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John Pitlick

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The present study examines variations in the reference shear stress for bed load transport (τr) using coupled measurements of flow and bed load transport in 45 gravel‐bed streams and rivers. The study streams encompass a wide range in bank‐full discharge (1–2600 m3/s), average channel gradient (0.0003–0.05), and median surface grain size (0.027–0.21 m). A bed load transport relation was formed for each site by plotting individual values of the dimensionless transport rate W* versus the reach‐average dimensionless shear stress τ*. The reference dimensionless shear stress τ*r was then estimated by selecting the value of τ* corresponding to a reference transport rate of W* = 0.002. The results indicate that the discharge...
Categories: Publication; Types: Citation; Tags: Water Resources Research
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Sites within the Pajarito Plateau have widespread, if low levels, of surface contamination. The major mechanism by which contaminants are moved and redistributed is surface runoff and associated soil erosion. To better understand the processes involved, we have been making detailed measurements of water and sediment movement at three sites across the plateau, one located in a ponderosa pine forest, one in a stable pinyon-juniper woodland, and one in a rapidly eroding pinyon-juniper woodland. For the ponderosa pine site, both surface runoff (overland flow) and subsurface runoff (interflow) are important. Overland flow can be generated by intense summer rain storms, more gentle frontal storms, or snowmelt while soils...
Categories: Publication; Types: Citation
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Elastohydrodynamic theory and measurements of particle impacts on an inclined glass plane in water are used to investigate the mechanics of interparticle collisions in sediment‐transporting flows. A collision Stokes number is proposed as a measure of the momentum of an interparticle collision versus the viscous pressure force in the interstitial gap between colliding particles. The viscous pressure force opposes motion of the particles on approach and rebound. A Stokes number of between 39 and 105 is estimated as the critical range below which particle impacts are completely viscously damped and above which impacts are partially elastic. The critical Stokes number is shown to roughly coincide with the Bagnold number...
Categories: Publication; Types: Citation; Tags: Water Resources Research
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The availability of high-resolution, multi-temporal, remotely sensed topographic data is revolutionizing geomorphic analysis. Three-dimensional topographic point measurements acquired from structure-from-motion (SfM) photogrammetry have been shown to be highly accurate and cost-effective compared to laser-based alternatives in some environments. Use of consumer-grade digital cameras to generate terrain models and derivatives is becoming prevalent within the geomorphic community despite the details of these instruments being largely overlooked in current SfM literature. This article is protected by copyright. All rights reserved.A practical discussion of camera system selection, configuration, and image acquisition...
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Local variations in boundary shear stress acting on bed‐surface particles control patterns of bed load transport and channel evolution during varying stream discharges. At the reach scale a channel adjusts to imposed water and sediment supply through mutual interactions among channel form, local grain size, and local flow dynamics that govern bed mobility. In order to explore these adjustments, we used a numerical flow model to examine relations between model‐predicted local boundary shear stress (тj( and measured surface particle size (D50) at bank‐full discharge in six gravel‐bed, alternate‐bar channels with widely differing annual sediment yields. Values of тj and D50 were poorly correlated such that small areas...
Categories: Publication; Types: Citation; Tags: Water Resources Research
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