Headwater catchments have been our group’s research bread and butter for many years. We now have a number of sites where we have performed similar physical, chemical and isotopic studies. These headwater catchments are all in the range of 1-50 ha. Our active sites include: Maimai in New Zealand, Sleepers River, Vermont USA, Panola, Georgia USA, HJA WS10 Oregon USA.

The mechanisms of runoff generation in forested headwater catchments have been debated since the 1930s. While individual experimental approaches have evolved considerably over time, combination of hydrometric observations and tracer approaches is now a standard methodology for constraining a sound perceptual model and formal conceptualization of runoff generation in headwater catchments. Studies of subsurface stormflow in steep wet catchments have shown that channel stormflow is supplied largely by pre-event water moving via subsurface routes to the channel. Nevertheless, the exact mechanism of rapid pre-event water mobilization remains highly equivocal in most studies and has been shown to originate from a range of hydrological processes, including groundwater ridging, transmissivity feedback, pressure waves and pipe flow. Determining these mechanisms a priori has proved very difficult and has led some researchers to reach the rather dire conclusion that each catchment is unique. Most of the published work to date has focused on the study of single catchments. The field of study has focused on documentation of the idiosyncrasies of individual catchments rather than a systematic examination of the first order controls on catchment hydrology in particular classes of systems (e.g. steep wet environments). Indeed, it has been easier to publish new findings of new mechanisms than simply confirmation that some mechanism or process is occurring a yet another site.

Although research at each intensively studied CATCHNET small basin sites has (and continues to) produce many valuable insights, it has been difficult to derive general hydrologic principles from these basin-centric approaches. Our CATCHMENT intercomparison is a means to better see/define first order controls.

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