We have several monitored hillslopes where we have worked for many years. These include trenched slopes at Maimai in New Zealand, Panola in Georgia USA and Low Pass in Oregon USA. Together with our research partners working at other slope sites in Japan (Taro Uchida), Canada (Markus Weiler) and Germany (Stefan Uhlenbrook), we are working on intercomparisons Our objective was to whittle down the complexities of lateral subsurface stormflow and pipe flow on hillslopes by looking for commonality across different hillslope types. Despite the large differences between sites in topography, climate, soil type and soil matrix hydraulic conductivity, the SLOPENET sites show several common pipe flow responses to storm rainfall: (1) the relationship between total rainfall amount and total pipe flow volume was highly non-linear at each site, (2) initiation of measurable pipe flow was threshold-dependent, controlled by the total rainfall amount and the pre-storm wetness, (3) once significant pipe flow response occurred, the maximum pipe flow rate was sensitive to the measured rainfall intensity, and (4) the ratio of total pipe flow to total hillslope discharge for each site is constant, regardless of total rainfall amount once the precipitation threshold for significant pipe flow response was reached. We are using these results to develop a decision tree to determine the conditions necessary for significant subsurface stormflow flow to occur. SLOPENET is our organizational framework to summarize and organize comparative analyses and may provide a structure for defining the hierarchy of process controls necessary for model development at the hillslope scale.

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