'Determination of Hydraulic Conductivity from Grain-Size Distribution for Different Depositional Environments'

摘要

We thank Vienken and Dietrich for their comment on our recent paper (Vienken and Dietrich 2014). As these researchers point out, there are a number of limitations on the accuracy of the various empirical methods developed for the estimation of hydraulic conductivity from grain-size distribution including the general lack of experimental database size to the physical aspects of the aquifer hydrogeology. Even relatively uniform deposits, such as beach sand, contain heterogeneities related to bedding with horizontal hydraulic conductivity commonly being three to five times greater than vertical hydraulic conductivity. In most cases, the empirical methods using grain-size distribution to estimate hydraulic conductivity produce lower values than found using slug, aquifer performance (pumping), and tracer tests, which is to be expected based on scale of measurement. Grain shape, pore geometry, and compaction all influence the hydraulic conductivity as well as the sedimentary structures within an aquifer. While some compensation within many of the equations has been developed to deal with the grain shape factor (C coefficient) or the specific surface area (S in Barr 2000), no empirical method can be developed to compensate for changes in pore geometry and compaction.