DERIVING HYDRAULIC CONDUCTIVITY FROM DRAINAGE PATTERNS - A CASE STUDY IN THE OREGON CASCADES

This study introduces a new method of extracting hydraulic conductivity from a drainage dissection pattern derived from a digital elevation model (DEM). The study area is the Cascade Range in Oregon which has a sharp contrast in dissection pattern. The dissection pattern is derived from DEM using a morphology-based method. Under DuPuit assumption for unconfined aquifer, we apply Darcy's law to the watershed contributing to each channel segment and calculate the hydraulic conductivity based on estimation of the channel depth from DEM and assuming a reasonable aquifer thickness. The channel depth is estimated by subtracting the valley bottom elevation from the valley shoulder elevation, which is approximated as the 75 percentile value within a 3-km radius moving circular window. The aquifer thickness is assumed to be 500 m. The hydraulic conductivity for each watershed in the study area is estimated using this method and the results range from 10^-7 m/s and 10^-11 m/s. These results are not only consistent in magnitude with field measurements, but also in spatial distribution, which shows that the older, Western Cascades have a lower hydraulic conductivity than the younger, High Cascades. The contrast in hydraulic conductivity reflects the contrast of geology between the Quaternary (High Cascades) and the Tertiary (Western Cascades) regions. This method has great potential for estimating hydraulic conductivity of aquifers in remote locations on Earth and on other planets such as Mars.