The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
G B Pasternack - One of the best experts on this subject based on the ideXlab platform.
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virtual manipulation of topography to test potential pool Riffle maintenance mechanisms
Geomorphology, 2015Co-Authors: Jim Jackson, G B Pasternack, Joseph M. WheatonAbstract:In this study, numerical experimentation with two-dimensional hydraulic modeling of pool–Riffle river topography drawing on the testbed data from the classic Keller (1971) study was used to investigate the effect of synthetically manipulating topography on the occurrence and magnitude of velocity and Shields stress reversals in a pool–Riffle sequence. Reversals in velocity and shear stress have been used to explore mechanisms of pool–Riffle maintenance, while Shields stress (a combined measure of transport capacity and substrate erodibility) is emerging in importance. The original site topography was modeled alongside six altered ones to evaluate the sensitivity of hydraulic reversals to subtle morphology — five incrementally wider pools and a filled pool. The Caamano (2009) criterion, a simplified geometric threshold for predicting velocity reversals, was applied to each terrain to evaluate its utility. The original pool–Riffle topography was just over the threshold for a velocity reversal and well over the threshold for a strong Shields stress reversal. Overall, pool widening caused a predominantly local response, with change to pool hydraulics and no change in section-averaged velocity in the Riffle beyond the initial widening of 10%. Filling in the pool significantly increased the magnitude of reversals, whereas expanding it eliminated the occurrence of a reversal in mean velocity, though the Shields stress reversal persisted because of strong differentiation in bed material texture. Using Shields stress as a reversal parameter enabled the quantification of pool modification effects on pool–Riffle resiliency. The Caamano (2009) criterion accurately predicted reversal occurrence for the altered terrains with exaggerated effects, but failed to predict the weak reversal for the original topography. Two-dimensional modeling coupled with previously accepted hydrologic, geomorphic, and engineering analyses is vital in project design and evaluation prior to construction.
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geospatial organization of fluvial landforms in a gravel cobble river beyond the Riffle pool couplet
Geomorphology, 2014Co-Authors: J R Wyrick, G B PasternackAbstract:Abstract Morphological units (MU) are landforms with distinct local form–process associations at ~ 1–10 channel widths scale that may be the fundamental building blocks describing the geomorphic structure of a river. Past research has disproportionately focused on the two MUs of pool and Riffle, conjecturing that they are the central linked couplet in the process–form association. The goal of this study was to delineate and map spatially explicit fluvial landforms in two-dimensional planview within a gravel–cobble bed river using two-dimensional hydrodynamic delineation and then to statistically examine MU geospatial patterns for indicators of deterministic geomorphic control. This procedure is not discharge-dependent like mesohabitat methods, but gets at the geometry of underlying landforms. Statistical testing confirmed that eight delineated in-channel MU types comprise a complex and diverse channel morphology in which pools and Riffles are not directly coupled. Specifically, gravel–cobble river channels (1) exhibit nonrandom spatial organization of their longitudinally and laterally variable landform morphology; (2) consist of a variety of MU types, not just pools and Riffles; and (3) show distinct MU collocations and avoidances, with Riffles linked to chutes and runs, while pools are linked to slackwaters and glides. Planview MU delineation with two-dimensional hydrodynamic modeling provides a ‘bottom-up’ approach to understanding and linking channel morphology with ecosystem services and geomorphic processes and is being used to guide river management and rehabilitation strategies.
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valley width variation influences Riffle pool location and persistence on a rapidly incising gravel bed river
Geomorphology, 2010Co-Authors: Jason Q White, G B Pasternack, Hamish J MoirAbstract:Abstract Decades of research have demonstrated that gravel-bed rivers exhibit multiple spatial scales of landform nonuniformity. Landform features such as valley wall oscillations, alluvial fans, terraces, river meanders, point bars, boulder clusters, and logjams contribute to river corridor heterogeneity. Further, studies have shown that the locations of Riffles and pools in gravel-bed rivers are closely associated with the spatial pattern of river corridor morphological variability. These studies imply (but do not directly test) that persistence of Riffles and pools through time is also conditioned by landform variability. Mechanistically, it may be hypothesized that overbank flows interact hydraulically with oscillating valley walls by way of a mechanism known as flow convergence routing. In such circumstances, can variation in valley width influence channel morphology, forcing Riffle–pool location and persistence? To address this question, research was performed on a valley-confined, wandering, gravel-bed reach of the regulated lower Yuba River, California, USA that is incising from reduced sediment supply and flow regulation after a historic period of mining-related valley sedimentation. This study quantified stream planform change 1984–2006 and elevation change 1999–2006 using eight aerial photo sets and two digital elevation models, and it qualitatively assessed channel change in older aerial photos going back to 1937. Analysis revealed that the river has undergone rapid incision (0.11 m/year) and planform change in response to frequent floods, yet eight Riffles persisted in the same locations, which coincided with the locally wide areas of the valley. Longitudinal profiles revealed that deep pools were associated with long valley constrictions. Geomorphic analysis and design need to explicitly account for multiple scales of landform nonuniformity in order to rehabilitate natural fluvial processes.
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linking geomorphic changes to salmonid habitat at a scale relevant to fish
River Research and Applications, 2010Co-Authors: Joseph M. Wheaton, D A Sear, G B Pasternack, James Brasington, Stephen E Darby, Joseph E Merz, Damia VericatAbstract:The influence of geomorphic change on ecohydraulics has traditionally been difficult to quantify. With recent improvements in surveying technology, high-resolution, repeat and topographic surveys have become a common tool for estimating fluvial sediment budgets and documenting spatial patterns of net erosion and net deposition. Using a case study from a spawning habitat rehabilitation (SHR) project on California's Mokelumne River, some new DEM-differencing analytical tools and ecohydraulic models were used to test whether hypotheses about pool-Riffle maintenance mechanisms used in designing SHR projects were producing self-sustaining spawning habitat when subjected to competent flows. Following peak flows associated with the spring snow-melt, a total of 999.6 m3 of erosion and 810.1 m3 of deposition were recorded throughout the study area, with a net loss of 196.2 m3. Using an ecohydraulic spawning habitat suitability model to segregate the sediment budget, over 53% of the area in which gravel was placed in a 2005 SHR retained the same habitat quality characteristics, and 22% improved. The response to the flood was generically characterized by shallow deposition associated with areas of divergent flow over Riffles and scour associated with areas of convergent flow in pools. Areas where habitat remained stable generally experienced only low-magnitude elevation changes, and accounted for only 19.5% of the total volumetric change. Areas where habitat quality degraded (primarily pool exit slopes) were dominated by larger magnitude erosion and made up 46% of the total volumetric change. By contrast, areas where habitat quality improved (primarily constructed Riffle) accounted for 34.5% the total volumetric change, and were dominated by shallow, low magnitude deposition. The results support hypotheses about pool-Riffle maintenance mechanisms used to design the rehabilitation projects, while also highlighting some simple but powerful techniques for linking ecohydraulic and geomorphic field monitoring data at a salmon-relevant spatial scale.
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Riffle pool maintenance and flow convergence routing observed on a large gravel bed river
Geomorphology, 2010Co-Authors: April M Sawyer, G B Pasternack, Hamish J Moir, Aaron A FultonAbstract:Abstract Geomorphologists have studied and debated over the processes responsible for natural Riffle-pool maintenance for decades. Most studies have focused on small wadable rivers, but they lack much description of overbank flood conditions or a spatially explicit characterization of morphodynamics. In this study, 1-m horizontal resolution digital elevation models were collected from a Riffle-pool-run sequence before and after an overbank flood with a 7.7-year recurrence interval on the relatively large gravel-bed lower Yuba River, California. Digital elevation model differencing was used to quantify the magnitude and pattern of flood-induced morphodynamic change. Cross section based analysis and two-dimensional hydrodynamic modeling of flows ranging from 0.147 to 7.63 times bankful discharge were completed to evaluate the hydraulic mechanisms responsible for the observed topographic changes. One key finding was that Riffle-pool relief increased by 0.42 m, confirming the occurrence of natural hydrogeomorphic maintenance. Spatially complex patterns of scour and deposition exceeding 0.15 m at the scale of subwidth morphological units were reasonably predicted by the two-dimensional mechanistic model that accounts for convective acceleration. The one-dimensional cross section based method underperformed the two-dimensional model significantly. Consequently, multiple scales of channel non-uniformity and a dynamic flow regime caused the observed maintenance of the pool-Riffle morphology through the mechanism of “flow convergence routing” proposed by MacWilliams et al. [MacWilliams, M.L., Wheaton, J.M., Pasternack, G.B., Kitanidis, P.K., Street, R.L., 2006. The flow convergence-routing hypothesis for Riffle-pool maintenance in alluvial rivers. Water Resources Research 42, W10427, doi:10.1029/2005WR004391].
Barbara J Downes - One of the best experts on this subject based on the ideXlab platform.
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maternal behaviours may explain Riffle scale variations in some stream insect populations
Freshwater Biology, 2014Co-Authors: Jill Lancaster, Barbara J DownesAbstract:Species composition and abundance of larval insects can vary significantly between similar channel units (Riffles) on the same stream as well as between similar streams. The source of this variation is largely unexplained, but important because such spatial variations can influence population and community dynamics and the design of sampling programmes. The maternal and oviposition behaviours of some aquatic insects are specialised, such that eggs are laid in particular locations, and this could influence the spatial distribution of eggs and larvae within a stream. In a relatively short length of stream (1 km), we tested whether the number of oviposition sites influenced the number of larvae of different instars in whole Riffles that ranged in area from 80 to 460 m . We examined two species, a mayfly Baetis rhodani and a caddisfly Rhyacophila dorsalis, with larvae that are Riffle specialists and adults that oviposit exclusively on emergent rocks in Riffles. For comparison, we also examined a control species, blackflies Simulium spp., with larvae that are also Riffle specialists, but adults that oviposit on trailing vegetation. As an alternative hypothesis, we tested whether the numbers of larvae per Riffle were associated with habitat availability, as measured by Riffle area. Numbers of early-instar B. rhodani and R. dorsalis were positively associated with the numbers of oviposition sites per Riffle, but not Riffle areas. In contrast, numbers of early-instar Simulium per Riffle (the control species) were not associated with either predictor variable. For later instars, Riffle area was a good predictor of larval numbers per Riffle for all species, even though the number of oviposition sites still explained much variation for B. rhodani and R. dorsalis. This ontogenetic shift in distribution patterns suggests an adjustment of densities during larval life, and the evidence points to density-dependent mortality of early-instar larvae. Contrary to the prevailing view that Riffle-to-Riffle variations in the numbers of aquatic insect larvae can be explained by larval habitat, this study demonstrates a strong influence of adult behaviour, and oviposition site availability can explain significant amounts of this variation for some species. These results challenge traditional views about aquatic insect populations, which may have more complex and interesting dynamics than considered previously. © 2013 John Wiley & Sons Ltd. 2
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Habitat structure and invertebrate assemblages on stream stones: A multivariate view from the Riffle
Austral Ecology, 1995Co-Authors: Barbara J Downes, Phillip Spencer Lake, E S G SchreiberAbstract:Highly structured habitats, those with complex or heterogeneous physical structure, commonly contain more species than simply structured ones. However, tests of this relationship have been hampered by habitat-specific definitions and measurements of habitat structure and, in stream studies, by insufficient information on spatial variation in faunal abundances. We sampled the fauna of 90 stones collected from an order 4 section of the Taggerty and Steavenson Rivers, southeastern Australia. The spatially nested sampling design encompassed three spatial scales (sites within the same stream order, Riffles at the same site and groups of stones within the same Riffle) but no temporal replication, as we were only able to sample once. Habitat structure of stones was quantified by measuring the amount and type of epilithon on stones, together with stone shapes, sizes, textures and surface complexities. For the latter two attributes, we used a new method, involving image analysis, which can be used to quantify habitat structure in comparable ways in other systems. Species richness (S) was related to some measures of habitat structure, being higher on stones with a rough texture and weakly related to the amount of epilithon present. Total numbers of individuals (N) were also higher on rough stones, and faunal composition (as quantified by hybrid multidimensional scaling) was related to abundance of epilithon. However, flow environments, as quantified by water velocities and depths, were also related to faunal composition. Riffles varied in both faunal densities and near-bed flow environment, but not in any consistent way. Such variability means that individual Riffles cannot be reasonably used to ‘represent’ stream sections or orders, an assumption commonly made in stream studies. Neglect of such issues has also resulted in poor conceptual integration between large- and small-scale studies in stream ecology.
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spatial variation in the distribution of stream invertebrates implications of patchiness for models of community organization
Freshwater Biology, 1993Co-Authors: Barbara J Downes, P S Lake, E S G SchreiberAbstract:SUMMARY 1 Variation in abundances of stream fauna across a range of spatial scales has been neglected, yet such variation can have important implications for experimental and descriptive work. We tested the hypothesis that the abundances of stream animals living on stones vary between sites within the same stream order, Riffles within the same site and groups of stones within the same Riffle. We also examined how epilithon and water depth and velocity varied over these spatial scales. 2 Thirty stones were sampled from each of three sites in a fourth-order section of the Taggerty and Steavenson Rivers, south-eastern Australia. At each site, fifteen stones were taken from each of two Riffles; within each Riffle, the fifteen stones were collected as five groups of three stones within 0.5m of each other. For each stone, we measured water depth and velocity, took samples of epilithon to estimate chlorophyll a concentrations, organic biomass and bacterial and algal cell densities, and collected all macroinvertebrates. 3 Hierarchical analyses of variance revealed that species richness did not vary over any of the spatial scales, but densities of individuals varied substantially between Riffles and groups of stones. Of the thirty-five most abundant taxa, three-quarters (twenty-seven) varied over one or more of the spatial scales, with variation between Riffles being particularly common. DECORANA analyses confirmed that two of the three sites had Riffle faunas that were dissimilar to each other, whereas the third site had Riffle faunas that were very similar. Significant spatial variation was observed also in water velocities and depths and chlorophyll a and organic biomass concentrations. 4 Overall, we have demonstrated that significant variation in faunal densities may occur over small spatial scales, such as those represented by groups of stones. Moreover, such variation was not consistent between taxonomically or functionally related species within the assemblage. 5 The results emphasize the need for stream ecologists to be aware of the ramifications of such variation. Neglect of small-scale variation has produced spatially confounded designs in both surveys and experimental studies. Additionally, the assumption that variation over small scales does not occur or is trivial seems to have been responsible for the virtual enshrinement of certain large-scale models of community organization.
D A Sear - One of the best experts on this subject based on the ideXlab platform.
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spatial variations in surface sediment structure in Riffle pool sequences a preliminary test of the differential sediment entrainment hypothesis dseh
Earth Surface Processes and Landforms, 2013Co-Authors: Rebecca Hodge, D A Sear, Julian LeylandAbstract:Riffle-pool sequences are maintained through the preferential entrainment of sediment grains from pools rather than Riffles. This preferential entrainment has been attributed to a reversal in the magnitude of velocity and shear stress under high flows; however the Differential Sediment Entrainment Hypothesis (DSEH) postulates that differential entrainment can instead result from spatial sedimentological contrasts. Here we use a novel suite of in-situ grain-scale field measurements from a Riffle-pool sequence to parameterise a physically-based model of grain entrainment. Field measurements include pivoting angles, lift forces and high resolution DEMs acquired using Terrestrial Laser Scanning, from which particle exposure, protrusion and surface roughness were derived. The entrainment model results show that grains in pools have a lower critical entrainment shear stress than grains in either pool exits or Riffles. This is because pool grains have looser packing, hence greater exposure and lower pivoting angles. Conversely, Riffle and pool exit grains have denser packing, lower exposure and higher pivoting angles. A cohesive matrix further stabilises pool exit grains. The resulting predictions of critical entrainment shear stress for grains in different subunits are compared with spatial patterns of bed shear stress derived from a 2D Computational Fluid Dynamics (CFD) model of the reach. The CFD model predicts that, under bankfull conditions, pools experience lower shear stresses than Riffles and pool exits. However, the difference in sediment entrainment shear stress is sufficiently large that sediment in pools is still more likely to be entrained than sediment in pool exits or Riffles, resulting in differential entrainment under bankfull flows. Significantly, this differential entrainment does not require a reversal in flow velocities or shear stress, suggesting that sedimentological contrasts alone may be sufficient for the maintenance of Riffle-pool sequences. This finding has implications for the prediction of sediment transport and the morphological evolution of gravel-bed rivers.
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linking geomorphic changes to salmonid habitat at a scale relevant to fish
River Research and Applications, 2010Co-Authors: Joseph M. Wheaton, D A Sear, G B Pasternack, James Brasington, Stephen E Darby, Joseph E Merz, Damia VericatAbstract:The influence of geomorphic change on ecohydraulics has traditionally been difficult to quantify. With recent improvements in surveying technology, high-resolution, repeat and topographic surveys have become a common tool for estimating fluvial sediment budgets and documenting spatial patterns of net erosion and net deposition. Using a case study from a spawning habitat rehabilitation (SHR) project on California's Mokelumne River, some new DEM-differencing analytical tools and ecohydraulic models were used to test whether hypotheses about pool-Riffle maintenance mechanisms used in designing SHR projects were producing self-sustaining spawning habitat when subjected to competent flows. Following peak flows associated with the spring snow-melt, a total of 999.6 m3 of erosion and 810.1 m3 of deposition were recorded throughout the study area, with a net loss of 196.2 m3. Using an ecohydraulic spawning habitat suitability model to segregate the sediment budget, over 53% of the area in which gravel was placed in a 2005 SHR retained the same habitat quality characteristics, and 22% improved. The response to the flood was generically characterized by shallow deposition associated with areas of divergent flow over Riffles and scour associated with areas of convergent flow in pools. Areas where habitat remained stable generally experienced only low-magnitude elevation changes, and accounted for only 19.5% of the total volumetric change. Areas where habitat quality degraded (primarily pool exit slopes) were dominated by larger magnitude erosion and made up 46% of the total volumetric change. By contrast, areas where habitat quality improved (primarily constructed Riffle) accounted for 34.5% the total volumetric change, and were dominated by shallow, low magnitude deposition. The results support hypotheses about pool-Riffle maintenance mechanisms used to design the rehabilitation projects, while also highlighting some simple but powerful techniques for linking ecohydraulic and geomorphic field monitoring data at a salmon-relevant spatial scale.
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modelling three dimensional flow structures and patterns of boundary shear stress in a natural pool Riffle sequence
Earth Surface Processes and Landforms, 2001Co-Authors: D J Booker, D A Sear, Antony J PayneAbstract:Fluid-sediment interactions control river channel forms and processes. Analysis of spatial hydraulic patterns and the resulting boundary shear stress are required to aid understanding of river system behaviour. In this paper, the hydraulic processes active in a natural pool-Riffle sequence are simulated using a three-dimensional computational fluid dynamics (CFD) model. Methods employed for the prescription of model boundary conditions are outlined. Model calculations are assessed using comparisons with field observations acquired over a range of flows. Simulations are then used to illustrate flow structures and patterns of boundary shear stress for a near-bankfull and an intermediate flow event. Results are used to assess existing theories that seek to explain the development and maintenance of pool-Riffle sequences. Simulated results suggest that near-bed velocities and bed shear stresses decrease on Riffles and increase in pools as discharge increases. Model simulations indicate that secondary flow acts to route near-bed flow over the downstream side of Riffles and into the pool-head away from the centre of pools. Implications for sediment transport and pool maintenance are discussed.
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sediment transport processes in pool Riffle sequences
Earth Surface Processes and Landforms, 1996Co-Authors: D A SearAbstract:This paper reviews the published data for sediment transport in pool–Riffle sequences which suggests that a velocity or shear stress reversal hypothesis does not explain all of the published evidence of sediment transport. This conclusion is explored in more detail using observations of sediment transport from the regulated River North Tyne. Sediment transport rates at discharges of <30 per cent bankfull are initially highest on Riffles. As discharge increases, sediment transport rates in pools rise sharply, and values locally exceed those on Riffles. Tracing experiments using a combination of magnetic and painted tracers are used to show the downstream dispersal of fine and coarse sediments through the pool–Riffle sequence. Coarser particles experience longer transport paths and faster virtual rates of travel in pools during bankfull floods. Analysis of entrainment data reveals evidence for additional restraint operating on Riffles and causing higher dimensionless entrainment thresholds. An appraisal of the possible mechanisms controlling sediment entrainment, transport and deposition in pool–Riffle sequences is made which reveals evidence for the operation of a combination of hydraulic, sedimentological and interactive processes. A descriptive model of sediment transport processes in pool–Riffle sequences is presented.
Luz Boyero - One of the best experts on this subject based on the ideXlab platform.
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the effect of Riffle scale environmental variability on macroinvertebrate assemblages in a tropical stream
Hydrobiologia, 2004Co-Authors: Luz Boyero, Jaime BoschAbstract:In a tropical stream (at the Soberani;a National Park, Panama), different environmental factors were quantified in Riffle habitats (water characteristics: velocity, depth, turbulence, and direction; stone characteristics: surface area, sphericity, and degree of burial; and others: substrate type, and canopy cover). Characteristics of macroinvertebrate assemblages (mean density of individuals, mean taxon richness, and cumulative taxon richness in three stones at each Riffle) were related to both mean values and variability of these environmental factors at Riffle scale. Macroinvertebrate density was higher in shallow, fast flowing, stony Riffles, with low variability in dominant substrate type. Taxon richness was also higher in shallow Riffles with loose, not buried stones, and water direction more or less parallel to the bank. Environmental variability resulted as important as mean values of environmental factors to explain variation in macroinvertebrate assemblages. This is the first study, to our knowledge, that quantifies substratum variability and demonstrates its influence on macroinvertebrate assemblages in a tropical stream.
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multiscale patterns of spatial variation in stream macroinvertebrate communities
Ecological Research, 2003Co-Authors: Luz BoyeroAbstract:Our ability to detect patterns of variation of communities depends on the spatial scale of observation. I examined the spatial variation of macroinvertebrate community structure: abundance, richness, evenness, percentage of Ephemeroptera, Plecoptera and Trichoptera (EPT), and taxonomic composition across a wide range of spatial scales in two mountain streams. In a nested design, three segments were selected within each basin, three Riffles within each segment, three sections within each Riffle, and three samples within each section. Significant variation of communities occurred mainly at sample and Riffle scales, although different community characteristics may vary at different scales. Environmental factors were strongly related to communities, but these relationships depended on spatial scale in many cases, suggesting that the influence of the environment is ultimately regulated by the grain and extent of organisms. This study highlights the importance of multiscale studies to obtain a complete understanding of the spatial variation of macroinvertebrate communities and their relationship with the environment.
Shawn M. Chartrand - One of the best experts on this subject based on the ideXlab platform.
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morphodynamics of a width variable gravel bed stream new insights on pool Riffle formation from physical experiments
Journal of Geophysical Research, 2018Co-Authors: Marwan A Hassan, Shawn M. Chartrand, Mark A Jellinek, Carles FerrerboixAbstract:Field observations, experiments, and numerical simulations suggest that pool-Riffles along gravel bed mountain streams develop due to downstream variations of channel width. Where channels narrow, pools are observed, and at locations of widening, Riffles occur. Based on previous work, we hypothesize that the bed profile is coupled to downstream width variations through momentum fluxes imparted to the channel surface, which scale with downstream changes of flow velocity. We address this hypothesis with flume experiments understood through scaling theory. Our experiments produce pool-Riffle like structures across average Shields stresses t* that are a factor 1.5–2 above the threshold mobility condition of the experimental grain size distribution. Local topographic responses are coupled to channel width changes, which drive flows to accelerate or decelerate on average, for narrowing and widening, respectively. We develop theory which explains the topography-width-velocity coupling as a ratio of two reinforcing timescales. The first timescale captures the time necessary to do work to the channel bed. The second timescale characterizes the relative time magnitude of momentum transfer from the flowing fluid to the channel bed surface. Riffle-like structures develop where the work and momentum timescales are relatively large, and pools form where the two timescales are relatively small. We show that this result helps to explain local channel bed slopes along pool-Riffles for five data sets representing experimental, numerical, and natural cases, which span 2 orders of magnitude of reach-averaged slope. Additional model testing is warranted.
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pool Riffle sedimentation and surface texture trends in a gravel bed stream
Water Resources Research, 2015Co-Authors: Shawn M. Chartrand, Marwan A Hassan, Valentina RadicAbstract:A 3 year field campaign was completed to investigate spatial and temporal variability of sedimentation trends for a single pool-Riffle pair located in the Santa Cruz Mountains, California. Our measurements represent a range of hydrologic conditions over 11 sediment-mobilizing events. Two different statistical methods were used to explore Riffle sedimentation. Cochran's Q and McNemar's nonparametric tests (one method) indicate that Riffle sediment surface texture was spatially and temporally varied at the transect level. For McNemar's test, variation was significant at p<0.05, with several trends evident, including strong Riffle fining triggered by a 20 year flood event. A nonlinear empirical orthogonal function method known as self-organizing maps (SOMs; the second method) shows that Riffle sediment surface texture is well described by two characteristic temporal signals, and one transitional signal at the sampling node level. SOM mapping to each sampling node clearly shows Riffle sediment surface texture change was spatially organized over the 11 sediment-mobilizing events. Observations of pool sediment storage indicate that the pool-Riffle pair exhibited a coupled sedimentation response (i.e., similar texture trends between pool and Riffle) following the 20-year flood. The coupled response was characterized by a trend toward overall sedimentation conditions that were similar to those measured at the beginning of the study. The reported texture trends may be of interest to salmonid habitat studies that examine factors contributing to successful versus unsuccessful fry emergence.
