Non-linear quickflow response as indicators of runoff generation mechanisms |
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| Authors: | Charles I Scaife Nitin K Singh Ryan E Emanuel Chelcy Ford Miniat Lawrence E Band |
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| Institution: | 1. Department of Environmental Sciences, University of Virginia, Charlottesville, Virginia, USA;2. Geosciences and Geological and Petroleum Engineering, Missouri University of Science and Technology, Rolla, Missouri, USA;3. Department of Forestry and Environmental Resources, North Carolina State University, Raleigh, North Carolina, USA;4. Coweeta Hydrologic Laboratory, Southern Research Station, USDA Forest Service, Otto, North Carolina, USA;5. Department of Environmental Sciences, University of Virginia, Charlottesville, Virginia, USA
Department of Engineering Systems and Environment, University of Virginia, Charlottesville, Virginia, USA |
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| Abstract: | Linking quickflow response to subsurface state can improve our understanding of runoff processes that drive emergent catchment behaviour. We investigated the formation of non-linear quickflows in three forested headwater catchments and also explored unsaturated and saturated storage dynamics, and likely runoff generation mechanisms that contributed to threshold formation. Our analyses focused on two reference watersheds at the Coweeta Hydrologic Laboratory (CHL) in western North Carolina, USA, and one reference watershed at the Susquehanna Shale Hills Critical Zone Observatory (SHW) in Central Pennsylvania, USA, with available hourly soil moisture, groundwater, streamflow, and precipitation time series over several years. Our study objectives were to characterise (a) non-linear runoff response as a function of storm characteristics and antecedent conditions, (b) the critical levels of shallow unsaturated and saturated storage that lead to hourly flow response, and (c) runoff mechanisms contributing to rapidly increasing quickflow using measurements of soil moisture and groundwater. We found that maximum hourly rainfall did not significantly contribute to quickflow production in our sites, in contrast to prior studies, due to highly conductive forest soils. Soil moisture and groundwater dynamics measured in hydrologically representative areas of the hillslope showed that variable subsurface states could contribute to non-linear runoff behaviour. Quickflow generation in watersheds at CHL were dominated by both saturated and unsaturated pathways, but the relative contributions of each pathway varied between catchments. In contrast, quickflow was almost entirely related to groundwater fluctuations at SHW. We showed that co-located measurements of soil moisture and groundwater supplement threshold analyses providing stronger prediction and understanding of quickflow generation and indicate dominant runoff processes. |
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| Keywords: | antecedent soil moisture Appalachian Mountains emergent behaviour forested catchments piecewise linear regression rainfall intensity riparian groundwater wells storage–flux relationships |
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