Arts, Faculty of
Geography, Department of
DSpace
UBCV
McIntyre, Amy
Master of Science - MSc
University of British Columbia
Sediment pulses into gravel-bed rivers in mountainous basins, such as those found throughout BC, Canada, can alter river systems. Pulses are generated through hillslope erosion, landslides, and debris flows. Human activity such as mining and logging can increase the frequency and magnitude of these events. There is research regarding impacts of increased streamflow on urban river systems, however, there is relatively little research on the impact of increased sediment. Knowing how urban stream channels respond to sediment pulses can help guide stream management and restoration projects. Experiments were conducted using a generic physical model of a gravel bed stream at the University of British Columbia. Three physical model configurations were used: a model of a channelized urban stream; a model of a channelized urban stream with a widened central reach representing a restoration technique; and an urban stream with a widened reach has been reenforced with a layer stabilizing grains on the floodplain surface. Two main experiments were conducted on each configuration, one where sediment was kept constant and a second where sediment pulses were introduced to the channel. Overall, sediment pulses into urban streams result in increased bed elevation and channel flooding localized to the upstream area. The urban channelized stream was resilient to a 25% pulse, whilst widening a reach reduced sediment transport and was unable to cope with any sediment increase. This demonstrates that bank protection would need to be introduced to prevent aggradation even at the background sediment supply rate. The use of additional bank protection increased the resilience of the restored channel to sediment pulses by increasing sediment transport. However, this set up flooded at the 25% pulse. Even with mitigation, the fully channelized urban streams are most resilient to increases in sediment supply.
Sediment transport and storage in urbanstreamsbyAmy McIntyreB.Sc. Geography, University of York, UK, 2020A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THEREQUIREMENTS FOR THE DEGREE OFMaster of ScienceinTHE FACULTY OF GRADUATE AND POSTDOCTORAL STUDIES(Geography)THE UNIVERSITY OF BRITISH COLUMBIA(Vancouver)August 2023© Amy McIntyre, 2023The following individuals certify that they have read, and recommend to the Faculty of Graduate andPostdoctoral Studies for acceptance, the thesis entitled:Sediment transport and storage in urban streamssubmitted by Amy McIntyre in partial fulfillment of the requirements forthe degree of Master of Sciencein GeographyExamining Committee:Brett Eaton, Professor, Geography, UBCSupervisorIan McKendry, Professor, Geography, UBCSupervisory Committee MemberLucy MacKenzie, Water Resources Scientist, BGC EngineeringAdditional ExamineriiAbstractSediment pulses into gravel-bed rivers in mountainous basins, such as those found through-out BC, 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.iiiLay SummaryIn gravel bed rivers, such as those found throughout British Columbia, sediment pulses fromhillslope erosion and debris flows can alter the channel. Human activity through mining andlogging can increase the likelihood of these events. There is little research on the impact ofsediment pulses on urban stream channels. Understaning how urban channels respond tothese events can help aid restoration projects and mitigation strategies.ivPrefaceThis thesis is based on experiments designed by Brett Eaton and Amy McIntyre, and con-ducted by Amy McIntyre. All writing and analysis presented in this thesis was completedby Amy McIntyre.vTable of ContentsAbstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iiiLay Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ivPreface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vTable of Contents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . viList of Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . viiList of Figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . viiiAcknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xDedication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xi1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.1 Urban Streams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.2 Restoration of Urban Streams . . . . . . . . . . . . . . . . . . . . . . . . . . . 21.3 Room for the River Approach . . . . . . . . . . . . . . . . . . . . . . . . . . . 31.4 Sediment Delivery in Gravel Bed Streams . . . . . . . . . . . . . . . . . . . . 41.5 Future of Rivers in a Changing Climate . . . . . . . . . . . . . . . . . . . . . 51.6 Aims and Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61.7 Thesis organisation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72 Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82.1 Experimental Set Up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82.2 Sediment Feed Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112.2.1 Constant Sediment Feed . . . . . . . . . . . . . . . . . . . . . . . . . . 112.2.2 Sediment Pulse Experiments . . . . . . . . . . . . . . . . . . . . . . . . 112.3 Experimental Designs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132.3.1 Urban Stream . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142.3.2 Restored Stream . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152.3.3 Restored Stream with Bank Protection . . . . . . . . . . . . . . . . . . 162.4 Data Collection and Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . 172.4.1 Digital Elevation Models . . . . . . . . . . . . . . . . . . . . . . . . . . 172.4.2 Bed Elevation Profiles . . . . . . . . . . . . . . . . . . . . . . . . . . . . 172.4.3 Channel Complexity Analysis . . . . . . . . . . . . . . . . . . . . . . . 173 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183.1 Channelized Stream Channel . . . . . . . . . . . . . . . . . . . . . . . . . . . 183.1.1 Constant Sediment Feed . . . . . . . . . . . . . . . . . . . . . . . . . . 183.1.2 Impact of Sediment Pulses . . . . . . . . . . . . . . . . . . . . . . . . . 203.2 Restored Stream Channel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 233.2.1 Constant Sediment Feed vs Recirculating Sediment . . . . . . . . . . . . 233.2.2 Impact of Sediment Pulses . . . . . . . . . . . . . . . . . . . . . . . . . 263.3 Restored Stream with Bank Protection . . . . . . . . . . . . . . . . . . . . . . 28vi3.3.1 Constant Sediment Feed . . . . . . . . . . . . . . . . . . . . . . . . . . 283.3.2 Impact of Sediment Pulses . . . . . . . . . . . . . . . . . . . . . . . . . 313.4 Comparison of Techniques for Urban Stream Management . . . . . . . . . . . 333.4.1 Resilience to Sediment Pulses . . . . . . . . . . . . . . . . . . . . . . . . 333.4.2 Channel Complexity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 333.5 Results Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 364 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 384.1 Sediment Transport in Restored Reaches . . . . . . . . . . . . . . . . . . . . . 384.2 Response to Sediment Pulses . . . . . . . . . . . . . . . . . . . . . . . . . . . 394.3 Geomorphic River Engineering Technique . . . . . . . . . . . . . . . . . . . . 424.4 Implications for Restoration . . . . . . . . . . . . . . . . . . . . . . . . . . . . 425 Concluding remarks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47Appendices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53Appendix A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53DEMs of difference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53Appendix B . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56Sediment Output Rates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56viiList of Tables2.1 Grain Size distribution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102.2 Experiments Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132.3 Sediment input used during experiments. Pulse values based on a percentageincrease on Experiment 1b constant feed . . . . . . . . . . . . . . . . . . . 133.1 Results Summary for Constant Feed Experiments . . . . . . . . . . . . . . 373.2 Results Summary for Sediment Pulse Experiments . . . . . . . . . . . . . . 37viiiList of Figures2.1 Components of the Stream table in the Ponderosa Fluvial Lab at the Uni-versity of British Columbia. A shows the sediment conveyor belt used toinput sediment. B is the sediment trap at the downstream end of the streamtable and C shows the mobile cart with cameras. . . . . . . . . . . . . . . . 92.2 Grain size distribution of the bed material . . . . . . . . . . . . . . . . . . 102.3 Sediment feed conditions for sediment pulse experiments. Blue areas showtime where flow was running, whilst black indicates times flow was stoppedto allow for surveying of the bed . . . . . . . . . . . . . . . . . . . . . . . . 122.4 Examples of channel flooding during Exp 1c. A shows water flooding ontothe channel banks whilst flow is running. B shows sediment deposited onbricks when the bed is drained . . . . . . . . . . . . . . . . . . . . . . . . . 122.5 Urban stream channel design . . . . . . . . . . . . . . . . . . . . . . . . . . 142.6 Restored stream channel design . . . . . . . . . . . . . . . . . . . . . . . . 152.7 Restored stream channel with GRE stablization technique . . . . . . . . . . 163.1 Stream table sediment output for the Urban Channel design using a recir-culating feed (Booker, 2018) and constant feed (Experiment 1b) . . . . . . 193.2 Graph showing bed elevation of the stream table during Experiment 1b . . 193.3 Digital Elevation model showing Experiment 1b after a run time of 8 hours.Colours correspond to bed elevation in metres. . . . . . . . . . . . . . . . . 203.4 Digital Elevation Models of Experiment 1c showing the response to sedimentpulses. Colours correspond to bed elevation in metres. . . . . . . . . . . . . 223.5 Bed elevation for sediment pulses in the urban stream channel (Exp 1c) . . 233.6 Stream table sediment output from Exp 2a and 2b . . . . . . . . . . . . . . 253.7 Bed elevation of the stream table after a run time of 8 hours for Experiment2a and 2b . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 253.8 Digital Elevation model from Exp 2a and 2b after a run time of 8 hours.Colours correspond to bed elevation in metres. . . . . . . . . . . . . . . . . 263.9 Digital Elevation Models of Experiment 2c showing the response to sedimentpulses. Colours correspond to bed elevation in metres . . . . . . . . . . . . 273.10 Bed elevation profile for sediment pulses during Experiment 2c . . . . . . . 283.11 Graph showing bed elevation profile for Experiment 3b . . . . . . . . . . . 293.12 DEMs for Experiment 3b. Colours correspond to bed elevation in metres. . 303.13 Graph showing bed elevation profile for Experiment 3c . . . . . . . . . . . . 313.14 DEMs for Experiment 3c showing the response of the channel to sedimentpulses. Colours correspond to bed elevation in metres. . . . . . . . . . . . . 323.15 DEMs for the active channel within the central 4 m of the stream table forthe urban stream, restored stream and stablity seeding expeirments. DEMsshown are shown after a run time of 8 hours at constant feed. The central 4mrepresent the location of a floodplain in the restored stream, and stabilisinggrains for the stability seeding set up. Flow is shown from left to right, andthe coloured bar represents the bed elevation of the channel. Distributions ofthe bed elevations for each experiment are shown in the histograms. A solidblack line represents the median value, whilst the 16th and 84th percentilesare shown through dashed lines. . . . . . . . . . . . . . . . . . . . . . . . . 354.1 Bed elevation profiles for Experiment 1b, 2b and 3b after a run time of 8 hours 39ix4.2 Digital Elevation models for Exp 1c, 2c and 3c, after flooding has occurred 41A2.1 DODs for Experiment 1b, 2b and 3b, comparing the use of a constant sed-iment feed. DODs show the changes in elevation at Hour 8 compared toHour 1, with red area showing increased elevation whilst blue areas show adecrease in elevation. The alternate red and blue areas seen in the DOD forExp 1b are indicative of riffle-pool morphology . . . . . . . . . . . . . . . . 53A2.2 DODs for Experiment 1c, showing changes in bed elevation for different sizedsediment pulses. DODs show the changes in elevation after the sedimentpulse compared to before, with red area showing increased elevation whilstblue areas show a decrease in elevation . . . . . . . . . . . . . . . . . . . . 54A2.3 DODs for Experiment 2c, showing changes in bed elevation for different sizedsediment pulses. DODs show the changes in elevation after the sedimentpulse compared to before, with red area showing increased elevation whilstblue areas show a decrease in elevation . . . . . . . . . . . . . . . . . . . . 55A2.4 DODs for Experiment 3c, showing changes in bed elevation for different sizedsediment pulses. DODs show the changes in elevation after the sedimentpulse compared to before, with red area showing increased elevation whilstblue areas show a decrease in elevation . . . . . . . . . . . . . . . . . . . . 55A3.1 Stream table sediment output rate for Experiment 1c . . . . . . . . . . . . 56A3.2 Stream table sediment output rate for Experiment 2c . . . . . . . . . . . . 57A3.3 Stream table sediment output rate for Experiment 3c . . . . . . . . . . . . 58A3.4 Stream table sediment output rate for Experiment 1b, 2b and 3b . . . . . . 59xAcknowledgementsThanks must firstly go to my supervisor Dr Brett Eaton. He has been an inspiring mentorand I am incredibly grateful for his expertise and advice over the course of my degree. Thankyou to Kabir Rasouli for his guidance on my thesis proposal and experiments as part of mycommittee before moving on from UBC. Wishing him the very best in the next steps of hiscareer. Thanks must also be given to Ian McKendry for agreeing to step into the role ofcommittee member at such short notice.This thesis wouldn’t have been completed without the support from my lab group; inparticular Will and Dave for their impressive knowledge of the stream table and answering themillion questions I had about working in the lab. Thankyou to the rest of my cohort withinthe Geography department for the last two years as well as the fantastic Earthballers softballteam for providing much needed breaks from thesis writing. Particular thanks must got toEmma, Billy and Holly whose support has been constant throughout. From lunch breaks inthe department to some questionable hiking adventures; they have been the highlight of mypostgraduate studies and I am so proud of all their achievements so far. Also, thank you toall my friends outside of UBC both at home and in Canada for their unwavering supporteven when most of the time they have no idea what I research.And lastly I must thank my family for their never ending encouragement. No matterthe challenges I have faced they have always been there for me and I could not have completedthis without them.xiDedicationThis thesis is dedicated to everyone who helped to pick blue grains out of the stream table.xiiChapter 1Introduction1.1 Urban StreamsMany urban centers have developed around rivers due to the resources they provide. There-fore many rivers have been altered in a variety of ways, notably disconnecting rivers and flood-plains, channelization and pollution (Everard & Moggridge, 2012). Design and constructionof artificial waterways has been practised since the earliest civilizations, with human alter-ations having been found as early as 3200BC (Copeland et al., 2001). Channelization is oneof the main ways that humans have altered river systems and is defined as the modificationof river channels for the purpose of flood control, land drainage, navigation, and preventionof erosion (Keller, 1978). Additionally, channelization was implemented to expand traderoutes, improve irrigation, and allow for the exploitation of floodplains for agriculture anddevelopment (Copeland et al., 2001). Channelization usually involves the straightening ofa river and placing it in an artificial channel. There are a variety of methods, includingrealignment, which uses artificial cut-offs for meanders to shorten river channels and divertflood flows through urban areas, and bank protection to protect against abrasion (Nunnally& Keller, 1979). One of the main aims of these alterations it to reduce flooding in areas ofurbanized floodplains to maximize efficiency of water transport through an area (Copelandet al., 2001).There are a variety of documented impacts of channelization on river systems, al-though the degree of change is highly dependent on the degree of channelization (Keller,1978). Channelization alters channel morphology which is detrimental to ecosystems andhabitats (Brookes, 1987). Channelization results in a loss of riffle and pool sequences, as wellas removal of natural bars and sorting of bed load, which removes habitats for fish speciesand contributes to a reduction in biodiversity (Bray & Cullen, 1976). Studies have shownthat channelization results in a reduction in fish density due to loss of habitat and changes tosediment (Pilcher et al., 2004). Additionally, there are impacts for channel stability and dy-namics, with a study by Van Niekerk et al. (1995) finding increased channel depth, channel1instability and incision (Brookes, 1987). Confinement of a stream results in deeper channeland higher shear stress, combined with straightening resulting in a steeper channel gradient(Brookes, 1987). This increases the rate of sediment transport through and area (Bray &Cullen, 1976; Brookes, 1987). This can cause morphological adjustments to a downstreamnatural or widened river channel where sediment transport capacity is lower (Bray & Cullen,1976 ; Brookes, 1987). Attitudes and management strategies are now beginning to shift asthe negative impacts of channelization and the desire for natural flood protection grows.1.2 Restoration of Urban StreamsRiver restoration is defined as a variety of modifications with the aim of improving hydrologic,geomorphic, and ecological processes in degraded watersheds (Pardo et al., 2012; Wohl etal., 2005). River restoration has accelerated in the past three decades, notably in NorthAmerica and Europe and is now conducted on a variety of settings from headwater streamsto urban areas (Wohl et al., 2015). There are a variety of methods including dam removal,reversal of channelisation and floodplain reconnection (Wohl et al., 2015).Throughout the 20th century, river management in Europe and North America wasfocused on solving issues such as flooding and water scarcity, leading to widespread infras-tructural developments within river systems (M. F. Johnson et al., 2020). Restoration ofriver systems emerged in the latter half of the 20th Century with the aim to reverse pasttrends in river degradation (M. F. Johnson et al., 2020). Initially, restoration focused onaltering channel form and fish habitat creation, mostly for recreation purposes, althoughflood control remained the main objective (Wohl et al., 2015). After the 1970s, many coun-tries began restoration to improve water quality, for example Canada implemented theirWater Act in 1970 (Geist & Hawkins, 2016; Wohl et al., 2015). Many restoration projectshaven’t delivered the hydrological, ecological, and morphological benefits expected (Geist& Hawkins (2016)). This is due to a reliance on reconstructing stable channels that mimicnatural forms (Geist & Hawkins, 2016). Auerswald et al. (2019) affirm this by concludingthat these river management aims failed to reverse declining trends in river systems andcould amplify river hazards like flooding. In the 21st Century process-based restoration hasincreased to prioritize river function and processes, rather than just river form (Bernhardt& Palmer, 2007; McDonald et al., 2004). Examples include promoting channel-floodplainconnectivity and allowing lateral flow (Wohl et al., 2015). Process-based restoration aimsto re-establish normal rates and magnitude of physical, chemical, and biological processesthat sustain river and floodplain ecosystems, and correct human adjustments (T. Beechie etal., 2013). This form of restoration removed human adjustments, allowing rivers to respondthrough physical adjustments (T. J. Beechie et al., 2010; McDonald et al., 2004).2Restoration of human-adjusted river channels is critical to reverse tong-term trendsof deterioration in the river environments and the negative impacts of channelization (Geist& Hawkins, 2016; M. F. Johnson et al., 2020). Free-flowing rivers help support diverseecosystems, and provide ecosystem services such as fishing (M. F. Johnson et al., 2020).Re-naturalization can recreate suitable habitats for plant and fish species, helping improvethe ecological status of rivers (Brookes, 1987). In addition, natural channels have moremorphological variability and aesthetic quality (Brookes, 1987).However, a major issue with river restoration is what is the pre-disturbance referenceconditions for restoration (Woelfle-Erskine et al., 2012). Many rivers have been altered formany decades or even centuries, meaning it is difficult to determine what the natural riverchannel should look like. Other challenges include sediment dynamics and anthropogenicclimate change (Wohl et al., 2015). It is often only possible to restore sections of a riversystem, due to land-use constraints and infrastructure. This raises questions for the inter-action between channelized reaches upstream and restored areas, highlighting the need for abalance between process-based restoration and channel stability for land use (T. J. Beechieet al., 2010).1.3 Room for the River ApproachDesire for restoration and alternatives to hard engineering to combat risks of flooding andclimate channel increased interest in the ‘room for the river’ approach, pioneered by theNetherlands (Rijke et al., 2012a). In response to severe flooding in the 1990s, Netherlandsadopted the Room for the River Programme in 2007 with the goal of reducing flood risk andimprove environmental quality (Rijke et al., 2012a). There are currently over 30 projectsin the Netherlands restoring natural floodplains and relocating levees to allow the river toflood safely away from infrastructure (Buuren et al., 2012; Rijke et al., 2012a). The general‘room for the river’ approach focuses on river widening to allow increased channel movement,particularly in urban areas where rivers have been spatially limited (Buuren et al., 2012; Klijnet al., 2013). This is done by removing channel constrictions such as concrete channels andflumes, in order to restore fluvial processes and re-establish natural riparian communities(Buuren et al., 2012; Rijke et al., 2012b). There is increased interest in this approach dueto proposed benefits for natural flood management and river restoration. Active channelwidening has already been shown to aid morphological recovery of degraded alpine gravel-bed rivers (Brousse et al., 2021). Studies have shown the channel widening can increase theabundance and biomass of species, as well as the diversity of macroinvertebrates (Kail et al.,2015). Several projects have already been completed or are planned within BC. Examplesinclude Still Creek in Vancouver, where a concrete flume has been removed and restored the3river to a more natural habitat (Munro & Schwark, 2018; Parsons, 2015). Work is currentlyongoing within Volunteer and Tatlow Park to daylight an area of stream and widen it (Jin,2016).1.4 Sediment Delivery in Gravel Bed StreamsRivers are shaped by processes acting upon them and channel morphology is a result of thesediment supplied to the river and the stream flows available to transport it (Hoffman &Gabet, 2007). In mountainous gravel bed rivers, sediment delivery is sporadic and largelyepisodic, mostly generated through hillslope erosion, although the largest sediment pules aretypically generated through landslides or debris flows (Hoffman & Gabet, 2007; Schumm,1985). Anthropogenic factors such as mining, infrastructure building and logging, can in-crease the magnitude of these events (Madej & Ozaki, 1996). Sediment pulses can signifi-cantly alter and affect river systems, dependent on their magnitude and duration (Griffiths,1979). However, entirely urbanized watersheds are unlikely to experience large inputs ofsediment into channels due to the disconnect between river channels and surrounding land-scape. Previous research found that large sediment pulses into stream channels resulted inchannel aggradation and widening, as well as braiding and fining of rock material (Griffiths,1979; Madej & Ozaki, 1996; Miller & Benda, 2000).Flume experiments by Cui et al. (2003) showed that in alternate bar mountainousriver channels, sediment pulses decreased the bed relief and there was floodplain aggradation.However, relief increased again after the sediment pulse has moved through an area (Cuiet al., 2003). This study also found that an increase in slope at the downstream end of asediment pulse temporarily increased sediment capacity of the river system due to an increasein tractive force, whilst large pulses of fine sediment into artificial channels increased sedimenttransport rate (Cui et al., 2003). Results found in these flume experiments are reinforcedby Sutherland et al. (2002), Lisle et al. (1997) and P. R. Wilcock (1998) who all foundsimilar responses by river channels to sediment pulses. For a river channel to maintain itsstability and morphological integrity the disturbance caused by a sediment pulse must berectified (Benda & Dunne, 1997; Cui et al., 2003). Sediment pulses move through riversystems by some combination of translation and dispersion of the initial sediment pulse (Cuiet al., 2003). Dispersion is where the impact to the stream channel is local to the pointof sediment input, and diffuses downstream over time (Cui et al., 2003; Hoffman & Gabet,2007). Translation results in bed degradation at the point of sediment input due to increaseserosion and transport rates, whilst causing bed aggradation further downstream (Cui et al.,2003; Roberts & Church, 1986). Both field-based studies, such as a study by Roberts &Church (1986) and a numerical model used by Benda & Dunne (1997) have shown that4translation is the main mechanism for the movement of sediment pulses downstream, withdispersion playing a supporting role (Benda & Dunne, 1997; Roberts & Church, 1986)).Gravel-bed rivers in Canada, particularly those in snow-dominated and glacier fedbasins will also face impacts from anthropogenic climate change, which will in turn alter thesediment supply to these channels.1.5 Future of Rivers in a Changing ClimateRivers are sensitive to climate change (natural or anthropogenic), flow modification andchanges in land-use (Ashmore & Church, 2000). River systems are a result of the localgeographical conditions and hydrological processes which are controlled by climatic condi-tions and changes to climate can drastically alter river dynamics (Ashmore & Church, 2000).River morphology and dynamics adjust to the delivery of water and sediment and tempo-rary changes; however, climate change is worrying due to widespread and permanent impacts(Ashmore & Church, 2000).The IPCC predicts that global mean temperatures will continue to rise, likely past2∘C, if greenhouse gas emissions continue unmitigated (Collins et al., 2013). Most impor-tantly for river systems, precipitation is predicted to increase by 1-3% globally by the end ofthe 21st century, with the highest latitudes likely experiencing the greatest increases (Collinset al., 2013). A study by Nijssen et al. (2001) using climate models also found the mostdramatic responses to climate change will be in the mid-high latitudes in snow-dominatedbasins, such as in Canada. Canadian climate models predict a 90 mm increase in precipita-tion over the winter season per year, and that based on a 1.5∘C increase in temperature, theincrease will be over 10% by 2100 (Ashmore & Church, 2000; Collins et al., 2013).Rivers are more sensitive to changes in precipitation than temperature, and theincrease in precipitation has the potential to significantly impact river systems throughchanges to streamflow, sediment, and channel dynamics (Derksen et al., 2019; X. Zhanget al., 2019). Areas of southern Canada such as the Southern Cordillera are particularlyvulnerable to changes due to the interactions between precipitation, glacier mass loss andsediment dynamics (Ashmore & Church, 2000; X. Zhang et al., 2019). A study by B. Zhanget al. (2018) on rivers in Northern Lake Erie Basin in Canada show streamflow in Canada’srivers has already been altered and is expected to significantly change further in future,which in turn impacts sediment. Increased precipitation will greatly increase landslide riskfor rivers in mountainous basins, thus sediment pulses into river channels in these area willlikely increase in frequency and magnitude (Ashmore & Church, 2000; Collins et al., 2013).Snow, ice and permafrost are decreasing across Canada due to climate change, with a 5-10%decrease in snow cover predicted across Canada in the next 30 years (Derksen et al., 2019).5It is predicted that glaciers across the Western Cordillera will lose between 74-96% of theirvolume by 2100 (Derksen et al., 2019). As many rivers in Western Canada are fed by glaciers,this will increase the sediment input into to river systems during melt season (Derksen etal., 2019).The predicted increase in sediment supply will impact channel dimensions and therate of bed aggradation/degradation (Ashmore & Church, 2000). Changes to the flow regimeand increased landslides will increase channel migration rates which will threaten surroundingland, river ecosystems, and surrounding infrastructure. The time scale will range from yearsto centuries with different basins sizes, topography and geology resulting in a variety ofpotential river adjustments (Ashmore & Church, 2000; Derksen et al., 2019).1.6 Aims and ObjectivesSediment pulses into gravel-bed rivers in mountainous basins, such as those found throughoutBritish Columbia, can alter river systems, (Griffiths, 1979). Climate change will increase sed-iment supply to these river channels (Ashmore & Church, 2000). There is research regardingimpacts of increased streamflow on river systems, however there is relatively little researchon the impact of sediment pulses on urban streams. The main objective of this research isto investigate the response of channelized and restored urban streams to sediment pulses.Knowing how urban stream channels respond to larger and more frequent sediment pulsescan help aid restoration projects, notably downstream of channelized reaches. Within thisthesis, the resilience of the streams to sediment pulses is discussed, referring to the streamsability to throughput a sediment pulse without channel flooding occurring. In response tothese objectives, a series of hypothesis based questions have guided my research:• How will reducing the confinement of an urban stream by widening the channel alterchannel morphology?• Will removing bank protection and reducing channel confinement result in sedimentaggradation? Will it destabilize the river system, or will the river be able to transportthe sediment through and remain stable?• How resilient is the river system to sediment pulses?• How will the impact of sediment pulses alter the success of restoration aiming to reduceurban stream confinement?• Can the use of Geomorphic River Engineering (GRE) stabilization mitigate againstaggradation?61.7 Thesis organisationTo investigate these objectives, scaled physical modelling was used to compare typical chan-nelized streams and restored urban streams. Sediment pulses were used to investigate theresponse of these channels to increased sediment supply.Chapter 2 discusses the experimental set up, detailing the channel designs andmethodology. Information on data collection and analysis is also given in chapter 2. Chap-ter 3 presents the experimental results, focusing on changes in bed elevation and areas ofchannel aggradation and degradation. Morphological adjustments are discussed as well asthe response of channel designs to sediment pulses. Results include comparisons of channelcomplexity through bed elevation distributions.Chapter 4 synthesizes the results found and proposes implications restorationprojects, as well as potential for future research.This thesis also provides Appendices of supplementary results. Appendix A pro-vides DEMs of difference for the sediment pulse experiments, whilst Appendix B providesadditional sediment output data.7Chapter 2MethodsThe following chapter discusses the physical models used to investigate the researchobjectives, with three different channels designed around urban streams and restoration. Thefirst set of experiments was a confined urban stream, whilst the second set used a restoredchannel design. The third set of experiments used stability seeding as a method of channelbank protection in a restoration setting. This chapter discusses the physical models used inchannel design and experimental set up, as well as data collection and analysis.2.1 Experimental Set UpAll experiments were conducted using a generic physical model of a gravel bed stream witha gradient of 0.02 m/m at the University of British Columbia. The model has a geometricscaling of 1:25. The model consists of a 12 m long, 1.5 m wide stream table that has a tiltingslope of 2 degrees, along with a sediment conveyor belt at the upstream end and recirculatingwater pump to generate flow conditions (See figure 2.1). All sediment transported past theend of the stream table was collected in a metal trap and weighed at 15 minute increments.Five ‘Canon Rebel T7 DSLR’ cameras placed on a mobile cart collected photographs every20 cm. Metashape used these photos to build a DEM of the bed using control points surveyedwith a total station using an arbitrary coordinate system established in the lab.Channels built within the stream table for these experiments were all constrained bya brick boundary (See Figure 2.1). Bricks were laid down on top of wooden slats along thelength of the stream table at the desired channel width, representing a channelized urbanstream. All experiments started with a initial flat bed surface, kept level with the weir atthe downstream end of the stream table. The flow regime was also kept constant for eachchannel design, kept at 1.5 L/s, representing a ‘bank full’ flow for the channel.The sediment mixture for the bed material and the sediment feed is the same as themixture used in previous experiments by Eaton et al. (2020) and Booker (2018). Figure 2.2and table 2.1 show the grain size distribution of the stream table bed mixture. 1.1The D value refers to the particle size distribution8Figure 2.1: Components of the Stream table in the Ponderosa Fluvial Lab at the University of BritishColumbia. A shows the sediment conveyor belt used to input sediment. B is the sediment trapat the downstream end of the stream table and C shows the mobile cart with cameras.90.5 1.0 2.0 5.0 10.00.00.20.40.60.81.0Grain Size (mm)ProportionD50 D84 D90StabilitySeedingFigure 2.2: Grain size distribution of the bed materialTable 2.1: Grain Size distributionMaterial mix Material Size (mm)D50 1.63D84 3.71D90 5.90Dmax 8.00102.2 Sediment Feed Conditions2.2.1 Constant Sediment FeedA constant base sediment feed was used throughout experiments to allow easier comparisonsbetween pulse experiments. To calculate a suitable constant feed, recirculating experimentswere first conducted, in which the sediment output collected in one 15-minute interval wasused as the sediment input at the upstream end of the stream table for the next 15-minuteinterval; these experiments continued for 8 hours to allow the system to reach a stableequilibrium transport state. The average sediment output was used as the constant sedimentfeed rate for pulse experiments. Once the average sediment feed rate was determined froma recirculating experiment, another experiment was conducted in which the sediment feedrate was held constant at that rate in order to confirm that the stream could maintainan equilibrium transport state under constant feed conditions. The morphology and bedelevation for this second set of experiments serves as the reference condition against whichexperiments involving sediment pulses are compared.2.2.2 Sediment Pulse ExperimentsThe sediment pulse experiments began with a period of constant feed followed by pulses of1 hours. To develop suitable channel morphology, 2 hours at constant sediment feed wasrun. A 1 hour 10% sediment pulse was run before a further 2 hours at constant feed rate toallow for channel recovery prior to subsequent pulses. Sediment pulse values were based ona percentage increase on the average channelized stream constant feed, starting with 10%,then 25% and 50% pulses (See table 2.3). Figure 2.3 visualizes the sediment feed conditionsduring the pulse experiments. The experiment was stopped after a pulse that resulted inwater over topping the bricks constraining the channel (See Figure 2.4). The typical distancebetween the top of the water and the top of the bricks at equilibrium is 1.5 cm.11Figure 2.3: Sediment feed conditions for sediment pulse experiments. Blue areas show time where flow wasrunning, whilst black indicates times flow was stopped to allow for surveying of the bedFigure 2.4: Examples of channel flooding during Exp 1c. A shows water flooding onto the channel bankswhilst flow is running. B shows sediment deposited on bricks when the bed is drained122.3 Experimental DesignsThree physical model configurations were used for the experiments: a model of an urbanstream that has been channelized; a model of a channelized urban stream with a shortreach floodplain on either side of the channel representing a restoration technique; and anurban stream with a short reach of floodplain that has been reinforced with a layer stabilizinggrains on the floodplain surface, as proposed under the Geomorphic River Engineering (GRE)approach published by Eaton et al. (2020). Table 2.2 shows conditions for each experiment,whilst Table 2.3 shows the corresponding sediment input values.Table 2.2: Experiments SummaryExperiment Name Physical Model Configuration Sediment Feed Conditions1b Channelized Constant1c Channelized Pulses2a Widened reach with floodplain Recirculating2b Widened reach with floodplain Constant2c Widened reach with floodplain Pulses3b Widened reach with GRE stabilization Constant3c Widened reach with GRE stabilization PulsesTable 2.3: Sediment input used during experiments. Pulse values based on a percentage increase on Ex-periment 1b constant feedExperimentconditionsExperiment1bExperiment2bExperiment3b10%pulse25%pulse50%pulseSediment Input Rate(kg/min)0.57 0.51 0.51 0.63 0.72 0.86132.3.1 Urban StreamThe physical model configuration representing a channelized urban stream was a 30 cm widechannel confined by bricks along the entire 12 m length of the stream table (See Figure 2.5).The bricks acting as a pipe to move water through the channel due to elevated shear stress,typical of a channelized stream. Channelization eliminates lateral movement of the channelto protect infrastructure, however has been shown to limit the habitat potential (Keller,1978).Figure 2.5: Urban stream channel design142.3.2 Restored StreamThe physical model configuration representing a typical restoration project for urban streamsinvolves widening the central 4 m of the channelized urban stream by 30 cm on either side ofthe channel (See figure 2.6). Within this widened treatment zone, a 30 cm wide floodplainwas constructed on either side of a channel. The banks of the channel were not stabilized inany way, allowing the channel to migrate laterally within the treatment zone.Figure 2.6: Restored stream channel design152.3.3 Restored Stream with Bank ProtectionThe final physical model configuration consisted of the restored stream described abovewith the addition of bank protection (See figure 2.7). A layer of stabilizing sediment wasplaced on top of the reconstructed floodplain (see Eaton et al. (2020), for a full descriptionof the stabilization methodology), which was recruited to the stream channel when andwhere bank erosion occurred. This approach to channel stabilization allows limited channelmovement and morphologic adjustments to occur, whilst still offering bank protection. Thistechnique uses grains, in the upper end of the Grain Size Distribution of the bed material(See figure 2.2) to stabilize the bed in the vicinity of eroding cutbanks where those grainsare recruited to the stream. Eaton et al. (2020) suggest that this technique can be useful inareas where restoration is desirable, but limitations with surrounding infrastructure requiresome control over channel migration. Blue stabilizing grains were used as the stabilizingsediment, between 4-7 mm in size (See figure 2.7). Colored grains ensured that they couldbe distinguished from the stream table bed mixture. The grains were placed one-grain thickwithin the central treatment zone (4-8 m) across the 30 cm floodplains either side of thechannel.Figure 2.7: Restored stream channel with GRE stablization technique162.4 Data Collection and AnalysisThere were three types of data collected during the experiments: a) digital elevation models(DEMs) of the channel bed and banks collected at 1 to 2 hr intervals; b) sediment transportrates based on the recorded sediment output collected every 15 minutes; and qualitativevisual observations supported by photography made during the experimental runs.2.4.1 Digital Elevation ModelsTo generate Digital Elevation Models, the bed was drained and the bed surveyed usingthe mobile cart to take high resolution photos every 0.2 m along the channel. The bedwas surveyed at hour 0, at hour 2 after the initial channel set up, then before and aftereach sediment pulse. The RAW images were converted into JPEGS using IrfanView andXnConvert, before being imported into Agisoft Metashape. Within Metashape, the photoswere aligned using 14 markers along the stream table and point cloud data generated. Finally,DEMs were generated and exported. The DEMs were read into R studio using the Rasterpackage, where bed elevations could be imposed on a hillshade images to visualize the changesin bed elevation over the experiment duration. DEMs were used to assess changes in channelmorphology as well as being used to assess the sediment volume changes within the upstream,treatment zone and downstream sections of the channel.2.4.2 Bed Elevation ProfilesTo assess bed elevation profiles, a bed matrix of the DEMS was generated using the Terrapackage in R Studio. Each matrix column represented cells across the channel width. Theaverage elevation for each was calculated and plotted against distance along the stream table.Profiles were created to show the impact of pulses along the entire stream table. 22.4.3 Channel Complexity AnalysisAn analysis of channel complexity was completed to determine habitat potential. Thereare a variety of definitions, but channel complexity generally refers to the heterogeneity ofstream morphology (Palmer et al., 2010) and can be used as a proxy for habitat potential.Geomorphic complexity is linked to habitat potential and subsequently the ecological func-tion of a stream (Eaton et al., 2020; Palmer et al., 2010). Using the treatment zone, theactive channels were determined and a cropped DEM generated. This was used to createhistograms of elevation distributions and calculate skewness values as well as quantiles.2Distance along the stream table is shown as an tributary coordinate system established in the lab using control points alongthe stream table17Chapter 3 ResultsThe following chapter evaluates the results of seven experiments conducted acrossthree different experimental set ups; a confined stream, restored stream and stabilizing grainsset up. Two main experiments were conducted on each set up, one in which sedimentwas kept constant throughout and a second where sediment pulses were introduced to thechannel. Discharge was kept constant throughout the experiments at 1.5 L/s. Morphologicaladjustments as well as sediment storage were analysed to help determine the resilience ofthese systems to sediment pulses in urban channels. Comparisons of channel complexitywere used to investigate the potential for the restoration techniques to improve the habitatpotential and ecological value of urban streams.3.1 Channelized Stream Channel3.1.1 Constant Sediment FeedRecirculating experiments conducted by Booker (2018) showed a average sediment output of0.57 kg/min which was used in these experiments as the constant sediment feed. Figure 3.1shows similar sediment output seen through the eight hour recirculating experiment and theeight hour constant feed experiment (Exp 1b), particularly in the initial two hours. Sedimentoutput from experiment 1a showed less variation after two hours, and overall had a slightlylower average output of 0.55 kg/min.Figure 3.3 shows the DEM of the stream bed surface at hour 8 of experiment 1a.Beginning from the flat-bed surface at the start of the experiment, alternate bar riffle-poolmorphology developed within the first 30 minutes of run time, whilst scour could be seen onthe outside of pools against the brick sides. Morphology remained stable from one hour upto the end of the experiment at eight hours. In addition, bed elevations in Figure 3.2 showa consistent elevation along the stream table, indicating no areas of substantial aggredationor degradation over time. Variations in bed elevations throught time indicate the continuedtransport and reworking of sediment through the stream table. Peaks and troughs seen inthe bed elevation profile are indicative of the riffle-pool morphology created. Overall, theuse of constant sediment feed through the channelized urban channel resulted in a channelwith stable morphology, but slightly lower sediment output .180 100 200 300 4000.20.40.60.81.0Experiment run time (minutes)Sediment output rate (kg)Sediment output rates for Urban channelized stream designRecirculatingConstant feedRecirculating averageConstant feed averageFigure 3.1: Stream table sediment output for the Urban Channel design using a recirculating feed (Booker,2018) and constant feed (Experiment 1b)92 94 96 98 1000.100.110.120.130.140.15Distance along streamtableBed elevation (m)Bed elevations for Experiment 1bHour 2Hour 4Hour 8Approximate starting bed elevationFigure 3.2: Graph showing bed elevation of the stream table during Experiment 1b1992 94 96 98 10095969798959697980.1000.1100.1200.1300.1400.150Flow directionExperiment 1b − Hr 8Distance along streamtableFigure 3.3: Digital Elevation model showing Experiment 1b after a run time of 8 hours. Colours correspondto bed elevation in metres.3.1.2 Impact of Sediment PulsesOnce the stability of the urban stream and constant feed was established, Experiment 1binvestigated the systems response to sediment pulses. Results showed some resilience topulses, with the channel successfully through putting a pulse a 10% and 25% increase onthe constant feed. However, after 25 minutes of a 50% pulse, sediment had been depositedin the upstream area, causing water to flood over the urban channel. By the end of theone-hour pulse, sediment was also being deposited on top of the channel banks as the waterleft the channel. Flooding of the channel occurred across the first two meters of the streamtable. It can therefore be concluded that the urban channel set up was unable to cope with a50% pulse, and that a pulse of this magnitude represents a hazard to potential surroundinginfrastructure to urban streams due to water flooding over the channel.Figure 3.4 and 3.5 showing the DEMs and bed elevation profiles after each sedimentpulse confirm the visual observations from the experiments. For the 10% pulse, the channelhad the capacity to throughput the excess sediment. There was a slight increase in bedelevation with the 25% pulse in the first three meters of the stream stable, although the rifflepool morphology remained stable and water remained within the confined channel. The 50%pulse resulted in a 1.5 cm increase in bed elevation, also in the first three meters. By theend of the 50% pulse, bed elevation reached the top of the channel banks in this area, witha net upstream deposition of 25.4 cm3. This highlights the area of flooding of the channeland the most aggradation. Figure 3.4 and 3.5 also show that there were fewer changes inelevation within the central and downstream areas for the 10% and 25% pulse, with thechannel still exhibiting the same riffle pool morphology as prior to pulses. In comparison,elevation increased along all reaches for the 50% pulse. DEMs of difference in AppendixA also highlight the extent of channel change from pulses. Overall, sediment pulses into20channelized streams result in increased bed elevation and channel flooding localized to theupstream area, with the system being resilient up to a 25% pulse.2192 94 96 98 10095.095.596.096.597.097.598.095.095.596.096.597.097.598.00.1000.1100.1200.1300.1400.150Flow directionExperiment 1c − Hr 292 94 96 98 10095.095.596.096.597.097.598.095.095.596.096.597.097.598.00.1000.1100.1200.1300.1400.150Flow directionExperiment 1c − 10% pulse92 94 96 98 10095.095.596.096.597.097.598.095.095.596.096.597.097.598.00.1000.1100.1200.1300.1400.150Flow directionExperiment 1c − 25% pulse92 94 96 98 10095.095.596.096.597.097.598.095.095.596.096.597.097.598.00.1000.1100.1200.1300.1400.150Flow directionExperiment 1c − 50% pulseDistance along streamtableFigure 3.4: Digital Elevation Models of Experiment 1c showing the response to sediment pulses. Colourscorrespond to bed elevation in metres.2292 94 96 98 1000.100.110.120.130.140.15Distance along streamtableBed elevation (m)Bed elevations for Experiment 1cHour 210% pulse25% pulse50% pulseApproximate starting bed elevationFigure 3.5: Bed elevation for sediment pulses in the urban stream channel (Exp 1c)3.2 Restored Stream Channel3.2.1 Constant Sediment Feed vs Recirculating SedimentThe restored stream experiments consisted of treatment zone in the central 4 m of thestream channel, consisting of 30 cm channel with a 30 cm floodplain either side bounded bybricks creating a total width of 90 cm. Experiment 2a, which had a recirculating sedimentfeed, resulted in an average sediment output of 0.51 kg/min. This is a 10% decrease inthe channelized stream average output, highlighting that restoring an area of the streamchannel lowered the rate of sediment transport through the stream table. Supplementaryexperiments showed that the restored channel was unable to cope with the constant feedof the confined stream (0.57 kg/min), with water and sediment over topping the channelbanks within 3 hours at this sediment feed due to significant aggradation in the upstreamand treatment zones. This demonstrates that additional design elements would need to beintroduced to prevent aggradation even at the background sediment supply rate.This average sediment output found from Experiment 2a was used as the constant23feed inputs for Experiment 2b and 2c. Similar to the urban stream comparison, therewas less variation in sediment output during experiment 2b with a range of 0.33 kg/mincompared to 0.74 kg/min for experiment 2a (see figure 3.6. Using a constant sedimentfeed means that sediment discharge is imposed on the stream, thus must adjust in order tosuccessfully transport that volume of sediment feed (Parker &Wilcock, 1993). In comparison,when sediment feed is recirculating the stream is better at adjusting its sediment-transportbehavior, resulting in greater variations in output (Parker & Wilcock, 1993). For bothexperiments, the morphology had stabilized by 4 hours of run time with only minor changesfor the rest of the duration.Complex morphology was established in the treatment area from the initial flat bedsurface and was similar for both experiment 2a and 2b, with DEMs in Figure 3.8 showingthe final morphology that developed. Within the first hour, the channel began to widen anderode into the floodplain. The main channel developed a meandering pattern, eventuallyreaching the non-erodible banks on both sides within two hours. Throughout the experi-ments, secondary channels developed along with areas of scour, notably at the end of therestored area where the channel narrowed again. In addition the building of bars was focusedon first two meters of the restored area, particularly in the recirculating experiment. By theend of the experiment, much of the floodplain had been eroded and sediment reworked, 79%of the floodplain during experiment 2a and 82% for experiment 2b. Upstream and down-stream of the restored area exhibited riffle pool morphology, whilst downstream of the arearemained at a lower elevation. This is due to the narrowing the channel back to a 30 cmchannelized area, resulting in increased stream power along the downstream reach.Figure 3.7 shows that both experiments resulted in higher elevations across the up-stream and treatment sections of the stream table compared to the downstream channel.Elevation drops sharply at the point of narrowing of the widened channel back to a 30 cmbricked channel, indicative of incision of the bed. This difference in elevations across thestream table is greater when using a recirculating sediment output, which can also be seen inFigure 3.8 showing a comparison of DEMs of both experiments after a 8 hour run time. Theresultant higher elevations in the upstream and widened area indicate that this restorationtechnique already has a sediment aggradation issue as a result of widening an area of thechannel, creating a system more vulnerable to increases in sediment supply.240 100 200 300 4000.20.40.60.81.0Experiment run time (minutes)Sediment out (kg)Sediment output rates for Experiment 2a and 2bRecirculatingConstant feedRecirculating averageConstant averageFigure 3.6: Stream table sediment output from Exp 2a and 2b92 94 96 98 1000.100.110.120.130.140.15Distance along streamtableBed elevation (m)Restored ReachBed Elevations for Exp 2a and Exp 2bExp 2aExb 2bInitial elevationFigure 3.7: Bed elevation of the stream table after a run time of 8 hours for Experiment 2a and 2b2592 94 96 98 10095969798959697980.1000.1100.1200.1300.1400.150Flow directionExperiment 2a − hr0892 94 96 98 10095969798959697980.1000.1100.1200.1300.1400.150Flow directionExperiment 2b − hr08Distance along streamtableFigure 3.8: Digital Elevation model from Exp 2a and 2b after a run time of 8 hours. Colours correspondto bed elevation in metres.3.2.2 Impact of Sediment PulsesThe restored stream in Experiment 2c showed little resilience to sediment pulses, flooding atthe first pulse of 10% sediment increase. After two hours run time at constant feed to buildup the morphology of the channel from the flat bed, a 10 % sediment pulse was inputtedfor one-hour. During the pulse, sediment was deposited along the bed in the upstream area(36.7 cm3) and within the treatment zone (51.9 cm3), particularly at 4 meters where theurban channel widened out. After 50 minutes, water began flood onto the channel in thefirst two meters of the stream table. In areas of the treatment zone, particularly where thechannel flowed against the non-erodible banks, the water level reached bank height.Figure 3.9 shows the DEM comparison between the initial stream table set up andthe result of a 10% sediment pulse in experiment 2c. Bed elevation increased across thestream table. Riffle-pool morphology still occurred in the upstream and downstream reaches,however there were smaller bar amplitudes. Morphology within the treatment section wasalso altered as a result of the pulse. Deposition was focused along the side of the channels,resulting in the cutoff of side channels, with flow focused on one main channel. With a more26focused flow, greater scouring occurred where the channel reached the non-erodible bankson both sides. There was little change in the downstream reach, with a net erosion of 2.87cm3 during the pulse, showing the translation of the pulse only reached the restored zone.Results already show the bed elevation of the restored stream set up in the upstream andcentral sections is higher than the urban stream prior to sediment pulses. Therefore, therestored stream has a lower resilience and is less capable of through putting excess sediment,as less aggradation is required to cause flooding.92 94 96 98 10095969798959697980.1000.1100.1200.1300.1400.150Flow directionExperiment 2C − Hour 292 94 96 98 10095969798959697980.1000.1100.1200.1300.1400.150Flow directionExperiment 2C − 0.57kg/min92 94 96 98 10095969798959697980.1000.1100.1200.1300.1400.150Flow directionExperiment 2c − 10% pulseDistance along streamtableFigure 3.9: Digital Elevation Models of Experiment 2c showing the response to sediment pulses. Colourscorrespond to bed elevation in metres2792 94 96 98 1000.100.110.120.130.140.15Distance along streamtableBed elevation (m)Restored ReachBed elevations for Experiment 2cHour 210% pulseInitial elevationFigure 3.10: Bed elevation profile for sediment pulses during Experiment 2c3.3 Restored Stream with Bank Protection3.3.1 Constant Sediment FeedExperiment 3 consisted of placing the blue stabilizing grains along the floodplain of thewidened treatment zone as a layer one grain thick. In Exp 3b, a constant feed of 0.51kg/min was used which is the same as in Exp 2b, the widened urban stream. 3. Figure3.12 shows DEMs highlighting the morphological changes of the channel throughout an 8hour run time at constant feed. Within 1 hour, riffle-pool morphology developed across thestream table, remaining stable in the upstream and downstream reaches. Two riffles andpools formed within the treatment zone, where the channel gradually widened across thefloodplain. Overall, channel expansion was limited in the treatment reach, and only 18.4%of the stabilizing grains and floodplain area were eroded by the end of the experiment.3no recirculating feed experiment was run for this set up, so there is no Exp 3a28The elevation profile remained stable for the duration of the experiment in the centraland downstream reach, as can be seen in Figure 3.11, however elevation in the upstreamreach increased inthe first six hours. Equilibirum was reached after six hours, with a netaggradation of 0.67cm3 occurring between six and eight hour run time in the upper 4 m ofthe stream table and no flooding occurred. The restored channel was able to cope with theconstant sediment feed from the confined channel (0.57 kg/min) for a experiment duration of8 hours, however there was aggredation in the upstream area across the experiment run time.This indicates that even with the use of the stability seeding technique, restored channelsmay not have the capacity to handle the same sediment feed as prior to restoration in thelong-term.92 94 96 98 1000.100.110.120.130.140.15Distance along streamtableBed elevation (m)Restored ReachBed elevations for Experiment 3bHour 2Hour 4Hour 8Initial elevationFigure 3.11: Graph showing bed elevation profile for Experiment 3b2992 94 96 98 10095969798959697980.1000.1100.1200.1300.1400.150Flow directionExperiment 3b − Hour 092 94 96 98 10095969798959697980.1000.1100.1200.1300.1400.150Flow directionExperiment 3b − Hour 492 94 96 98 10095969798959697980.1000.1100.1200.1300.1400.150Flow directionExperiment 3b − Hour 8Distance along streamtableFigure 3.12: DEMs for Experiment 3b. Colours correspond to bed elevation in metres.303.3.2 Impact of Sediment PulsesExperiment 3c showed some capacity to throughput to sediment pulses; being able tothroughput a greater pulse then Exp 2c but less resilient than Exp 1c. Figure 3.14 and3.13 show the DEMs and associated bed elevation profiles for the sediment pulses experi-ment on the restored stream with stability seeding. The 10% sediment pulse did result 36.2cm3 aggradation within the upstream zone, however flow did not over top the channel banks,and morphology remained constant throughout the length of the stream table. In compar-ison, the channel flooded after 20 minutes of the 25% pulse, with water over topping thechannel in the first meter of the stream table on both sides. This was due to the depositionof 45.6 cm3 of sediment in the upstream reach, raising bed elevation. Flooding also occurredtemporarily at the upper boundary of the treatment zone (4 m) for 15 minutes. Riffle-poolmorphology was still observed throughout the treatment zone and downstream reach, how-ever a small build up of the alternate bars in the treatment zone was observed. There wasonly a net aggradation of 2.1 cm3 in the treatment zone and 1.2 cm3 in the downstreamreach during the 25 % pulse, indicating the localized impact of the pulse in the upstreamarea.92 94 96 98 1000.100.110.120.130.140.15Distance along streamtableBed elevation (m)Restored ReachBed elevations for Experiment 3cHour 210% pulse25% pulseInitial elevationFigure 3.13: Graph showing bed elevation profile for Experiment 3c3192 94 96 98 10095969798959697980.1000.1100.1200.1300.1400.150Flow directionExperiment 3C − hr0292 94 96 98 10095969798959697980.1000.1100.1200.1300.1400.150Flow directionExperiment 3c − 10% pulse92 94 96 98 10095969798959697980.1000.1100.1200.1300.1400.150Flow directionExperiment 3c − 25% pulseDistance along streamtableFigure 3.14: DEMs for Experiment 3c showing the response of the channel to sediment pulses. Colourscorrespond to bed elevation in metres.323.4 Comparison of Techniques for Urban Stream Man-agement3.4.1 Resilience to Sediment PulsesOverall, results suggest that widening a reach of a channelized stream without any additionalstabilization measures could result in channel aggradation and flooding upstream of thewidened reach. The channelized urban stream showed some resilience, flooding at the 50% pulse, whereas the restored channel flooded with even a 10% pulse. This highlightsthe need for mitigation strategies in restored reaches for increased sediment supply, or theneed for alternative restoration strategies. The use of additional bank protection helped toincrease the resilience of the restored channel to sediment pulses and increase the transport ofsediment through the stream table. However, this set up flooded at the 25% pulse, indicatingthat even with mitigation, the fully channelized urban channels are most resilient to increasesin sediment supply. This has implications for urban river restoration projects, which willbe discussed in chapter 4, particularly regarding the desire for greater habitat potential ofstreams.3.4.2 Channel ComplexityA key incentive for river restoration is the enhancement of habitat potential. Channel di-versity can be used as a proxy for habitat potential, although there are other complexitiesand factors that also influence the habitat potential of a stream. The channelized urbanstream created a stable riffle pool morphology, whilst widening the central reach resulted inmore complex morphology with multiple channels. The use of additional bank protectionrestricted lateral movement of the channel, but still generated a more varied channel thanthe channelized reach.One way in which to quantify habitat potential is to assess the variability in bedelevation along a channel. A larger distribution in bed elevations indicates more variablewater depths and velocities, which in turn correlate with increased habitat diversity (Eatonet al., 2020) In order to compare the potential habitat quality in Exp1b (channelized stream),2b (widened reach) and 3b (widened and stabilized using GRE approach) the central fourmeters of the stream table were assessed to focus on the treatment reach. The area of theactive channels in this area were digitized from DEMs of the experiments, and correspondedto the wetted area of the channel during the 1.5 L/s flow. The active channels are shown inFigure 6 along with the corresponding bed elevation distributions for the DEM cells. Bedelevation is given in meters and are shown relative to the bottom of the stream table.33Figure 3.15 shows distinct differences between the three experiments particularlybetween Exp 1b (channelized) and Exp 2b (widened). The channelized stream has a moder-ately negatively skewed distribution (skewness value of -0.94), with the lowest median valueof 0.114. In comparison, Exp 2b had a highly negatively skewed distribution (-1.19) with ahigher median elevation (0.126 m) and quantiles. GRE stablization in Exp 3b also resultedin a higher median elevation (0.123 m), but slightly lower than Exp2b, whilst the quantilesare similar. The distributions of this experiment are fairly symmetrical (-0.47). Exp 2band 3b also resulted in higher median elevations, suggesting shallower flows along the activechannel compared to Exp 1b. This has potential implications for stream temperatures, asshallower flows have increased temperature (Leach et al., 2023; Sinokrot & Stefan, 1993)In addition, Exp 1b had the lowest range of elevation (0.032 m), whilst Exp 2b hadthe highest range (0.053 m). The range of elevations of Exp 3b sits between at 0.048 m.Visualization of the active channel highlights these differences. Exp 2b had the largest activechannel, whilst Exp 1b exhibited the smallest active channel. In addition, DEMs indicatedExp 1b had the least varied morphology, with smaller, less built up bars.A wider range of elevations indicates greater variation in flow depths and veloci-ties and therefore greater habitat potential, thus restoration through channel widening andproviding an erodible floodplain resulted in greater habitat potential. The use of GRE sta-bilization did also result in a more ecologically valuable stream than the channelized stream.34Urban streamvFrequency0.09 0.10 0.11 0.12 0.13 0.14010000200000.108 0.114 0.118FrequencyBed elevationRestored streamvFrequency0.09 0.10 0.11 0.12 0.13 0.14010000200000.1190.1260.132FrequencyBed elevation0.095 0.11 0.12 0.13 0.14Stability seedingvFrequency0.09 0.10 0.11 0.12 0.13 0.14010000200000.1160.1230.132FrequencyBed elevationFigure 3.15: DEMs for the active channel within the central 4 m of the stream table for the urban stream,restored stream and stablity seeding expeirments. DEMs shown are shown after a run time of8 hours at constant feed. The central 4m represent the location of a floodplain in the restoredstream, and stabilising grains for the stability seeding set up. Flow is shown from left to right,and the coloured bar represents the bed elevation of the channel. Distributions of the bedelevations for each experiment are shown in the histograms. A solid black line represents themedian value, whilst the 16th and 84th percentiles are shown through dashed lines.353.5 Results SummaryChapter 4 described the key results from seven experiments, with the implications of thesefindings being discussed further in chapter 5. Table 3.1 and 3.2 provides an overview of thekey results discussed.The use of a constant sediment feed was found to result in a stable river system, withcomparable morphology to recirculating experiments, albeit with small changes to sedimenttransport.The channelized urban stream design had the greatest resileince to sediment pulses,being able to cope with a 10% and 25% pulse without overbank flooding. Flooding occuredat a 50% pulses in the first 2 metres of the stream table as a result of aggradation in theupper reach.The restored stream design had a 10% reduction in sediment transport rate comparedto the urban stream design and exhibited higher bed elvations in the upstream and treatmentreaches compared the downstream area. This design displayed no reslience to sedimentpulses, with aggradtion in the upstream and treatment reaches during 10% pusle causingoverbank flooding.The use of additional bank protection increased the resilience of a restored design,having the capacity to cope with a 10% pulse. However flooding occurred during a 25%pulse, also in the upstream area.The restored design and restored design with additional bank protection had similarelevation distributions however the restored area had the largest active channel. The chan-nelized stream had the lowest habitat potential due to lower elevation distributions reflectingless variable water depths and velocities.Further analysis highlighting aggradation from sediment pulses for the experimentsdiscussed in chapter 4 can be found within Appendix A, whilst sediment output data foreach experiment such as those shown in figure 4.1 can be found within Appendix B.36Table 3.1: Results Summary for Constant Feed ExperimentsExp. ChannelFeedkg/minOutputkg/minFloodplainRe-worked MorphologyMedianEleva-tion(m)ElevationRange(m)1b Channelized 0.57 0.55 N/A Riffle-pool morpholgoy 0.114 0.0322b Restored 0.51 0.48 82% Alternate bar channel withback channelsreaching-non erodiblebanks.0.126 0.0533b Restoredwith GREstabilization0.51 0.53 18% Riffle-pool morphology 0.123 0.048Table 3.2: Results Summary for Sediment Pulse ExperimentsExp. ChannelPulseresultinginfloodingPulsefeed(kg/min)Floodingloca-tionTimetofailure(min)Upstreamaggrada-tion(cm^3)Treatmentaggrada-tion(cm^3)Downstreamaggrada-tion(cm^3)1c Channelized 50% 0.86 Upstreamreach25 25.4 6.3 3.802c Restored 10% 0.63 Upstreamreach50 36.7 51.9 -2.873c Restoredwith GREstabiliza-tion25% 0.72 Upstreamreach20 45.5 2.1 1.2037Chapter 4 Discussion4.1 Sediment Transport in Restored ReachesNatural channel restoration designs aim to create a geomorphically stable system in dynamicequilibrium with the watershed, whilst having capacity to transport the sediment withoutexcessive storage or erosion (Byars’ & Kelly, 2001). Results on the experimental stream showthat designing a restored reach created a geomorphically stable area but a large volume ofsediment was stored in the upstream and treatment reach. Erosion and deposition of materialis a function of sediment transport capacity and stream competence Carson & Griffiths(1987). Widening the central reach and providing erodible banks resulted in a wider channel,decreasing stream depths and shear stress force. This resulted in lower stream competence(Carson & Griffiths, 1987; Niezgoda & Johnson, 2005), leading to aggradation and increasedbed elevations which can be seen in comparisons found in figure 4.1. The rate of sedimenttransport for the experimental stream decreased by 10% from the average sediment supplyof the confined stream, however these systems are often downstream of channelized reacheswhere sediment transport is higher. Therefore, sediment supply into restored reaches fromchannelized areas may exceed the transport capacity. When the supply of sediment into therestored stream was increased to the supply of the channelized urban stream, aggradation ofthe bed in the upstream zone and channel flooding occurred. This system was unable to copewith the background sediment supply from the channelized stream. This has implicationsregarding channel designs and restoration aims, as to prevent aggradation strategies wouldbe needed to ensure the ideal ratio of sediment transport to storage. Sediment supply intorestored areas would need to be reduced, or additional bank protection and stabilizationmeasures could be installed to increase sediment transport through a restored reach.3892 94 96 98 1000.090.100.110.120.130.140.15Distance along streamtableBed elevation (m)Restored ReachBed elevations for Experiment 1b, 2b and 3b after a run time of 8 hoursExp 1bExp 2bExp 3bInitial ElevationFigure 4.1: Bed elevation profiles for Experiment 1b, 2b and 3b after a run time of 8 hours4.2 Response to Sediment PulsesThe main impact of sediment pulses on the experimental steam across all three channeldesigns was elevated bed level and channel flooding. Once the sediment transport capacityof the stream was reached, large volumes of sediment were deposited in the upstream reachand restored reach (See figure ??) Bed elevation increased, eventually resulting in overbankflooding as the channel capacity was reduced. Studies of sediment pulses into non-urbanizedgravel bed rivers reported similar findings. Pulses were found to raise bed levels, widenstreams and simplify bed forms such as riffle pool morphology as well as decrease channelcomplexity (James, 2006; Sims & Rutherfurd, 2017; Wohl et al., 2015). Sims & Rutherfurd(2017) also found a reduction in hydraulic capactiy of the channel, increasing the frequencyof overbank flooding. In forested mountain gravel bed streams there is a decrease in waterdepth and variability of bed elevation (Madej, 2001).39Fully channelized urban streams exhibited some resilience to sediment pulses, beingable to cope with a 25% pulse, although flooding occurred with a 50% pulse. With a predictedincrease in sediment pulse magnitude and frequency due to anthropogenic activity and debrisflows, the management strategies of urban streams will need to incorporate sediment pulsesin order to prevent aggradation and flooding as the transport capacity of these streams isreached.In comparison, the urban stream with a restored reach exhibited no resilience tosediment pulses, flooding at the first pulse of 10%. Due to a reduction in stream competence,restoring a reach through channel widening created a system vulnerable sediment pulseswhich are inherently part of a gravel-bed river system. This results in a greater flood risk toan area, having the potential to generate large economic losses if surrounding infrastructureand industry is impacted. A greater resilience of channelized urban streams compared towidened reaches with more erodible boundaries mirrors findings by Rutherford et al. (2001)showing rivers confined by bedrock or stable vegetation are better able to remain stable andunaltered.Sediment pulses are important in gravel bed rivers (Venditti et al., 2010), and haveshown to have similar impacts in urban and non-urban settings. However, the impacts ofpulses on urban streams in particular generate a hazard due to surrounding infrastructureand people, so understanding the resilience of these streams to pulses will be crucial to aidmitigation strategies.4092 94 96 98 10095969798959697980.1000.1100.1200.1300.1400.150Flow directionExperiment 1c − 50% pulse92 94 96 98 10095969798959697980.1000.1100.1200.1300.1400.150Flow directionExperiment 2c − 10% pulse92 94 96 98 10095969798959697980.1000.1100.1200.1300.1400.150Flow directionExperiment 3c − 25% pulseDistance along streamtableFigure 4.2: Digital Elevation models for Exp 1c, 2c and 3c, after flooding has occurred414.3 Geomorphic River Engineering TechniqueThe use of additional bank protection through the Geomorphic river Engineering approachof a layer of stabilizing grains was shown to improve the resilience of a restored reach tosediment pulses. By limiting the lateral migration of the stream within the restored reach andensuring a single channel throughout, sediment transport increased and the system was ableto cope with a 10% sediment pulse before flooding at a 25% pulse. As the channel widened,the stabilizing grains fell into the channel and these coarse grains were incorporated into thechannel as the banks erode. Research by MacKenzie et al. (2018) showed that incorporating asmall proportion of coarser grains into the bed increases channel stability and reduces lateralmigration because larger grains cause a greater proportion of the bed surface to becomeharder to erode (Schmetterling, 2001). In this process, the stream engineered its own channel,which resulted in some level of channel adjustment and bank migration, whilst creating stablechannel. The use of GRE stabilization resulted in a stream with greater channel complexityand thus habitat potential then the channelized urban stream, with similar bed elevationdistributions to the restored reach with no additional bank protection. Research by Eatonet al. (2020) and MacKenzie & Eaton (2017) found that using this technique could be usedto promote channel stability whilst allowing some degree of natural channel adjustments,whilst reducing lateral migration during flood events. This work also finds that the use ofthe Geomorphic River Engineering approach can increase the resilience of a restored urbanreach to sediment pulses whilst maintaining some natural channel adjustment desired inrestoration strategies.4.4 Implications for RestorationThere are often assumptions in urban restoration that sediment loads will be similar topre-restoration conditions and resilient to change (Niezgoda & Johnson, 2005). However,sediment pulses into urban channels have the ability to cause channel flooding and posea hazard to surrounding infrastructure, raising implications for restoration. The risks as-sociated with sediment pulses and increased sediment supply need to be incorporated intorestoration goals.Results showed that flooding during sediment pulses occurred upstream of restoredzones, indicating that when restoring a reach, upstream is a key area to understand how toreduce the risk of flooding from pulses. Also, this shows the impacts of sediment pulses mayoccur in an area that is not owned or under the control of the group that has performed thechannel widening. There is potential for risk transfer out of the area where restoration isfocused, thus restoration groups need to incorporate stakeholders in the area upstream andsurrounding the restoration reach for risk management and mitigation strategies.42The hazards posed upstream of a restored reach also highlight the need for catchmentwide assessments and management. In urban streams in BC, sediment is supplied furtherupstream in the watershed where there are fewer channel modifications and greater sedimentinput from debris flows and anthropocentric activities (Byars’ & Kelly, 2001). Watershedassessments can help determine the likelihood of sediment pulses into urban stream setting,allowing restoration groups to incorporate this into their projects (T. Beechie et al., 2008;Smith et al., 2014).The incorporation of catchment wide management and assessment would allow thecontrolling of sediment supply into urban channels and restored reaches as the avoidance ofdeposition is key to prevent flooding from sediment pulses (Byars’ & Kelly, 2001; Clifford etal., 2008). Altering logging practices and reforesting areas of a watershed can reduce sedimentpulses into gravel-bed rivers (Sims & Rutherfurd, 2017), controlling sediment at the sourceand reducing potential hazards within the stream network. Dredging of channels to extractsediment pulses can reduce downstream impacts, which has already been successful in theColumbia River, Washington (Sims & Rutherfurd, 2017). Dredging has been also been foundto have ecological impacts by removing fish habitat and altering channel bed morphology;so can counteract restoration objectives (Harvey & Lisle, 1998).Overall sediment pulses are predicted to increase in gravel bed rivers, resulting ina flooding hazard downstream in urban streams. Sediment pulses will not cause an issueto all urban streams; channels within entirely urbanized watersheds are disconnected tosediment inputs from surrounding land and often operate within a sediment deficit (Niezgoda& Johnson, 2005; Quader & Guo, 2009). Urban streams such as Lynn Creek, Vancouverthat area are connected to a natural watershed upstream, are more susceptible to sedimentinputs from soruces such as debris flows. When managing these urbans streams, pulses needto be incorporated into restoration strategies and planning in order to mitigate. Restoringareas of urban stream through channel widening results in reduced sediment transport andless resilience to sediment pulses, increasing the hazard risk of flooding. This casts doubt onthe feasibility of the ‘room for the river’ approach in gravel-bed urban streams.Additional design measures such as GRE stabilization would be needed due to re-duced sediment transport, whilst also providing some restoration benefits. The use of vege-tation in stream management has been found to increase bank stability, with bank strengthas a result of vegetation in small streams found to be a large control over channel geometry(Eaton & Giles, 2009; Simon & Collison, 2002). Roots help to stabilize the soil matrix andreduce bank erosion, thus vegetation could be used to limit lateral erosion within a restoredreach (Easson & Yarbrough, 2002). Tree planting alongside GRE stabilization could be onemethod of improving the resilience of a restored reach to sediment pulses by reducing bankerosion and increasing shear stress to ensure sufficient sediment transport through a reach.43Stabilizing sediment provides immediate bank protection whilst allowing some lateral mi-gration of a channel, with the banks becoming further reinforced as vegetation root systemsdevelop. In addition, vegetation along a stream channel plays an important role in streamtemperature (Knight & Bottorff, 1984). Results showed that the restored reach resulting inlower flow depths, which will increase stream temperatures within restored areas (Leach etal., 2023; Sinokrot & Stefan, 1993). Riparian vegetation has been shown to provide shad-ing to stream channels playing an important role in controlling small stream temperature(Beschta, 1997; S. L. Johnson, 2004; Knight & Bottorff, 1984). The use of riparian vegeta-tion within restored reaches of urban streams could help limit temperature increases causedby lower flow depths.If we still want to restore habitat of urban streams, the sediment supply into theseurban streams may need to be controlled or monitored to ensure that the system can copewith the supply. There may also be a need for human interference upstream to remove pulsesor limit sediment supply into urban areas. This could result in ecological and morphologicalchanges further upstream in the watershed nearer the sediment source (Sims & Rutherfurd,2017). This raises the question of whether the ‘room for the river’ approach is a viableoption in the future in urban gravel-bed streams, with the risk of sediment pulses limitingrestoration potential when there is a limit to the spatial extent of the project (Bernhardt& Palmer, 2007). Even with additional measures, fully channelized urban streams werefound to be the most resilient to sediment pulses with greater sediment transport. However,channelized reaches provide less habitat potential and morphological diversity, indicating acompromise is needed between pulse resilience and habitat creation.44Chapter 5 Concluding remarksThe experiments conducted for this thesis aim to investigate the impact of sedimentpulses into urban gravel-bed rivers through a series of research questions. Sediment delivery isa key determinant of channel morphology in gravel-bed rivers, being sporadically generatedthrough hillslope erosion and debris flows (Hoffman & Gabet, 2007). Predicted increasesin sediment pulses due to climate change and anthropogenic activities such as mining andlogging will alter river systems in the future (Griffiths, 1979). Understanding how sedimentpulses interact with channels is useful for watershed management. There has been previousresearch into the impact of sediment pulses into gravel bed streams through field observationsand flume models, however the impact of pulses within urban channel settings is unknown.This thesis used a scaled physical model of a gravel bed stream to investigate sedimentpulses using three channel designs to replicate a classic channelized urban stream, restoredurban stream, and finally a restored urban stream with additional bank protection. The useof a constant sediment feed resulted in similar morphology within the experimental streamtable when compared to recirculating set ups, although further research could be undertakenon comparisons particularly regarding sediment transport.By reducing the confinement of an channelized urban stream through the restorationset up, a more varied channel morphology was created and it can be concluded there wasgreater habitat potential. Results do suggest that a restored reach did stabilize when ana-lyzing bed elevations and morphology, suggesting that the restoration approach of wideningareas of urban streams by removing bank protection can successful. However, the reductionin sediment transport through a restored system indicates the need to monitor sedimentsupply into restored urban streams and reduce the supply if needed to ensure channel sta-bility. Watershed level management is required to manage sediment supply and transportthrough natural channels into urban stream systems to ensure aggradation is not an issuein restored channels. This can be achieved through dredging channels to remove sedimentpulses or areas of aggradation.Channelized streams were found to have a greater resilience to sediment pulses thanrestored reaches, so river management authorities need to account for the potential hazardsediment pulses pose in order to successfully achieve restoration aims. By restoring areas ofurban streams to improve habitat potential, the risk of flooding as a result of large sedimentpulses increases as the channel resilience is compromised.45One way to mitigate this increased risk, if restoration is still prefer over a channelizedstream, is to include additional bank protection measures to increase sediment transportthrough a restored reach and reduce aggradation from sediment pulses. The GeomorphicRiver Engineering approach using stabilizing grains did improve the resilience of the restoredstream to pulses whilst still improving the habitat potential indicating it may be successfullyimplemented in restoration projects to provide a balance between habitat potential andhazard management.46ReferencesAshmore, P., & Church, M. (2000). The impact of climate change on rivers and riverprocesses in Canada.Auerswald, K., Moyle, P., Seibert, S. P., & Geist, J. (2019). 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DODs were used to calculate volume changes in theupstream, treatment and downstream reaches of the channel.92 94 96 98 10095.095.596.096.597.097.595.095.596.096.597.097.5−0.030−0.020−0.0100.0000.0100.02092 94 96 98 10095.095.596.096.597.097.595.095.596.096.597.097.5−0.050−0.040−0.030−0.020−0.0100.0000.0100.02092 94 96 98 10095.095.596.096.597.097.595.095.596.096.597.097.5−0.040−0.0200.0000.0200.040Figure A2.1: DODs for Experiment 1b, 2b and 3b, comparing the use of a constant sediment feed. DODsshow the changes in elevation at Hour 8 compared to Hour 1, with red area showing increasedelevation whilst blue areas show a decrease in elevation. The alternate red and blue areasseen in the DOD for Exp 1b are indicative of riffle-pool morphology5392 94 96 98 10095.095.596.096.597.097.595.095.596.096.597.097.5−0.040−0.0200.0000.0200.04092 94 96 98 10095.095.596.096.597.097.595.095.596.096.597.097.5−0.020−0.0100.0000.0100.02092 94 96 98 10095.095.596.096.597.097.595.095.596.096.597.097.5−0.030−0.020−0.0100.0000.0100.0200.030Figure A2.2: DODs for Experiment 1c, showing changes in bed elevation for different sized sediment pulses.DODs show the changes in elevation after the sediment pulse compared to before, with redarea showing increased elevation whilst blue areas show a decrease in elevation5492 94 96 98 10095.095.596.096.597.097.595.095.596.096.597.097.5−0.020−0.0100.0000.0100.020Figure A2.3: DODs for Experiment 2c, showing changes in bed elevation for different sized sediment pulses.DODs show the changes in elevation after the sediment pulse compared to before, with redarea showing increased elevation whilst blue areas show a decrease in elevation92 94 96 98 10095.095.596.096.597.097.595.095.596.096.597.097.5−0.010−0.0050.0000.00592 94 96 98 10095.095.596.096.597.097.595.095.596.096.597.097.5−0.015−0.010−0.0050.0000.0050.0100.0150.020Figure A2.4: DODs for Experiment 3c, showing changes in bed elevation for different sized sediment pulses.DODs show the changes in elevation after the sediment pulse compared to before, with redarea showing increased elevation whilst blue areas show a decrease in elevation55Appendix BSediment Output RatesThis section presents information on sediment output rates from pulse experiments (Exp1c, 2c and 3c). A comparison graph is also shown with the output rates for the constantfeed experiments across all three channel designs (Exp 1b,2b and 2c).0 100 200 300 400 5000.20.40.60.81.0Experiment run time (minutes)Sediment output rate (kg)10% pulse 25% pulse 50% pulseSediment output rate for Experiment 1cFigure A3.1: Stream table sediment output rate for Experiment 1c560 100 200 300 4000.10.20.30.40.50.60.70.8Experiment run time (minutes)Sediment output rate (kg)Urban stream constant feed 10% pulseSediment output rate for Experiment 2cFigure A3.2: Stream table sediment output rate for Experiment 2c570 100 200 300 400 500 6000.20.40.60.81.0Experiment run time (minutes)Sediment output rate (kg)Urban stream constant feed 10% pulse 25% pulseSediment output rate for Experiment 3cFigure A3.3: Stream table sediment output rate for Experiment 3c580 100 200 300 4000.00.20.40.60.81.0Experiment run time (minutes)Sediment out (kg)Sediment output from constant feed experiments of all experimental set ups Experiment 1b Expeirment 2bExperiment 3bFigure A3.4: Stream table sediment output rate for Experiment 1b, 2b and 3b59–>60
Thesis/Dissertation
eng
Geography
Vancouver : University of British Columbia Library
Attribution-NonCommercial-NoDerivatives 4.0 International
Graduate
Eaton, Brett C.
Sediment transport and storage in urban streams
Text