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The assessment of river channels widely focusses on using channel form to identify channel character but fails to capture the more nuanced variations in morphodynamics without the analysis of process. This paper presents a method using an index of channel behaviour, the throughput ratio (ζ), which is calculated from morphologic change and sediment transport, and explores the viability of inferring process from channel form to act as an indicator of channel behaviour. Two experiments using the same initial width, slope, discharge, and grain size were used to demonstrate the effectiveness of this method in representing different morphodynamics. In one experiment the channel was allowed to laterally deform, whilst the other had inerodible elements placed at its boundaries. As a result the experiment with mobile banks widened and reduced sediment transport to zero, whereas the fixed-bank experiment – unable to decrease its shear stress – continued to output material. In both, the rate of morphologic change tended to zero despite their marked differences in sediment transport over time. The differences in evolution are due to the differences in process available to each channel despite an initial similarity in bed mobility and their gross similarity of a meandering planform. The throughput ratio allows new representations of the temporal and spatial patterns of the morphodynamics, providing additional measures with which to analyse the processes acting in river channels.

Channel processes under high-magnitude flow events are of central interest to river science and management as they may produce large volumes of sediment transport and geomorphic work. However, bedload transport processes under these conditions are poorly understood due to data collection limitations and the prevalence of physical models that restrict feedbacks surrounding morphologic adjustment. The extension of mechanistic bedload transport equations to gravel-bed rivers has emphasised the importance of variance in both entraining (shear stress) and resisting (grain size) forces, especially at low excess shear stresses. Using a fixed-bank laboratory model, we tested the hypothesis that bedload transport in rivers collapses to a more simple function (i.e. with mean shear stress and median grain size) under high excess shear stress conditions. Bedload transport was well explained by the mean shear stress (1D approach) calculated using the depth–slope product. Numerically modelling shear stress to account for the variance in shear stress (2D) did not substantially improve the correlation. Critical dimensionless shear stress values were back-calculated and were higher for the 2D approach compared to the 1D. This result suggests that 2D critical values account for the relatively greater influence of high shear stresses, whereas the 1D approach assumes that the mean shear stress is sufficient to mobilise the median grain size. While the 2D approach may have a stronger conceptual basis, the 1D approach performs unreasonably well under high excess shear stress conditions. Further work is required to substantiate these findings in laterally adjustable channels.

It is understood that the interaction between sediment supply and discharge drives first-order behaviour of alluvial deposits. The influence of the grain size distribution over the mobility and resultant evolution is, however, unclear. Four experiments were conducted in a scaled physical model for two grain size distributions, analogous to a one-dimensional self-formed alluvial fan. We demonstrate the unsuitability of the median grain size as a predictor of deposit behaviour at flows when the material is not equally mobile. The results instead suggest, during conditions of unequal mobility, that the largest grains control the transport efficiency of the overall sediment mixture, and thus also the morphodynamics of the deposit and its tendency to store or evacuate material. Deposits appear to show a dependence upon the rate of material supply more strongly when the likelihood of its motion is less equally distributed (i.e. under partial transport conditions). If the coarse fraction (e.g. greater than 84th percentile) is instead mobile due to increased discharge or because of their relative size, transport rates will increase and the behaviour of the mixtures converge to a common state, with morphology influenced by the material's mobility.

Most studies of gravel bed rivers present at least one bed surface grain size distribution, but there is almost never any information provided about the uncertainty in the percentile estimates. We present a simple method for estimating the grain size confidence intervals about sample percentiles derived from standard Wolman or pebble count samples of bed surface texture. The width of a grain size confidence interval depends on the confidence level selected by the user (e.g., 95 %), the number of stones sampled to generate the cumulative frequency distribution, and the shape of the frequency distribution itself. For a 95 % confidence level, the computed confidence interval would include the true grain size parameter in 95 out of 100 trials, on average. The method presented here uses binomial theory to calculate a percentile confidence interval for each percentile of interest, then maps that confidence interval onto the cumulative frequency distribution of the sample in order to calculate the more useful grain size confidence interval. The validity of this approach is confirmed by comparing the predictions using binomial theory with estimates of the grain size confidence interval based on repeated sampling from a known population. We also developed a two-sample test of the equality of a given grain size percentile (e.g., D50), which can be used to compare different sites, sampling methods, or operators. The test can be applied with either individual or binned grain size data. These analyses are implemented in the freely available GSDtools package, written in the R language. A solution using the normal approximation to the binomial distribution is implemented in a spreadsheet that accompanies this paper. Applying our approach to various samples of grain size distributions in the field, we find that the standard sample size of 100 observations is typically associated with uncertainty estimates ranging from about ±15 % to ±30 %, which may be unacceptably large for many applications. In comparison, a sample of 500 stones produces uncertainty estimates ranging from about ±9 % to ±18 %. In order to help workers develop appropriate sampling approaches that produce the desired level of precision, we present simple equations that approximate the proportional uncertainty associated with the 50th and 84th percentiles of the distribution as a function of sample size and sorting coefficient; the true uncertainty in any sample depends on the shape of the sample distribution and can only be accurately estimated once the sample has been collected.

Quantitative habitat suitability models (HSMs) are frequently used to inform the conservation and management of lotic organisms, often in the context of instream flow management. Correlative statistical models relating hydraulic variables to habitat preferences (habitat suitability curves based on use:availability ratios) are the most common form of HSM, but face significant criticism on the grounds that habitat preference may not reflect the fitness consequences of habitat use. Consequently, there has been a drive to develop mechanistic approaches that link habitat to direct correlates of fitness. Bioenergetic foraging models relating hydraulic conditions to energy balance are particularly well‐developed for drift‐feeding fishes (e.g. salmonids) and show promise as a more mechanistic approach to modelling suitability. However, these models are rarely validated empirically or quantitatively compared with correlative HSMs. We addressed these gaps by comparing the ability of a bioenergetics‐based HSM and two correlative HSMs (a traditional suitability index and a resource selection function) to predict density and growth of stream salmonids (juvenile steelhead, Oncorhynchus mykiss, and coastal cutthroat trout, Oncorhynchus clarki). Suitability estimates differed between the approaches, with both correlative models predicting higher suitability relative to the bioenergetic model at shallow depths and low to intermediate velocities, but lower suitability as depth increased. The bioenergetic model explained over 90% of variation in trout growth, compared to c. 50% for the correlative model. The bioenergetic model was also better at predicting fish density; however, the improvement was less striking and a high proportion of variation remained unexplained by either method. Differences in suitability estimates between approaches probably reflect biotic interactions (e.g. territorial displacement or predation risk) that decouple realised habitat use from energetics‐based estimates of habitat quality. Results highlight fundamental differences between correlative HSMs, based on observed habitat use, and mechanistic HSMs, based on the physiology and behaviour of the focal taxa. They also suggest that mechanistic bioenergetics‐based models provide more rigorous estimates of habitat suitability for drift‐feeding stream fishes. The bioenergetics approach is readily accessible to instream flow practitioners because model predictions are expressed in terms of traditional habitat suitability curves.

Avulsion is a key process in building alluvial fans, but it is also a formidable natural hazard. Based on laboratory experiments monitored with novel high-frequency photogrammetry, we present a new model for avulsion on widely graded gravel fans. Previous experimental studies of alluvial fans have suggested that avulsion occurs in a periodic autogenic cycle, that is thought to be mediated by the gradient of the fan and fan-channel. However, these studies measured gradients at low spatial or temporal resolutions, which capture temporally or spatially averaged topographic evolution. Here, we present high-resolution (1 mm), high-frequency (1-minute) topographic data and orthophotos from an alluvial fan experiment. Avulsions in the experiment were rapid and, in contrast to some previous experimental studies, avulsion occurrence was aperiodic. Moreover, we found little evidence of the back-filling observed at coarser temporal and spatial resolutions. Our observations suggest that avulsion is disproportionately affected by sediment accumulation in the channel, particularly around larger, less mobile grains. Such in-channel deposition can cause channel shifting that interrupts the autogenic avulsion cycle, so that avulsions are aperiodic and their timing is more difficult to predict.

On steep alluvial fans, debris floods happen rarely but are often catastrophic. Debris floods and their associated hazards are well documented, but the time between flood events has generally been ...

It has been observed that the relation between sediment storage and sediment transport rate in gravel-bed rivers exhibits counter-clockwise hysteresis, or aggradation-degradation cycles. Previous work has attributed these cycles to external changes to the sediment supply rate. We present a set of nine flume experiments that test the hypothesis that aggradation-degradation cycles can occur even under steady sediment supply conditions when the sediment transport rate temporarily nears the sediment supply rate. The experiments are designed to examine the transport-storage relations under a range of conditions with different initial bed condition, sediment supply rate, discharge, and supply material texture. The sediment transport efficiency of the experimental channel was strongly influenced by the existing bed morphology inherited from historical flows. The discharge and grain size distribution of the supply material played a secondary role, with higher discharge conditions and finer sediment feed material producing increased transport efficiencies. The transport-storage relations revealed that the transport rate of the channel changed with the volume of sediment stored and was, therefore, mediated by the channel morphology. Aggradation-degradation cycles were observed even under steady sediment supply and discharge conditions and were mediated by morphologic adjustments within the channel that temporarily led the transport rate to be near equal to the sediment supply rate. In other words, the probability of hysteresis in the transport-storage relation increases when the channel is near a transport equilibrium. The findings demonstrate the complexity associated with developing a unique relation between sediment transport and storage in gravel-bed rivers, and highlights the importance of considering the morphologic evolution and historical bed conditions.

While the stabilizing function of large grains in step-pool streams has long been recognized, the role they play in gravel-bed streams is less clear. Most researchers have ignored the role of large grains in gravel-bed streams, and have assumed that the median bed surface size controls the erodibility of alluvial boundaries. The experiments presented herein challenge this convention. Two experiments were conducted that demonstrate the significant morphodynamic implications of a slight change to the coarse tail of the bed material. The two distributions had the same range of particle sizes, and nearly identical bulk d50 values (1.6 mm); however the d90 of experiment GSD1 was slightly finer (3.7 mm) than that for experiment GSD2 (3.9 mm). Transport rates during GSD1 were nearly four times greater than during GSD2 (even though the dimensionless shear stress was slightly lower), and the channel developed a sinuous pattern with well-developed riffles, pools and bars. During GSD2 the initial rectangular channel remained virtually unchanged for the duration of the experiment. The relative stability of GSD2 seems to be associated with a slightly larger proportion of stable (large) grains on the bed surface: at the beginning of GSD1, 3.5% of the bed was immobile, while almost twice as much of it (6.1%) was immobile at the beginning of GSD2. The results demonstrate that the largest grains (not the median size) exert first-order control on channel stability. Copyright © 2017 John Wiley & Sons, Ltd.

It is understood that the interaction between sediment supply and discharge drives first-order behaviour of deposits. The influence of the grain size distribution shape over the mobility and resultant evolution is, however, unclear. Four experiments were conducted in a scaled physical model for two grain size distributions, analogous to a one-dimensional self-formed alluvial fan. We demonstrate the unsuitability of the median grain size as a predictor of deposit behaviour at flows when the material is not equally mobile. The results instead suggest, during conditions of unequal mobility, that largest grains control the transport efficiency of the overall sediment mixture, and thus also the morphodynamics of the deposit and its tendency to store or evacuate material. Deposits appear to show a dependence upon the rate of material supply more strongly when the likelihood of its motion is less equally distributed (i.e., under partial transport conditions). If the coarse fraction (e.g., greater than 84th percentile) is instead mobile due to increased discharge or because of their relative size, transport rates will increase and the behaviour of the mixtures converge to a common state, with morphology influenced by the material's mobility.

Most studies of gravel bed rivers present at least one bed surface grain size distribution, but there is almost never any information provided about the uncertainty of the percentile estimates. We present a simple method for estimating the confidence intervals about the grain size percentiles derived from standard Wolman or pebble count samples of bed surface texture. Our approach uses binomial probability theory to generate confidence intervals for all grain sizes in the distribution. We find that the standard sample size of 100 observations is associated with errors ranging from about ±15 % to ±30 %, which may be unacceptably large for many applications. In comparison, a sample of 500 stones produces an uncertainty ranging from about ±9 % to ±18 %. In order to help workers develop appropriate sampling approaches that produce the desired level of precision, we present simple equations that approximate the proportional uncertainty associated with the median size and the 84th percentile of the distribution as a function of the sample size and the standard deviation of the distribution, assuming that the underlying distribution is log-normal. However, the true uncertainty of any sample can only be accurately estimated once the sample has been collected, so these simple equations complement – but do not replace – the basic uncertainty analysis using binomial probability theory.

We illustrate an approach to quantify patterns in hydraulic habitat composition and local heterogeneity applicable at low cost over very large river extents, with selectable reach window scales. Ongoing developments in remote sensing and geographical information science massively improve efficiencies in analyzing earth surface features. With the development of new satellite sensors and drone platforms and with the lowered cost of high resolution multispectral imagery, fluvial geomorphology is experiencing a revolution in mapping streams at high resolution. Exploiting the power of aerial or satellite imagery is particularly useful in a riverscape research framework (Fausch et al., 2002), where high resolution sampling of fluvial features and very large coverage extents are needed. This study presents a satellite remote sensing method that requires very limited field calibration data to estimate over various scales ranging from 1 m to many tens or river kilometers (i) spatial composition metrics for key hydraulic mesohabitat types and (ii) reach-scale wetted habitat heterogeneity indices such as the hydromorphological index of diversity (HMID). When the purpose is hydraulic habitat characterization applied over long river networks, the proposed method (although less accurate) is much less computationally expensive and less data demanding than two dimensional computational fluid dynamics (CFD). Here, we illustrate the tools based on a Worldview 2 satellite image of the Kiamika River, near Mont Laurier, Quebec, Canada, specifically over a 17-km river reach below the Kiamika dam. In the first step, a high resolution water depth (D) map is produced from a spectral band ratio (calculated from the multispectral image), calibrated with limited field measurements. Next, based only on known river discharge and estimated cross section depths at time of image capture, empirical-based pseudo-2D hydraulic rules are used to rapidly generate a two-dimensional map of flow velocity (V) over the 17-km Kiamika reach. The joint distribution of D and V variables over wetted zones then is used to reveal structural patterns in hydraulic habitat availability at patch, reach, and segment scales. Here we analyze 156 bivariate (D, V) density function plots estimated over moving reach windows along the satellite scene extent to extract 14 physical habitat metrics (such as river width, mean and modal depths and velocity, variances and covariance in D and V over 1-m pixels, HMID, entropy). A principal component analysis on the set of metrics is then used to cluster river reaches in regard to similarity in their hydraulic habitat composition and heterogeneity. Applications of this approach can include (i) specific fish habitat detection at riverscape scales (e.g., large areas of riffle spawning beds, deeper pools) for regional management, (ii) studying how river habitat heterogeneity is correlated to fish distribution and (iii) guidance for site location for restoration of key habitats or for post regulation monitoring of representative reaches of various types.

Large wood has historically been removed from streams, resulting in the depletion of in-stream wood in waterways worldwide. As wood increases morphological and hydraulic complexity, the addition of large wood is commonly employed as a means to rehabilitate in-stream habitat. At present, however, the scientific understanding of wood mobilization and transport is incomplete. This paper presents results from a series of four flume experiments in which wood was added to a reach to investigate the piece and reach characteristics that determine wood stability and transport, as well as the time scale required for newly recruited wood to self-organize into stable jams. Our results show that wood transitions from a randomly distributed newly recruited state to a self-organized, or jam-stabilized state, over the course of a single bankfull flow event. Statistical analyses of piece mobility during this transitional period indicate that piece irregularities, especially rootwads, dictate the stability of individual wood pieces; rootwad presence or absence accounts for up to 80% of the variance explained by linear regression models for transport distance. Furthermore, small pieces containing rootwads are especially stable. Large ramped pieces provide nuclei for the formation of persistent wood jams, and the frequency of these pieces in the reach impacts the travel distance of mobile wood. This research shows that the simulation of realistic wood dynamics is possible using a simplified physical model, and also has management implications, as it suggests that randomly added wood may organize into persistent, stable jams, and characterizes the time scale for this transition.

Large wood governs channel morphology, as well as the availability of in-stream habitat, in many forested streams. In this paper, we use a stochastic, physically based model to simulate wood recruitment and in-stream geomorphic processes, in order to explore the influence of disturbance history on the availability of aquatic habitat. Specifically, we consider the effects of fire on a range of stream sizes by varying the rate of tree toppling over time in a simulated forest characterized by a tree height of 30 m. We also consider the effects of forest harvesting with various riparian buffer sizes, by limiting the lateral extent of the riparian stand. Our results show that pulsed inputs of wood increase the availability and variability of physical habitat in the postfire period; reach-averaged pool area and deposit area double in small streams, while side channels increase by over 50% in intermediate-sized channels. By contrast, forest harvesting reduces the availability of habitat within the reach, though the effects diminish with increasing buffer size or stream width; in laterally stable streams the effects are minimal so long as buffer width is large enough for key pieces to be recruited to the reach. This research emphasizes the importance of natural disturbance in creating and maintaining habitat heterogeneity and shows that scenario-based numerical modeling provides a useful tool for assessing the historical range of variability associated with natural disturbance, as well as changes in habitat relevant to fish. It can be also used to inform forest harvesting and management.

The effects of large floods on river morphology are variable and poorly understood. In this study, we apply multi-temporal datasets collected with small unmanned aircraft systems (UASs) to analyze three-dimensional morphodynamic changes associated with an extreme flood event that occurred from 19 to 23 June 2013 on the Elbow River, Alberta. We documented reach-scale spatial patterns of erosion and deposition using high-resolution (4–5 cm/pixel) orthoimagery and digital elevation models (DEMs) produced from photogrammetry. Significant bank erosion and channel widening occurred, with an average elevation change of −0.24 m. The channel pattern was reorganized and overall elevation variation increased as the channel adjusted to full mobilization of most of the bed surface sediments. To test the extent to which geomorphic changes can be predicted from initial conditions, we compared shear stresses from a two-dimensional hydrodynamic model of peak discharge to critical shear stresses for bed surface sediment sizes. We found no relation between modeled normalized shear stresses and patterns of scour and fill, confirming the complex nature of sediment mobilization and flux in high-magnitude events. However, comparing modeled peak flows through the pre- and post-flood topography showed that the flood resulted in an adjustment that contributes to overall stability, with lower percentages of bed area below thresholds for full mobility in the post-flood geomorphic configuration. Overall, this work highlights the potential of UAS-based remote sensing for measuring three-dimensional changes in fluvial settings and provides a detailed analysis of potential relationships between flood forces and geomorphic change. Copyright © 2015 John Wiley & Sons, Ltd.

Experiments using a 1∶30 scale physical model show that channel degradation on alluvial fans is dominated by lateral channel migration rather than vertical incision. The results are used to...

Presented in this paper is a hydraulic model that combines a rational regime theory with an at-a-station hydraulic geometry simulator (ASHGS) to predict reach-averaged hydraulic conditions for flows up to but not exceeding the bankfull stage. The hydraulic conditions determined by ASHGS can be paired with an empirical joint frequency distribution equation and applicable habitat suitability indices to generate weighted usable area (WUA) as a function of flow. ASHGS was tested against a 2-dimensional hydrodynamic model (River2D) of a mid-size channel in the Interior Region of British Columbia. By linking ASHGS to a regime model, it becomes possible to evaluate the direction and magnitude of habitat changes associated with a wide range of environmental changes. Our regime model considers flow regime, sediment supply, and riparian vegetation: these governing variables can be used to simulate responses to forest fire, flow regulation and changes in climate and land use. Practitioners can examine ‘what-if’ scenarios that otherwise would be too expensive and time consuming to fully explore. The model boundaries of commonly used data-intensive hydraulic habitat models (e.g. PHABSIM) are not easily adjusted and such models are not designed to estimate future morphological and hydraulic habitat conditions in rivers the undergo significant channel restructuring. The proposed model has the potential to become an accepted flow assessment tool amongst practitioners due to modest data requirements, user-friendliness, and large spatial applicability; it can be used to conduct preliminary assessments of channel altering projects and determine if in-depth habitat assessments are justified.

Small unmanned aircraft systems (UASs) are often suited to applications where the cost, resolution, and (or) operational inflexibility of conventional remote sensing platforms is limiting. Remote sensing with small UASs is still relatively new, and there is limited understanding of how the data are acquired and used for scientific purposes and decision making. This paper provides practical guidance about the opportunities and limitations of small UAS-based remote sensing by highlighting a small sample of scientific and commercial case studies. Case studies span four themes: (i) mapping, which includes case studies to measure aggregate stockpile volumes and map river habitat; (ii) feature detection, which includes case studies on grassland image classification and detection of agricultural crop infection; (iii) wildlife and animal enumeration, with case studies describing the detection of fish concentrations during a major salmon spawning event, and cattle enumeration at a concentrated animal feeding operation; (iv) landscape dynamics with a case study of arctic glacier change. Collectively, these case studies only represent a fraction of possible remote sensing applications using small UASs, but they provide insight into potential challenges and outcomes, and help clarify the opportunities and limitations that UAS technology offers for remote sensing of the environment.

In this paper, we assess the capabilities of an unmanned/uninhabited aerial vehicle (UAV) to characterize the channel morphology and hydraulic habitat of a 1-km reach of the Elbow River, Alberta, Canada, with the goal of identifying the advantages and challenges of this technology for river research and management. Using a small quadcopter UAV to acquire overlapping images and softcopy photogrammetry, we constructed a 5-cm resolution orthomosaic image and digital elevation model (DEM). The orthomosaic was used to map the distribution of geomorphic and aquatic habitat features, including bathymetry, grain sizes, undercut banks, forested channel margins, and large wood. The DEM was used to initialize and run River2D, a two-dimensional hydrodynamic model, and resulting depth and velocity distributions were combined with the mapped physical habitat features to produce refined estimates of available habitat in terms of weighted usable area. Based on 297 checkpoints, the vertical root-mean-squared error of the DEM was 8.8 cm in exposed areas and 11.9 cm in submerged areas following correction of the DEM for overprediction of elevations as a result of the refractive effects of water. Overall, we find several advantages of UAV-based imagery including low cost, high efficiency, operational flexibility, high vertical accuracy, and centimetre-scale resolution. We also identify some challenges, including vegetation obstructions of the ground surface, turbidity, which can limit bathymetry extraction, and an immature regulatory landscape, which may slow the adoption of this technology for operational measurements. However, by enabling dynamic linkages between geomorphic processes and aquatic habitat to be established, we believe that the advantages of UAVs make them ideally suited to river research and management. Copyright © 2014 John Wiley & Sons, Ltd.

[1] A stochastic model is used to investigate how the geomorphic function of wood changes with watershed scale, assuming wood recruitment occurs due to the mortality of individual trees, not to mass recruitment events such as landslides or episodic bank erosion. The model replicates the downstream decline in total wood load observed in the field, but predicts that the functional wood load peaks in channels having bankfull widths about 33% of the characteristic riparian tree height. The model also predicts that the greatest potential impact of jams on channel pattern—both in terms of sediment stored behind individual jams and the potential for jams to trigger avulsions—will typically be associated with channel widths between 25% and 67% of the riparian tree height. The simulation results are used to refine the categories that describe wood in alluvial channels, and the equivalent terms that describe the size of streams with forested riparian areas: small channels (or channels with large wood) are associated with widths less than 25% of the tree height; large channels (or channels with small wood) are associated with widths greater than 67% of tree height; and medium channels (or channels with intermediate wood) have widths between 25% and 67% of the tree height. We surmise that large wood acts primarily to store bed material (in small channels); intermediate wood tends to form channel-spanning jams, which can induce channel avulsions and create anabranched channel patterns (in medium channels); and small wood may increase the morphologic diversity, but does not store significant quantities of bed material or form channel-spanning jams capable of inducing stream avulsions (in large channels).

Anthropogenic modification of forests has often decoupled streams from riparian ecosystems and altered natural wood recruitment processes. Extensive research has shown that large wood significantly impacts channel dynamics, especially in small and intermediate sized forested streams where wood pieces are similar in length to channel width, and many stream rehabilitation efforts now involve the addition of large wood to streams. The primary objective of this research is to investigate the relation between large wood and reach scale channel morphology and hydraulics using a physical model, in order to better inform stream rehabilitation programs and future modeling efforts. Four experiments, each comprising numerous five hour runs, were conducted using a Froude-scaled stream table with wood loads scaled to 0 m3/m2, 0.011 m3/m2, 0.016 m3/m2, and 0.022 m3/m2. The addition of large wood significantly decreased the reach-averaged velocity in all experiments, and was associated with decreased sediment transport and increased sediment storage in the reach. Increases in bed and water surface slope compensated for the loss of energy available to transport sediment, and enabled the system to reach a new steady state within the equivalent of 6 to 9 years. Adding wood increased pool frequency, as well as the variability in cross-sectional depth, while causing the reach to undergo a transition from a plane-bed to a riffle-pool morphology. Retention of fine sediment increased the availability of fish spawning substrate, while increased water stage improved connectivity between the channel and the floodplain. The changes in habitat complexity were generally related to the wood load added to the reach, but were also dependent on the orientation and arrangement of the pieces. These results demonstrate that wood may exert a primary control on channel morphodynamics and the availability of aquatic habitat in intermediate sized streams, and suggest that the benefits from stream rehabilitation efforts are highly dependent on project scale. The relatively long time needed to realize habitat benefits demonstrates that long term monitoring of rehabilitation projects is necessary.

In August 2003 a severe wildfire burnt 62% of Fishtrap Creek, a 158 km 2 watershed in central British Columbia, Canada. Streamflows were obtained for the period 1980–2010 and suspended sediment fluxes were determined for the period 2004–2010 for Fishtrap Creek and these were compared to data for nearby Jamieson Creek, which was not affected by the wildfire. Peak streamflows in Fishtrap Creek after the wildfire were not significantly higher than before the wildfire, although total annual runoff had increased. Perhaps the most important change in streamflows following the wildfire was that peak flows associated with the annual freshet occurred earlier in the year (by ca. 2 weeks). Following the wildfire, monthly total suspended sediment fluxes peaked in April in Fishtrap Creek and May in Jamieson Creek, which reflects the change in timing of peak streamflows in Fishtrap. Specific suspended sediment yields were low in the first year following the wildfire (2004), and peak values for the 2004–2010 monitoring period occurred in 2006. Average specific suspended sediment yields over the monitoring period were similar for both watersheds at 2.8 and 2.9 t km − 2 year − 1 for Fishtrap and Jamieson watersheds, respectively. The muted responses of streamflows and suspended sediment fluxes following this severe wildfire are due to the lack of winter precipitation and the low intensities of summer rainfall events in the first year following the wildfire. Greater winter precipitation and associated snowmelt in subsequent years coincided with vegetation recovery. The major changes in the wildfire-affected watershed were increased bank erosion and channel migration due to a loss of root strength and cohesion, which occurred 3–5 years after the fire. This work demonstrates that the hydrological and geomorphological responses of watersheds to wildfires are a function of the severity of the wildfire and the timing and nature of driving forces (i.e. rainfall intensity, winter precipitation and snowmelt) during the progression of vegetation recovery.

NSERC's HydroNet is a collaborative national five-year research program initiated in 2010 involving academic, government, and industry partners. The overarching goal of HydroNet is to improve the understanding of the effects of hydropower operations on aquatic ecosystems, and to provide scientifically defensible and transparent tools to improve the decision-making process associated with hydropower operations. Multiple projects are imbedded under three themes: 1) Ecosystemic analysis of productive capacity offish habitats (PCFH) in rivers, 2) Mesoscale modelling of the productive capacity offish habitats in lakes and reservoirs, and 3) Predicting the entrainment risk of fish in hydropower reservoirs relative to power generation operations by combining behavioral ecology and hydraulic engineering. The knowledge generated by HydroNet is essential to balance the competing demands for limited water resources and to ensure that hydropower is sustainable, maintains healthy aquatic ecosystems and a vibr...

The concept of stream channel grade – according to which a stream channel reach will adjust its gradient, S, in order to transport the imposed sediment load having magnitude Qb and characteristic grain size Db, with the available discharge Q (Mackin, 1948, Geological Society of America Bulletin59: 463–512; Lane, 1955, American Society of Civil Engineers, Proceedings81: 1–17) is one of the most influential ideas in fluvial geomorphology. Herein, we derive a scaling relation that describes how externally imposed changes in either Qb or Q can be accommodated by changes in the channel configuration, described by the energy gradient, mean flow depth, characteristic grain size and a parameter describing the effect of bed surface structures on grain entrainment. One version of this scaling relation is based on the dimensionless bed material transport parameter (W*) presented by Parker and Klingeman (1982, Water Resources Research18: 1409–1423). An equivalent version is based on a new dimensionless transport parameter (E*) using dimensionless unit stream power. This version is nearly identical to the relation based on W*, except that it is independent of flow resistance. Both versions of the scaling relation are directly comparable to Lane's original relation. In order to generate this stream power-based scaling relation, we derived an empirical transport function relation relating E* to dimensionless stream power using data from a wide range of stable, bed load-dominated channels: the form of that transport function is based on the understanding that, while grain entrainment is related to the forces acting on the bed (described by dimensionless shear stress), sediment transport rate is related to the transfer of momentum from the fluid to the bed material (described by dimensionless stream power). Copyright © 2010 John Wiley & Sons, Ltd.

A new channel pattern classification is presented based on theoretically derived channel pattern discriminant functions. The thresholds are formulated as power laws that relate the critical slope associated with a change in channel pattern to dimensionless discharge and relative bank strength. One threshold demarcates the boundary between stable single-thread channels (both straight and meandering) and stable multiple-thread channels (anabranching). Another threshold separates anabranching from braided channels, where braided channels are considered to be fundamentally unstable. The exponents of the thresholds are nearly identical to that in the threshold equation originally proposed by Leopold and Wolman (1957), and the coefficients are quite similar as well. An analysis of their data set using our dimensionless approach reveals that no fundamental difference exists between meandering and straight patterns, and thus data from both types are grouped together under the more general heading of single-thread channels. Furthermore, we demonstrate that over a limited range of conditions, an unstable single-thread channel can form stable multiple-threads; but that for systems far from the threshold bounding the single-thread channels, the number of divisions required to produce stable anabranches grows geometrically: this motivates a separation of multiple-thread channels into anabranching and braided types. Our theoretical thresholds are then compared against several large data sets of field data, and the results broadly confirm our proposed thresholds.

In 2003, a wildfire burned nearly two-thirds of the Fishtrap Creek watershed, including the forested floodplain. Annually repeated surveys of the stream channel — combined with bed material tracer studies in 2006 and 2007 — indicate that the channel has become unstable and that the bed material transport dynamics have changed since the fire. Using these data, the morphologic changes have been quantified and event-scale bed material transport rates have been estimated for four post-fire freshets. The immediate response of the channel (during the 2005 and 2006 freshets) was a progressive shift in channel morphology from a relatively featureless plane-bed morphology devoid of significant sediment accumulations to a riffle-pool morphology in which bars cover a significant proportion of the bed. This transformation occurred in association with moderate bed material sediment transport rates and only minor bank erosion within the study reach. Extensive bank erosion occurred during the 2007 and 2008 freshets, producing a dramatic change in channel morphology and increasing the local bed material transport rates by an order of magnitude. Post-fire monitoring of streamflow and suspended sediment concentrations (a surrogate for upstream sediment supply) indicates that post-fire increases are not detectable (presented in Eaton et al., in press), and our analysis demonstrates that major morphologic changes can occur following wildfire even when the common external drivers of stream discharge and sediment supply remain unchanged.

Bank strength due to vegetation dominates the geometry of small stream channels, but has virtually no effect on the geometry of larger ones. The dependence of bank strength on channel scale affects the form of downstream hydraulic geometry relations and the meandering-braiding threshold. It is also associated with a lateral migration threshold discharge, below which channels do not migrate appreciably across their floodplains. A rational regime model is used to explore these scale effects: it parameterizes vegetation-related bank strength using a dimensionless effective cohesion, Cr*. The scale effects are explored primarily using an alluvial state space defined by the dimensionless formative discharge, Q*, and channel slope, S, which is analogous to the Q–S diagrams originally used to explore meandering-braiding thresholds. The analyses show that the effect of vegetation on both downstream hydraulic geometry and the meandering-braiding threshold is strongest for the smallest streams in a watershed, but that the effect disappears for Q* > 106. The analysis of the migration threshold suggests that the critical discharge ranges from about 5 m3/s to 50 m3/s, depending on the characteristic rooting depth for the vegetation. The analysis also suggests that, where fires frequently affect riparian forests, channels may alternate between laterally stable gravel plane-bed channels and laterally active riffle-pool channels. These channels likely do not exhibit the classic dynamic equilibrium associated with alluvial streams, but instead exhibit a cyclical morphologic evolution, oscillating between laterally stable and laterally unstable end-members with a frequency determined by the forest fire recurrence interval. Copyright © 2008 John Wiley & Sons, Ltd.

Review of recent research on river dynamics in Canada reveals a diverse, active and growing research community engaged in fundamental research at all scales and motivated by a concern for understanding the Canadian landscape, the impacts of development and resource activities and concerns for environmental quality. Several research groups and collaborative programs (national and international), and many individual researchers have made significant progress in areas such as fluvial turbulence, sand bedforms, eco-geomorphology, gravel-bed river morpho-dynamics, regime analysis, numerical modelling of fluvial dynamics and fine-sediment erosion and transport, all supported by new developments in instrumentation and remote sensing applications.

Nine submersible pressure transducers were installed at various locations in a study reach of Fishtrap Creek during the 2006 freshet. The channel morphology of the reach underwent a moderate change in 2006, due to the effects of the McLure forest fire which, in 2003, killed all of the riparian vegetation in the study reach and burned about 62% of the Fishtrap Creek watershed. By examining the changes in the rating relations between the water stage recorded by the pressure transducers and the discharge measured at a Water Survey of Canada gauging station located just downstream of the study reach, we were able to determine the timing of morphologic changes in the stream over the course of the freshet. Shifts in the rating curve were identified by first graphically analysing the stage-discharge relations, and then constructing stage discharge regressions for that part of the record for which the rating relation appeared to be stable. The residuals associated with the calculated rating equations were then co...

A new bank stability analysis procedure is developed for use in rational regime models predicting reach average channel dimensions. The performance of a regime model using this new bank stability formulation is compared against that for a model using the modified friction angle approach proposed by Millar and Quick (1993). The bank stability assessment is based on a conceptual model that more closely represents conditions found in gravel bed rivers with vegetated floodplains: the primary effect of vegetation is its contribution to a stable upper bank, the position of which is determined by erosion of unvegetated bed material at the toe of the bank. The vertical height of the upper bank is estimated using a simple slab failure model and assigning an effective cohesion to the vegetation-reinforced soil. The geometry of the lower slope and the width of the channel are determined iteratively using the regime approach described by Eaton et al. (2004). A comparison of the predicted stream channel widths for stable gravel bed channels classified according to riparian vegetation type (Hey and Thorne, 1986) showed that this new formulation increases model accuracy, especially for the more densely vegetated channel types. Since the strength parameters used in the model can be estimated from the observed bank geometry, the potential for applying and testing rational regime models in the field has been significantly improved. Copyright © 2006 John Wiley & Sons, Ltd.

A simple analytic model is presented relating local sediment transport capacity to variance in the transverse shear stress distribution in a stream channel. The model is used to develop a physically based conceptual model for the initiation of meandering in straight, bedload-dominated streams as a result of a feedback mechanism. The feedback maximizes the cross-sectional shear stress variance and – in order to achieve stability – ultimately minimizes the energy slope at repeated locations along the channel, subject to steady-state mass flux and the stability of the channel boundary. These locations develop into pools in a fully developed meandering channel; they represent attractor states wherein sediment continuity is satisfied using the least possible energy expenditure per unit length of channel. However, since the cross-sectional geometry of a pool (and the adjacent bar) is asymmetric, these attractor states are only conditionally stable, requiring strong, curvature-induced secondary circulation to maintain their asymmetry. Between two successive pools, a stream occupies a metastable, higher energy state (corresponding to a riffle) that requires greater energy expenditure per unit length of channel to transport the same volume of sediment. The model we present links processes at the scale of a channel width to adjustments of the channel sinuosity and slope at the scale of a channel reach. We argue that the reach-scale extremal hypotheses employed by rational regime models are mathematical formalisms that permit a one-dimensional theory to describe the three-dimensional dynamics producing stream morphology. Our model is consistent with the results from stream table experiments, with respect to both the rate of development of meandering and the characteristics of the equilibrium channel morphology. Copyright © 2006 John Wiley & Sons, Ltd.

To properly predict alluvial channel width using rational regime models, an analysis of bank stability must be included in the model. When bank stability is not considered, optimizations assuming maximum sediment transport capacity (MTC) typically under-predict alluvial channel width for natural and laboratory streams. Such discrepancies between regime model predictions and observed channel widths have been used to argue that optimizations such as MTC do not describe the behaviour of alluvial systems. However, rational regime models that explicitly consider bank stability exhibit no such bias and can predict alluvial channel widths quite accurately. We present an analysis of both laboratory and natural alluvial channels, using both kinds of models, and demonstrate the importance of bank stability in constraining optimization solutions. We also identify a scale effect, whereby the effect of vegetation on bank strength declines as the absolute scale of the system increases. We argue that comparisons of alluvial channel widths against predictions from rational regime models unconstrained by bank stability are inappropriate, because they introduce a known and quantifiable bias (toward under-prediction by the model) due to the absence of a bank stability constraint.

A theoretical model is developed for predicting equilibrium alluvial channel form. The concept of greatest relative stability, achieved by maximizing resistance to flow in the fluvial system, is presented as the basis for an optimization condition for alluvial systems. Discharge, sediment supply (quantity and calibre) and valley gradient are accepted as independent governing variates. The model is used to define a dimensionless alluvial state space characterized by aspect ratio (W/d), relative roughness (D/d), and dimensionless shear stress (τ*) or, equivalently, channel slope (S). Each alluvial state exhibits unique values of Froude number and sediment concentration. The range of alluvial states for constant values of relative bank strength (parameterized by an apparent friction angle, φ′) forms a single plane in the state space (W/d, D/d, τ* or S). The scaling relations produced by the model are consistent with laboratory channels exhibiting a range of bank strengths, and with the behaviour of natural channels. Copyright © 2004 John Wiley & Sons, Ltd.

A regionalization of flood data in British Columbia reveals a common scaling with drainage area over the range 0·5×102