REALITIES OF THE DIGITAL-DETERMINISTIC WORLD OF HYDROLOGY

Digital-determinism in hydrology arose in the 1960’s and holds that hydrologic systems can be described unambiguously by proper differential equations that rigorously represent physicochemical processes, and by a discretized set of parameters. Hydrologists, like our honoree Ed Sudicky, have embraced this view and now digital-determinism is accepted dogma for the analysis of hydrologic problems, including recent extensions to reactive chemical transport and hydrologic systems. This paper questions the foundation of this widely held belief using hydrologic results from Dry Run and Adena Brook, two urbanized watersheds in Columbus, Ohio. Detailed stream flow measurements and chemical data illustrate key weaknesses in the digital-deterministic approach – system complexity and uncertainty. In these watersheds, we argue that it is not practically possible to understand hydrologic processes in a deterministic manner and to characterize key hydrologic parameters controlling the fate and transport of key contaminants that impact chemical and biological systems. The loading of dissolved organic carbon and PAHs even from a relatively homogeneous setting, a parking lot, is surprising complex, even discounting subsequent reactive transport in the stream system. As we continue to work in our digital-deterministic world, it is important to explore alternative evaluative quantitative approaches that are also capable of capturing knowledge of complex systems.