Brett Eaton

In British Columbia, culverts are designed to pass the 100-year clearwater flow for a givenstream. However, the design criteria does not account for the influence that entrained sedi ment will have on the flow characteristics. It is common in the British Columbia mountainousregions to experience sediment entrainment during flooding events which lead to the genera tion of debris flows. To account for the impact that entrained sediment and debris may haveon the culvert’s ability to pass the flow, BC guidelines vaguely suggest site visits or con sultations with professionals. For my thesis, I ran experiments to compare culvert efficacywhen experiencing clearwater flows as well as debris flows. Debris flows containing largegrains and large wood were run to compare the effects that different materials may have onthe impact a debris flow could have on a forest service road crossing. The experiments wererun using the Debris Flow Simulator in the UBC Ponderosa Laboratory. This study focuseson small, mountainous streams that cross forest service roads which are prone to culvertfailures but are not frequently monitored. Protoype streams were found in the ChilliwackRiver watershed that were 2.5-meters wide with a drainage area of 0.27 km2 and on slopesranging from 32%-45%. The results show that sediment entrainment led to a bulking factorof 1.5-2 and an event as small as a 5-10 year clearwater flow event can lead to the failureof a culvert system. Large grains did not significantly affect the flow characteristics or theimpact on the culvert system. The addition of large wood resulted in several culvert fail ure events due to the jamming that took place at the culvert inlet. These results will aidin understanding debris flow impacts and encourage appropriate culvert designs which willdecrease the amount of resources put into restoring damaged culvert crossings over time.

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Sediment pulses into gravel-bed rivers in mountainous basins, such as those found throughoutBC, Canada, can alter river systems. Pulses are generated through hillslope erosion,landslides, and debris flows. Human activity such as mining and logging can increase thefrequency and magnitude of these events. There is research regarding impacts of increasedstreamflow on urban river systems, however, there is relatively little research on the impactof increased sediment. Knowing how urban stream channels respond to sediment pulses canhelp guide stream management and restoration projects.Experiments were conducted using a generic physical model of a gravel bed streamat the University of British Columbia. Three physical model configurations were used: amodel of a channelized urban stream; a model of a channelized urban stream with a widenedcentral reach representing a restoration technique; and an urban stream with a widenedreach has been reenforced with a layer stabilizing grains on the floodplain surface. Two mainexperiments were conducted on each configuration, one where sediment was kept constantand a second where sediment pulses were introduced to the channel.Overall, sediment pulses into urban streams result in increased bed elevation andchannel flooding localized to the upstream area. The urban channelized stream was resilientto a 25% pulse, whilst widening a reach reduced sediment transport and was unable tocope with any sediment increase. This demonstrates that bank protection would need to beintroduced to prevent aggradation even at the background sediment supply rate. The use ofadditional bank protection increased the resilience of the restored channel to sediment pulsesby increasing sediment transport. However, this set up flooded at the 25% pulse. Even withmitigation, the fully channelized urban streams are most resilient to increases in sedimentsupply.

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In the mountainous regions of British Columbia, debris flows are common, resulting in massesof coarse sediment entering larger streams in upland valleys. Relatively wide valleys formdistinctive debris flow fans that partially fill the valley bottom. Where valleys are narrowerand the streams in the valley bottom are confined, debris flows interact with the main stemstream in more complicated ways.This thesis presents eight experiments documenting the interactions between steeptributaries capable of generating debris flows and the main stem streams into which thedebris flows enter. Using imagery that provides a 2D comparison model of the channel bedand video photography, experiments reveal the role of tributary sediment inputs (TSI) incontrolling the behavior of mainstem stream profiles and defining features. The first setof experiments focuses on the natural channel and morphology changes with no influenceof tributary sediment pulse events. The second set observes the change in morphologicalbehavior as a function of the tributary confluence angle. A third set focuses on how debrisflow sediment texture influences the effects of these pulses. The investigations consider theeffect of changing the angle of tributary and effects on geomorphology of the main channel.The experiment iterations considered entrance angles of 90°, 75°, 60° and 45°. The secondexperiment involved adding coarse sediment to the bed material used for TSI in the first set,representing boulders found in step pool streams. Boulders are common in most debris flowmaterials but most mainstem streams are typically incompetent in their transportation; thisexperiment investigates the degree to which sediment alters behaviour at the confluence.The 90° and 75° junction angles formed less stable stream blockages which erodedrapidly and had lower elevation. The 60° and 45° angles posed a greater threat to up anddownstream areas. These angles caused blockages with higher elevation and persistence.Their stability within streams meant their elevation grew following consistent debris flowactivity creating greater geohazard threats downstream. Boulders (large grains) in the debrisflows caused a larger magnitude of risk because of higher dam elevations and stream blockagesposing potential outburst flood occurrence.

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Alluvial fans form through primary and secondary processes. Primary processes act to transport sediment from the drainage basin to the fan and secondary processes re-mobilize and rework sediment previously deposited on the fan. There is still a poor understanding of how primary and secondary processes interact on alluvial fans. The primary objective of this research is to isolate the role of secondary processes in determining alluvial fan behaviour and morphology. Four experiments were conducted, in which alluvial fans were created under different durations of secondary processes. In these experiments secondary processes were run between each primary process, or flood period. The duration of secondary process periods ranged from 5 to 40 minutes across the four experiments. Here primary processes reflect inputs of Q = 100 ml/s and Qb = 10 g/s, and secondary processes reflect inputs of Q = 50 ml/s and Qb = 0 g/s, wherein Q refers to water discharge and Qb refers to sediment feed rate. For each experiment, alternating primary and secondary processes were run until a total of 72 kg of sediment had been added to the fan. Following this, a sequence of nine flood events was run over the fan surface to evaluate fan response to flooding. Experiments with longer durations of secondary processes generated fans with larger areas and gentler gradients. In addition, longer secondary process durations led to increased flow channelization and channel incision between flood periods. The dominant channel pattern throughout the experiments was the formation of a single, centralized channel during secondary process periods, and the bifurcation of flow following the onset of primary processes. The increased incision and flow confinement during prolonged periods of secondary processes resulted in a decreased avulsion frequency during subsequent flood periods. In addition, the onset of avulsion was delayed for experiments with longer secondary process duration. These results indicate that the duration of secondary processes has important effects on both fan morphology and flow behaviour.

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The demand for development near rivers, coupled with changes to the hydrologic regime have resulted in an increase in the frequency of high magnitude flooding events. These flooding events pose a threat to infrastructure. To protect infrastructure along channels, traditional bank protection is installed. These structures prevent natural scour and limit bank migration, which can impair ecosystem function. As an alternative to traditional approaches, we propose a new approach to bank protection. Instead of aiming to control channel shape and form, bank protection should work with the processes that govern channel stability. Recent research has shown that the coarse-tail of a channel’s grain size distribution has surprisingly strong affects on a channel’s stability. This thesis aims to capitalize on this finding, by incorporating the coarsest grains on a channel's bed into a bank protection technique. We call this bank protection technique ‘Stability Seeding’. Stability Seeding consists of placing coarse grains onto a channel's banks. When the channel widens, these grains fall into the bed and promote channel stability. To assess the feasibility of using Stability Seeding as bank protection, proof-of-concept experiments were run using scaled physical models. Three experiments were run; the first used Stability Seeding, the second used Riprap as a traditional method of bank protection, the third experiment was composed of a natural channel without any bank protection. It was found that Stability Seeding dampens bank migration, while still allowing a small amount of natural channel adjustment. As a result, using Stability Seeding requires a larger minimum setback distance than traditional bank protection. However, as Stability Seeding allows for some level of bank migration, it results in less vertical degradation than Riprap. Therefore, Stability Seeding could lessen the chance of buried infrastructure being exposed compared to traditional bank protection techniques. In addition, Stability Seeding allows more morphological variation than traditional bank protection. This variation could allow a reach protected by Stability Seeding to be more ecologically productive than reaches protected by traditional bank protection. The findings of this thesis provide the basis for using Stability Seeding as an alternative to traditional bank protection.

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The Waiho River in Westland, New Zealand has been rapidly aggrading its bed as a result of lateral confinement by a stopbank network which restricts the river to 30% of its natural fan accommodation space. The ongoing aggradation has prompted the need to repeatedly raise the crest level of the stopbanks. This had led to the bed and stopbank elevation reaching unpreceded and dangerously high levels, putting the surrounding land, infrastructure and Franz Josef community at even greater risk than before should the stopbanks fail. This thesis investigates an alternative solution to the current management practice. Using a microscale model it tests the response of an experimental Waiho River and fan to the removal of the Southern stopbank and replacement with two alternatives which allow the river greater access to its Southern fan surface. In addition, the study allowed for an exploration of several microscale modelling techniques. The results found that an experimental fan in a state of dynamic equilibrium would not aggrade when confined as previously thought. Only when the fan was already aggrading did it continue to aggrade when confined. In this instance, when the confinement was removed it did not result in degradation to lower elevations. Aggradation continued, albeit at a reduced rate. This suggests that the Waiho was already in a state of aggradation prior to human interference, and that confinement exacerbated the rate. This result has implications for the future management of the Waiho. If the current aggradation trend is to continue, then increasing stopbank crest height is not a viable solution, however releasing the river to the South will reduce the rate of aggradation as well as the pressures on the Northern stopbanks which protect the Franz Josef township. Effectively, this buys time for more drastic action (i.e. relocation of the township) to be taken. In addition to these results, the experiments found that measurement tools and model materials used previously in other microscale models produced unreliable fan behaviour and results. That they have failed in this study, motivates the need for further investigation into the underlying principles of microscale modelling and its practice.

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This thesis presents the results of ten experiments conducted to examine the role grain size distributions play in the behaviour and evolution of one dimensional alluvial fans using a novel flume setup. The two grain size distributions share the same median grain size (D₅₀ = 1.42 mm), one (GSD₁) is composed of log normally distributed material from 0.25 to 5.6 mm and the other (GSD₂) is only composed of two classes: 1.4 and 2.0 mm. Images of the deposit profile and surface were used to monitor the evolution of the deposit and allow for the quantitative and qualitative assessment of behaviour, respectively. A detailed comparison of the aggrading phase of one run condition (Q = 0.1 l/s, Qb = 1 g/s) demonstrates a difference in the morphology that must originate from the grain size distribution. The addition of coarser grains in GSD₁ creates patches of immobility and allows the formation of bars more resistant to flow than in GSD₂. This reduction in transport efficiency of the material results in a higher slope and more stable bed configuration for GSD₁. More widely, this pair of experiments shows that differences in mobility may still manifest in aggrading environments. For all five pairs of experiments this difference is present. Overall, GSD₁ exhibits more stable behaviour: lower transport rates, higher slopes and later transport than GSD₂. However, the difference between the two grain size distributions decreases as discharge increases. That is, the difference is most pronounced at the lowest discharge where grains are less mobile due to the lower maximum stress and lower frequency of it occurring. This reduced mobility is due to a threshold of entrainment present in GSD₁ that is less commonly exceeded at low discharges, but that is not present to the same extent in GSD₂. Therefore, the proportion of immobile grains controls the behaviour and stability of an aggrading channel.

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Considerable effort has been dedicated to restoring sturgeon habitat within dammed rivers. However, sedimentation causes long-term failure because interstitial voids provide critical habitat during early life-stages. Based on the premise that a better understanding of geomorphic processes will improve restoration design, this study characterizes flow and sediment transport dynamics through a white sturgeon spawning reach on the Nechako River, BC.An extensive dataset was collected throughout the 2015 flood. Bedload transport was sampled on 36 days with flows ranging from 44 m³/s to 656 m³/s. During a high flow of 525 m³/s, channel bathymetry and water surface elevation were surveyed and velocity profiles were collected across 9 transects. Banklines, bars and island topography were later surveyed during low flow.Sediment transport into the reach was positively related with discharge. This relation was non-linear and transport rates increased rapidly once flows exceeded 400 m³/s. The relation weakened with downstream distance and sediment transport peaked progressively later throughout the year. No relation was observed at the downstream end of the reach, where transport rates remained low and constant relative to upstream.Sediment was primarily transported through secondary channels conveying a disproportionate amount of sediment compared to flow. Within the single-thread channel, the locations conveying the greatest amount of sediment remained spatially consistent over time.Hydrodynamic modelling indicates the Burrard Ave. Bridge causes backwatering once discharge exceed 225-275 m³/s. Velocity, shear stress and transport capacity at the downstream end of the reach do not increase with discharge because of the backwatering and the expansion in channel width through the island complex. The locations of maximum shear stress and transport capacity shift upstream with increasing discharge, but shear stress does not exceed 23 N/m² for flows up to 775 m³/s.The fluvial dynamics within the spawning reach create challenges and opportunities for habitat restoration. Backwatering is problematic because it causes mid-reach deposition during high flows and limits shear stress magnitude over the downstream spawning substrate. Meanwhile, the presence of sediment transport pathways through secondary channels and within the mainstem can be used to site restoration projects in areas apt to maintain suitable habitat.

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This study examines the short-term physical habitat conditions at four sites on the Kananaskis River, Alberta, where a hydropeaking dam was installed in 1955. This dam imposes both the approximate pre-dam minimum flow, and the pre-dam flood (from a small flood year) on a daily basis. The purpose of this study was to examine the extent of daily changes in physical habitat conditions that organisms in the stream would have to endure, and the extent to which these fluctuations might be reduced downstream due to distance from the dam and unregulated tributary influence. Physical habitat conditions monitored over low flow and high flow dam releases were: velocity; depth; bed mobility; ramping rates; and total suspended solids. River2D was used to calculate weighted usable area and potential habitat for Brown Trout (fry, juveniles and adults) and Mountain Whitefish (fry, juveniles and adults) at the low and high flow conditions. Of the factors examined, only ramping rates and total suspended solids showed signs of downstream attenuation. Differences in depth, velocity, weighted usable area, and potential habitat between low flow and high flow dam releases were variable, and showed no downstream pattern. Between low and high flow releases, significant (p = 0.05) changes in depth were observed at all sites, and significant changes (p = 0.05) in velocity were observed at all but the second site. The second site also saw the smallest changes in measures of habitat between low flow and high flow dam releases; however, all other sites saw median differences of 48.1% to 170.9%. Percent differences in habitat between low and high flow dam releases ranged from 2.6% (second downstream site, juvenile Brown Trout) to 193.3% (third downstream site, adult Mountain Whitefish). These habitat changes happen more often than before the dam was installed (many times weekly vs. about once a year during the spring freshet) and they occur more rapidly. Because these changes happen at times of the year that are out of synchronization with the biota of the river, and as these changes are extreme, this implies challenging physical habitat conditions for indigenous stream biota.

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Within this thesis the results of a set of four stream table experiments are presented in order to examine the role that bed texture adjustments play in the development of a equilibrium channel form in the presence of large wood. Experiments were conducted using two physical models of Fishtrap Creek, an intermediate sized stream in the interior of British Columbia. While both flumes were Froude-scaled models with fixed banks and mobile beds, Model 1 contained a single grain size representative of the D₅₀ of the prototype stream while Model 2 contained a scaled grain size distribution (GSD) of Fishtrap Creek. Two treatments of wood load were run in each model: a moderate wood load (a scale equivalent of 160 m³/m²) and a high wood load (a scale equivalent of 220 m³/m²). Channel morphology was captured at five-hour intervals in order to create DEMs of the evolving bed surface. The results of this study show that bed grain size composition plays a dominant role in shaping channel morphology, even in the presence of large wood. The addition of large wood increased sediment storage which resulted in an increase in reach-averaged bed slope, the magnitude of which was proportional to the wood load added. Large wood also caused new areas of scour and deposition to be imposed onto the channel morphology that had been established prior to the addition of wood, causing an overall decrease in pool spacing and median pool area. The presence of a grain size distribution constrained the range of depth values in the flume as it allowed the bed to self-stabilize by limiting scour depth through the process of armouring. Regardless of the presence of large wood, maximum depths were approximately twice as deep in the single grain size flume and pools were deeper relative to their area. These results highlight the necessity of considering the full grain size distribution when modelling channel response to changes in the governing variables that influence channel morphology.

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Empirical hydraulic distribution equations have been proposed as simple and inexpensive alternatives to traditional data-intensive flow assessment methodologies. Two proposed depth and three proposed velocity empirical equations were compared to measured hdraulic distributions for two channels in the Interior Region of British Columbia. Empirical velocity distributions adequately reproduced the measured velocity distribution for both channels. An empirical depth distribution was able to replicate measured depth distributions at a relatively undisturbed channel (Harris Creek) but were unable to predict the measured depth distribution following morphological change at a channel recently disturbed by forest fire (Fishtrap Creek). Furthermore, the empirical distributions were compared to modelled depth and velocity distributions produced by a 2-dimensional hydrodynamic model (River2D). The empirical distributions provided reasonable representation of the hydraulic distributions for flows
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The Pocaterra dam on the Kananaskis River provides a unique opportunity to assess dam induced changes in channel morphology because it has caused reduction in the magnitude of high flows and creation of daily peaking flows with no associated alteration in sediment supply. We assessed reach scale morphological change of the Kananaskis as a result of the hydropeaking flow regime considering change in geometry, planform, vegetation, and pool characteristics and distribution. Pre and post-dam channel conditions were assessed through historical photos, field measurements, remote sensing techniques and modeling. The channel just downstream of the dam widened, the middle six sites show no statistical change, and the most downstream three sites showed statistically significant narrowing. Further changes included a shift towards fewer active channels, abandonment of back channels, increase in density of riparian vegetation, and low diversity of successional stages within the riparian forests. A rational regime model reasonably predicted width adjustment and shift in number of active channels. We also found depth distributions to differ from statistical distributions in the most upstream sites with a higher proportion of low depths while the most downstream site matched the statistical distributions. Pool characteristics were associated with local attributes with large pools formed near large wood and back channels and numerous smaller free forming pools. The hydropeaking signal appears to drive channel change in the upper reaches where the models did not correspond to observed channel characteristics while the reduction in peak flows appears to drive channel morphology in the more downstream reaches. The interactions of the hydropeaking flows with winter ice dynamics also appear to control channel change in this system and contribute to the unique morphology. Channel change is likely associated with decrease in the quality and quantity of suitable fish habitat and thus may have driven declines in fish diversity along this river. Despite the complexity of this system, these modeling and remote sensing methods simply and accurately characterize changes on the Kananaskis and thus provide a useful and rapid method to assess morphological change in a disturbed system.

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The primary objective of this research is to investigate the relationship between wood load and reach-scale morphodynamics using a model system. Previous re- search has shown that large wood significantly impacts channel dynamics, espe- cially in small and intermediate sized forested streams where wood pieces are similar in length to channel width. Five experiments, each comprised of several five hour runs, were conducted using a stream table with wood loads scaled to 0 m³/m², 0.011 m³/m², 0.016 m³/m², 0.022 m³/m², and 0.028 m³/m². The addition of large wood significantly increased the flow resistance and decreased the reach-averaged velocity in all experiments. These hydraulic changes were associated with decreased sediment transport and increased sediment storage within the reach. Over time, increases in bed and water surface slope compensated for the loss of potential energy to flow resistance and enabled the system to reach a new steady state. The heterogeneity in the spatial distribution of the hydraulic changes – with flow velocity and shear stress decreasing upstream of obstructions and increasing downstream of log steps – increased the facies complexity and pool frequency in the reach at the new steady state, and thereby increased habitat complexity. These results show that wood load is a primary control on channel morphodynamics and the availability of aquatic habitat in intermediate sized streams.

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In August 2003, a wildfire burned through Fishtrap Creek Watershed north of Kamloops British Columbia. This high intensity fire killed almost all the trees within the burned area, including 90% of the riparian vegetation in the vicinity of our study site. The fire did not significantly alter the duration or magnitude of the peak flows within this creek, nor did it have substantial effects on the total suspended sediment concentrations. Changes in channel morphology during the first two years after the fire were minor. The first evidence of morphologic adjustment occurred in 2006 when the channel began to widen and develop very distinct channel bars - adopting a characteristically riffle pool morphology by the end of the 2006 freshet. The most dramatic channel reconfiguration occurred during the 2007 freshet, when the channel widened by as much as 15 m in places. Approximately 82% of the total volume of large wood (LW) recruited to the channel following the fire entered the channel as a result of bank erosion, and the majority of the bank erosion occurred during the 2007 flood season. The post-fire wood load in Fishtrap Creek is slightly higher than other disturbed systems, but is comparable to wood load in undisturbed rivers. LW has had significant influence on channel morphology and bed surface texture distribution. The number of LW pieces of wood in the channel is related to the channel morphology, and 80% of the pools are a result of LW. Most of the post-fire wood is suspended above the channel bed and is not currently functioning in the channel as effectively as pre-fire wood. Estimates of net erosion and deposition were made based on Digital Elevation Models (DEMs) and cross-sections located at regular intervals: a comparison of the two methods shows that cross-sectional analysis results in biased estimates of net erosion and deposition in various, identifiable circumstances, while revealing the same general pattern of channel change within the study reach.

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