Wood export varies among decadal, annual, seasonal, and daily scale hydrologic regimes in a large, Mediterranean climate, mountain river watershed

Abstract : The dynamics that move wood through and out of watersheds are complex and not yet fully understood. In this study, climatic conditions, hydrologic responses, and watershed processes were explored to better understand variations in wood export using aerial imagery, event-based video monitoring, and field measurements from the 1097 km² mountainous Mediterranean climate North Yuba River, California, watershed and its reservoir near the downstream outlet. Over a 30-year study period, 1985–2014, volumetric estimates of annual wood export into the reservoir, available for a subset of years, were used to investigate watershed-scale, wood export dynamics. Variations in annual peak discharge explained 79% of the variance in interannual wood export, with 84% of total observed wood export (ca. > 10,000 m³ of wood per event) delivered by years with discharge events of 19-year, 21.5-year, and 60-year flood recurrence intervals. Continuous video monitoring conducted during snowmelt season periods in 2010 and 2011 yielded wood discharge observations at minima 15% of statistical bankfull flow, while maximum daily discharge explained 55% of observed daily wood piece variation. No statistically significant wood discharge differences were found in snowmelt season observations, likely caused by domination of the hydrograph by diurnal pulses within the seasonal cycle. Wood piece sizes in upstream watershed locations were found to be significantly longer but not significantly larger in diameter than those observed in transport or measured in the reservoir, an indication that more downstream fining of length than diameter may occur during transport. A conceptual model and functional framework are introduced in support of a watershed-scale explanation of wood export, transport, and storage processes applicable to large, Mediterranean-climate, mountain watershed settings.
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Submitted on : Wednesday, October 18, 2017 - 10:29:43 AM
Last modification on : Wednesday, August 7, 2019 - 12:19:20 PM

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A.E. Senter, G.B. Pasternack, H. Piégay, M.C. Vaughan, J.S. Lehyan. Wood export varies among decadal, annual, seasonal, and daily scale hydrologic regimes in a large, Mediterranean climate, mountain river watershed. Geomorphology, Elsevier, 2017, 276, pp.164 - 179. ⟨10.1016/j.geomorph.2016.09.039⟩. ⟨halshs-01618564⟩

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