Instructive surprises in the hydrological functioning of landscapes

BUGS can arise in individual research projects, but also at the level of communities of researchers, leading to shifts in the scientific consensus.  These community-level BUGS typically arise from observations that are surprising to (or previously overlooked by) substantial fractions of the research community.  In this presentation, we summarize several community-level BUGS in our field: specifically, key surprises that have transformed the hydrological community's understanding of hillslope and catchment processes in recent decades.  

Here are some examples.  (1) Students used to learn (and some still do today) that storm runoff is dominated by overland flow.  But stable isotope tracers have convincingly shown instead that even during storm peaks, streamflow is composed mostly of water that has been stored in the landscape for weeks, months, or years.  (2) Maps, and most hydrological theories, have typically depicted streams as fixed features of the landscape.  But field mapping studies have shown that stream networks are surprisingly dynamic, with up to 80% of stream channels going dry sometime during the year.  (3) Textbooks have traditionally represented catchment storage as a well-mixed box.  But tracer time series show fractal scaling that cannot be generated by well-mixed boxes, forcing a re-think of our conceptualization of subsurface storage and mixing.  (4) Waters stored in aquifers, and the waters that drain from them, have traditionally been assumed to share the same age.  But tracers show that waters draining from aquifers are often much younger than the groundwaters that are left behind, and this was subsequently shown to be an inevitable result of aquifer heterogeneity. 

Several examples like these, and their implications, will be briefly discussed, with an eye to the question: how can we maximize the chances for future instructive surprises?