Marwan Hassan


Research Interests

Geological and Geomorphological Processes
Channel Stability,
Fluvial geomorphology
Landscape evolution
Sediment transport
Surface hydrology

Relevant Thesis-Based Degree Programs

Research Options

I am available and interested in collaborations (e.g. clusters, grants).
I am interested in and conduct interdisciplinary research.
I am interested in working with undergraduate students on research projects.

Research Methodology

Flume experiment


Master's students
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I support experiential learning experiences, such as internships and work placements, for my graduate students and Postdocs.
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I am interested in hiring Co-op students for research placements.
I am interested in supervising students to conduct interdisciplinary research.

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Dissertations completed in 2010 or later are listed below. Please note that there is a 6-12 month delay to add the latest dissertations.

Sediment storage and transport in gravel bed streams (2023)

In order to predict the response of mountain streams to perturbations caused by climate and land use changes, a better understanding of the sediment transport processes that drive channel morphodynamics is required. Rivers deform systematically, with zones of erosion and deposition related to units of channel morphology (e.g., bars, pools, riffles). Changes in bed topography that build and maintain this morphology are caused by the aggregated displacements of individual particles, either though their entrainment or deposition. Previous studies aiming to link individual particle displacements to channel morphology and topographic change only provide qualitative descriptions of these dynamics. This thesis uses bedload tracing and topographic surveys across a range of laboratory and field settings to link the motions of individual particles to resulting topographic change. First, we apply Bayesian statistics to quantify along-channel trapping probabilities, a measure of the depositional influence of channel segments. These trapping probabilities are used as inputs into a survival model which successfully reconstructs particle travel distances. The results from this model demonstrate that some segments of the channel preferentially trap particles and that these traps are a major control on particle path lengths. Second, we compare trapping probabilities estimated using tracers and topographic differencing across four fluvial environments. In doing so, we demonstrate how the displacements of individual particles scale to create depositional zones along the channel. Finally, we monitor the response of a small mountain stream to a large episodic sediment pulse. We compare stream morphodynamics before and after the pulse to demonstrate how the historical trapping behavior of a river guides the river's response.

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Sediment transport and channel morphology of small alluvial channels (2023)

A number of geomorphological and hydrological factors interact at multiple scales to control sediment transport processes and the resulting morphology of river channels. Predicting how these channels will adjust in response to climate and land-use change requires a thorough understanding of these processes at multiple spatiotemporal scales. Researchers’ ability to investigate these processes at multiple scales has been limited by the dearth of comprehensive long-term sediment monitoring programs. To address this gap, this thesis examines the spatial and time dependence of sediment transport and channel morphodynamics using a 20-year detailed dataset from Goodwin Creek, Mississippi (USA). To examine the timescale dependence of fine sediment transport, we apply wavelet transforms to time series of streamflow, suspended sediment concentration, and sediment load for 11 monitoring stations at Goodwin Creek, with each sub-watershed representing a different land-use and channel boundary condition. We find that although reduced cultivation has caused a decline in fine sediment transport across all time scales, the degree of this decline is considerably influenced by the composition of streambed, and the presence of physiographic features (e.g., gullies, ponds). Over longer timescales, the wavelet transforms suggest that sediment supply shifts from readily accessible to more distant sources. To examine the dependence of spatial scale on sediment transport, we construct sediment budgets for fines, sand, and gravel for two adjacent reaches with contrasting morphological settings. We demonstrate that along-channel variations in gravel and sand storage are controlled by sediment availability within the channel. Substantial changes in fine sediment storage, however, occur during medium magnitude, long-duration flood events. The effectiveness of these events was determined by riverbank stability and near-bank sediment storage inherited from historical flows. Finally, we examine the spatial dependence of bedload transport at the sub-reach scale using a 2D hydraulic model to estimate spatial distributions of shear stress and calculate fractional sediment mobility at East Creek, British Columbia. Results from this model indicate that sediment transport is highly localized and sporadic during low to moderate flows due to the influence of channel morphology.

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The stochastic movements of individual streambed grains (2021)

Bedload transport is the movement of coarse grains through river channels by bouncing, rolling, and sliding. Because coarse grains control river stability, predicting the rate of bedload transport is a fundamental problem in river science. This problem is usually approached with continuum mechanics, but this approach is questionable considering that coarse sediment grains rarely move in densities approximating a continuum.An alternative approach describes bedload transport from the trajectories of individual grains using statistical physics. This approach has become increasingly popular in recent decades, but many fundamental issues prevent this approach from being widely adopted. In particular, the connection between individual particle trajectories and transport rates remains unclear, and particle trajectory models remain highly simplified. Feedbacks between topography and sediment transport remain challenging to analyze, and basic properties of bedload motions like downstream travel velocities remain incompletely understood. Buried particles cannot appreciably move downstream, but even this simple observation has not been comprehensively described in the statistical physics approach.This thesis presents four projects completed in my PhD which overcome these issues to provide new understanding of bedload transport from a statistical point of view. First, I demonstrate how to calculate the sediment flux from the dynamics of individual grains, and I model the trajectories of grains alternating through motion and rest having fluctuating velocities in the motion state. This links the sediment flux to the grain-scale dynamics and describes particle trajectories with additional detail compared to earlier descriptions. Second, I include feedbacks between local bed elevations and sediment transport, quantifying the interplay of bed elevation changes and sediment transport rates and predicting how long particles can stay buried in the river bed. Third, I incorporate the sediment burial process into a model of downstream sediment transport, predicting how grains move downstream when they can become buried. Finally, I describe bedload dynamics on short timescales, predicting the movement velocities of bedload particles using methods adopted from granular physics. I conclude by summarizing these developments, discussing their implications for the statistical description of bedload transport, and suggesting how we can use this modeling progress to better understand landscapes.

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Linking sediment supply, channel morphology, and aquatic habitat in forested, gravel-bed streams: spatial and temporal considerations (2019)

Gravel-bed streams in mountain environments are complex systems which respond unpredictably to episodic inputs of sediment from hillslopes. Stream channel response to episodicsediment supply has implications for channel morphology, stability, and aquatic habitat. Whileinsight into the behaviour of these systems can be gained from numerical models and physical experiments, a paucity of long-term, comprehensive, and multi-scale field data has limitedresearchers’ ability to describe channel response to episodic sediment supply, and to situatethis response in a broader landscape context. This thesis aims to overcome these limitationsby examining long-term channel dynamics in response to episodic sediment supply and variable wood loading and then linking this variability to modeled aquatic habitat for juvenilesalmonids. A 45 year field dataset from Carnation Creek, a small forested, gravel-bed streamlocated in a deglaciated catchment on coastal British Columbia, is used for analysis.Results indicate that temporal patterns of sediment storage are governed by the sedimentconditions and local erosional and depositional processes, while spatial patterns are associated with sediment travel distance statistics. A conceptual model is proposed which presentschannel response to episodic supply as a function of channel position downstream relative tocolluvial input. In-stream wood is also found to influence channel morphology: logjams impactsediment throughput and lead to locations of elevated sediment storage, which decay exponentially over a 10-20 year period. A wood budget model indicates that wood loads will take upto 200 years to recover following riparian timber harvesting, with long-lasting implications forchannel morphology. Modeled habitat for juvenile salmonids, simulated using Carnation Creek topographic and wood data, is found to vary through time by up to a factor of ten as a function of variable channel morphology and wood abundance. These results are found to support a conceptual model which links the contribution to habitat variability from channel morphology to a watershed’s sediment supply regime. Collectively, this work has improved our understanding ofhow episodic sediment supply and wood impact channel morphology, sediment storage, andaquatic habitat in a forested, gravel-bed stream over the long term.

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Modelling fluvial responses to episodic sediment supply regimes in mountain streams (2019)

Large, episodically occurring sediment supply events may temporarily dominate channel morphology and sediment transport in mountain streams. Field studies of channel response to these events are challenging to undertake, as a long data record is needed to reasonably assess a system's state of response in the context of episodic supply. Greater confidence in the observed state of response of a system can be achieved with flume experiments where fluvial response can be observed in detail after episodic events are introduced in a controlled fashion. Yet, the amount of work necessary to carry out these experiments is large, which limits the number of experimental conditions that can be studied, and thus their utility for addressing applied problems of channel adjustment. To overcome this limitation, I developed the 1-D morphometric sediment transport model BESMo, which allows large numbers of simulations to be run in batches, generating ensemble results. This model was used to recreate results from flume experiments, after which the experimental conditions were extended to include a broader range of simulated pulse frequencies, magnitudes, and grain size compositions. It was shown that the sequencing of pulse events of different magnitudes has only a short term effect on the slope and grain size response of the channel. Furthermore, thresholds were identified that allow for the categorization of fluvial response to episodic sediment supply regimes into one of (a) constant-feed-like, or (b) pulse-dominated. The practical utility of BESMo for studying fluvial response to large sediment supply events was demonstrated through the study of potential geomorphic effects following the removal of a dam in the Carmel River, California, USA. This showed the advantage of BESMo for simulating many different future scenarios, as stochasticity could be explicitly included through varied hydrographs. This allowed results to be interpreted in light of the uncertainty in future flood occurrence. Finally, to overcome data limitations on surface grain size distributions, I developed machine-learning based methods to detect grain size distributions from images. Collectively, this work has advanced our understanding and ability to characterise downstream channel response to episodic supply events, and to better obtain data needed for this characterisation.

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Decadal-scale evolution of Elwha River downstream of Glines Canyon Dam : perspectives from numerical modeling (2018)

The goal of this study is to understand the legacy of dams on river channel evolution. Most major world rivers are dammed, and these features have pervasive impacts on downstream geomorphology. Dam removals have become a popular restoration technique. However, little is known about how rivers respond to dam removal on long timescales, especially with regards to sediment exchanges between the channel and floodplain. We examine how dam emplacement and removal have affected channel stability and migration along Elwha River, a cobble-bedded wandering stream. Two dams were built on the river in the early 20th century, blocking sediment supply to the reaches below them. The dams were removed between 2011 and 2014. A numerical model, MAST-1D, is adapted to simulate channel evolution on the set of reaches between the two dams. New representations of bank erosion, vegetation encroachment, and avulsion are developed to make the model suitable for cobble-bedded streams. In the model, channel width and migration oscillate between a range of values, increasing after avulsions due to reorganization of channel geometry. The model is successful at simulating channel change during the sediment-starved period following dam emplacement. While it replicates the general pattern of channel change following dam removal, the simulations underestimate the competence of the system to export the initial pulse of sediment from the former reservoir deposit. Constraining the volume and caliber of sediment supply from the reservoir is crucial for predicting sediment deposition and storage downstream.Model simulations indicate that dam emplacement results in channel armoring, which reduces the competence of the flow to undercut bank toes, reducing the migration rate and leading to net channel narrowing. Both field and model data show that activation of floodplain channels via avulsion and, to a lesser extent, bank erosion, were responsible for increased levels of channel-floodplain exchange during the post-removal period. We predict that in the future, Elwha River will be more laterally unstable than it was in the 20th century, both due to the legacy of the dam removal and because of climate change.

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Effects of episodic sediment supply on channel adjustment of an experimental gravel bed (2018)

A flume experiment was conducted to study channel adjustment of gravel beds to episodicsediment supply. The bed and sediment feed included grains 0.5–64 mm with geometric meansize 5.7 mm. Flow discharge was constant and every 40 h, 300 kg of sediment was suppliedthrough different feed regimes. Sediment transport and storage, bed slope, and bed surfacetexture responded to sediment supply regime. The preferential storage of grains > 8 mmcaused a cumulative increase in bed slope, which probably increased transport efficiency.Within a run, sediment transport rate qb and bed-surface texture were controlled by the magnitudeand frequency of sediment feed and not the total mass. Constant feed promoted gradualincreases in qb and small changes in bed surface texture, whereas large infrequent sedimentpulses caused pronounced increases in qb and strong surface fining, followed by monotonicdecreases in qb as surface re-coarsened. Pronounced trends caused stronger memory in bedloadtime series for runs with episodic feed than in those for runs with constant feed, althoughwithin each run, the structure of memory varied. Long memory was observed for periodswhen bedload rate was nearly stable, which indicates that it could result from local changesin storage. Patterns of grain-size dependence were not affected by sediment feed and the limitfor full-mobility was stable around 8 mm. Scaling statistics for total bedload were similar tothose for fine gravel, which was fully-mobile and dominated bedload. A decrease in the frequencyof movement with size for gravel fractions caused a reduction in the memory strengthof fractional bedload signals. Size-selective transport promoted the storage of coarse grainsupstream and downstream fining on the bed surface. Although fully-mobile, more than 60%of the sand fed got stored in the bed, probably because of its high potential to infiltrate and getcaught within larger grains. Memory was weaker for sand bedload rates than for fine gravel,which indicates that sand mobility was more influenced by short-term stochastic dynamics(e.g., clustering) and less affected by long-term processes like the evolution of large bedformsand sediment pulses.

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Identifying and characterizing the spatial variability of supraglacial hydrological features on the western Greenland Ice Sheet (2018)

Glacier and ice sheet response to climate change is modulated in part by the temporal and spatial delivery of surface water to the subglacial system which can enhance ice sliding. Surface-to-bed connections are formed by near-vertical pathways through the ice called moulins. The mechanisms through which moulins form and the hydrological implications of their distribution are inadequately constrained. This thesis focuses on the southwest Greenland Ice Sheet, where surface melt and related features are abundant and where meltwater drainage through moulins has been empirically linked to ice speedup. In the first part, I employ flow routing over a high resolution digital elevation model to delineate supraglacial channels and catchments. I compare my results to an independent dataset and demonstrate that flow routing is an effective tool for delineating channels in high detail. Whereas multispectral methods provide instantaneous discharge estimates and flow routing derived catchments can be used to build hourly hydrographs, the two methods are temporally incongruous and produce discharge estimates in small catchments that differ by several orders of magnitude. In the second part of the thesis, I contribute empirical insight into where moulins form and the hydrological implications of the resultant spatial organization of catchments. Using remotely sensed data on supraglacial lake distribution, bed elevation, ice thickness, surface velocity and strain rate, I show that moulins form predominantly in low velocity, high strain rate ice with adverse bed slopes. Moulins formed near moulin-drained lakes are typically located down-ice of the lake. The spatial distribution of moulins affects the physical characteristics of supraglacial catchments, including elevation, size, elongation, drainage network configuration and slope. This in turn impacts the temporal delivery of meltwater to the subglacial network. I use synthetic unit hydrograph theory based on catchment morphometrics to show that catchment diurnal hydrograph lag times in the study area vary by up to 11 hours. The hydrological implications of subglacial meltwater supply vary according to the configuration of the subglacial catchments, which vary temporally based on subglacial water pressure. Considering this additional level of complexity is a necessary next step in constraining the relationship between melt and ice flow dynamics.

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Pool-riffle dynamics in mountain streams: implications for maintenance, formation and equilibrium (2017)

It is common for mountain riverbeds to exhibit a repetitive pattern of topographic lows andhighs known respectively as pools and riffles. Pool-riffle structures are ecologically importantbecause salmon rely on them for birth, growth and regeneration, and they are physically important because pool-riffles are observed across diverse landscape settings. A common physical characteristic of pool-riffles is that pool spacing is proportional to channel width, for longitudinal bed slopes that vary by two-orders of magnitude. Furthermore, field, numericaland laboratory based studies observe that pools are colocated with points of channel narrowing,and riffles with points of widening. What is not known, however, is how downstreamchanges of channel width give rise to, and maintain pool-riffles. The goal of my thesis is toaddress this knowledge gap, and to specifically build physical understanding for the observedspatial correlation between channel width and pool-riffle architecture. I use field work, laboratoryexperiments and theory to address this goal. In Chapter 2 I apply non-parametricstatistics and self-organizing maps to understand the spatial and temporal character of rifflebed surface texture spanning 11 different sediment mobilizing floods, and conclude thatfrequent texture adjustment is part of the maintenance process for pool-riffles which exhibittopographic stationarity. I build from this finding in Chapters 3, 4 and 5 with laboratory experiments designed to investigate how pool-riffles form and evolve along variable width channel reaches. In Chapter 4 I conclude that pool-riffle formation is physically driven by two competing timescales which reflect the tendency to build riverbed topography through sedimentdeposition, vs. the tendency to destroy topography through net particle entrainment. I capturethese timescales in a mathematical model I develop using theory with physical scaling.In Chapter 5 I show that the (dis)equilibrium state of pool-riffle evolution is quantitatively described by a competition between two rates which reflect the temporal adjustment of riverbedtopography and riverbed surface texture. I conclude that equilibrium, or comparability betweenthe rates of topographic and sediment texture adjustment, is most likely to occur whenoverall sediment mobility and grain size sorting are relatively high.

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Hydrogeomorphic Controls on Spatial Pattern of Fish Habitat in a Mountain Stream (2015)

Spatial heterogeneity and arrangement of physical habitat strongly influence stream-dwelling organisms. A primary objective of this dissertation was to examine how hydrogeomorphic controls – channel morphology, bed sediment, and flow hydraulics – shape spatial patterns of habitat for small-bodied trout. Two complementary habitat types, spawning and foraging habitat, were investigated to gain more comprehensive understanding of these linkages. A secondary objective of the dissertation was to evaluate the effects of sample size on errors in estimates of hydraulic parameters critical for understanding channel dynamics and quantifying fish habitat. This research was conducted in four reaches of a small mountain stream with different channel morphologies and sediment textures. High resolution field surveys and a hydrodynamic model were used to map channel morphology, sediment, and flow properties. Habitat models, which included a bioenergetic foraging model, were then applied to evaluate fish habitat availability, quality, and disturbance at within and between-reach scales. Results indicated existence of two distinct spawning habitat domains. In coarser reaches with simple morphologies potential spawning substrate occurred only in small, hydraulically sheltered areas, which were also at high risk of disturbance due to excess fine sediment accumulation. In finer, pool-riffle reaches potential spawning substrate covered large proportion of the bed and was largely unaffected by fine sediment disturbance. Bed scour generally did not seem to be an important disturbance agent. During low flow, the most energetically profitable foraging habitat was located in deep, slow-flowing pools and zones of strong lateral gradients of velocity. Cross-channel patterns of net energy intake appeared to vary with fish body size. During high flow, however, energetically profitable habitat occurred mainly near the banks. The mean net energy intake and the proportion of channel area where fish energy budget was positive were somewhat higher in the reaches with better developed pool-riffle morphology, but the former trend partially reversed during high flow. Error analysis indicated that sample sizes commonly used in river science to represent hydraulic variables may generate large sampling errors. Errors of this magnitude in the estimated bed roughness parameter caused substantial differences in the flow field predicted by a hydrodynamic model.

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Landscape organization based on application of the process domain concept for a glaciated foothills region (2011)

The organization of a glaciated foothills and interior plain landscape was examined by analyzing the spatial distribution of process domains. Glaciations distribute patches of surficial materials with varying hydrologic properties across the landscape and create complex longitudinal profiles. These two factors complicate the use of a traditional method, drainage area – local slope plots, for explaining landscape organization; hence, an empirical approach using logistic regression models was applied. An automated procedure was developed that enabled extrapolation of model results across entire study areas. A 57 km² and a 10,000 km² study area were divided into hydrological response units (HRUs) with an average area of less than 5 km². The HRUs were classified into categories based on topography, hydraulic connectivity, and surface type. A preliminary drainage network was extracted from a LiDAR DEM. The network was sub-divided into reaches, each characterized by a suite of topographic predictors. Ground surveys entailed assigning a process domain class as hillslope, swale, seepage channel, or fluvial channel. Various types of logistic regression models, including mixed-effects, binary, ordinal, and multinomial, were used to predict process domain class. Predictors included longitudinal profile anomalies measured at the reach scale using a normalized stream length-gradient (SL/k) index. The candidate predictors, including SL/k index, soil moisture regime, and mean basin slope, were selected in consideration of groundwater flow systems that operate respectively at the reach, hillslope, and basin scales. Drainage area, the dominant factor controlling domain transitions, was complemented by various predictors, depending on transition and HRU type, including reach slope, and the three groundwater flow related predictors. The study revealed features of a stabilized landscape including an extensive network of swales. Headward channel migration into the swale network is not expected to proceed uniformly across the glaciated landscape; rather, minimal migration is expected where channel heads are anchored below confluences and within over-steepened areas, and higher migration frequencies are forecast in sections of the network that are more evenly graded in terms of both drainage area and slope.

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Experimental investigations of step-pool channel formation and stability (2009)

The stability of steep streams with step-pool and cascade morphologies cannot be assessed using knowledge developed from lowland streams due to the structured nature of headwater streams. Thus there is a need for experimental studies examining the stability of such channels. The structuring of these channels occurs as a result of boulders and cobbles jamming across the width of the channel and the more typical pattern of armouring and imbrication, which results from a relatively low rate of sediment supply. To conduct such a study, new experimental techniques were developed and an artificial stream channel (flume) was designed and built. Channel width, bed grain size and channel gradient were varied and step-pool bedforms were created and subsequently destroyed. The variables governing the dimensions, frequency and form of step-pools were observed to be channel slope, bed grain size and channel width. Video records show that on occasion groups of larger stones moved together as a coherent group, forming a line of stones that locked together across the width of the channel. The failure of a step most frequently occurred when the downstream scour pool undermined the step-forming stones and was often associated with headward migrating instabilities. With smaller jamming ratios (channel width/D84steps —the diameter at which 84% of the step stones are smaller than) stable beds persisted at larger Shields numbers (ratio of shear stress to grain size), confirming that such channels do gain stability by having grains jam across their width. The failure of the bed was shown to be a stochastic process with nearly half of the failures occurring within the first minute following an increase in discharge, while 26% of the failures did not start to occur until tens of minutes or more after the flow was increased. Detailed bed morphology, channel grain size and flow velocity measurements suggest that a dimensionless hydraulic geometry approach is the best method of predicting flow velocities in headwater channels. The bed stability criterion, in combination with a dimensionless hydraulic geometry approach, provides a means of assessing the stability of mountain stream channels.

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Some physical and biological factors influencing the fate of fine clastic particles in flowing water (2009)

An experimental flume study was conducted to assess the influence of several physical and biological factors on the movement and deposition of fine particles (
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Master's Student Supervision

Theses completed in 2010 or later are listed below. Please note that there is a 6-12 month delay to add the latest theses.

Channel adjustment in a small mountain stream over a long flood series: insights from the morphological method (2021)

The use of high-resolution topographical data (HRTD) with the morphological method has largely remained restricted to active channels with high sediment transport regimes, where disturbance is significantly higher than noise within HRTD, yet channels with low stream orders and low sediment transport regimes dominate watersheds. The morphological method with HRTD was used to determine spatial and temporal trends of channel adjustment in East Creek, a small gravel-bed channel with a low sediment transport regime near the Coast Mountains of British Columbia, over a fifteen-year flood series. A probabilistic threshold with 68% confidence intervals was used to determine distributions of significant bed elevation change in conjunction with a tracer data set, and these disturbance distributions were compared between different morphologies. These distributions were then used to determine the volumetric input from the bed to the net morphological displacement (NMD), a new term proposed to distinguish the net processes that occur after multiple events from bed material transport. Cross-sectional surveys were used to determine the NMD fraction originating from the channel banks since HRTD cannot capture undercutting. The disturbance distributions are best described by the log-normal distribution, although the distribution tails tend to deviate from the log-normal. These distributions were found to generally be statistically similar between the different morphologies within both depositional and erosional areas. Erosion from the bed was found to generally become more significant to the NMD relative to erosion from the banks going downstream, and both the NMD and mean disturbance depths were found to not be correlated with the hydrological conditions. This lack of correlation may be best explained by the channel history. The disturbance distributions and their volumes found from HRTD were compared to the same determined from tracer stone surveys and cross-sectional surveys, respectively, both more traditional surveys. The distributions found from HRTD were found to result in more robust estimations that can be studied at increased spatial levels than from those found using tracer stones alone, and disturbance volumes from cross-sections were found to differ from those found using HRTD by a maximum and minimum of six and one-sixth times.

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On the development of bed surface structures in response to variable flow regimes (2021)

The objective of this research is to use flume experiments to investigate the formation and development of bed surface structures and their impact on channel stability in response to variable flow regimes. A wide range of bed structures (clusters, stone cells, and transverse ribs) was reproduced in five sets of experiments, and data of sediment transport, bed surface grain size, and channel bed topography were systematically collected. A semi-automated method was developed to identify the bed structures, and used to record their temporal evolution regarding numbers and areal coverage. After the initial period of bed coarsening, D₅₀ and D₈₄ of surface grain size remained almost unchanged. In contrast, ongoing bedform development, longitudinal grain segregation, and evolution of bed structures were observed throughout the experiments. Bed structures developed and coexisted, and they constantly formed, disappeared, and transformed into other structures. The bed structure dynamic cannot be simply explained by flow regimes, but was significantly driven by particle interactions. The dynamic behaviour of bed structures concurred with the fluctuation of grain stability on the bed surface. Despite the active evolution of individual structures, their overall bed coverage remained around 15-20% most of the time. It can be inferred that the dynamic development of bed structures can be linked fundamentally to increasing channel stability, and that the fluctuation of bed mobility is partly associated with the development of bed structures.

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Exploring the importance of sediment disconnectivity and connectivity in glacierized catchments, Tahoma Creek, WA (2020)

In recent decades, connectivity has emerged as a prominent topic of discussion within the geomorphology community but lacks consensus around a general definition. On the other hand, disconnectivity is often an afterthought even though it is prevalent at most spatiotemporal scales. In response, we suggest defining disconnectivity as the dominant but inefficient state of the system in transferring matter and energy within and between system components at all spatial and temporal scales. Connectivity is then a special case within disconnectivity in which the efficient transfer of matter and energy occurs within the spatiotemporal scale of interest. In this study, we explore whether disconnectivity controls the spatial patterns of sediment dynamics, and how well current methods of quantifying connectivity captures these spatial patterns. We conducted a case study within the Tahoma Creek Watershed of Mount Rainier National Park, WA, in which we present fieldwork and historical data in the form of a geomorphic map and conceptual sediment budget and map all sources of disconnectivity. These analyses are compared to methods of measuring the influence of landscape history and hillslope-channel coupling, followed by several semi-quantitative connectivity indices. Slope-Area plots clearly show the topographic signature of Pleistocene glaciations within the confines of relict cirques, while the mainstem channel appears fully adjusted to contemporary fluvial processes. Hillslope-channel coupling estimates based on the method proposed by Whiting and Bradley (1993) generally match fieldwork evidence, where the uppermost 6 km of the channel are coupled to the hillslopes, and the lowermost 7 km are decoupled. We found that the spatial distribution of sources of disconnectivity and their upslope affected areas explains the spatial patterns of sediment transfers and assumed transfer efficiencies within the watershed. Even locations with intense morphodynamics, such as Mount Rainier, are predominantly disconnected over human-timescales. The methods of quantifying sediment connectivity all performed rather well within their stated limitations and inherent resolution, although discrepancies exist. The primary sources of error result from inaccurately modelling runoff pathways and overlooking the effects of vegetation. We suggest explicitly integrating sources of disconnectivity within disconnectivity indices for improved performance and physical grounding.

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A rapid and objective characterization of channel morphology in a small, forested channel using a remotely piloted aircraft. (2019)

The use of remotely piloted aircrafts (RPAs) in fluvial geomorphology has improved the ability to characterize streams at greater resolutions and spatial extents than was previously attainable using traditional survey techniques. However, their use has been generally limited to streams under ideal conditions that differ from the small, forested mountain channels common in the Pacific Northwest. These channels have remained difficult to characterize using modern techniques due to their dense canopies and rough terrain. A rapid and objective method of characterizing channel morphology across the river basin using a RPA is presented in this dissertation to help overcome this challenge. First, the accuracy of RPAs for extracting bed elevations, bathymetry and grain size along 3 km of Carnation Creek, a small, forested stream on Vancouver Island, was investigated through a sub-canopy survey. Relevant cross-sectional channel variables were then extracted to objectively characterize channel morphologies across the river basin using a principal component analysis-clustering (PCA-clustering) technique. Then the Shannon's diversity index was used to characterize the local diversity across the channel, and investigate the scale needed to study the system, to ensure its heterogeneity was characterized. The results demonstrate that RPAs provide a rapid alternative to characterizing these systems, through the construction of a 2-cm resolution digital elevation model spanning 3 km of channel, with a root-mean-square-error of 0.093 m for exposed bed check points and 0.1 m for submerged bed check points. The PCA-clustering analysis provided an objective means of classifying channel morphology with a correct classification rate of 85%. Altogether, the results provide a precedent for using a RPA to characterize the morphology and diversity of small, forested channels at a scale of ecological relevance to the life histories of Pacific salmonids.

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Influence of feed timing on sediment transport and bed evolution during hydrographs (2018)

Sediment transport in gravel-bed streams is an important component for river ecology, infrastructure design, and hazard assessment. Yet making accurate predictions of sediment transport remains elusive despite many decades of field, lab, and numerical modeling research. Most lab and modeling experiments use either constant discharge, constant feed, or both are constant. While these works have helped discover many aspects of sediment transport, they do not reflect the variability in discharge and sediment supply found in natural settings. We performed several flume experiments to challenge an assumption made by Parker, Hassan, and Wilcock (2007) that feed timing during a hydrograph does not matter for sediment transport behavior and bed evolution. We used mixed grain sizes for both the initial bed and feed (ranged between 0.5mm and 32mm; D 50 = 7.83mm), a symmetrical stepped hydrograph, and five different feed scenarios: no feed, constant feed, rising-limb only feed, falling-limb only feed, and capacity-scaled feed. All feeding scenarios had the same total mass fed. We show that the assumption made by Parker et al. is wrong. Feeding on the rising limb strongly controlled sediment transport rates, overall bedload yield of the hydrograph, and bed scouring severity, but not bedload grain sizes. Feeding on the falling limb controlled bedload grain sizes, bedload transport rates in the early portion of the falling limb, and recovery of the bed towards a pre-flood morphology (e.g. elevation and slope). Shifting the feed timing towards different parts of the hydrograph highlighted different processes and influenced the overall hysteresis trends.

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The formation and adjustment of a pool-riffle sequence in a gravel bed flume (2017)

Pool-riffle sequences are a dominant morphological feature found in a wide range of fluvial environments. The hydraulic and sedimentological complexity that they impart provides important aquatic habitat, resulting in their increasing implementation in river restoration projects, despite the fact that there are still many inconsistencies in the literature relating to the processes involved in their formation and maintenance. The main research objective was to study the formation, adjustment, and maintenance of pool-riffle morphology in gravel bed rivers. A variable width, mobile-bed flume was configured as a model of a pool-riffle reach in East Creek, British Columbia, and the development of a pool-riffle sequence under bankfull discharge, and subsequent adjustment to increased discharges were studied. The central pool-riffle sequence developed around a major width constriction and persisted in that location throughout the entirety of the experiment, increasing in amplitude in response to increased discharge. Bed texture was initially quite variable, but became relatively constant throughout the entire flume near equilibrium, including the pool and riffle. Hydraulic parameter reversals from low to high flow were observed between the pool and riffle, including water surface slope, section averaged velocity, and bed shear stress. Particle mobility was higher in the pool, but the virtual velocities of mobile particles were constant until the highest discharge. Evidence of secondary flow patterns was recorded in the pool, which could suggest a maintenance process in addition to velocity reversal. These results should inform future studies and design projects on pools and riffles, especially in relation to their behaviour during flood events.

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Water Grabbing and Conflict in the Nile River Basin: A Focus on Ethiopia (2016)

The phenomenon of large-scale land investments for agricultural production – also referred to as land grabbing – has grown in recent years all over the world, especially after the 2007-2008 international food price crisis. Ethiopia is among the most targeted countries by foreign investors concerning farmland demand. But not only that, the Ethiopian Government is actively promoting and encouraging private sector participation in large-scale farming, especially in the low land border areas of the country that are part of the Ethiopian Nile River basin. The development of land transferred to investors in these areas will necessarily result in an increase of Ethiopia’s Nile waters use. The intensification of Nile waters consumption in Ethiopia, in turn, may challenge the existing arrangement at the basin level, where Egypt has historically acted as the hydro-hegemon opposing any water resources development in the upstream countries. Thus, in this research I explore the implications of land grabbing on water resources as well as the ways in which specific ideas about water configure different power geometries at different scales. By using the agronomic model CROPWAT, I estimate the amount of water required to bring into production all the land that has been transferred to investors in the Ethiopian Nile River basin. Results from CROPWAT show that large-scale farming development could increase the pressure on water resources in some areas to unsustainable levels, as it is the case of the Pibor – Akabo – Sobat sub-basin. It could represent as well, a decline up to 3.4 % of Egypt’s Nile waters share – up to 10.2% in the case of Sudan – clearly challenging the existing hydro-hegemony in the basin. Furthermore, by interrogating different notions of water – those of the state, private investors and local communities – through the hydrosocial cycle framework, this research reveals how water discourses configure social structures and power relations at different scales; and how water injustices reveal or conceal themselves depending on the scale of inquiry.

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Spatial and Temporal Patterns of Sediment Mobility and Storage in a Small Mountain Stream (2015)

The study was conducted in East Creek, a headwater gravel-bed channel in the Fraser Valley foothills of the Coastal Mountains of British Columbia. Sediment transport was measured at three spatial scales using two measurement techniques in a study reach containing three unique morphological reaches: rapids, riffle pool, and step pool. At the largest spatial scale, the channel scale, channel stability was assessed between 2003 and 2009 using longitudinal profiles of channel elevation obtained from digital elevation mapping. The longitudinal profiles suggest that East Creek was in a relatively stable state over the six year analysis period, with the majority of erosion and deposition limited to localized fluctuations that varied in magnitude and direction. At the intermediate spatial scale, the reach scale, sediment transport estimates obtained from pit trap and digital elevation mapping data were used to create a sediment budget for the rapids reach and riffle pool sub-reaches of the channel. Using both measurement techniques, erosion and deposition fluctuated and could not be linked to flow regime or sediment supply alone. It is hypothesized that in-stream sediment supply and bed conditioning are important controls on sediment storage, and were used to explain observed fluctuations in erosion and deposition. The magnitude and direction of reach scale sediment storage fluctuations were not consistent across the two measurement techniques; however, elevation mapping estimates were nearly always higher than pit trap estimates. This is likely a result of overpassing of fine material and pit trap inefficiency. At the smallest spatial scale, the unit scale, spatial patterns of sediment transport were assessed across riffles and pools using digital elevation and morphological mapping data. There was increased sediment mobility in pools compared to riffles, which is likely a result of pools containing finer more loosely interacting particles compared to those in riffles. The high resolution unit scale sediment storage data demonstrated conservation of mass and a tight coupling of erosion and deposition in East Creek.

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The Effects of Channel Morphology on the Mobility and Dispersion of Sediment in a Small Gravel-Bed Stream (2015)

The role of channel morphology in sediment transport is poorly understood due to the complexity of the interactions between morphology, sediment characteristics and flow. A better understanding of the ways in which channel morphology affects sediment transport at all scales and under varying flow conditions can improve predictions of channel behavior and provide insights for better stream restoration applications. This study aimed to capture the effects of morphology on bed mobility and sediment dispersion in a small gravel-bed stream through the use of a 10 year tracer dataset. The characterization of bed mobility and sediment dispersion conducted at three spatial scales (the reach, morphological unit and local scale), revealed the importance of scale when examining the role or morphology on sediment transport. East Creek was found to be in conditions of marginal sediment transport, remaining near the critical conditions for sediment mobilization the majority of the time, and falling within a low sediment transport regime common in small gravel-bed streams. Both bed mobility and tracer travel distances increased with increasing flow conditions, and measures of cumulative flow energy had stronger relations to both variables than peak discharge. Grain size was not found to play no role in bed mobility or travel distance in East Creek. At the reach scale, morphology did not affect bed mobility, and influenced the travel distance of tracers only during high flows, or when averaged over long time periods. Although burial rates were high, burial depths were shallow, and burial showed no relation to flow or mobility. At the morphological unit scale, differences were observed in the rate of increase of bed area under mobility with increasing flow between reaches and between morphological units. Finally, at the local scale, bed mobility was highly localized and sporadic. Results of this study allow for the description of the role of morphology on bed mobility and sediment dispersion in a low sediment transport regime and throughout various spatial and temporal scales. Further research opportunities include the exploration of the role of morphology on bed mobility and sediment dispersion in a variety of morphological and sediment transport settings.

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Channel adujstment of a gravel-bed stream under episodic sediment supply regimes (2014)

Sediment supply is a key control on sediment transport rates and bed evolution in a stream. This study examined the adjustment of a gravel-bed stream under episodic sediment supply regimes by conducting a flume experiment in the Mountain Channel Hydraulic Experimental Laboratory at the University of British Columbia. The experiment consisted of a sequence of runs with no feed, constant feed and episodic supply regimes; but constant water discharge and feed texture. The observations indicated that sediment transport rates, the texture of bedload and the bed surface, sediment storage, bed slope, and bed topography adjusted to changes in sediment supply. The relative mobility of sediment instead did not change significantly. Under constant feed, transport rates showed a slow and small increase. The texture of the surface was fluctuating, the same as of the bedload. Sediment storage was relatively large, and the bed slope presented small changes. If the same amount of sediment entered in one or few pulses, transport rates and the texture of the surface exhibited pronounced changes just after the pulse, and returned to conditions similar to previous the pulse after some time. The size of the pulses influenced the results, and larger pulses caused larger increases of transport rates and finer textures on the bed surface. Cumulative storage, bed slope and bed morphology adjusted to episodic supply; but did not return to the conditions before the pulse, revealing that the effects of sediment supply over the bed were cumulative and persisted under periods of no feed. During these periods, transport rates decreased, the bed texture coarsened, and there was little change in the bed slope. After few hours of no feed, transport rates were relatively low and changes in elevation were small. Our results suggested that episodic supply produced interesting patterns of channel adjustment (different from constant feed regimes) that depend on the size and frequency of the supply.

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Reach-Scale Contributions of Road-Surface Sediment to the Honna River, Haida Gwai, B.C. (2014)

Unpaved resource road surfaces may act as dominant sources of fine sediment to streams, yet their relative contribution to in-channel sediment yields remains poorly understood. Significant quantities of road-surface sediment have been observed entering the Honna River, B.C, a 5th order channel located is close proximity to a major, intensively used resource road. In September 2012, a reach of the Honna River was selected for measurement and instrumentation to compile a sediment balance with a focus on the relative importance of road surface sediment over an annual scale. An additional four months of suspended-sediment data were collected at 6 locations in the reach to determine spatial and temporal dynamics of suspended-sediment concentrations and yields. Road surface sediment contributed 19% ± 6% of the total annual fine sediment balance for the reach, even though only ~20% of the road area was an effective sediment source. Persistent clockwise hysteresis was observed in the SSC-discharge relation in the main river channel, but was not as apparent in ditch drainage channels. As a proportion of total input, road surface material ranged from 0.5% to 15% during dry conditions from April to the end of September, and from 5% to 70% in the wet season from October to the end of March. Road surface material appears likely to settle on the river channel bed during low flow conditions, but only temporarily, and in small quantities relative to natural sediment sources. Additional research is needed to assess basin-scale contributions of road surface sediment.

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Temporal adjustments of a streambed following an episodic sediment supply regime (2013)

The objective of this research is to evaluate temporal adjustments of a streambed surface due to changes in the sediment supply regime. To achieve the goals, laboratory experiments were conducted in an 18 m long, 1 m wide flume with a gradient of 0.0218. The bed was brought to an armored state by running water with no sediment feed before releasing a sequence of sediment pulses. Water discharge and grain size distribution of the sediment feed were held constant over the set of experimental runs, while supply input rates and magnitudes varied. Sediment flux at the outlet of the flume was continuously measured. At frequent time intervals, bed surface texture, 1 mm vertical resolution bed elevation, and microtopographical cluster features were measured over a two meter section of the flume bed. Instantaneous three-dimensional observations of flow velocities were made using an Acoustic Doppler Velocimeter.Surface texture adjustments in response to the sediment supply regime followed similar patterns between all runs involving pulses of sediment in that (1) the D₁₆ – the diameter at which 16% of the particles are smaller than – was the most variable characteristic grain size value and (2) medium-gravel patch areas were least variable, likely due to higher relative mobility of fine material. Fine-gravel patch areas developed following sediment pulses and persisted over time even once the overall characterization of the bed had returned to an armored state. Increases in bed roughness, quantified by the standard deviation of bed elevations (σz), were consistently paralleled with increases in the number of identified clusters and their combined surface area. Cluster formation was seemingly random, but expansion occured only once surface texture became relatively coarse and bed roughness increased. These results inform about the degree of bed surface evolution complexity under conditions of variable sediment supply and can be linked to observations and predictions of sediment transport in field settings.

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Using LiDAR to detect in-stream woods: A scaled approach (2013)

In-stream woods significantly influence watershed hydrology, flow regime, channel morphology and stability, and processes in streams. Consequently, in-stream woods play a major role in the existence and conservation of riparian and aquatic ecosystems. In this thesis, I attempt to detect and quantify LWD in stream channels using a remote sensing method, LiDAR, in conjunction with the traditional fieldwork. To the best of my knowledge, LiDAR-based analysis has not been used to study woods in stream channels. I, initially, attempted to re-apply advanced medical image processing and segmentation techniques on the LiDAR intensity images in order to confine the LiDAR terrain-based analysis to the stream channel networks, optimizing time and computing resources. The results exhibited significant image enhancement and accurate segmentation in certain regions; however, an automatic and a unified framework to delineate the stream channel networks, across different scales and spatial locations, is still required. LiDAR-based analysis demonstrated a more comprehensive solution for detecting in-stream woods in relation to the fieldwork through a high rate of commission and a low rate of omission. The filtered approach predicted the presence of 95% of fieldwork-reported in-stream woods, highlighting a 5% rate of omission, but with 25% rate of commission indicated by the identification of at least 15 new LWD locations that were not initially reported by the field crew. The non-filtered approach identified 87% of field-reported LWD, highlighting a 13% rate of omission and, similar to the filtered approach, a %25 rate of commission. Overall, the non-filtered and the filtered LiDAR showed fairly accurate predictions for in-stream woods’ dimensional measurements (length, width, and height) with respect to the field data. However, the filtered approach showed better dimension estimation of in-stream woods compared to the unfiltered LiDAR. Although a margin of error existed for fieldwork and LiDAR methods, a careful examination of orthophotos showed that LiDAR results were more accurate than the Laser Range Finder (LRF) used in the field.

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Advancements in measuring bed load transport with a magnetic detection system (2012)

A large number of bed load measuring devices have been developed in order to estimate sediment transport in rivers. In spite of that, the geomorphic and engineering communities do not have a reliable method to estimate bed material load. Available techniques suffer from insufficient temporal and spatial resolution to capture the variability inherent in bed load movement. This work involves the design and construction of an in situ magnetic detection device, which shows promise as a method capable of overcoming these limitations. The sensors work by inducing a magnetic dipole in naturally magnetic stones via magnets installed in the bed of the channel. These stones then pass over a coil of wire, inducing a small voltage, which is recorded. The system is installed in a five meter flume and is calibrated using video based particle tracking as well as manual sediment collection and sieving. Initial results indicate the new design performs significantly better than its predecessor.

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Building a global sediment database (2012)

Global patterns of soil loss are poorly understood. While recent research has explored the physical processes that drive soil erosion, through the study of sediment transport, few spatial analyses of these processes have been conducted. One major reason why the spatial element of sediment dynamics has not been studied is a lack of data: datasets are often expensive and difficult to obtain. To meet this need, this thesis proposes the construction of a Global Sediment Database, which will be freely available to all. The Database will be updatable, and will contain a detailed Data Quality Report so researchers can determine the most effective use of the data. The Data Quality Report will also quantitatively summarize the error and uncertainty of each dataset. This thesis will also demonstrate how the Database can be used to conduct spatial analyses of sediment processes using Geographic Information Systems (GIS). To this end, various spatial interpolation methods will be explored and evaluated, using the Yellow River as an example.

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The effects of discharge and slope on hyporheic flow in step-pool morphologies using cold water as a tracer (2012)

The hyporheic zone is a transitional area between surface and groundwater systems that supports both a wide range of species ranging from bacteria to incubating fish embryos. A better understanding of the movement and extent of flows through the subsurface may lead to innovative habitat restoration techniques to make streams more productive and to enhance aquatic stream biology. While the majority of studies thus far have examined the hyporheic zone in low gradient streams with pool-riffle and dune-like morphology, this study has investigated hyporheic flow in a steep stream with step-pool morphology. A series of flume experiments were conducted which examined the effect of discharge and slope on hyporheic flow in step-pool channels using cold water as a tracer. The channel consisted of 3 step-pool units with 64mm sized steps, discharges between 0.3-4.5L/s and slopes of 8% and 4%. The results indicated the water moving along steeper slopes and the moderate discharges produced the deepest flows while downwelling at the base of steps was related to the stream discharge. Results produced by a model using hydraulic head measurements were inconsistent of those produced by temperature sensors. The model suggested hyporheic downwelling flows are largely unaffected by discharge while increases in residence times are related to decreases in discharge. We found the temperature tracer to provide a more accurate representation of hyporheic flows than that derived from piezometric measurements though the former procedure would be difficult to replicate in field experiments. This experiment emphasizes the importance of topography and roughness elements along the channel surface in dictating the locations and magnitude of downwelling and hyporheic exchange.

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Downstream characteristics of in-stream wood in Wigwam Creek, Alberta (2011)

In this study I examined downstream patterns of wood characteristics and stand dynamics in a small basin in the Upper Foothills of Alberta. Fourteen study reaches were surveyed for wood size, orientation, position, origin and function, channel parameters including bankfull width, depth, slope and bed surface texture, and tree diameter, density and species composition of the adjacent riparian forest using the point centred quarter method. Based on geomorphic process domains, total stream power estimations and critical thresholds of change among wood attributes, I determined that wood movement began between 7-10km² drainage area. Upstream of this point wood had relatively little geomorphic function and decay was the main output process. Wood characteristics responded strongly to the downstream increase in transport capacity. Wood loads ceased to resemble adjacent forests near the colluvial-fluvial boundary as wood began to be affected by transport. Total wood load decreased, and wood orientation changed from perpendicular to parallel as transport capacity increased downstream. Decay classes 1, 2 and 5 were more abundant in transport-limited reaches while decay class 3 was more abundant downstream. Log positions within the channel varied with transport capacity, with fewer bridges and more loose and braced wood found downstream of the valley step. Partial bridges and anchored wood occurred in the same amounts throughout the stream network. Wood distribution changed from segregated in transport-limited reaches to aggregated in transporting reaches. Most logs had been dead for less than 40 years, but some had persisted for over 125 years in transport-limited reaches. The mean age of woody debris did not change downstream since riparian stands were similar along the stream network. These findings have implications for forest management and aquatic systems in the Upper Foothills region.

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Spatial patterns of large wood debris in the northern interior of British Columbia (2010)

Large woody debris (LWD) patterns were investigated in 18 streams in the Interior of British Columbia for a variety of stream sizes (1.4-13.7 m bankfull width flow) and forest types (SBS and SBPS BEC Zones). Definition and scaling type for LWD are variable in the published literature. This research reported that both the definition used to define LWD and the scaling technique used to analyze and display LWD affected the results in LWD abundance and volume measures. Although LWD varies by forest type and stream size, the effect of the riparian forest on LWD loading was minimal compared to the effect of stream size for the 18 study sites. Stream characteristics were such as bankfull flow width and depth were identified as predictor variables for LWD abundance and volume. The distribution of LWD was different in wood associated with LWD jams than wood free in the stream. The importance of LWD jams increased relatively with stream size. LWD jams (1) were larger, (2) had an increasingly different distribution of LWD size classes, and (3) had a different distribution of position and orientation classes than free wood with increases in stream size. The patterns observed in the distribution of LWD for orientation and position classes as well as piece size was consistent with the literature: (1) perpendicular wood generally decreased while parallel increased with stream size; (2) bridged wood decreased while wood fully in the bed increased and (3) piece size generally increased with stream size.

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