae of cross-bedded units. Flow may be focused into some areas in finer-grained beds as well, if the adjacent gravel bed has been cut. Thus, most of the flow may be focused into a smaller volume of the material making up the aquifer. This result shows that terrestrial LIDAR can be successfully applied to produce synthetic stratigraphy for use in fluid flow models.