The Experts below are selected from a list of 1842 Experts worldwide ranked by ideXlab platform
Marwan A Hassan - 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 RadićAbstract: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
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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.
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modeling wood dynamics jam formation and sediment storage in a Gravel Bed Stream
Journal of Geophysical Research, 2012Co-Authors: Brett C. Eaton, Marwan A Hassan, S. L. DavidsonAbstract:[1] In small and intermediate sized Streams, the interaction between wood and Bed material transport often determines the nature of the physical habitat, which in turn influences the health of the Stream's ecosystem. We present a stochastic model that can be used to simulate the effects on physical habitat of forest fires, climate change, and other environmental disturbances that alter wood recruitment. The model predicts large wood (LW) loads in a Stream as well as the volume of sediment stored by the wood; while it is parameterized to describe Gravel Bed Streams similar to a well-studied field prototype, Fishtrap Creek, British Columbia, it can be calibrated to other systems as well. In the model, LW pieces are produced and modified over time as a result of random tree-fall, LW breakage, LW movement, and piece interaction to form LW jams. Each LW piece traps a portion of the annual Bed material transport entering the reach and releases the stored sediment when the LW piece is entrained and moved. The equations governing sediment storage are based on a set of flume experiments also scaled to the field prototype. The model predicts wood loads ranging from 70 m3/ha to more than 300 m3/ha, with a mean value of 178 m3/ha: both the range and the mean value are consistent with field data from Streams with similar riparian forest types and climate. The model also predicts an LW jam spacing that is consistent with field data. Furthermore, our modeling results demonstrate that the high spatial and temporal variability in sediment storage, sediment transport, and channel morphology associated with LW-dominated Streams occurs only when LW pieces interact and form jams. Model runs that do not include jam formation are much less variable. These results suggest that river restoration efforts using engineered LW pieces that are fixed in place and not permitted to interact will be less successful at restoring the geomorphic processes responsible for producing diverse, productive physical habitats than efforts using LW pieces that are free to move, interact, and form LW jams.
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Modeling wood dynamics, jam formation, and sediment storage in a Gravel‐Bed Stream
Journal of Geophysical Research: Earth Surface, 2012Co-Authors: Brett C. Eaton, Marwan A Hassan, S. L. DavidsonAbstract:[1] In small and intermediate sized Streams, the interaction between wood and Bed material transport often determines the nature of the physical habitat, which in turn influences the health of the Stream's ecosystem. We present a stochastic model that can be used to simulate the effects on physical habitat of forest fires, climate change, and other environmental disturbances that alter wood recruitment. The model predicts large wood (LW) loads in a Stream as well as the volume of sediment stored by the wood; while it is parameterized to describe Gravel Bed Streams similar to a well-studied field prototype, Fishtrap Creek, British Columbia, it can be calibrated to other systems as well. In the model, LW pieces are produced and modified over time as a result of random tree-fall, LW breakage, LW movement, and piece interaction to form LW jams. Each LW piece traps a portion of the annual Bed material transport entering the reach and releases the stored sediment when the LW piece is entrained and moved. The equations governing sediment storage are based on a set of flume experiments also scaled to the field prototype. The model predicts wood loads ranging from 70 m3/ha to more than 300 m3/ha, with a mean value of 178 m3/ha: both the range and the mean value are consistent with field data from Streams with similar riparian forest types and climate. The model also predicts an LW jam spacing that is consistent with field data. Furthermore, our modeling results demonstrate that the high spatial and temporal variability in sediment storage, sediment transport, and channel morphology associated with LW-dominated Streams occurs only when LW pieces interact and form jams. Model runs that do not include jam formation are much less variable. These results suggest that river restoration efforts using engineered LW pieces that are fixed in place and not permitted to interact will be less successful at restoring the geomorphic processes responsible for producing diverse, productive physical habitats than efforts using LW pieces that are free to move, interact, and form LW jams.
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 RadićAbstract: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
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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.
Colin R. Townsend - One of the best experts on this subject based on the ideXlab platform.
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flood effects on invertebrates sediments and particulate organic matter in the hyporheic zone of a Gravel Bed Stream
Freshwater Biology, 2005Co-Authors: Dean A. Olsen, Colin R. TownsendAbstract:Summary 1. We investigated the effects of a flood on the fauna and physical habitat of the hyporheic zone of the Kye Burn, a fourth order Gravel-Bed Stream in New Zealand. 2. Freeze core hyporheic samples (to 50 cm depth) and benthic samples (to 10 cm) were taken, along with measurements of vertical hydrological gradient, before, 2 days after and 1 month after the flood (estimated return period: 1.5 years, estimated Qmax = 10.4 m3 s−1). 3. The composition of the hyporheos differed over the three sampling occasions with fewer taxa collected immediately postflood than preflood. The equitability of the community was higher on both postflood occasions, consistent with the reduced densities of two abundant taxa (Leptophlebiidae and Copepoda). 4. Total invertebrate abundance was lower on the postflood occasions than preflood in both benthic (0–10 cm) and hyporheic (10–50 cm) sediments. Several taxa, including asellotan isopods and amphipods, recovered within 1 month of the event. Hyporheic densities of larval Hydora and nematodes did not differ among the three sampling occasions, but the water mite Pseudotryssaturus was more abundant 1 month after the flood than preflood. There was no evidence of vertical movements (to 50 cm) by any taxa in response to the flood. 5. The proportion of fine sediments (<1 mm) in the subsurface sediments (10–50 cm) increased over the three sampling occasions and median particle size declined, but sediment porosity did not change. More particulate organic matter was found in the sediments after the flood. 6. Our study provides little evidence that the hyporheic zone (to 50 cm) acted as a significant refuge during the flood event, although movements to or recolonisation from sediments deeper than 50 cm could explain the recovery of many crustacean and mite taxa within 1 month.
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Flood effects on invertebrates, sediments and particulate organic matter in the hyporheic zone of a Gravel-Bed Stream
Freshwater Biology, 2005Co-Authors: Dean A. Olsen, Colin R. TownsendAbstract:Summary 1. We investigated the effects of a flood on the fauna and physical habitat of the hyporheic zone of the Kye Burn, a fourth order Gravel-Bed Stream in New Zealand. 2. Freeze core hyporheic samples (to 50 cm depth) and benthic samples (to 10 cm) were taken, along with measurements of vertical hydrological gradient, before, 2 days after and 1 month after the flood (estimated return period: 1.5 years, estimated Qmax = 10.4 m3 s−1). 3. The composition of the hyporheos differed over the three sampling occasions with fewer taxa collected immediately postflood than preflood. The equitability of the community was higher on both postflood occasions, consistent with the reduced densities of two abundant taxa (Leptophlebiidae and Copepoda). 4. Total invertebrate abundance was lower on the postflood occasions than preflood in both benthic (0–10 cm) and hyporheic (10–50 cm) sediments. Several taxa, including asellotan isopods and amphipods, recovered within 1 month of the event. Hyporheic densities of larval Hydora and nematodes did not differ among the three sampling occasions, but the water mite Pseudotryssaturus was more abundant 1 month after the flood than preflood. There was no evidence of vertical movements (to 50 cm) by any taxa in response to the flood. 5. The proportion of fine sediments (
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hyporheic community composition in a Gravel Bed Stream influence of vertical hydrological exchange sediment structure and physicochemistry
Freshwater Biology, 2003Co-Authors: Dean A. Olsen, Colin R. TownsendAbstract:Summary 1. We studied the relative contributions of the magnitude and direction of vertical hydrological exchange, subsurface sediment composition and interstitial physicochemistry in determining the distribution of hyporheic invertebrates in the Kye Burn, a fourth order Gravel-Bed Stream in New Zealand. 2. In winter 2000 and summer 2001, we measured vertical hydrological gradient (VHG), dissolved oxygen, water temperature and water chemistry using mini-piezometers, each installed in a different upwelling or downwelling zone. Next to every piezometer, a freeze core sample was taken to quantify the sediment, particulate organic matter and invertebrates. 3. Dissolved oxygen concentration at 25 cm was high on both occasions (>9 mg L−1) but was higher in winter than summer. Interstitial water temperature was higher in down than upwellings and was substantially higher in summer than winter. Other features of the subsurface sediments and interstitial nitrate–nitrite concentrations were similar on both occasions and in up and downwellings. Interstitial ammonium and soluble reactive phosphorous concentrations were higher in winter than summer and ammonium was higher in up than downwelling areas. 4. The proportion of fine sediment (63 μm–1 mm), sediment heterogeneity and VHG accounted for the greatest proportion of variance in invertebrate distributions in both summer and winter. 5. The hyporheos was numerically dominated by early instar leptophlebiid mayfly nymphs and asellotan isopods. Water mites were a taxonomically diverse group with 13 genera. Taxonomic diversity (Shannon–Weaver), but not taxon richness, was higher in upwelling areas, reflecting lower numerical dominance by a few taxa in these locations. 6. Sediment composition (particularly the amount of fine sediments) and vertical hydrological exchange determined the composition and distribution of the hyporheos. Patchiness in these factors is important in planning sampling regimes or field manipulations in the hyporheic zone.
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Hyporheic community composition in a Gravel‐Bed Stream: influence of vertical hydrological exchange, sediment structure and physicochemistry
Freshwater Biology, 2003Co-Authors: Dean A. Olsen, Colin R. TownsendAbstract:Summary 1. We studied the relative contributions of the magnitude and direction of vertical hydrological exchange, subsurface sediment composition and interstitial physicochemistry in determining the distribution of hyporheic invertebrates in the Kye Burn, a fourth order Gravel-Bed Stream in New Zealand. 2. In winter 2000 and summer 2001, we measured vertical hydrological gradient (VHG), dissolved oxygen, water temperature and water chemistry using mini-piezometers, each installed in a different upwelling or downwelling zone. Next to every piezometer, a freeze core sample was taken to quantify the sediment, particulate organic matter and invertebrates. 3. Dissolved oxygen concentration at 25 cm was high on both occasions (>9 mg L−1) but was higher in winter than summer. Interstitial water temperature was higher in down than upwellings and was substantially higher in summer than winter. Other features of the subsurface sediments and interstitial nitrate–nitrite concentrations were similar on both occasions and in up and downwellings. Interstitial ammonium and soluble reactive phosphorous concentrations were higher in winter than summer and ammonium was higher in up than downwelling areas. 4. The proportion of fine sediment (63 μm–1 mm), sediment heterogeneity and VHG accounted for the greatest proportion of variance in invertebrate distributions in both summer and winter. 5. The hyporheos was numerically dominated by early instar leptophlebiid mayfly nymphs and asellotan isopods. Water mites were a taxonomically diverse group with 13 genera. Taxonomic diversity (Shannon–Weaver), but not taxon richness, was higher in upwelling areas, reflecting lower numerical dominance by a few taxa in these locations. 6. Sediment composition (particularly the amount of fine sediments) and vertical hydrological exchange determined the composition and distribution of the hyporheos. Patchiness in these factors is important in planning sampling regimes or field manipulations in the hyporheic zone.
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influence of reach geomorphology on hyporheic communities in a Gravel Bed Stream
New Zealand Journal of Marine and Freshwater Research, 2001Co-Authors: Dean A. Olsen, Colin R. Townsend, Christoph D. MatthaeiAbstract:Abstract The surface sediment, subsurface sediment, and hyporheos were sampled by freeze‐coring at three sites of contrasting geomorphology in a New Zealand Gravel‐Bed Stream. No differences in size class composition were detected among the subsurface sediments of the three sites but the forced pool‐riffle (a stretch of Stream where the sequence of pool and riffles is controlled by in‐channel Bedrock outcrops) had significantly finer surface sediments than the other sites. The hyporheos of all sites was dominated numerically by insects, including nymphs of Deleatidium and Oniscigaster, and chironomid larvae. Of the non‐insect taxa, Isopoda, Oligochaeta, and Acari were most common. No significant differences existed between total invertebrate density or taxon richness at the sites. Aoteapsyche was found only in the plane Bed site, whereas Nesameletus was found only in the forced pool‐riffle. Psilochorema and Nematoda occurred at significantly lower densities in the forced pool‐riffle than in the plane Bed ...
W. K. Annable - One of the best experts on this subject based on the ideXlab platform.
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quasi equilibrium conditions of urban Gravel Bed Stream channels in southern ontario canada
River Research and Applications, 2012Co-Authors: W. K. Annable, C. C. Watson, P. J. ThompsonAbstract:Urban Gravel-Bed Stream channels in southern Ontario, Canada identified to be in a state of quasi-equilibrium have been studied over the past 15 years and compared against rural Gravel Bed Stream channels of the same hydrophysiographic region. Bankfull width and depth versus bankfull discharge were not found to increase as a function of increasing urbanization as has been found in many other studies. The observed annual frequency of bankfull discharge was typically less than a 1-year return period with many sites ranging between 2 and 18 bankfull events per year with higher intensity and shorter duration urban flood responses, which further identified significant limitations in using annual peak discharge methods for predicting morphological forming flows in urban watersheds. The cumulative volume of bankfull and larger flood events from the urban Stream channels were very similar to the same annual event volumes in the rural comparison study reaches. Bed material supply was found to decrease with increasing urbanization and the reduction in Bed material supply appears to be off-set by the smaller bankfull channel width, depth and access to floodplains during large flood events. Field evidence may also suggest a even greater reduction in channel width trajectory, relative to the rural setting, with expansive floodplains to maintain quasi-equilibrium conditions as Bed material supply continues to decrease with increased anthropogenic activity. Copyright © 2010 John Wiley & Sons, Ltd.
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Quasi‐equilibrium conditions of urban Gravel‐Bed Stream channels in southern Ontario, Canada
River Research and Applications, 2010Co-Authors: W. K. Annable, C. C. Watson, P. J. ThompsonAbstract:Urban Gravel-Bed Stream channels in southern Ontario, Canada identified to be in a state of quasi-equilibrium have been studied over the past 15 years and compared against rural Gravel Bed Stream channels of the same hydrophysiographic region. Bankfull width and depth versus bankfull discharge were not found to increase as a function of increasing urbanization as has been found in many other studies. The observed annual frequency of bankfull discharge was typically less than a 1-year return period with many sites ranging between 2 and 18 bankfull events per year with higher intensity and shorter duration urban flood responses, which further identified significant limitations in using annual peak discharge methods for predicting morphological forming flows in urban watersheds. The cumulative volume of bankfull and larger flood events from the urban Stream channels were very similar to the same annual event volumes in the rural comparison study reaches. Bed material supply was found to decrease with increasing urbanization and the reduction in Bed material supply appears to be off-set by the smaller bankfull channel width, depth and access to floodplains during large flood events. Field evidence may also suggest a even greater reduction in channel width trajectory, relative to the rural setting, with expansive floodplains to maintain quasi-equilibrium conditions as Bed material supply continues to decrease with increased anthropogenic activity. Copyright © 2010 John Wiley & Sons, Ltd.
Valentina Radic - One of the best experts on this subject based on the ideXlab platform.
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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.
