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Gerard P Closs - One of the best experts on this subject based on the ideXlab platform.
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seasonal variation in diel activity and microhabitat use of an endemic new zealand stream dwelling galaxiid fish
Freshwater Biology, 2003Co-Authors: Bruno David, Gerard P ClossAbstract:Summary 1. Seasonal variation in microhabitat use and activity of 14 giant kokopu Galaxias argenteus, a drift-feeding galaxiid fish, was compared using radiotelemetry. 2. During winter giant kokopu predominantly used low velocities and intermediate depths by night and day. Activity recorded during 24 and 72 h periods indicated that fish were consistently active at night and inactive during the day. Activity data corresponded with point-in-time habitat use data, both of which indicated that fish were concealed amongst cover during the day and used open water habitats at night. 3. During summer, giant kokopu used higher water velocities, shallower depths and coarser substrata, particularly at night but also occasionally during the day relative to winter. Giant kokopu were active by both day and night in summer, although periods of activity were less defined and less predictable than during winter. 4. Adults used predictable home reaches at base-flow, with most individuals repeatedly using of one or two cover locations within their ‘home’ reach. Reaches used by fish were relatively short (rarely exceeding 26 m) irrespective of season and always included a single Pool-Riffle Sequence. 5. Diel and seasonal behaviour of giant kokopu was generally comparable with that exhibited by other drift feeding fish species in small temperate streams. However, the nocturnal activity of giant kokopu contrasts with activity patterns in various salmonids, indicating that the impact of predation by different drift feeding fish may vary considerably.
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Seasonal variation in diel activity and microhabitat use of an endemic New Zealand stream‐dwelling galaxiid fish
Freshwater Biology, 2003Co-Authors: Bruno David, Gerard P ClossAbstract:Summary 1. Seasonal variation in microhabitat use and activity of 14 giant kokopu Galaxias argenteus, a drift-feeding galaxiid fish, was compared using radiotelemetry. 2. During winter giant kokopu predominantly used low velocities and intermediate depths by night and day. Activity recorded during 24 and 72 h periods indicated that fish were consistently active at night and inactive during the day. Activity data corresponded with point-in-time habitat use data, both of which indicated that fish were concealed amongst cover during the day and used open water habitats at night. 3. During summer, giant kokopu used higher water velocities, shallower depths and coarser substrata, particularly at night but also occasionally during the day relative to winter. Giant kokopu were active by both day and night in summer, although periods of activity were less defined and less predictable than during winter. 4. Adults used predictable home reaches at base-flow, with most individuals repeatedly using of one or two cover locations within their ‘home’ reach. Reaches used by fish were relatively short (rarely exceeding 26 m) irrespective of season and always included a single Pool-Riffle Sequence. 5. Diel and seasonal behaviour of giant kokopu was generally comparable with that exhibited by other drift feeding fish species in small temperate streams. However, the nocturnal activity of giant kokopu contrasts with activity patterns in various salmonids, indicating that the impact of predation by different drift feeding fish may vary considerably.
Antony J Payne - One of the best experts on this subject based on the ideXlab platform.
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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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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.
Edward A. Keller - One of the best experts on this subject based on the ideXlab platform.
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Modeling forced Pool-Riffle hydraulics in a boulder-bed stream, southern California
Geomorphology, 2006Co-Authors: Lee R. Harrison, Edward A. KellerAbstract:The mechanisms which control the formation and maintenance of pool–riffles are fundamental aspects of channel form and process. Most of the previous investigations on pool–riffle Sequences have focused on alluvial rivers, and relatively few exist on the maintenance of these bedforms in boulder-bed channels. Here, we use a high-resolution two-dimensional flow model to investigate the interactions among large roughness elements, channel hydraulics, and the maintenance of a forced pool–riffle Sequence in a boulder-bed stream. Model output indicates that at low discharge, a peak zone of shear stress and velocity occurs over the riffle. At or near bankfull discharge, the peak in velocity and shear stress is found at the pool head because of strong flow convergence created by large roughness elements. The strength of flow convergence is enhanced during model simulations of bankfull flow, resulting in a narrow, high velocity core that is translated through the pool head and pool center. The jet is strengthened by a backwater effect upstream of the constriction and the development of an eddy zone on the lee side of the boulder. The extent of flow convergence and divergence is quantified by identifying the effective width, defined here as the width which conveys 90% of the highest modeled velocities. At low flow, the ratio of effective width between the pool and riffle is roughly 1:1, indicating little flow convergence or divergence. At bankfull discharge, the ratio of effective width is approximately 1:3 between the pool and downstream riffle, illustrating the strong flow convergence at the pool head. The effective width tends to equalize again with a ratio of 1:1 between the pool and riffle during a modeled discharge of a five-year flood, as the large roughness elements above the pool become drowned out. Results suggest that forced pool–riffle Sequences in boulder-bed streams are maintained by flows at or near bankfull discharge because of stage-dependent variability in depth-averaged velocity and tractive force.
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Velocity‐reversal hypothesis: A model approach
Earth Surface Processes and Landforms, 1993Co-Authors: Edward A. Keller, Joan L. FlorsheimAbstract:Hydraulic modelling of a riffle-Pool-Riffle Sequence in a straight reach of Dry Creek near Winters, California, indicates that while at low flow the mean (section average) velocity at riffles exceeds that of an adjacent pool, during high flow the mean velocity of the pool exceeds that of adjacent riffles. This supports the velocity-reversal hypothesis which is based on limited field measurements of near-bed flow velocity. A velocity reversal does not occur at the same discharge in both riffle-pool Sequences modelled, and a more detailed explanation is necessary to account for complex aspects of channel form and process in riffle-pool Sequences. Nevertheless, the velocity-reversal hypothesis helps to explain many of the observations and processes that operate in the riffle-pool environment.
Joseph M. Wheaton - 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: James R Jackson, Gregory 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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Flow convergence routing hypothesis for Pool-Riffle maintenance in alluvial rivers
Water Resources Research, 2006Co-Authors: Michael L. Macwilliams, Joseph M. Wheaton, Gregory B. Pasternack, Robert L. Street, Peter K. KitanidisAbstract:[1] The velocity reversal hypothesis is commonly cited as a mechanism for the maintenance of Pool-Riffle morphology. Although this hypothesis is based on the magnitude of mean flow parameters, recent studies have suggested that mean parameters are not sufficient to explain the dominant processes in many Pool-Riffle Sequences. In this study, two- and three-dimensional models are applied to simulate flow in the Pool-Riffle Sequence on Dry Creek, California, where the velocity reversal hypothesis was first proposed. These simulations provide an opportunity to evaluate the hydrodynamics underlying the observed reversals in near-bed and section-averaged velocity and are used to investigate the influence of secondary currents, the advection of momentum, and cross-stream flow variability. The simulation results support the occurrence of a reversal in mean velocity and mean shear stress with increasing discharge. However, the results indicate that the effects of flow convergence due to an upstream constriction and the routing of flow through the system are more significant in influencing Pool-Riffle morphology than the occurrence of a mean velocity reversal. The hypothesis of flow convergence routing is introduced as a more meaningful explanation of the mechanisms acting to maintain Pool-Riffle morphology.
Bruno David - One of the best experts on this subject based on the ideXlab platform.
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seasonal variation in diel activity and microhabitat use of an endemic new zealand stream dwelling galaxiid fish
Freshwater Biology, 2003Co-Authors: Bruno David, Gerard P ClossAbstract:Summary 1. Seasonal variation in microhabitat use and activity of 14 giant kokopu Galaxias argenteus, a drift-feeding galaxiid fish, was compared using radiotelemetry. 2. During winter giant kokopu predominantly used low velocities and intermediate depths by night and day. Activity recorded during 24 and 72 h periods indicated that fish were consistently active at night and inactive during the day. Activity data corresponded with point-in-time habitat use data, both of which indicated that fish were concealed amongst cover during the day and used open water habitats at night. 3. During summer, giant kokopu used higher water velocities, shallower depths and coarser substrata, particularly at night but also occasionally during the day relative to winter. Giant kokopu were active by both day and night in summer, although periods of activity were less defined and less predictable than during winter. 4. Adults used predictable home reaches at base-flow, with most individuals repeatedly using of one or two cover locations within their ‘home’ reach. Reaches used by fish were relatively short (rarely exceeding 26 m) irrespective of season and always included a single Pool-Riffle Sequence. 5. Diel and seasonal behaviour of giant kokopu was generally comparable with that exhibited by other drift feeding fish species in small temperate streams. However, the nocturnal activity of giant kokopu contrasts with activity patterns in various salmonids, indicating that the impact of predation by different drift feeding fish may vary considerably.
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Seasonal variation in diel activity and microhabitat use of an endemic New Zealand stream‐dwelling galaxiid fish
Freshwater Biology, 2003Co-Authors: Bruno David, Gerard P ClossAbstract:Summary 1. Seasonal variation in microhabitat use and activity of 14 giant kokopu Galaxias argenteus, a drift-feeding galaxiid fish, was compared using radiotelemetry. 2. During winter giant kokopu predominantly used low velocities and intermediate depths by night and day. Activity recorded during 24 and 72 h periods indicated that fish were consistently active at night and inactive during the day. Activity data corresponded with point-in-time habitat use data, both of which indicated that fish were concealed amongst cover during the day and used open water habitats at night. 3. During summer, giant kokopu used higher water velocities, shallower depths and coarser substrata, particularly at night but also occasionally during the day relative to winter. Giant kokopu were active by both day and night in summer, although periods of activity were less defined and less predictable than during winter. 4. Adults used predictable home reaches at base-flow, with most individuals repeatedly using of one or two cover locations within their ‘home’ reach. Reaches used by fish were relatively short (rarely exceeding 26 m) irrespective of season and always included a single Pool-Riffle Sequence. 5. Diel and seasonal behaviour of giant kokopu was generally comparable with that exhibited by other drift feeding fish species in small temperate streams. However, the nocturnal activity of giant kokopu contrasts with activity patterns in various salmonids, indicating that the impact of predation by different drift feeding fish may vary considerably.