MORPHOLOGY OF THREE SEM-ALLUVIAL STREAM CHANNELS IN SOUTHERN ONTARIO

by

Giflian E. Foster

Department of Geography

Submitted in partial fblfiIIment of the requirements of the degree of Master of Science

Faculty of Graduate Studies The University of Western Ontario London, Ontario November, 1998

O Gillian E. Foster 1998 National Library Bibliothèque nationale 1+1 of,", du Canada Acquisitions and Acquisitions et Bibliographic Services services bibliographiques 395 Wellington Street 395. nie Wellington Ottawa ON K1A ON4 Ottawa ON KIA ON4 Canada Canada Your t% Votre refër~nte

Our Ne Notre retéfence

The author has granted a non- L'auteur a accordé une licence non exclusive licence allowing the exclusive permettant à la National Library of Canada to Bibliothèque nationale du Canada de reproduce, loan, distribute or sell reproduire, prêter, distribuer ou copies of this thesis in microform, vendre des copies de cette thèse sous paper or electronic formats. la fome de microfiche/fïlm, de reproduction sur papier ou sur format électronique.

The author retains ownersbip of the L'auteur conserve la propriété du copyright in this thesis. Neither the droit d'auteur qui protège cette thèse. thesis nor substantid extracts from it Ni la thèse ni des extraits substantiels may be printed or otherwise de celle-ci ne doivent être imprimés reproduced without the author's ou autrement reproduits sans son permission. autorisation. Stream in southwestern Ontario are commonly incised into a variety of erodible glacial matenals, ranging fiom cohesive clay to boulders, which they often lack competence to transport. Detailed longitudinal profiles surveyed along three such 'semi- alluvial' channels (Dingrnan, Oxbow and Nissouri Creeks) indicate that pool-riffle spacing is short, irregular and morphology is poorly developed. Common features include a disordered bed material sequence, deep sculpted till-lined pools, multiple riffies, over-widened bends and till ledges. Stream rehabilitation is ofien based on simple assumptions of alluvial chamel characteristics, such as a mean pool-nffle spacing of five to seven times the channel width. Various techniques for defining bedforrn spacing are invest igat ed. Spacing is found to be sensitive to its definition, frequency distributions are positively skewed and both mode and mean spacings are less than 5-7 widths. Natural Channel Design and habitat restoration therefore needs to incorporate differences in pool-rime features that exist in semi-alluvial streams.

Keywords: Pool, Riffle, Bedform, Semi-Alluvial, Fluvial Geomorphology, Dingman Creek, Oxbow Creek, Nissourî Creek, Natural Channel Design 1 wish to thank my advisor, Dr. Peter Ashrnore, without whom this thesis couid not have corne to hition. His hom of counseling and generous financial support through an N.S.E.R.C. operating gant are much appreciated. Thanks are also owed to Bill Snodgrass. the Credit Valley Conservation Authority and the Ontario Ministry of Naturd Resources for mermonetary suppon during the field season. Thanks to Rick GoIdt of the Upper Thames River Conserva~ionAuthority, who provided documentation about the study area. I greatly appreciate the CO-operationof the local residents who gave permission to be on their land and who supplied information about the creeks and area. Thank you to the many and varied field assistants; Barb for wanting to get started yesterday, Matt for not ietting go of that tree û-unk when up to his chin in water, Alex for helping when he didn't have to, for being patient and for swiving my stress. Peggy and Serge ("lovely"), Rob for taking a break fiom tree rings to try out rivers for a day. the various animals that tagged dong and provided amusement (Casey the dog. the bat. and the bu11 that came a bit too close), but most of alI, thanks to Heather for stepping in when al1 seemed lost, for her dedication, patience. ceaseless enthusiasm. amazingly neat field notes, hilarious sketches and for acquainting the crayfish with Skittles. Thanks tu Fred. without whose encyclopedic knowledge of computer software. surveying savvy and patient teaching 1would be tnily lost. Thank you to my parents, who (when they werenotgetting married or Ieaving the country) were always there for me - my mother's leîters are always something to look forward to. nianks to my brother for supplying me with 'real' music and for being rq7 confidant across the miles - I'm proud of you Nick. Thanks to the gang who are still going through this emotional roller-coaster that is grad school, and to those who have already made it out the other end: to Emma (when she was actually around) and Gary for Chapters trips and for keeping me domto earth. to Bonnie for cleaning (repeatedly) around my jungle of plants and for sharing her mother's lemon loaf, to LeeAnn for teaching me not to 'cave', to Rob for providing amusement and fixing my computer, and Andrea for always smiling, to Rich - someone who also understands why rivers are exciting, to Steve and Stacey (good luck you two), to Tmdy or Strudel (guac queen and taxi extraordinaire), and to Scott for not succeeding in his efforts to bring Star Wars into my life. Thanks also to Trish and Dave for knowing that real coffee cornes hmout west, to Melissa, Cheryl, Jen, Kumari, Came, Dendro Don (OK, ifs not a purse), Connie, Dan, Evan, and Ethan (for giving up his room). And finally, thanks to Pepper, my cat- for comforting me and easing the stress - and for only putting me in hospital the one time.. .

I wouid like to dedicate this thesis to my grandmother, Marie Foster. who passed away before 1 could make her really proud.

Ho- GidL TABLE OF CONTENTS Page. CERTIFICATE OF EXAMINATION ...... 11 ... ABSTRACT ...... 111 ACKNO WLEDGEMENTS ...... iv TABLE OF CONTENTS ...... vi LIST OF TABLES ...... x LIST OF FIGURES ...... xi LIST OF APPENDICES ...... xlv

CfFAPTER 1. Introduction ...... 1

1.1 General introduction ...... ,, ...... ,, 1 1.2 Pools and riffles and chamel restoration ...... -2 1.3 Research objectives ...... -4 1.4 Framework of the study ...... 4

CHAPTER II .Pools and rimes: tbeir form. definition. and signifieance ...... 6

2.1 Characteristics of the ideal pool-riffle sequence in regularly meandering alluvial rivers ...... 6 2.1.1 Pook ...... 6 2.1.2 Riffles ...... 7 2.1 -3 Pools and riffles ...... 8 2.1.4 Meanders and the pool-riffle sequence ...... -9 2.2 Problems associated with pool-rime identification ...... 10 2.2.1 Definition of the pool-rime sequence ...... 10 2.2.2 Field identification of pools and riffles ...... 13 2.3 Pool-riffle spacing ...... 14 2.3.1 Deviations from the ideal pool-riffle pattern ...... -16 2.3.1.1 Irregular planform ...... 16 2.3.1 -2Local sediment supply ...... 17 2.3.1.3 Forced pool-riffle morphologies ...... -18 2.3.1.4 Streams in bedrock ...... 18 2.3-2 Standardkation by channel width ...... 19 2.4 Influence of glacial material on pool-rifle sequences in southem Ontario ...... -20

CHAPTER III .Study area and research methods ...... 24

3.1 Physical characteristics of the mdy area ...... -24 3.2.1 Geology and Geomorphology ...... 24 3.1 -2 Soils and vegetation ...... -25 3.1.3 Ciimate ...... -26 3 -2 Site selection ...... -26 3 -3 Study site description ...... 29 3 .3.1 Dingman Creek ...... 31 3 .3.2 Oxbow Creek ...... -34 3 .3.3 Nissouri Creek ...... 36 3 -4 Field techniques ...... 38 3.4.1 Bed profile and planform survey ...... 38 3.4.2 Bathymetricsurvey ...... 41 3 -5 Data preparation and analysis ...... 41 3.5.1 Channel planform ...... -42 3.5.2 Bedprofile ...... 42 3.5.2.1 Pool-riffle definition problem ...... 42 3 S.2.2 Field identification of bedforms in test reach .....43 3.5.2.3 Visual inspection of test reach bed profile ...... -43 3.5 .2.4 Linear regression of test reach bed profile ...... -45 3.5 .2.5 Polynomial regression of test reach bed profile ....-46 3.5-2.6 Bedform differencing technique on test reach bed profile ...... 46 3.5.2.7Standardkation of the test reach bedforms by chamel width ...... -49 3.5.2.8 Cornparison of identification methods in test reach ....-51 3 53 Bedform identification in the study site long profiles .....52 3 54 halysis ...... 54

CHAPTER IV .Channel morphology in semi-alluvial streams ...... 55

4.1 Introduction ...... -55 4.2 Longitudinal channel profile ...... -56 4.3 Valley scale topography ...... 57 4.4 Channel pattern features ...... 57 4-41 Channel width ...... -57 4.4.1.1 Sediment delivery to the channel ...... -65 4.4.2 Planform adjustment ...... -66 4.5 Bed material ...... 71 4.5.1 Glacial till in the channel ...... 71 4.5.1.1Micro-forms in glacial till ...... -72 4.5.2 Downstream bed matenal sequence ...... -72 4.5.3 Sediment transport in semi-alluvial streams ...... 77 4.6 Channel scale bed topography ...... 79 4.6.1 Rimes and bars ...... 79 4.6.2 Pools ...... -85 4.6.2.1Unusual pool morphologies ...... 85 4.6.2.1.1 Scour pools ...... 85 4.6.2.1.2 Circular meander pool ...... 86 4.6.3 Other channel scale bed features - till ledges ...... -90 4.7 Summary ...... 90

vii CHAPTER V .Poo1 and rime characteristics in semi-alluvial streams ...... 94

5.1 Introduction ...... -94 5.2 Charactenstics of pools and riffles in the chamel profile ...... 96 5.2.1 Dingman Creek ...... -96 5.2.2 Oxbow Creek ...... -98 5.2.3 Nissouri Creek ...... -98 5.3 Bedform spacing ...... 100 5.3.1 Standardization of bedform spacing by channel width . . -101 5.3.2 Frequency distribution of bedform spacing ...... -103 5.3.3 Forced mean bedform spacing of seven times the channel width ...... -105 5.3.4 Comparison between bedform spacing in till and alluvial reaches ...... Il 1 5.3.5 Bedform spacing in the downstream direction ...... 114 5.4 Pools and riffles in the channel planform ...... 118 5.4.1 Bends with no pools ...... -122 5 .4.2 Bends with pools ...... -122 5 .4.3 Riffles in bends ...... -122 5 .4.4 Bedforms in straight reaches ...... -123 5.4.5 Featureless reaches ...... 123 5.4.6 Planform location of bedforms forced to a mean spacing of seven times the channel width ...... -123 5.5 Bedform amplitude ...... 127 5.5.1 Pool depth ...... -128 5.5.2 Pool depth with distance along the channel ...... 130 5.5.3 Comparison between pool depth in till and alluvial reaches . . -132 5.5.3.1 Pools in bends and straight reaches ...... 134 5.5-3 -2 Radius of curvature and pool depth ...... -138 5.5 -3-3 Pool depth and confinement ...... 138 5.6 Summary ...... 140

CHAPTER VI .Discussion ...... 142

6 1 Introduction ...... -142 6.2 Pool-riffle identification problems ...... -142 6.2.1 Pool-riffle definition techniques ...... -142 6.2.2 Pool-riffle spacing definition ...... -143 6.2.2.1 Identification of features ...... -143 6.2.2.2 Choice of bed feature upon which to base measurement ...... 144 6.3 Variability in pool-riffle spacing ...... -146 6.4 The formation of pools and riffles in semi-alluvial channels ...... 149 6.5 State of chamel adjustment ...... 151 6.6 Morphological relationships in semi-alluvial strearns ...... -152 6.6.1 Relationship between drainage basin area and bankfûll ... Vlll width and depth ...... -152 6.6.2 Relationship between pool spacing and width ...... -152 6.6.3 Relationship between bend radius of curvature and bankfiill width ...... 154 6.6.4 Relationship between stream sinuosity and bankfull width ..... 154 6.7 Conclusion and implications for stream management ...... 154

CHAPTER VII .Summary and conclusions ...... -157

7.1 Introduction ...... ,...... 157 7.2 Surnmary of major research findings ...... -157 7.2.1 Morphology of semi-alluvial strearns ...... -157 7.2.2 Pool-riffle spacing and amplitude in semi-alluvial streams ....-158 7.2.3 Pool-riffle identification techniques ...... 159 7.3 Implications for effective Stream management ...... -160 7 -4 Recornmendations for friture research ...... 160

REFERENCES ...... -163

APPENDIX 1 ...... -171 APPENDIX II ...... 184 APPENDIX III ...... -200 APPENDIX TV ...... -214

CURRICULUM VITA ...... -215 LIST OF TABLES

Table Description Page

2.1 Selected pool-rime spacings reported in the iiterature ...... -15

3.1 Grid references for study site locations ...... -29 3 -2 Channel summary data ...... -30 3 -3 Study site surnmary data ...... -31 3.4 Previous studies conducted on Dingman Creek ...... -31 3.5 Number and lengths of bedforms identified using a variety of techniques in the Dingman Creek test reach ...... SI 3 -6 Tolerance values used in bedform differencing technique for Dingrnan, Oxbow and Nissouri Creeks ...... -52

4.1 Study Site Concavity Indices ...... -56 4.2 Length of study site occurring in glacial sediments ...... -71 4.3 Dingman and Nissoun Creek Stream power ...... -79 4.4 Comparison between dimensions of streams containing circular meander pools ...... 89

Bankfiill channel width dimensions for the study sites ...... 33 Surnmary statistics for bedform spacing fkequency ...... IO5 Tolerance value and number of bedforms required to force spacing to 7W .. 1O6 Surnmq statistics for bedform spacing frequency where mean spacing is forced to 7 channel widths ...... -111 Cornparison between bedform length in alluvium and glacial till reaches .... 114 Number of bends and bedfonns in study streams ...... 118 Number of bends and bedforms in study streams when mean spacing is 7 times the channe1 width ...... 127 Bedform amplitude (m) in study streams ...... 128 Surnmary statistics for pool depth in the study channels ...... 130 Comparison between pool depths in alluvial and glacial till reaches ...... 132 Proportion of deep pools formed in tif1 and alluvium ...... 134 Sumrnary statistics for pool depth in bends ...... 137 Summary statistics for pool depth in straight reaches ...... -137 Radius of curvature and pool depth in confined and unconfined bends ....140

6.1 Simple statistics for bedform spacing fiequencies ...... -148 LIST OF FIGURES

Figure Description Page

2.1 Idealized pool-rime sequence illustrating cross-section and location of pools and riffles within the planform ...... 7 2.2 Meander definition diagram showing location of pools and riffles ...... 10 2.3 Frequency distribution of pool-pool spacing for streams in southem Ontario.. 22

Long profiles of each channel showing locations of shidy sites ...... 28 Map of southern Ontario showing approximate boundary of Thames River watershed and study site locations ...... -28 Dingrnan Creek study site map ...... -32 Oxbow Creek study site map ...... 35 Nissouri Creek study site map ...... -37 Equipment used during field survey ...... -40 Bed profiles of Dingman Creek test reach, showing locations of pools and riffles identified during the field survey, by visual interpretation, linear and polynomial regression techniques ...... -44 Bed profiles of Dingman Creek tea reach, showing locations of pools and riffles identified by the bedform differencing technique using various T values ...... -48 Frequency distributions of bedform spacing along the Dingman Creek test reach ...... 50

Hypothetical cross-sections of two semi-alluvial channels ...... -58 Aerial photograph of incised section of Dingman Creek ...... 59 Map of Dingman Creek study reach showing occurrence of glacial till visible in charnel bed and banks. bend number. distance along channel and significant features ...... -60 Map of Oxbow Creek study reach showing occurrence of glacial till visible in channel bed and banks. bend number. distance along channel and significant features ...... 61 Map of Nissouri Creek study reach showing occurrence of glacial till visible in channel bed and banks. bend number. distance along channel and significant features ...... -62 Bankfull channel width with distance along the charnel for Dingman, Oxbow and Nissouri Creeks ...... -63 Tills composed of large cobbles and boulders held tightly within a matrix of clay and fine silts ...... -64 Alluvial material deposited over cohesive till ...... 64 Groundwater seeps at tiIValluvium contact ...... -67 Cracks and lumps of clay broken away from clay-till bank ...... 67 Examples of mass wasting of glacial deposits ...... -68 Exposed tree roots in the chamel banks ...... 69 Clay-till sculpted by the flow of water ...... 73 Pitîed and sculpted till rnicroforms ...... -74 Downstrearn dominant bed material ...... -75 Remnant boulders dong Nissouri Creek ...... -76 lüffle depleted of alluvial material in its upstream end ...... 80 Till exposed in stream bed ...... 80 Featureless plane-bed reach on Nissoun Creek ...... -82 Concave rime face composed entirely of till ...... -82 Riffle at entrance to bend 023 ...... -83 Downstream view showing deflection of thalweg past bend ...... 84 Scour pool formed against resistant block of clay-till in channel bed ...... 84 Deep 'bath-tub' shaped scour pool in till in cul-off reach of Oxbow Creek ..... -87 Unusual circuiar pool on Dingman Creek ...... -88 Till ledge extending into channel fiom base of bank ...... 91 Bathymetric survey of bend D3 8 showing till ledge ...... -92 Sharp contact between till in bed and alluvial ...... -93

Bed profiles for Dingman, Oxbow and Nissouri Creeks ...... -95 Bed profiles of Dingman Creek. showing locations of rimes and pools identified by the bedform differencing technique using a T value of 0.578(SD)=O.175 ...... 97 Bed profiles of Oxbow Creek, showing locations of riffles and pools identified by the bedform differencing technique using a T value of 0.54(SD) = 0.118 ...... 99 Bed profiles of Nissouri Creek, showing locations of riffles and pools identified by the bedform differencing technique using a T value of 0.75(SD) = 0.090 ...... -100 Definition diagram for methods of measuring bedform spacing ...... 102 Frequency distributions of bedform spacing using bedform differencing technique ...... 104 Forecast curves used to obtain T values required to give a mean spacing of 7 times the bankfiill channel width ...... 107 Bed profile of Dingman Creek, showing locations of riffles and pools when mean spacing is forced to 7 times the bankfull channel width ..... 108 Bed profile of Oxbow Creek, showing locations of riffles and pools when mean spacing is forced to 7 times the banicfûll channel width ..... 109 Bed profile of Nissouri Creek, showing locations of riffles and pools when mean spacing is forced to 7 times the bankfull channel width ..... 110 Frequency distribution of bedform spacing at a mean spacing of 7W ..... 112 Bedform spacing with distance along channel ...... 116 Cumulative departure from mean pool spacing with distance along channel ... 117 Map of Dingman Creek study reach showing location of pools and rimes identified by the bedform differencing technique. T=0.578(SD) ..... 119 Map of Oxbow Creek study reach showing location of pools and rimes identified by the bedform differencing technique. T=0.54(SD) .....120 Map of Nissouri Creek study reach showing location of pools and nffles

xii identified by the bedform differencing technique. T=0.75(SD) ..... 121 Map of Dingman Creek study reach showing location of pools and nffles spaced a mean of 7W ...... 124 Map of Oxbow Creek study reach showing location of pools and rimes spaced a mean of 7W ...... -125 Map ofNissoun Creek study reach showing location of pools and riffles spaced a mean of 7W ...... -126 Frequency distributions of pool depth in study reaches ...... 129 Cumulative departure fiom mean pool depth with distance along channel ..... 131 Frequency distnbutions of pool depth in till and alluvial material in study reaches ...... 133 Frequency distributions of pool depth in bends ...... 135 Frequency distributions of pool depth in straight reaches ...... 136 Scatter plots showing the relationship between pool depth and radius of curvature in bends ...... -139

Meander planform showing placement of pools and riffles (i. after Dietrich. 1987; ii. in smdy sitesj ...... 145 Cornparison of bedform spacing fiequency distributions between study reaches and those in the literature ...... -147 Channel relationships for strearns in southem Ontario ...... 153

... Xlll LIST OF APPENDICES

Appendix Page

Field data for Dingman Creek ...... 171

Field data for Oxbow Creek ...... -184

Field data for Nissouri Creek ...... 200

Concavity Index Calculation ...... -214

xiv 1 General introduction The morphology of a natural stream channel is the result of a combination of hydrological charactenstics, such as discharge, valley gradient, sediment source and supply. Most of the world's rivers are 'alluvial'; they flow upon thick unconsolidated deposits of previously lain fluvial material and have an associated floodplain. Exceptions to this are nvers whose beds are in full or partial contact with bedrock and therefore lack significant quantities of alluvial material for portions of their length. Classical empirical studies of river form have established well-known simple finctional relations between river form and process variables such as discharge (see Leopold and Maddock, 1953; Leopold et al., 1964; Richards, 1982). The use of these relationships, which were developed primarily for regular sinuous alluvial rivers, is cornmon in describing a particular river system and in restoring hydrological balance in disturbed streams (Gore, 1985). However, the characteristics of non-alluvial streams are much Iess well known. Streams that are confined and incised into cohesive glacial and proglacial deposits (Campo and Desloges, 1994), rather than alluvial matenal or bedrock, are seldom mentioned in the literature. These streams lack well-developed floodplains, are limited in their ability to erode and adjust their characteristics, and receive their sediment supply fiorn the glacial deposits through which they flow (Church and Slaymaker, 1989; Kellerhals and Church, 1989). Thus they are not stnctly alluvial streams, but neither are they bedrock channels. The bed material varies in size fiom resistant clay, through non- cohesive sands and gravels, to large boulders, which the stream is often not competent to transport. The stream gradient is extemally imposed and pool-riffle development may be inhibited by numerous coarse sediment inputs along the channel and by the presence of till in the bed. Erosion of the channel boundary exposes till which is frequentty covered by a thin veneer of 'alluvial' material, derived originally from the till itself. These charnels do not fit in the conventiond 'diuvia17 river model, being ody superfïcialiy alluvial, instead, they fa11 somewhere on the continuum between alluvial and bedrock charnels in their rnorphological response and are perhaps better described as 'semi- alluvial '. Current data for southem Ontario (Annab le, 1995) indicate t hat semi-alluvial conditions may exist, while the Quatemary history of large areas of Canada would suggest that rnany more semi-alluvial channels occur than are presentiy recognized.

1.2 Pools and rimes and channel restoration The pool-tiflie bedform sequence is a significant element in the dynamic adjustment between form and process in alluvial streams (Clifford and Richards, 1992). Knowledge of the flow-sedirnent dynamics and regulatory role in low ilow hydraulics of pool-riffle topography is integral to maintenance of healthy stream ecology (Cliflord and Richards, 1992). PooCriffle spacing is scaled by discharge and channel width (Leopold et al., 1964; Keller and Melhorn, 1978). A regular mean spacing for pools and riffles, in the range of five to seven times the channel width (W), was first observed by Leopold et al. (1964) and has been supported in the literature for decades (Keller, 1972; Lisle, 1982; Gregory et al., 1994; Jurmu and Andrle, 1997) in spite of the fact that the range in reported spacing varies considerably around this mean (see Keller and Melhom, 1978; Hooke and Harvey, 1983). A number of methods for determining pool-riffle spacing are used in the literature, but as yet, no definitive objective rnethod is agreed upon. Simple assumptions, such as regular pool-riffle spacing of 5-7W,are used increasingly in chamel restoration procedures and natural channel design (National Research Council, 1992; Newbury et al., 2997). Restoration seeks to return an ecosystem to its condition prior to disturbance. In the case of rivers, restoration stnves to restore the natural channel geometry, riparian and aquatic vegetation, and sediment and flow regime (National Research Council, 1992) required to support and maintain a healthy fish population (Newbury et al., 1997). Conservationists, particularly those interested in improving fish habitat, have developed a vviety of stream restoration measures, of which constmction of artificial pool-riffle habitat is a widely used and relatively successful technique. Pools and rimes provide a variety of habitat types necessary to support a wide selection of aquatic organisrns. High velocities and turbulent flow at riffles increases oxygenation of the water, and as such, rimes are preferentiaily used as spawning sites by salmon. Conversely, pools often intersect the water table and provide deeper coder water habitats for the rearing of young (Beschta & Platts, 1986). Poor development or loss of pool-riffle habitat can therefore decrease biotic produaivity and diversity of a strearn. Even if mean spacing were a reliable design guide in alluvial streams, such an assumption may not be appropriate in semi-alluvial streams. It is necessary to have a clear understanding of each stream feature in the context of the strearn system as a whoie before such measures may be taken. The hydrologic, geologic and vegetative constraints of a particula. location must be considered before engineering any channel 'improvement' structures (Beschta & Platts, 1986). Rehabilitation based on a tacit assumption that riffle spacing occurs on a 5 to 7W cycle and that riffle to pool length is 1: 1 (Gordon et al., 1992; National Research Council, 1992) may be outdated. Current data for southern Ontario (Amable, 1995) indicate a mean pool spacing of 4.6W (range 0.6-1 1W), while the mean riffle:pool ratio is in the order of 1:2.4 (range 1:0.2- 1: 1O), both of which lie outside the expected range of values (Leopold et al., 1964). Research on river characteristics and restoration practices in alluvial channels are abundant in the literature; however, there is little work concerned with the semi-alluvial nature of streams in previously glaciated areas (see Church and Slayrnaker, 1989), nor is there any literature concerning procedures for rnitigation or restoration in these potentially cornmon environments. ûther than the data set collected by Annable (19951, the pool-rime morphology of these streams has not been directly investigated in southem Ontario, or elsewhere. Few researchers have recognized that there rnay be fundamental morphological and hydraulic distinctions between 'semi-alluvial' streams and 'normal' alluvial streams. The pool-riffle sequence may be used as an indicator of the potential effect of semi-alluvial conditions on stream morphology. It is anticipated that serni-alluvial conditions may restrict pool-riffle development or cause irregularities in bedform spacing and amplitude owing to confinement at bluffs, wildly variable bed material characteristics and overall low excess energy. The initial task, therefore, is to develop a thorough descriptive base of pool-rime morpholagy in a sample of semi-alluvial streams in order to attempt an understanding of the implications for fluvial geomorphology, irnprove restoration techniques that currently follow 'text-book' principles derived for alluvial streams, and provide morphological data for the effective management of many of Canada's lowland nvers. Process-based theory of pool-riffle formation rnay require modification if there are significant differences in rnorphology between alluvial and semi-alluvial streams.

1.3 Research objectives To test the proposition that the pool-riffle morphology of semi-alluvial streams is irregular, poorly developed and short-spaced owing to low Stream competence, limited availability of alluvial material, irregular meanders and confinement at bluffs, the following objectives must be met:

describe the morphology and bed material characteristics of three semi-alluvial streams in southern Ontario, examine the utility of a number of pool-riffle definition methods and to assess the sensitivity of the results to the various procedures, describe and explain pool-rime spacing distributions in cornparison with those of alluvial and bedrock streams reported in the literature, examine the effect of confinement at valley-sides on channel morphology and bed topography, and examine the effect of channel width on pool-;iffie spacing.

Framework of the study Chapter II gives a brief background into the mechanics involved in the formation of the pool-riffle bedform, outlines a variety of problems associated with methods used in bedform definition, and identifies southem Ontario as a iandscape in which conventional relationships developed for alluvial streams may not be applicable. A description of the study area, specific field sites, field techniques and bedform identification procedures are given in Chapter III. Chapter N supplies an account of semi-alluvial Stream morphology, while Chapter V investigates various aspects of the pool-riffle sequence. Chapter VI supplies further discussion of the peculiarities of semi-alluvial stream morphology, evaluates the utility of the bedform differencing technique, and suggests some implications that the differences in rnorphology may have for effective stream management and restoration. Finally, Chapter W provides a sumrnary of the thesis and indicates areas for fiirther research. CHAPTER II POOLS AND RIFFLES: TEtEIR FORM, DEFINITION, AND SIGMFTCANCE

2.1 Characteristics of the iddpool-rime sequence in regularly meandering alluvial rivers Natural rivers rarely have featureless beds for any great distance; instead the bed material is shaped into a senes of 'bedforms' dependent on the flow geometry for their size and location. Alternatkg deeps (pools) and shallow depositional bars (riEles) are characteristic channel-scale bedforms found in most meandering gravel-bed and mixed load strearns of moderate gradient (dope <0.0 15) (Milne, 1982; Sear, 1996) and are considered an equilibrium form (Kmghton, 1984). The pool-ae unit is regarded as a single bedfom (Dietrich, 1987) (figure 2.1) and is distinct fiom other bed features such as npples, dunes and antidunes that are nomally formed in sand. The capability of a Stream to mode its bed depends on the mobility of the bed materiai and Stream energy, which are dictated in part by bed matenal size and the fiequency of competent channel-forrning flows (Knighton, 1984). Bedforms can oniy form where excess energy is available for the rnobilization of sediment. Pools and rifnes are intemelated with the meandenng plan-fom (Richards, 1976a), where pools typically occur at the outside of bends, and rimes are located in straight reaches between bends (Yang, 1971). The distribution of bedforms is assumed to be regular, with spacing scaled by the channel width (Leopold et ai., 1964). The mean spacing of bedfonns was observed to be in the order of 5 to 7 times the channel width by Leopold et al. (1964), and rnany years of further investigation has done Little to alter this hding (Thorne et al., 1997) even though the range in reported spacing varies considerably, and 'additional' rimes are ofien observed between bends (Hooke and Harvey, 1983).

2.1..1 Pools Pools, topographie low areas in the channel bed, are usudy located closest to the concave bank downstream of the apex of a meander bend where flows converge at the bed (Keller and Mehorn, 1973; Knighton, 1984). At low flow, pools are deeper regions where the velocity and water surface gradient are cornparatively low, while during higher flows they are locations of intense scour and energy dissipation (Beschta and Plans, 1986).

v Water daœat hi& flm -- Flow direction

Figure 2.1. Ideaiized pool-riffle sequence Uustrating cross-section and location of pools and riines within the planform. Note: difference in water surface profile between low and high flow. Adapted Born Gordon et al. (1992, p3 18) and Dietrich (1987, p 18 1).

Ritnes are depositional features that nonnaily denve their material fiom scour of upstrearn pools and are relatively fixed in location. Ritnes tend to have coarser, better- sorted, and more tightly packed bed material (Hïrsch and Abrahams, 198 1; Sear, 1996) than pools. This is attributed in part, to winnowing of fines fiom fies at low flows. Some particles may protmde above the water surface at low stage when d3es become dominant features of the channel geometry (Gordon et al., 1992). They occur at thalweg ideetion points, which were thought to be located rnidway between channel bends (Leopold et al., 1964), but more recent work suggests rifles occur closer to the downstream pool (Dietrich, 1987) (see figure 2.1). Ritnes are ofien lobate in shape and commonly slope altemately fiom one bank to the other giving a sinuous flow path even in straight reaches. They may extend obliquely or transversely across the entire channel and are attached to successive point bars (Ferguson, 1981; Dietrich, 1987).

2.1.3 Pools and riffles The cross-section profile at a riffle is generaliy rectangular in shape, whde pools tend to have a more asymmetrical protile (Keller and Melhom, 1973; Knighton, 1984; Gordon et al., 1992) that promotes flow convergence in a lirnited area, producing zones of intense scour. As water passes out of the constricted area, it diverges towards the opposite bank, depositing gravels and developing a shdower symmetncal cross-profile at rifnes (Keller and Melhorn, 1973). Featureless sections of bed may also occur. They are usually intermediate in depth between pools and riffles, and exhibit less turbulent flow than at d3es (Gordon et ai., 1992; Wohl et al., 1993). Few researchers recognize the existence of plane bed reaches within the pool-rifne bed topography, yet they are frequently observed in locations where pool-ntne development is inhibited, and ulthately affect bedform spacing (Wohl et al., 1993). Together, pools and rif£ies act to regulate energy expenditure in strearns. The presence of bedfoms creates flow resistance which in tum influences energy losses (Knighton, 1984). Rifnes act as natural weirs that pond water in the upstream pool at low and intermediate flows (Thorne et al., 1997), velocities are greater over the steep downstream face of the riflles and the water surface gradient is steeper (figure 2.1). Energy is dissipated through turbulence in this rougher section, particularly immediately downstream from the rime crest @eschta and Platts, 1986; Gordon et al., 1992), while upstream, stream power is reduced through the backwater and pool. As discharge increases, the velocity and water surface slope is observed to equalize between the two locations, eventually becomuig highest through pools (Keller, 1971 ). 2.1.4 Meanders and the pool-rime sequence Given an initidy straight channel with a flat bed, there is some debate in the kterature over the precise mechanism by which the development of pools and riffies matches development of the sinuous planform over tirne. Yang (1971) observed that similarity of spacing between pools and rifiies in straight and meandering channels may be an indication that pardel mechanisms create pools and rinles in both environments. A reversal phenornenon was proposed by Keller (197 1) to explain the fonnation of pools and ses; however, the precise mechanism of pool-riale formation and maintenance continues to be a subject of intense discussion in the literature (see Knighton, 1984; Clinord and Richards, 1992; Sear, 1996). Several hypotheses have been put forward, for exarnple: kinematic wave theory (Langbein and Leopold, 1968), bed material dispersion and sorîing (Yang, 1971), and convergence and divergence of flow (Kelier and Melhorn, 1973). The initiation of meandering is believed to be a result of turbulent velocity fluctuations associated with large scale coherent flow structures whose characteristic wavelength is some function of flow width (Richards, 1976a; Thome et al., 1997). This results in regularly spaced alternating zones of sediment accumulation and scour in the bed along the axis of flow (Richards, 1976b; Thorne et al., 1997). The deformations of the bed interact with the flow, generating lateral and vertical non-uniformiiy which, in tum, maintain the perturbations (Richards, 1976a). The rnorphological result is the development of a sinuous thalweg (Rhoads and Weiford, 1991 ; Thome et al., 1997) (see figure 2.2) which is directed towards the bank downstrearn from the rifne. Scour adjacent to one bank generates bank retreat and meander enlargement, while deposition of a bar occurs along the opposite bank. Because the location of pools is linked with the planform, the inter-pool spacing can be expected to be half the meander wavelength (Ferguson, 198 1). ..-...... A Meander wavetength R, Radius of curvature ,, ,,- Thalweg R meat crossover/ inflection point 0Pool

Figure 2.2. Meander definition diagram showing location of pools and riEles (adapted from Leopold et al., 1964, and Dietrich, 1987).

Data fiom meandering alluvial channels shows that pool depth increases as bend radius becomes tighter (Ferguson, 1981). Wohl et al. (1993) found that relative pool depth also increases as channel gradient decreases and therefore hypothesize that the balance between stream power and boundary resistance to erosion determines pool-rifne characteristics, such that changes in energy expenditure in a downstream direction (i.e. increasing stream power) are the cause for the rnorphological changes they observed. As discharge increases and slope decreases downstream, total aream power increases such that more energy is available for channel bed scour and thus, deepening of pools.

2.2 Problems associated with pool and rifile identification 2.2. t Definition of the pool-rime sequence Researchers have identified pools and =es through a variety of methods. Many merely idente them in the field with no reference to the specific critena they used, while others have used indicators such as particle size, water sufiace slope, the index d/d or vl+i (where v is the mean velocity, and d is the mean depth of fiow), the Froude number, regression or daerencing of elevations dong the channel (O'Neill and Abrahams, 1984). There is still no consensus about a consistent, objective and reproducible method of identification. Yang (1971) defhed pools and rifnes in tems of energy gradient represented by the water surface slope. Under this definition, riffies are areas where the energy gradient is steeper than the average, while in pools it is lower than the average. Richards (1 976a) cautions that the water surface slope over bedfom is stage dependent. As discharge increases towards bank£ùil, the diEerence in water surface siope between pools and fies is diminished, such that the effect of the meis 'drowned out' (Leopold et al., 1964) and identification of pool-He units using the water surface slope as an indicator is impossible. Bren (1990, in Gordon, 1992) suggested using Froude numbers less than 0.1 to indicate pools and Froude numbers greater than 0.1 to define non-pools. Dolling (1968) used a v/d ratio to identify 30 pools and nffles on Bronte Creek in south central Ontario. He assumed low values of the velocity to depth ratio indicated the presence of pools, whiie a high ratio indicated the occurrence of a rifne. Any ratio with a value in excess of the median was classified as a rifTle, while any value less than the median was assumed to be a pool. This method is highly subjective, depending entirely on the number and placing of cross-sections, laterai constriction and flow stage, and consequently its use is not a reliable method for distinguishing between pools and rimes. Bed material size is typicdy coarser over nales than in pools and Leopold et al. (1964) have used this to distinguish the two forms. While surface bed matenal has produced results that support this definition, larger bulk samples reveal less dserentiation in sediment sizes at depth (Miine, 1982). The degree of association between downstream variations in bed material size and the bed elevation oscillation were compared using the b-axis dimensions of surface particles. Mean particle sue was detennined to be the most effective measure for distinguishing between pools and riEles, although the relationships were weak (Milne, 1982). Richards (1976a) notes that most of the above criteria developed for the identincation of pools and rifnes are based on previous discharge events, and according to the velocity reversal hypothesis, a recent high flow may remove al1 fine sediment fiom a pool, thus leaving little dflerence in bed material size between pool and rifne. Flow parameters may Vary with the scale of the river system, gradient, roughness and discharge at which the measurements were recorded. As a solution to the reliable identification of pools and rif£ies, Richards (1976a) put forward the 'regression technique' in which regression analysis is used for demgpools and rifnes. A regression equation is fitted to a plot of bed elevations against channel distance and any value falhg below the regression line (a negative residual) is classified as a pool, while any value that plots above the regression line (a positive residual) is considered to be a me. Miine (1982) refined Richards' technique by definhg the length of pools and ritnes as the distance between points of intersection on the regression he and the bed profile. Non-iinear curves cm be used for large data sets. Richards' technique was the first objective method for identifjmg pools and rifnes that had been put forward in the Literahire, however, it is not without weaknesses. Large scale undulations in the channel bed may lead to extraordinarily long or short bed forms being identified which do not exist in reaiity (O'Neill and Abrahams, 1984). Where this occurs, pools and nnles do not appear as discrete groups of positive or negative residuals, such that the technique gives rise to inaccurate identification of bedforms in many streams that have minor concavity or convexity within their long profiles. Milne (1982) used the regression technique, but disregarded any residuals that appeared out of place to avoid definition of excessively long deunit s, thereby re-introducing subjectivity into his resuhs. O'Neill and Abrahams (1984) proposed a new method, cailed the bedform dserencing technique, which focuses on cumulative elevation change between successive measurement points dong the channel. Successive bed elevations are differenced in a domtream direction and the standard deviation (SD) of the resulting Merence values is calculated. Bedforms are identified when the cumulative elevation change since the last bedform exceeds a tolerance value, 'T', which is based on some measure of the standard deviation of the ciifference values. For the most realistic identification of bedforms, O'Neill and Abrahams suggest that when the fixed samphg interval approximates the channel width, T should be set equal to 0.75s~. When compared with the regression technique, the differencing technique proves more dependable in correctly identwg d3es and pools (O'Neill and Abrahams, 1984; Jurmu and Andrle, 1997). Advantages of the technique Lie in the fact that it @ves spatially consistent results, it involves basic mathematics and is therefore easy to employ, and it avoids the problem of identification of excessively long or short bedfonns. One drawback, however, is that subjectivity stiU exists since the choice ofthe tolerance value is at the discretion of the operator and WU ulthately aEect the number and spacing of bedforms

identified. The method requires fùrther independent testing and assessrnent .

2.2.2 Field identification of pools and rimes A variety of methods are used for the definition of pools and riffles in the field. Dserences in field procedure or perception of what constitutes a pool or ritne may potentially resuIt in a range of spacings being defined for the same reach by different researchers. Measurements are commonly taken along the channel centre-line or thalweg between rifile crests (see Harvey, 1975), pool bottoms (see Keller and Melhorn, 1978; Annable, 1995) or at breaks in the water surface dope (see Clinord and Richards, 1992; Stirling, 1998). Several assumptions are made when using these techniques: 1) that pools and riffles are altemately distnbuted along the channel, 2) that identification of bedforms is unbiased by perceptions of the field crew, 3) that the entire bed profile is composed exclusively of pools and fies, 4) that discharge does not change during the course of the survey, thereby 'drowning out' dinèrences in the water surface proflie when it is used as an indicator, and 5) that ail researchers define the ntfle crest and pool centre in the same manner. Differences in bedform spacing may arise sirnply as a result of the measurement technique. For example, int er-pool and inter-ritne spacings given by O 'Neill and Abrahams (1984, fig. 6) iilustrate a unimodal positively skewed distribution for inter-fie distances, while no single preferred spacing for inter-pool distances is found, even though the data are derived fkom the same reach of channel. Pool to pool measurements are most commonly used, however a sunrey based on regular intervals should allow unbiased detection of bedforms for later examination in the Iab. 2.3 Pool-riine spacing Regular spacing of pools and riInes is found in meandering, straight, ailuviai, bedrock, and dry ephemerai strearns (Gordon et al., 1992) and is a fundamental aspect of channel morphology (Montgomery et al., 1995). A well-established tenet, that the spacing of rifnes falls within a defined range of between 5 and 7 times the channei width (Leopold et al., 1964) continues to be referenced in the fiterature even though spacings that Vary considerably around this figure are ofien reported (see table 2.1) (JGughton, 1984; Gordon et al., 1992). One tends to loose sight of the fact that the ideal spacing of5 to 7W descnbes only an average condition and that both channel width and the inter-ritne or inter-pool distance are highly variable (Kmghton, 1984). Where the mean spacing is 6W (i. e. fds within the expected 5-7W range), Keller and Meihom (1978) find a high range in spacing of 1.5 - 16.7 W for ffeely meandering alluvial streams. Similarly, for a mean spacing of 7.4 W, Miine (1980) kds a range of 2 -22W. Hooke and Harvey (1983) were unable to define a single preferred dlie spacing in a range between 3 and 10W for bends with multiple mes. Frequency distributions of pool-rifne spacing are rarely given in the literature, thus another important condition is &en overlooked; the meun spacing of the pool-rBie sequence in alluvial grave1 bed streams may be in the range of 5 to 7W, but the modal spacing is ofien between 3 and SW (Keller, 1972; Keller and Meihorn, 1973). That the modal fiequency of bedform spacing is consistently less than the mean may indicate some systematic process is at work creating an abundance of short bedforms (see Keller, 1972). Reports of both high ranges in spacing and positively skewed frequency distributions (see Myers and Swanson, 1997) are not uncornmon, but are seldom addressed in the literature. Table 2.1. SeIected pool-nffle spacings reported in the literature Spachg (W) Notes Source Forested channeis, highest to lowest LWD loading (respectively),> 9W for most plane bed reaches, 24W for Montgomery et ai. (1995) pool-riffie sections, 0.2-3W for forced pool spacing Used median spacing Harvey (1975) Bedrock reach of the underfit Co10 River. New South Wales Dury (1966) Skirden Beck norîhwest Engiand Thompson (1984)

In flume, pool spacing for hi& amplitude meanders Whiting and Detrich (1 993)

Channelized reaches KelIer (1975)

Beschta and Platts ( I 986) Pd-Pool spacing, x 4W Kingledoors Bum. 3-7W River Ferguson (1 98 1) Fowey Range 2-24 for ben& in and out of phase with rifle units Hooke and Harvey (1983)

Unforested drainage basin and wooded. respectiveiy Keller and Taiiy ( 1979) Range 0.6- 11, Southern Ontario streams. 53% of the data Annable (1995) < 5W Lisle (1982)

Most fiequentiy referenced spacing Leopold et ai. (1964)

Range 1-16 Keller (1 972)

Review of pool-dlie papas, findings support LeopoId Gregory et ai. (1994)

Nevada rangeland streams Myers and S\vanson ( 1997) For 102 pool-riIBe sequences (individual 2 = 5.0,5.3, 5.9, Keller and Meihorn ( 1973) 6.0), 5.7 for straight reaçhes, 6.1 for simous reaches Width 6.15~1, spacing 34.16m Clifforcl (1993)

Wetland streams Jurmu and Andrle (1 997) Range 1.5-23.3 (one of highest ranges reportai, includes Keller and Melhom ( 1978) bedrock streams) Used bedform differençing technique to idenhify pools and O'Neill and Abrahams nnles ( 1984) North Tyne River, ûreat Britain Sear ( 1996)

UnpubLished Ph.D. thesis referenced in Ferguson ( 198 1), Milne (1980) range 2-22. mode 4-6 Kingtedoors Buni MiJne (1982)

8-1 Wi.0fo.37.~.-spac~g.~300m...... -...... -...... - .... carhg (1991) * highiighted spacmgs are affecteci by ex-tenial idluences 2.3.1 Devintions from the ideal pool-rime pattern In reality, numerous opportunities exist for disruption of the ideal bedform and meandering sequence. Variations in the regular pattern and spacing of bedfoms may result from local controls such as underlying geological constrictions (e-g. joints, fractures in bedrock), pockets of more cohesive material, changes in sedirnent supply, mass movements on slopes into the chamel, tree roots, organic debris forcing, planform irregularities or human intervention. Such disrupting influences are likely to prevail in the semi-alluvial environment in southern Ontario where streams pass through a variety of glacial materials that dBer in size, cohesiveness and delivery mechanism, such that determination of a single mean bedform spacing rnay be problematic and non- representative any way. Although pools are reported to occur cyciically in specific locations, it cm be seen that their size, frequency and distribution are likely to Vary considerably with the mechanism of their formation (Beschta and Platts, 1986). The implication of an average spacing persisting in the literature is that the problem is over-sirnplified. Many restoration organizations ignore the fact that there is likely to be variation of spacing and amplitude in the natural environment, yet variety of pool morphologies are necessary to provide vital habitat for dserent stages of development of young fish. This rnay prove detrimental as structures are placed in streams based on simplistic assumptions, such as mean spacing in the 5-TW range. improper placing of enhancernent structures ofien leads to detrimental feedback mechanisms in the channel or failure of the structure itself. Restoration measures should therefore consider the fiequency distribution of pool-rMe spacing in addition to mean conditions. It can be seen that the issue of pool-ri££ie spacing is a dilemma £?om both a theoretical and a channel design point of view.

2.3.1.1 Irregular planform Keller (1972) observed that the ideal regularly meandering pattern is rarely found for more than a few bends; instead, rnixed reaches occur with both straight and meandering sections that may have more than two pools between bends even though a mean bedfonn spacing of 5-7W occurs. He asserts that pool-rinle spacing appears to be independent of channel pattern and proposed a five-stage model by which alluvial stream channels develop in which he attempts to explain the break-dom in the expected planfom location of bedforms. As channels evolve fiom straight to meandering, altemating 10 bate bars deflect the thalweg from one side of the channel to the other and concentrate erosion on the outer bank, thereby increasing the curvature and overall channel length while decreasing the slope of the channel (Keller, 1972; Keller and Melhom, 1973). These bars dominate in the initial araight condition and give way to well developed pool-dfie sequences in the later meandering planform. As channel length and sinuosity increases however, new pools are inserted in order to maintain a constant spacing. He suggests that beyond a threshold path length of approxirnately 9 channel widths, spacing becomes unstable and breaks up hto two pool- rBe sequences, presumably because regular flow structures cannot be maintained over such distances (Hooke and Harvey, 1983). This may explain why a mean spacing of 5-7W is obtained, yet the most comrnon spacing may be less than this. Similar disruption of the regular bedform sequence rnay be expected in the study area where meanders are quite irregular and are separated by long straight reaches.

2.3.1.2 Local sediment supply Wohl et al. (1993) observed mass movernents fiom the valley walls to be a dominant control on the location of fies(over pools or runs) in the Bear River, California. Mass movernents serve as point source coarse sediment inputs into the channel and disrupt the pool-Mie sequence. Sunilarly, Miller (1958) and Leopold et al. (1964) found that pool-ritne morphology tends to be absent or poorly developed in boulder bed mountain streams incised into a Wisconsin age glacial moraine, even though stream gradient is conducive to their formation. They attribute this to the fact that the streams derive coarse bed material &om glacial deposits in steep cWs that is too large to be moved by the present flow regime. In this way, local sediment supply controls the development of pools and riffles through the Stream's ability to re-work its channei. Energy is dissipated overcoming roughness elements rather than being directed towards mobiIization of the bed and fbli pool-rime formation (Wohl et al., 1993). Such controls on bedform formation are directly applicable to streams in southern Ontario, which also experience deep incision into glacial deposits, that will be expressed in poorly developed bed topography .

2.3.1.3 Forced pool-rime morphologies Montgomery and Bufigton (1997) recognize distinct 'forced pool-riin.e' channel types in which pools and bars are forced by scour around obstructions, such as boulders or large woody debris (LWD) rather t han fonning in relation to channel and meander dimensions. They found spacings extending beyond the range characteristic of fiee formed morphologies: ranges were both greater than 9W7and shorter than 2-4W in plane- bed and forced pool-rifne channels, respectively. Myers and Swanson (1997) found exponentially distributed inter-pool distances in forced-pool streams. They suggest that a stream-size or flow rate threshold might ex&, which divides streams with random and regularly spaced bedforms; larger streams being able to 'flush-out' LWD and therefore more likely to have regularly spaced bedforms, while in srnalier streams, heterogeneities in the channel boundary control planfoxm and pool locations. The significance of forced pool-rifne morphology, and therefore difTerent spacing than predicted for a particular environment, is ofien ignored. Annable (1995) intentionaily disregarded micro-scale pools associated with boulders and LWD in his bedform survey of southwestem Ontario streams. Yet, if large boulders and LWD are a characteristic of particular strearns, then a sigdicant portion of the aquatic habitat is being ignored and bedform spacing is in fact shorter than is being reported. Recognition of forced pool-dBe morphologies is important as interpretation of whether these obstructions play an important role in governing bed morphology will have implications in determining charme1 response and hence restoration or mitigation procedures.

2.3.1.4 Streams in bedrock Analogies from the literature conceming bedrock streams may be applicable in semi-ailuvial environments. Cohesive glacial till may act to some extent like bedrock where it outcrops in the channel margins. In such an environment, the flow pattern and pool-ritne development is disrupted where channels impinge on bedrock bluffs. Secondary circulation is initiated, causing basal scour and over-deepening of portions of the channel bed (Rabeni and Jacobson, 1993), thereby forcing pools in locations other than meander bends. In a study of pools and rifnes in bedrock streams, Keller and Meihorn (1978) found pool spacing (6W) and channel width to be related regardless of whether the channels were in bedrock or aiiuvium. However, Roy and Abrahams (1980) reanalyzed Keller and Melhom's data and conclude that the spacing of pools is sigmficantly greater in bedrock streams (7W) and for that reason is not independent of channel boundary materiai.

2.3.2 Standardization by channel width Further to the variations in bedform spacing that are introduced by heterogeneity in the natural environment, is an issue that does not appear to have been addressed: bedform spacing is usually standardized by dividing by some measure of the channel width. However, there is little discussion about the sensitivity of this standardkation to the choice of width measurement . Channel width is commonly measured at a variety of locations within the channel: bankfùli width (the point at which a channel cannot contain an increase in discharge without overtopping its banks), water width, base flow width (see Richards, 1976b) or bed width (see Keller and Melhom, 1978). Each of these locations will give slightly different measurements for width and ultimately bedform spacing. Most studies use the bankfiili width. Additional variation may be introduced by using width measurements taken at rime or pool locations, which have been shown to dEer systematicdy. Richards (1976a; 1978; 1982) supplies evidence that nffle widths are more than 12% wider than associated pools under most flow conditions, the peak width occumng just downstream fiom maximum rfle elevation. He concludes that the width relation must be a function of flow conditions induced by the bed topography, i.e. riffles deflect flow towards the outside of the channel, thereby increasing undercutting of one or both banks and consequently widening the channel. 2.4 Influence of glacial material on pool-rime sequences in southern Ontano Channel morphology of alluvial rivers is determined by the geology and hydrological characteristics of the drainage basin (Schumm, 1967), which is usudy assumed to be homogeneous in nature. Existing literature contains many empincal observations and well-established relationships on the controls of alluvial river form, while little attention has been paid to non-alluvial chamel examples. The general assumption is that al1 rivers are alluvial, that is, they flow through unconsolidated sediments they have previously transported and deposited (Church, 1994). Yet the surticial geology in southem Ontario is such that many strearns are degrading through deep glacial as, fluvioglacial or lacustrine deposits that were laid down dunng the late Pleistocene approximately 12,000- 10,000 abp (Campo and Desloges, 1994). The main sediment supply to the rivers is therefore the cohesive glacial deposits, not the underlying alluvium or bedrock. Valley slopes are externaily irnposed and the rivers adjust to this by increasing or decreasing their length by adjusting sinuosity. Where the strearns are deeply incised in cohesive material, they may not possess the energy required to alter the pldorm and therefore compensate by degrading further or by alteting bed topography through insertion or elongation of pools and rifnes. This case is not unusual; according to Kellerhals and Church (1989) the great majority of the world's nvers are not flowing on seif-deposited material, although Little attention has been paid to this in the literature other than for bedrock channels. Development of pools and riffles is possible in streams that are in contact with bedrock where alluvial material is also available for transport. Keller and Melhorn (1978) observe that rifles in bedrock streams are fkequently formed entirely on bedrock, with only a thin veneer of alluvial material, while pools are scoured to the bedrock bed and are completely devoid of alluvial material. One could expect a similar situation where till is exposed in the channel bed and some loose material is available for bedforrn formation. The high silt and clay content of the glacial tas has contnbuted to cohesive banks that are somewhat resistant to erosion. Schumm (1963) found the percent silt-clay in the channel banks and bed to be a significant contributing factor in channel morphology. Streams with a high silt-clay content in their banks were found to have narrower channels. FoIIowing this argument, channel width is likely to be extremely variable where semi- alluvial streams pass through both cohesive tiUs and unconsolidated floodplain deposits and wiIi contribute to irregular pool-me spacing. It is not uncornmon that rivers shodd retain features inherited f?om previous conditions, such as those that prevailed du~gthe recession of the Pleistocene ice sheets. Dury (1 970) observed extra riflles in the straight reaches between meanders of the Osage River in the U.S.A., while Dury et al. (1972) noted that exhting climate and discharge relationships for the manifestly underfit river Severn, England, were not reflected by the meanders on the present channel. Ferguson (198 1) observed that many present-day British rivers flow through valleys cut into deep glacial fill previously eroded by late- glacial or postglacial rivers. The present-day rivers are ofien constrained by the vailey walls, such that some meander loops become 'stuck' at the vdey sides where they are unable to remove the influx of coarse sediment released fiom the glacial deposits. The coarse material remains in the channel filhg pools or fomiing ses where they would not ordinarily be expected. The meanders' lateral growth is also restricted, resulting in dominant downvdey migration. The bends themselves take on a square shape, with maximum curvature at the point of contact with the valley wall. These 'historical hangovers' are a result of the channel geometry being adjusted to a previous set of environmental conditions that would not be attainable under the present hydrological regime. Lower energy conditions of the present river are sufficient to mode the bed topography, where bed material is available, yet not competent to alter the banks and consequently the planform (Ferguson, 198 1). Similar geological conditions and existing data for southem Ontario (Annable, 1995) indicate that comparable 'misfit' conditions and inhibited bedform development may exist for streams of the region. Greater than 50% of the streams investigated by Annable fdbelow the expected 10- l4W meander wavelength range. Furthemore, the data show unusually short inter-pool distances (mean less than SW), and the fiequency distributions of bedfom spacing indicate a greater number of short bedforms spaced at 2 and 4-SW (figure 2.3). The fùll range in bedfom spacing is 0.6-1 1W. Annable did not present the pool-rime fiequency distribution. Figure 2.3. Frequency distribution of pool-pool spacing for streams in southern Ontario (data fiom Annable, 1995)

One might expect channel morphology in southem Ontario to be unusual in a variety of ways. In particular, the pools and rifnes will be irregular, short and erratically located with respect to the meandering plan form. Several potential explanations are:

1) The influence of semi-alluvial characteristics of the streams flowing in tiil rather than unconsolidated alluvial material, - Irregular, conhed meanders and bluffs (after Ferguson, 198 1) - Random obstacles in the channel such as boulders and outcrops of resistant till forcing erosion and deposition in random locations within the channel (after Montgomery and Buffington, 1997) - Lùnited sediment mobiiity as non-alluvial bed material (composed of ta, coarse cobbles and boulders) is mavailable for transport (afier Wohl et al., 1993) - General lack of alluvial material for rifne formation 2) Underfit conditions in which reduced energy of flow results in adjunment of the bed topography but not channel width or wavelength (after Dury, 1970), and 3) Insertion of extra -es during channel extension (afier Keller, 1972; Hooke and Harvey, 1983).

Recent urban expansion across southem Ontario has led to an increase in the need for stream channel redesign. However, current practices in southem Ontario are based on stream type class~cationsand neither recognize nor consider the semi-alluvial nature of the streams, or appreciate the ambiguity involved in bedform definition. None of the above has been systematically observed or measured in southem Ontario or in equivdent Stream types elsewhere. No basic documentation of channel morphology currently exists and is necessary in order to provide a base for better remedial action. CaAPTER III STUDY AREA AND RESEARCH METHODS

3.1 Physical characteristics of the study area Southwestern Ontario is typical terrain for the development of semi-alluvial strearns. Rivers are flowing through till and reworked glacial material instead of alluvium, while bedrock is buned tens of metres below the bed. Three rural streams near London, Ontario, were chosen for study.

3.1.1 Geology and geomorphology Southem Ontario is underlain by a series of sedimentary rocks of early and rnid Paieozoic age, which in turn cover igneous and metarnorphic rocks of the Canadian Shield (Chapman and Putnam, 1984). Layers of limestone, shaie, dolostone and sandstone dip gently to the south and southwest, and have been subject to warping, faulting and erosion pnor to the late Wisconsin glaciation (23000BP - 10000BP). They are now largely obscured by deep glacial deposits (Dreimanis, 196 1 ;Chaprnan and Putnam, 1984; Bowles, 1994) of the Wisconsin stage which Vary in thickness from a few rnetres dong the Niagara escarpment to hundreds of metres in some bedrock depressions. A complex suite of deposits and landforms, including glacial tiil, fluvio-glacial outwash, lake deposits, and terminal moraines, resulted fiom multiple advances and readvances of several glacial lobes onginating 6om the Canadian Shield dunng recession of the ice sheets. The tas in southem Ontario are cornposed of material originating fiorn both soft and easily eroded bedrock and recently ground bedrock fragments. Ponding between the Huron and Erie lobes resulted in large pro-glacial lakes and the subsequent deposition of fine lakebed sedhents. Lakes Maumee, Wittlesey, Warren and Lundy were responsible for the deposition of lacust~esilts, deltaic deposits and stratified clays across southem Ontario during the penod when drainage to the east was blocked by the Lake Ontario ice lobe (Chaprnan and Putman, 1984). Repeated reworking of eariier lain tills by multiple glacial advances and re- advances is common, such that sandy and clayey tas are found supenmposed on older coarser tas in some areas @reimanis, 1961). Coarse-grained tus, resulred fiom erosion of pre-existing non-consolidated Pleistocene sediments and subsequent deposition of the fiesh bedrock eagments. Fine silt and clay-rich tills resulted where clays and silts became incorporated into tills during re-advances which overrode previous lacustrine deposits; examples are found in the tills of the Westminster, Ingersoll and St. Thomas moraines. As a result of its Quatemary geology and surficial deposits, the landforms of southem Ontario are complex (McCarthy, 1989). Recessional moraines and till plains are prominent geomorphologic landforms giving rise to a gentiy rolling topography. The existing blanket of till and ground moraine was modified by the release of ponded water that created wide spillways (Bowles, 1994). Present-day rivers comrnonly dissect thick Quatemary deposits or occupy glacial spillways (Chapman and Putnam, 1984). Sediment delivery to the creeks is therefore ofien a direct result of incision into glaciaily deposited material and floodplain development is confined between the valley sides of the spillways. Isostatic uplift following degiaciation in southem Ontario is estimated at rates of 0-0.1 mkentury (Larsen, 1%S), therefore, there has been negligible modification of present river gradients.

3.1.2 Soils and vegetation The soils of the study area are typically well-drained loams, sands and silty-sands overlying poorly drained unsorted glacial till beneath. The parent material tills are of mked clay, silt, sand and grave1 and are fiequently exposed in channel banks and valley- sides (Bowles, 1994). The soi1 supports a variety of arable crops. The Tharnes watershed lies within the Great Lakes Deciduous forest region and is part of the northern most extent of the Carolinian vegetation zone (Bowles, 1994). Forested areas are largely Limited to deybottoms and isolated woodlots, most of the land having been cleared for agriculture or urban settlernents. 3.1.3 CIimate Southwestern Ontario expenences the mildest climate of the province. The mean annuai temperature is 7"C, with a muiimum of -1 1°C in January and a maximum of 26OC in Juiy (London station). Average annual precipitation is 955mrn, approxhately half of which falls during the summer months (Environment Canada, 1998). Winter temperatures cause many rivers and streams to fieeze over entirely, the spring ice break-up being responsible for substantiaI erosion of the channel banks.

3.2 Site selection The ideal study site would be a naturai rural strearn that has expenenced no anthropogenic or livestock modification and for which historical strearnflow data are available. The strearn must be shallow so as to be safely wadeable, yet not too small that bed features are poorly developed. In this way, the selection of each reach attempts to minirnize 'extemal' impacts on the channel. The selection of appropriate snidy sites was based on a number of ordered criteria. The Water Survey of Canada maintains gauging stations on a number of rural and urban watercourses within the stiidy area. An initial list of 44 potential sites was drawn from streams for which historical streadow sumrnaries of greater than five years exist in southwestern Ontario. Proximity of the sites to London was considered in order to minirnize travel time. In addition, easy access into the channel provided by bridge crossings or trails between concession roads was essential. The gauged streams were identified on 150 000 topographie maps. Stream were eliminated fiom the list if they had many tributaries or flowed through urban areas for substantial portions of their length near the gauge or were outlets from lakes or reservoirs. Such channels are likely to have undergone modification of both their morphology and flow regime and are therefore discounted in an attempt to select sites that are as undisturbed as possible. Despite this control, some degree of modification or disturbance is inevitable in a region as populated as southem Ontario. The rernaining streams were identified and gauges marked on 1: 10 000 Ontario Base Maps and pinpointed on aenal photographs. From an examination of these sources, streams which had obviously had their courses straightened, relocated or experienced other modifications such as 'manicuring' through a golf course or changes as a result of water extraction for irrigation, were removed from the potential sample. As the survey required wading through the channel, those streams that were too large to be walked through were aiso removed from consideration. After examination of surficial geology maps of each site to determine incision into glacial deposits, six channels within two hours drive £?om London were identified for site reconnaissance. These were: Dingman Creek, Fish Creek, Medway River, Nine Miie River, Nissouri Creek, and Trout Creek. An additional Stream, Oxbow Creek, near London was also included in the sample, despite the fact it is not gauged. A previous visit to the site suggested that the channel morphology was peculiar and worthy of investigation. The final determination of the stream's suitability for study was made dunng field reconnaissance. Attempt was made to select streams that differed slightly in morphology from each other. Several of the streams were discarded fiom the set owing to presence of altered reaches in proximity to their gauges. Fish Creek showed obvious bank modifications and man-made pools in the vicinity of a campsite, while Trout Creek (one of the sites investigated by Amable, 1995) had artficial riffies and stepping nones placed across the channel. The Medway River was too deep to wade dthough it does show some sections of the channel deeply incised into glacial till. Similady, the Nine Mile River was too deep and fast flowing to be surveyed safely. The rernaining three streams, Dingrnan Creek, Oxbow Creek and Nissouri Creek, therefore form the basis for observation in this research. Following the decision to use the three aforementioned sites, selection of specific study reaches was necessary. Al1 three streams are located within the Thames River watershed. The channels are small, therefore, the lower reaches close to their confluence with the Tharnes River were chosen for study. The locations of each study site are given in Table 3.1 and figure 3.1. Dingman Creek was too deep to be waded where it joins the 360 Nissouri Creek 340

320 ? d 2 300 wE .- 280 ri) 6 z& 260 340

220 - smdy reach location

200 1 I I I 1 1 O 10 20 30 40 50 60 Distance dong channel (km) Figure 3.1. Long profiles of each channel showing location of study reaches.

- - -- Figure 3.2. Map of southem Ontano showing approximate boundary of Thames River watershed and study site locations, a) Dingman Creek, b) Oxbow Creek, and c)Nissouri Creek. Tharnes; the selected reach was therefore located 5 km upstream between the towns of Delaware and Lambeth. The swey on Oxbow Creek comrnenced several hundred metres upstream from its confluence with the Thames River owing to ponding effects on the morphology from an old dam. As the land in the study areas is privately owned, permission to access the creek was sought nom the landowners prior to and dunng the su rvey .

Table 3.1. Grid references for snidy site locations. Dourneam Upstream Doisnstream Upstream Map sheets end of study end of end of end of 1: 10000 1 :25000 1 :50000 site stuciy site channel ~ha~~el(stuc@ site (entire (entim on&) charnel) channel)

Dingrnan 67452 1 695524 6465 17 987544 Creek

Oxbow 678568 618566 682567 704763 Creek

Nissouri 03 1735 025755 03 1735 O 148 18 Creek

47750 * Grid reference accutate at 1:25000 scale; 1: 10000 maps from bfinïs~of Natural Resources. 1:25000 and 1:50000 £rom Department of Energ)., Mines and Resources.

This study focuses on detailed surveys of three semi-alluvial streams. The unique morphology of the chosen streams indicates that there are characteristics that differ from 'textbook' alluvial channels yet it is accepted that they are not necessarily representative of a11 semi-alluvial streams in southen Ontario.

3.3 Study site description The Thames River drainage basin is 200 km in length and has an area of 5825 km2 (figure 3.2). The main river flows westward into Lake St. Claire. The highest point in the watershed is 420 m above sea level. Upstream from London, the longer North Branch flows south from several small creeks around Brodhagen (-96 km), while the main-stem rises f?om a swamp area West of Tavistock (-87 km). Between the confluence with its two major branches at London and its downstrearn end, the river is 187 km in length. The river descends a total of 213 m fiom the headwaters of the Avon River (388 m a.s.1.) to Lake St. Claire (175.4 + m a.s.1.) (Upper Thames River Conservation Authonty, 1997). The lower Thames drains level lake plains and has a low gradient (0.00029), while the upper Thames is steeper (0.00 19) and drains till plain and moraine topography. The upper Tharnes occupies in a glacial spillway that is incised into the topography. The three sub-basins of the Thames River watershed chosen for study are Dingman Creek ('a' in figure 3.2), Oxbow Creek ('b') and Nissouri Creek ('c'). The creeks in this study Vary in drainage basin area, Length and dope (table 3.2). Dingman Creek is the largest of the three, followed by Oxbow Creek then Nissouri Creek. The full long profile for each channel was taken from 1 :25000 topographie maps (see table 3.1). The study sites are al1 located at the downstrearn end of the channels, the study site on Nissoun Creek being the only one to end at its downsrrearn confluence (figure 3.1). Figures 3 -3, 3 -4, and 3 -5show the study site locations in greater detail and table 3.3 gives surnrnary data for each study site. Approximately 5 km of channel was surveyed on Dingman and Oxbow Creeks, and 3.3 km on Nissoun Creek. Al1 three creeks are single thread, irregularly meandenng, confined in places and are predorninately grave1 bedded with occasional till visible in the channel bed and banks. Bedrock is buried up to 60 rn below the glacial deposits (Geologicai Survey of Canada, 1953), such that no bedrock is exposed by downcutting of the creeks. The 'floodplains' or surfaces over which the creeks are flowing are often mined for glacial gravels.

Table 3 -2. Channel summary data Length of Average Drainage Max. uidth of Length of channel channel basin area drainage basin drainage basin Oon) dope am2) Oa) Ocm) Dingman Creek 56 0.0014 170 8.8 35 Oxbow Creek 40 0.0022 84 5 27

Nissouri Creek 14 0.0045 29.5 4.5 10 Table 3.3. Study site summary data Reach fricts Length of Stu- site Average Mean Mean Sinuosi- stuc& site as a % of slope of baddkll bankfitll (ml entire mdy width depth channel reach (ml (ml Dingman Creek 4776 9 0.0024 14.0 1.5 1.5 0;Ubow Creek 49 10 12 0.0044 10.7 1 .O 1.4 Nissouri Creek 3335 23 0.0042 9.1 0.8 1.4

3.3.1 Dingman Creek Dingman Creek is a small Stream that flows east to West through North Dorchester, London, Westminster and Delaware Townships and drains into the Thames River at Delaware (figure 3.3). It is approxirnately 56 km long, has a drainage area of 170 km2 and is fed by 60 tributaries (determined using blue-he network on 1:25000 National Topographie Survey maps), many of which have been altered by agriculture and urbanization. The impacts of urbanization on the flow regime have raised interest and as a consequence several research projects have been carried out in the watershed (table 3 -4):

Table 3.4. Previous studies conducted on Dingman Creek Dingman Creek studies Schaffner (1 997) Bank Morphology of Dingrnan Creek Aquafor Beech (1995) Dingman Creek Subwatershed Study Bowles ( 1994) Life Sciences hventory: Dingman Creek Proctor and Redkrn Ltd. ( 199 1) Dingman Creek Erosion Study, final report Fisher ( 199 1) The Impact of Urbanisation upon the Dingman Creek Drainage Basin Min. Natural Resources (1988) Dingman Creek Erosion Stucly Spence (1967) The process of water cooling, ice formation. and ice thickening on srnaII Stream in the ara of London. Ontario Thompson ( 1967) Fluvial Processes During The Winter on Dingman Creek Westmuister Tonaship, Middlesex County. Ontario Sullivan (1 966) A Watenhed in Thc ~rbanShadorv. ~ingm&Creek

Along most of its length, the creek Bows through a low-lying glacial spillway that passes between two inter-Iobate moraines south of London: the Ingersoll moraine to the north and the Westminster moraine to the south, both of which were deposited by the recession of the Erie lobe during the Wisconsin. The Ingersoll moraine is composed of silty clay till with a few kames. The Westminster moraine is similar in composition to the Ingersoll moraine and stands approximately 20 m high (Chapman and Putnam, 1984). The creek is thus confined between the two moraines but has a wide valley floor approxirnately 200 - 300 m across. It impinges frequently on the valley sides reveding till overlain by sand in the channel banks. The headwaters near Mossley, south of London, originate on a broad flat clay plain deposited by glacial Lake Maumee, while the lower reaches flow through a spillway incised into the Caradoc sand plain, clay plain and till deposits below (Bowles, 1994). The silt and clay plains are deep-water deposits of up to 10m in thickness which overlie till (Chapman and Putnam, 1984). The underlying shale and limestone bedrock (3060m below) has no influence on the creek morpholog. Natural vegetation has been reduced to only 1 1% of the watershed through removal of forest cover; much of wkch is restricted to isolated woodlots and wetlands. The charme1 is bordered by woodland and scrub brush through the study site. Sixty percent of the drainage basin is occupied by agriculturd land, while 1400 is designated urban (Aquafor Beech, 1995). The majority of the tributaries and sections of the main channel upstream nom Wellington Road have been altered by municipal drainage practices for agriculture and crop production or channelized to carry stomwater runoff £iom urban areas. One pumping station and 2 sewage plants discharge into Dingman Creek. The water quality of the creek has deteriorated owing to high nutrient concentrations, bacteria levels, algae, sediment concentrations and high temperatures brought about by the lack of shade (Aquafor Beech, 1995). As land use has changed from forest to agriculture to urban, the channel has had to adjust to new hydraulic conditions and increased sediment loads. Recent expansion of the city of London and Lambeth has resulted in dramatic changes in channel form downstream of the city of London. Instability of the channel is particularly evident west of Lambeth, where braiding, abandoned channels and bed scour are visible. Of the 453 erosion sites along Dingman Creek identified by the Ministry of Natural Resources (1 988), 17 sites occur within the study reach. Flooding has become a significant problem, especially in the mid-reaches of the broad flat floodplain (Aquafor Beech, 1995). The Water Survey of Canada has maintained a manual gauging station (no. 02GE005) below Lambeth at Concession rd. 46 since 1965. Mean annual discharge is 1.446 m'k, and the maximum flow on record was recorded in February 1968 at 66.3 m3/s during ice conditions (Water Survey of Canada, 1998). Over the period of record, the 1-5 year return interval is 30 m3/s. An examination of these records shows that since urban development began (approximately 1973), annual maximum daily flows have increased by IO%, average annual discharge increased by 20%, average summer discharge has increased by 100%, and minimum daily discharge has increased by 40% (-4quafor Beech, 1995). However, one third of the base flow originates downstream of the gauge where groundwater contributions are higher owing to coarser more permeable materials than in the eastern part of the watershed.

3.3.2 Oxbow Creek Oxbow Creek, previously known as Spnngers Creek, flows south and southwest to Komoka through Lobo and London Townships in Middlesex County. Frorn there it flows east to its confluence with the Tharnes River at Kilworth, approximately 9 km nonh of Dingman Creek (figure 3.4). It is approximately 40 km long, has a drainage area of 84 km2, and is fed by 41 tributaries. Its headwaters are near Birr, nonh of London. The creek is steep and deeply incised for a distance of 2 km dong its downstream end as it cuts down to the base level of the Thames River. The channel is incised through glacio-lacustrine and glacio-fluvial silt, clay, sand and gravel deposits of former Lake Wittlesey. Till samples collected in the first 100 m of this survey are composed of 3% coarse sand (>2 mm), 3 1% sand, 39% silt, and 27% clay. Many sand and gravel mining pits are located in the area. The remainder of the channel flows through till-plain bordering the distal side of the north-south trendhg Lucan end-moraine, deposited by the Huron glacial lobe. The stream is predominately gravel bedded. The creek is not gauged. The drainage area is roughly half the size of Dingman Creek; therefore, the discharge may be approximately haif (mean annual discharge - 0.7 m3/s). A dam, located two hundred and fifty meters fiom the confluence with the Thames River, was removed under the supe~sionof the Ministry of Natural Resources in 199 1. \ \ - 'L- The dam was causing erosion of adjacent property, floodmg, ice-jams, silting-in of the upstrearn reaches, obstruction of fish passage, and was in imminent danger of failure (Upper Thames River Conservation Authority, 1991). The upper limit of the head-pond extended approximately 80 m upstrearn. Soils of the study site are weii to irnperfectly drained loams of the Brant, Caledon, and Teeswater formations (Ontario Ministry of Agriculture and Food, 199 1). Land use dong the channel is prirnarily agriculture, ranging from cropland to cattle grazing. A border of deciduous trees in the vailey bottom generally buffers the channel fiom agricultural activity. Cattle have access to the creek in the upstream end of the study site and bank damage is evident.

3.3.3 Nissouri Creek Nissouri Creek, in Oxford County, flows south through West Zorra and East Nissouri Townships to its confluence with the Middle Thames River (figure 3 -5). At the confluence, the Middle Tharnes River is a misfit flowing through a deep glacial spillway. Nissouri Creek is approximately 14 km long and has a drainage area of 30 km2. It is fed by 8 tributaries, most of which are seasonal. Its headwaters are located south of Lakeside. It is the smallest creek of the study sites and was gauged fiorn 1987 to 1993 by the Water Survey of Canada (02GD022) on the upstream side of the bridge at Road 78. Mean annual discharge is in the order of 0.385 m3/s (roughly one quarter that of Dingman Creek), the maximum flow being recorded in March 1993 at 26 m% (Water Survey of Canada, 1998). The 1.5 year return interval flow is 13 m3/s. The creek flows through the Odord till plain. Bedrock (Detroit Limestone) is overlain by up to 27 m of yellowish silt-nch Huron lobe glacial till deposits (Ontario Department of Mines, 1959; Ontario Department of Mines and Northem M'rs, 1971). Huron lobe tills are fiequently veneered with windblown or lacustrine silts; indeed sediment samples collected during this smdy @end 38) are composed of high percentages of silt (64%, 6% sand and 29% clay). Pockets of grave1 of glaciofluvial outwash origin occur and are mined through the area. Figure 3.5- Nissouri Creek study site map The watershed is the least urbanized of the three study sites, the dominant land use being corn crops. The stream gently cuts through the silty alluvial deposits of the Embro soi1 series to the slightly stony Guelph series below. Drainage is good over gently rolling topography.

3.4 Field techniques The field survey was carried out by three people between July 8th and October 2 1st, 1997. Specific tasks were assigned to each member of the survey team in order to maintain consistent observations throughout the course of the survey. Al1 observations of stream morphology were made by the author, operation of the survey instrument and survey notes were made by one assistant and the stadia rods were managed by another assistant and the author. The survey was conducted using a Leica WILD NA 2002 automatic digital level, two NEDO GPCL3 invar bar-code staffs, a Brunton compass, and a 50 m measunng tape. The survey instrument was set up on the banks whenever a clear line-of-sight was possible; however, tail banks and thick vegetation most fiequently required that the instrument be set up in the channel itself. Twelve-inch aluminium nails, flagged for undenvater visibility, served as survey pins over which the instrument was centered and Ievelied.

3.4.1 Bed profüe and planform survey The initial instrument set-up was selected to give a clear line-of-sight along the channel. The horizontal circle was set to north. Care was taken to ensure the magnetic field of the instrument did not interfere with the compass reading. No mapped benchmarks were present in the study areas; therefore al1 elevatiom ai-= relative. Sturdy objects such as boulders, tree trunks, or concrete blocks were selected for use as benchmarks and marked using fluorescent waterproof marker. An arbitrary elevation of 200 m was assigned to the first benchmark in each of the three study sites. Measurements of the bankfull channel width and depth were taken at instrument set-up locations along the channel. A 50 m tape was stretched across the channel and held horizontally at the break of dope at the top of the banks to measure the wid* whde an assistant with the stadia rod measured the approximate bankfi11 depth at the location of the thalweg. Surveys on Dingman and Oxbow Creeks were conducted in an upstrevn direction, and downstream on Nissouri Creek. A back-sight was shot to the benchmark, followed by intermediate sights dong the thalweg (deepest part) of the channel. Intermediate sights were spaced at approximately two-thirds of the channel width apart, deterrnined by measunng between two personnel operating the stadia rods in the channel. This spacing was chosen as it was observed in the data set collected by Annable (1995) that many bedforms occurred at intervals of only one charme1 width apart. By using a two-thirds width interval, it was anticipated that greater detail of the bed profile might be obtained. This meant that in many cases, where the channel was narrow, readings might have been taken at intervals of only 4 m apart. On occasion it was necessary to Vary the space between inter-sights in order to manoeuvre through a woody debns jam, around a fallen tree or to obtair~a clear line-of-sight through tree branches. Once al1 possible intersights were taken corn each instrument set-up, foresights were shot to the nea instrument position and to a new benchmark. The instrument was rnoved, re-IevelIed, the benchmark was re-established and the backsight angle re-set on the previous instrument position by adding or subtracting 180" f?om the bearïng. The following data were recorded for each inter-sight (see Appendix 1, II, and UI): 1) the elevation 2) the horizontal distance f?om the instrument 3) the bearing fiom the instrument 4) the water surface height 5) the channel bed material 6) the spacing between inter-sights 7) notes Based upon a signal received fiom the visible section of bar-coded staff, the digital level (figure 3.6), which contains a single dimensional image processor, detemiines the elevation and horizontal distance between the level and the measuring staff (Leica, 199 1) . The data were stored in a WLD GRMl O REC module for subsequent retrieval. Figure 3.6. Equipment used during field survey: Leica WILD NA 2002 automatic digital Ievel and NEDO GPCL3 invar staff. A) Bar-code face of staff read by the automatic digital level to determine elevation and horizontal distance between level and staff. B) Optically read face of staff. The bearing was taken manually fiom the horizontal circle and read to an accuracy of 0.1 degrees. It is recognized that use of the horizontal circle to obtain bearings of each inter-sight fiom the instrument is not a reliable method when compared to a vernier scale. Therefore, using the Brunton compass, the bearing was routinely checked when the instrument was moved. If a significant discrepancy occurred between the compass bearing and that read from the circle, the horizontal circle was re-set, and the change noted. The water surface height was read manually from the reverse side of the staff by the stafî operator to an accuracy of 1 mm whenever possible. Often the water surface height was estirnated to the nearest centimetre when the staff was held in fast flowing water that piled-up on the upstrearn side of the staff The bed matenal size was visually classed as clay-till (c0.004 mm), silt (0.004-0.052 mm), sand (0.052-2.0 mm), pebble (2.0-64.0 mm), cobble (64.0-356 mm), or boulder (>256.0 mm) (with a qualifier of coarse, fine, small or large whenever necessary) by the author and one other assistant. If more than one sedirnent size was deemed to occur at the inter-sight location, classes were aven to the note-taker in order of dominant coverage. This scale is modeled after the Wentworth- Lane class limits given by Chorley et al. (1984).

3.4.2 Bathymetric survey Several bends exhibited multiple pools and till ledges extending into the flow from the base of the banks. Bend 38 on Dinpan Creek was selected for a detailed bathymetric survey to illustrate these features. Two hundred and thirty random inter-sights were measured to give a three dimensionai image of the bed through the bend. The elevation, horizontal distance from the instrument, bearing, water surface height and channel bed materiai were recorded. The data were initially plotted in AutoCAD and imported into Surfer32 for manipulation of the contoured image.

3.5 Data preparation and analysis A variety of cornputer software packages were used duiing data preparation and analysis: AutoCAD 12, Surfer32, Map Factory, SigmaPlot, Statistica, Corel Presentations and Microsoft Excel. 3.5.1 Channel planforni The channel planform data were plotted daily in AutoCAD to dowcorrection of any errors before they were carried through the entire field survey. Ushg the horizontal distance recorded by the automatic level, and the bearings taken fiom the horizontal circle, each inter-sight location was plotted with respect to the instrument location. Successive inter-sights were joined to give the thalweg location. The daily planforms were joined and any angular corrections were made by distributing the emor over the number of intersights between correct bearings. The final planforms for Dingman and Nissoun Creeks contain a srriail angular error (approxirnately 3" over the whole length), but this is not considered a concern, as the purpose of the survey is to map the bends for identification of bed features within the planform. Simple queries can be made in AutoCAD to obtain the distance between inter- sights, valley length, total thalweg length and bend radius. The location of till outcrops dong the channel was marked on the planforrn by changing the colour of the corresponding line segment and the total length of channel in direct contact with glacial material obtained. Once the location of pools and nffles was determined in the profile, their location was mapped in the pladorm.

3.5.2 Bed profile The bed elevation and water surface elevation data were reduced, corrected and entered in Microsoft Excel. The elevation data for each channel were plotted against distance to obtain a plot of the bed profile. The location of major features, such as bridges and bank failures, was plotted on the profiles. Following this, several objective methods for definhg the pool-rime sequence were explored.

3.5.2.1 Pool-Rime definition problem The bed profiles of the three channels are not linear (see figure 3.1); instead, Oxbow Creek exhibits a strongly convex shape, while the study reaches on Nissoun and Dingman Creeks are only moderately straight. Each creek shows zones of minor concavities or convexities within the overall profile that pose a problem when one wishes to define the pool-nffle sequence by traditional regression methods. The linear regression method is of limited use as an objective method for defining bedforms over long irregular reaches. One solution would be to break the profiles into smali reaches of similar siope and to use the regression technique on these smaller sections; however, this would introduce subjectivity into the methcd in the choice of where to break the profiles, and in how many breaks to use. To examine other methods for defining pools and riffles and to see ifbedform spacing is sensitive to the choice of definition, an 1100 rn test reach of Dingman Creek between 2900 m and 4000 m was chosen. One hundred and thirty-two surveyed bed elevations were measured over this distance. Five different methods of identification are compared. These are field observation, visual inspection, linear regression, non-linear regression, and the bedform dflerencing technique.

3.5.2.2 Field identification of bedforrns in test reach Those features that were identified during the field survey are shown in figure 3.7A. The recording of features observed in the field was intended to facilitate interpretation later and was not to icientiQ every bedform. Consequently eleven riffles and five pools were identified. Interpoiating for those pools that presumably occur between riffles that were recorded, 1 1 pools and 12 desare present. This gives a mean spacing of 100 m between bedforms, and using a reach average bankfull width of 14 m, a spacing of 7W is obtained. However, when one examines the profile, several features were not recorded. For exarnple, two pools occur at 3800 and 3900 m that are deeper than the pool that was noted between them. By definition, rifnes must occur on either side, thereby decreasing the spacing between features. Identification of features will Vary between field personnel and is therefore not accepted as a reliable method.

3.5.2.3 Visual inspection of test reach bed profde A visual inspection of the bed profile was carried out before alternative identification methods were used so as not to bias the interpretation (figure 3.7B). Eleven pools and 12 rimes were identified, the sarne numbers as in the field-survey, but they differ A Bedforms identified during field survey

1

I ! 1

B Bedforms identified by visual interpretation of profile plot

1

I

C Bedforms identified using linear regression

D Bedfom identified using pol ynomial regression /N= 35 F1 1

2900 3000 3100 3200 3300 3400 3500 3600 3700 3800 3900 4000 Distance dong channel (m)

Figure 3.7. Beû profiles of Dingrnan Creek test reach, showing locations of pools and riMes identified during the field survey (A). by visual kterpretation (B), iinear regression (C). and polqnomial regression @) techniques. N is the number of rimes and pools identifieci in their location. In choosing which bed-features to idente, only major undulations in the bed were selected, without regard for the distance between features or for their location in the pladorm. When a nffle had severai peaks, the tallest was selected as the nffle crest. Sirnilarly the lowest trough was chosen for the pool bottom. The approximate spacing is m. As an experiment, 1 had several subjects, who are familiar with fluvial geomorphoiogy, classi@ the same reach in order to gain some idea of the potential variation in results. The numbers of bedforms (pool-ifne unit) defined were 1 1, 15, 20, 24 and 32. The spacing these values produce is between 2.5 and 7W. Clearly this method is subjective and depends entirely on the criteria used by the personnel involved. However, it provides a useful cornparison for the 'objective' methods descnbed in the literature.

3.5.2.4 Linear regression of test reach bed profile In the regression method, uninterrupted groups of residuals of the same sign constitute a bed-feature. Positive residuals represent pools, while negative residuals represent riffles. The length which the same-sign group of residuals covers is taken to be the length of the pool or rifne. A bedform is considered to be the length of a pool plus the length of the nffle immediately downstream. Assuming no irregularity in the channel long profile, we could expect a near linear relationship between bed elevation and distance, with elevation residuals clustered around zero. The residual plot would effectively remove the downstream trend and define the pools and -es. When the bed elevations are regressed against distance dong the channel, 18 pools and 19 Mes are disthguished, giving a mean spacing of 4.4W between bedforms (figure 3.7C). Two particularly short riffles are identified at 3034 and 3234 m and short pools at 2972 and 3227 m. The length of each pool and riffle is defined by the point at which the regression line cross the bedform plot. Although these may not be the exact inflection points in reality, it gives an objective definition. A disadvantage is that the pool centre or rifne crests are not identified. One cm either assume the pool centre is located halfway along the pool to obtain a pool to pool spacing, or use the bedfonn length to determine spacing. Thus introducing fùrther ambiguity into the definition. The regression Line fits the data well in the upstream end, where it bisects the nffles approximately halfway between the rime crest and the pool bottom, but in the downmeam end where the bed is slightly concave, severai srnail bedforms are misclassified as the regression Line fds higher on the plot. The use of Linear regression for the full length of the channel wiil not provide useful results.

3.5.2.5 Polynomiiil regression of test reach bed profde Richards (1976b) suggested the use of more complex curves for longer reaches for which simple linear regression is not suitable. A sixth order polynomial regression of the test reach results in the identification of 17 pools and 18 riffles, giving a mean spacing of 4.6W between features (figure 3 -7D).Two short riEies are identified at 3 110 and 3556 m along the surveyed channel. The r2 value for a polynomial improves the fit of the linear regression line by only 0.0 1. It irnproves the fit in the lower end of the profile, effectively removing those short bedforms identified in figure 3 .7C, but introduces a new bedform at 3 110 m. The rnethod is stili found lacking.

3.5.2.6 Bedform differencing technique on test reach bed profile The bedform differencing technique (O'Neill and Abrahams, 1984) provides an objective method for defining the pool-rifne sequence based on the accumulated elevation change between one pooVriffle and the next. Using fixed interval bed elevation data, spaced approximately equal to the mean channel width, successive bed elevations (Bi, B2, BPetc.) are diEerenced in a downstrearn direction and the standard deviation (SD)of the resulting dserence values (Bi-B2, B2-BI, etc) is calculated. The dBerence values are assessed as collective run of values, where a run is taken to be an unintempted sequence of difference values of the sarne sign (+ or -). The highest or lowest point of a bedform is represented by the endpoint of a series of difference values ( 1 Z E; 1 ) and is termed the absolute maximum or minimum. Pools and fies are identified at the endpoint of the series where 1 Z E; 1 ,is greater than a tolerance value, T. The tolerance value is selected based on pre-selected function of the standard deviation of the dEerence values. Where 1 Z Ei 1 is les than the tolerance value, the end point is considered a local minimum or maximum and is therefore not considered a bedform; differencing continues until 1 Z Ei 1 exceeds the tolerance value at which point a pool or rime is identified. Wherever a rime or pool is cataloged, Z Ei is reset to zero, and the process is repeated until the downstream end of the channel is reached. The rifne crest or pool bottom is identified rather than the bedform length as in the preceding regression methods. The standard deviation of the difference values for the test reach is 0.3 13, which is higher than the 0.128 found by O'Neill and Abrahams (1984) in their study of Mansfield Creek, owùig to a diEerence in sarnpling interval and bedform amplitude between the two creeks. O'Neill and Abrahams also used a survey interval equal to the channel width, while the survey interval used in the present study is approximately equal to two thirds of the width. The standard deviation is multiplied by a variety of constants (OSOSo, 0.75S~, 1.OSo, and 1.25s~)to determine the T value that gives the most reasonable results (figure 3.8). By increasing the T value, the number of bedforms identified decreases. A 'T' value of 0.50SDresults in the identification of 38 features or 19 bedforms, while a T value of 1.25So gives 24 pools and rifles or 12 bedforms. An 'X' indicates discrepancies between bedforms identified by different T values. When the amplitude of bedforms is high, there is Little diEerence in definition between successive T values. However in reaches where the amplitude is low, e.g. 2900 to 3 100 m, greater variability in results occurs. When the T value is increased to 1.25SD,excessively long bedforms are identified (shown in grey) . A T value equd to the standard deviation gives the most realistic pool-riffle sequence identification for the test reach (figure 3.8C). This yields a mean bedform spacing of 4.4W. Although the same nurnber of bedforms are identified by a T value of 0.75SD,their placement is more reasonable for a T of 1.OOSD (for example, compare ses at 3002,3224, and 3463 in figure 3.8B, and rifles at 2953,3209, and 34 17 m in figure x Discrepanc y between bedforms identifieci by j i diffërent T values Il I ' l 1 Reach ~.herebecifomis are not identifid by 11 1.25(SD) ! 1 2900 3000 3100 3200 3300 3400 3500 3600 3700 3800 3900 4000 Distance dong channel (m) Figure 3 -8. Bed profiles of Dingman Creek test reach, showing locations of pools and nffles identified by the bedfonn differencing technique using various T values. N is the number of riffles and pools identified, M is the mean spacing in channel widths. 3.8C). A 'T' greater than Z .OO& overlooks many feahires, including sorne identified as riffles in the field, while a 'T' less than 1.OOSo identifies every smd bed undulation and places crests/bottoms in iiiogicai locations.

3.5.2.7 Standardization of test reach bedforms by channel width In addition to the problems arising fiom the choice of definition method, is the use of the channel width to standardize the bedform spacing. Width measurements were not made at each pool-rifile unit in the field, therefore an average width is requked for standardization. This study uses the bankfull channel width; however, the width in the test reach ranges corn 8.6 to 17.1 m. The mean width is 14 m, while the range for a five period moving average of the width is 12 rn to 15.2 m. O'Neill and Abrahams (1984) used a mean channel width over a distance of 5 19 m, however, with such variability in this study a mean width may not be appropriate. To assess whether the bedform spacing is sensitive to the choice of width measurement, three measures of width were used on the test reach: the local bankfidl width, a moving average of the width, and the mean reach width. The actual distance between each bedform is used to calculate spacing rather than a reach average (as in the discussion above). Each bedform spacing in metres is divided by the appropriate channel width to give spacing in channel widths. Frequency plots Uustrating bedform spacing in channel widths (figure 3 -9)show there is little effect in width measurement chosen on the mean spacing of bedforms, but that there are some changes in the fiequency distribution of bedform spacing. The modal spacing for bedforms deîïned by the polynomial regression is 3 or 4 depending on the width measurernent used, and for the dBerencing technique 2,3, 4 or 5. The shape of the plot is closest to a normal distribution for bedforms identified using a linea. regression and the actuai width, but this changes if other measures of width are used to calculate the spacing. The range of spacing is altered nom 1 to 12 (using actual width), to 1 to 9 (reach mean width) for bedforms identified by the differencing technique (T=1.OOSD). Bedforms defined by Bedfom~sdefined by Bedforms defined by Bedforms identified using visual interpretation linear regression polynomial regression the bedform differencing of the profile of the profile of the profile technique, T = 1 .OOS, el0 1 Actual Y 8 M = 6-30 M = 4.26 M = 4.00 width 3 3 "4 rneasured 8 n Go O2 46 81012 Spacing Spacing Spacing

Moving average width

O 2 4G81012 O 2 4681012 O 2 4 6 8 1012 Spacing Spacing Spacing Spacing

Mean width (14 m) -JzaaEL 246810 0246 81012 Spacing Spacing Spacing Spacing

Figure 3.9. Frequency distributions of bedform spacings along the Dingman Creek test reach. Bedforms identified by visual inspection, linear regression, polynomial regression and the bedform differencing technique using a variety of measures of t he bankfûll channel width (actual values, moving average and mean). Spacing is given in cliannel widths, M is the mean spacing. 3.5.2.8 Cornparison of identification methods in test reach If one considers bedforms identified only by objective methods, the nurnber of pools and rifles defined varies between 24 and 38. The mean spacing for al1 is approximately 4W (except for the differencing technique, T=1 .25SD,where the mean spacing is 6.6W) (table 3.5). The spzcing intervals al1 fall below those lirnits suggested by Leopold et al. (1964). The range in bedform spacing is 1 to 12W which compares with ranges cited in the Literature (see table 2.1). The shape of the frequency distributions for bedform spacing (figure 3.9) differs slightiy depending on the rnethod used for bedform identifkation. Most of the distributions are positively skewed, uidicating that a greater number of short bedforms are identified. There is no-single technique that produces markedly different results. The reach was selected for its lack of human modification. yet the regular spacing and high amplitude give little opportunity for inconsistent identification of features between methods.

Table 3.5. Number and lengths of bedforms identified using a variety of techniques in the Dingman Creek test reach. Meuiod of No. No.pools No. Me.& Mean& Mean& Bedform defining rifnes identifieci bedfonns SD fie SD pool SD ~pacing bdorm identified identifiai Iength (m) length (m) bedfom (channel spacing wimhs)*' (m)

Linear regression

Polynornial regression Differencing technique *' 18 18 17 30, 15 30, 15 61,31 4 (T=1.00SD) *' PooVrinle length for ditferencing technique calculateci by half the distance berneen adjacent ritneipool. *' Using actuai aidth. The choice of technique for demgthe full profles of each creek remains. AU the techniques have their limitations; however, the advantages of the bedfom differencing technique in this exarnple surpass the alternatives. Both the linear and polynomid regressions are impractical over longer reaches and redt in the identification of exceptiondy long or short bedforms. The main advantage of the differencing technique is that it may be used over long irregular bed profiles and that it is reproducible.

3.5.3 Bedform identification in the study site long profiles The bedform differencing technique was used to ident* pools and rifnes in the long profiles of the three study sites. A number of set T values were used for di creeks in order to determine the most realistic identifkation of bedfoms (table 3 -6). Cornparisons were made between bedforms identified by using the set T values, and a specifk T value was selected for use on each creek. Note was made of which bedforms were consistently defined by each T value, the specific T value being chosen to include or exclude desired bedforms and improve the placement of the ritne crests and pool bottoms. Once a particular spacing was chosen, the location of pools and rifnes were identified in the pldom in AutoCAD.

Table 3.6. Tolerance values used in bedfonn diEerencing technique for Dinpan, Oxbow and Nissouri Creeks. T value No. bedfom identified No. % of Chosen bedforms ciifference T value identified values o.50sD 0.75SD l.OOSD 0.50% 0.75s~ 1.00s~ at chosen

Dingman Creek 0.3024 0.1512 0.2268 0.3024 96 85 72 0.578SD 93 Oxbow Creek 0.2179 0.1090 0.1635 0.2179 125 103 77 OSGD 120 Nissouri Creek 0.1205 0.0602 0.0903 O. 2205 da 80 63 0.75SD 80

For the test reach on Dingman Creek, T=0.3 125 (1 .OOSo) was chosen as the most realistic definition of the bed profile. When the elevation daerence values for the entire 5 km of channel are used the standard deviation is 0.3024, which is 0.0101 Iess than for the test reach. This results in some changes in the number of features identified at the T=Z.OOSD level, such that it is not the best T value for use over the whole channel. A 'T' value of 0.7SSDand O.SOSD improved the placement of bedforms, but T = 0.50SD identified many of the smaller features of the bed. A 'T' value in-between these values would therefore be best for ident*g the bedfoms dong Dingrnan Creek. The profües were examined to hdthe exact boundary where the required T value would remove those smaller features identified, but maintain the improved placement obtained by using the T of 0.75SD. Consequently a tolerance value of 0.578 was chosen. A similar procedure was employed to select the chosen T values for the Oxbow and Nissouri Creek profles. A 'T' value of 1.OOSD (0.2179) for Oxbow Creek did not result in the detection of many of the bed features, whiie on Nissouri Creek a T vaiue of 1.OOSD (0.1204) was found to be quite sensitive. Nevertheless, several reaches of Nissouri Creek had excessively long bedforms at T=1 .OOSD. A 'T' value of 0. 75SDidentified 18 further bedforms for Nissouri Creek, suggesting that bed profles that are low in amplitude are extremely sensitive to changes in the T value (compared with 13 additional bedforms between T values of l.OOSD and 0.75SDon Dingman Creek). Tolerance values of O.%& and 0.75So were used as the chosen spacing for Oxbow and Nissoun Creek, respectively. AU the T values chosen in the present study are equal to or lower than 0.75So. 1 felt it was appropriate to use lower T values because tightly spaced small pools were often observed in both Dingman and Oxbow Creeks during the field survey. O'Neill and Abrahams (1984) chose a T value of 0.7SSa rejecting lower T values because they found a tendency for some pools and rinles to have two bottoms or crests when iow T values were used. Jurmu and Andrle (1997) found a SDof 0.24 for their wetland Stream, Roa~g Brook, and chose to use a T value of 0.50SD,their justification being that its exclusion would remit in a "lengthy stretch between the pool and desequence up- and downstream from the bend"(p93 1) and alter the mean spacing fkom 5 -71 W to 6.43W. An exarnination of the bed profile reveals Uiconsistencies in this logic. A comparable long stretch is left defined as a riffle yet there is a similar rninor pool that was not identified. During assessrnent of the bed profile, identified pools or riffles are ofien demoted to local rnidmaximum if the next bedform in the series is of the same sign. In aU three charnels, pools are more often demoted to local feahires than ritnes. The Lip of a ritne downstream fiom a pool is lower in the bed profle than the crest of the preceding rifile. 1l the T value is greater than the accurnulated nse in elevation out of the pool, the next pool downstream becomes the absolute rnirrimum, and the first pool is subsequently demoted to a local minimum.

3.5.4 Analysis Analysis in this study is predominantly qualitative. A description of semi-alluvial channel morphology is given in Chapter N.Assessrnent is made of the locations of pools and riffles to determine where they occur within the planform and in relation to glacial material in the channel. The spacing, amplitude and frequency distribution of bedforms is compared in Chapter V. CHAPTER IV CHANNE;E MORPHOLOGY IN SEMI-ALLUVIAL STREAMS

4.1 Introduction This chapter provides a detailed morphological description of three semi-alluvial streams in southwestern Ontario. The descriptions cover features at scales ranging fiom valiey scale topography to till micro-forms, and include charnel scale topography and channel pattern features. Descriptions involving mention of the right or ieft bank are given as if one is looking downstream. Bend descriptions relate to figures 4.3, 4.4 and 4.5, where D is Dingman Creek, O is Oxbow Creek and N is Nissouri Creek, followed by the bend number found on the maps; for example, bend 16 on Dingman Creek is D16.

The main common characteristics of the three semi-alluvial streams are: Exposed glacial deposits in channel banks and bed Wide variety of bed material that changes over short distances and that possesses no obvious downstream fining pattern Absence or very thin alluvial cover in the channel bed Till ledges or shelves which extend into the channel from banks thereby forcing thalweg away fiom the outside bank of a meander Short or poorly-formed riffles Several pools located in a single bend Circular meander pool and over-widened bends Incision of the creek bed into glacial deposits resulting in the floodplain being 'lefi behind' as downcutting progresses Confinement Ta11 bluffs in glacial deposits Lack of a well-developed floodplain and alluvial valley-fil1 4.2 Longitudinal channel profile A visual inspection of the long profiles of Dingman, Oxbow and Nissouri Creeks (figure 3.1) shows that none are simple concave curves, as one would expect in an equilibrium alluvial case. Nissouri Creek has a relatively straight profile, while both Dingman and Oxbow Creeks are convex over-al1 and are slightly concave towards their source. Overholt (199 1) observed that classic concave profiles were absent in streams flowing through unconsolidated glacial deposits in southem Ontario, a characteristic she attributed to the inability of the small streams to adjust their slope to a variety of coarse sediment inputs. Gradient non-adjusmient may therefore be symptomatic of semi- alluvial streams. Concavity indices (Appendix IV), used to describe the degree of chamel concavity, were devised by Langbein (1964) and Wheeler (1979), and modified by Overholt (1991), who noted that some streams had regions of both concavity and convexity, although one was usually dominant. A positive index indicates concavity of the longitudinal profile, while a negative value denotes convexity. Indices closer to zero show little concavity / convexity of the profile, while indices closer to one are more concave / convex. By this definition, Dingman and Oxbow Creeks show greater convexity with some concave zones and Nissoun Creek is oniy slightly concave (table 4.1). Nissoun Creek lacks suficient strearn power required to move the large cobbles and boulders found along its course. Al1 three streams therefore have externally imposed gradients that affect the shape of the long profile.

Table 4.1. Studv Site Concavitv Indices Dingman O'rbow Nissouri Creek Creek Creek 0.04 Conmity Indices '.O3o.07 0.15

-0.02 Convexity Indices 6.12 -0.19 4.3 Valley scale topography The streams are strongly influenced by the Wisconsinan glacial deposits through which they flow. They are incised and confined within cohesive glacial deposits, such that development of an extensive fioodplain is limited (figure 4.1). Where floodplains do occur, they are composed of thin alluvial deposits over till and may be restncted to only one side of the valley where the channel follows the opposite valley wall.

4.4 Channel pattern features The channels are sinuous and have irregular meanders that fiequently impinge on the valley sides (figure 4.2) resulting in ta11 bluffs. The lower valley wall is composed predorninantly of cohesive glacial matenal, which inhibits fiee migration of meanders. This results in long straight reaches in bends or over-tightening of bends where confinement occurs: see for example, long bends D 13, D29, D4 1,028-29, and N3 7-3 8 and tight bends D4, D7, and D27 in figures 4.3,4.4, and 4.5 (these figures are explained fully in section 4.5). Material delivered to the channel at these and other bluffs also affects channel width, pool-riHe development and the large-scale bed material trend.

4.4.1 Channel width The bankfull channel width, measured progressively along each study reach, varies considerably around the mean (figure 4.6) and shows no significant downstream widening trend, except for Oxbow Creek, where the dope of the regression line is significantly different form zero at P=0.05.Contrary to established observation that suggests riffles (between bends) are 12% wider than pools (in bends) (Richards, 1976a), bends on Dingman Creek were fiequently observed to be wider than intervening straight reaches. Width can be expected to Vary naturally in adjustment with prevailing flows, sedirnent type and local channel morphology. With no major tributaries, there is little increase in discharge except for groundwater seepage and therefore no corresponding increase in channel width downstream, except for Oxbow Creek. The limits for channel width will be quite different for strearns in cohesive sediments than for those in fine- grained non-cohesive matenal. Channels flowing through a variety of sediment types are likely to encounter pockets of both cohesive and non-cohesive material and the width --mT------=CI-- Water surface-- -- AlIuvialfl oodplain material on- , .\.\ - * -S-+?*- Glacial deposits

Glacial till Alluvial material on floodplain

Figure 4.1. Hypotheticai cross-sections of two semi-ailuvial channels. Scenario A: channel incised into till with alluvial floodplain. Scenario B: channel deeply incised into till with alluvial floodplain on only one side of the vailey. Note ailuvium may be absent all-together. Figu~4.2. Aerial photograph of incised seciion on Dingman Creek showing non-vegetated failing cutbanks in glacial til l (A, B, C, and E) as the channel impinges upon ihe valley wüll, over-widened bend (D), and bends 12-24, Note scars on temces indicating former chnnnel position, and mncted floodplain extent. Flow direction is from nght to lcft. Source: Ministiy of Natural Resources, photograph numbers 78 4264 182 - 77 & 73,1978.

Oxbow Creek Orn,

II by railway Bluff Bluff in till einbankment

Coldstreain A I~ailtiresin n--3 l bank Flow '' Till shcl( directioii

Till in bed or bniiks Alluviiini Distance froii~dowilstreain- Figure 4.4. Map of Oxbow Creek study 500111 end of study rcacli reach sliowing occurrence of glacial till visible in channel bed and banks, beiid Q i yo 200 number, distance along cliannel and Mctrcs significant features. Nissouri Creek

a Till in bed or banks AT-

Distance fiom Confluence with Middle 500rn downstream end Thames River of study reach 14 Bend nurnber A Stream gauge 02GD022 --- Figure 4.5. Map of Nissouri Creek study reach showing occurrence of glacial tiIl visible in channe1 bed and banks, bend number, distance along channel and O 100 200 significant features. Mem ;; Dingman Creek Mean width = 14.0 m n = 76 A i = 0.027 20 , dope = -0.00028

OsbourCreek Mean widih = 10.7 rn n =94 ? = 0.321 3 dope = 4-001 14

Nissoun Creek

18

Distance dong channel (m) Figure 4.6. Bankfull channel width with distance along the channel for Dingman, Oxbow and Nissouri Creeks. Figure 4.7. Tills are typically composed of large cobbles and boulders held tightly within a matrix of clay and fine silts (bend D8).

Figure 4.8 A and B. Alluvial material deposited over cohesive till @end D8). rnay Vary accordingly, being generally narrower in cohesive reaches. Variability in width is probably due to frequent coarse sediment inputs at bluffs and local channel topography.

4.4.1.1 Sediment delivery to the channel Unstable, steep non-vegetated cut-banks commonly occur at meander bends where the charnel is incised and impinges on the valley wail. Aerial photographs of Dingman and Oxbow Creeks show that active cutbanks have been significant features for many years (figure 4.2). Along the Dingman Creek study site alone, there are 11 locations where the stream abuts the valley-sides (for example, bends D4, D27, and D41) causing the banks to fail and supply sediment to the channel. In alluvial charnels, this sediment supply may be closer in size to the material already being transported by the stream, however, in the semi-alluvial examples, some of the sediment is coarser than the stream is competent to move. Large boulders and cobble-size material are held tightly within a matnx of clay- till in the bed and banks (figure 4.7). Repeated wetting and scour at high flow or gravitational effects such as dumping and failure of the unstable slope causes rnatenal to be moved to the base of the banks or directly into the channel. Collections of coarse rnaterial are found lying upon till at the channel margins (figure 4.8A and B), at the base of banks, and in the chamel immediately downstream of many till cutbanks. Snowmelt and rain events are responsible for the delivery and entrainment of most fine material into the channel. Surface wash and rills typicdly occur on the surface of the banks. The water of Dingman Creek was observed to increase in turbidity during and immediately after thunderstorm events. Sheet wash over the non-vegetated fine clay- till banks mobilizes clay fiom the surface and delivers it directly into the channel as a cloudy sediment plume which is diluted with distance away from the bank. Campo and Desloges (1994), who found that 64% of fine sedirnent output was derived from glacial material in the South Saugeen River, have observed similar processes. Disturbance of the bank material by the lapping of turbulent water is also sufficient to cause clouding of the water at the chamel margins as fine silt and clay particles are entrained. Recent mass- movements cause lobes of material to protrude into the channel, where they are repeatedly eroded and replenished by further failures. Along ail three streams the till-bank surface is sofi and easily erodible where groundwater seeps flow over the surface (figure 4.9). Small rock fiagrnents, fossils and pebbles supported on 'pedestals' remain, while the surrounding material is washed away. As the surface of the clay-till bank dries-out, it cracks and contracts into lumps. The clods of clay break away and collea at the base of the bank or fa11 directly into the creek (figure 4.10). They are recognizable as light coloured cccobbles"among other bed material, and are subsequently transported away as bedload matend. They are easily rounded and broken-down during transport and therefore do not persist in the channel for great distances downstream.

4.4.2 PIanform adjustment Evidence for planform adjustments occur in al1 three streams. Active migration through cutbank recession is particuiarly evident on Dingman Creek (figure 4.1 1 A and B). A survey conducted by the Ministry of Natural Resources (1988) identified 453 erosion sites, 25 of which were classified as a major priority for restoration. Most of the critical sites are located in the lower incised reaches of the creek in which the study area is located. One resident contacted during this study reported losing approximately two acres of land since 1980 owing to the retreat of a cutbank at bend Dl8 (figure 4.1 1B). Pnor to this, the bank retreated by only two feet in twenty years. The increase in erosion rate coincides with the on-set of upstrearn developrnent (Aquafor Beach, 1995) and corresponding increases in discharge owing to accelerated urban drainage. Lack of established vegetation on cutbanks, in conjunction with fallen or leaning trees, slump or slide units, and 'embayments' between riparian trees dl suggest current planimetic adjustment or widening (see Thorne et al., 1997; Simon, 1995). ûther indicators take the fom of exposed tree roots (figure 4-12), trimming of the banks behind point bars, erosion at the sides of riffles, numerous islands, non-vegetated bars and living trees growing in the channel. Reaches straightened approximately thirty years ago on Nissouri and Oxbow Creeks have begun to meander. Evidence for channel degradation is cornmonplace dong Dingrnan and Oxbow Creeks. Till exposed in the bed and the existence of terraces and alluvial material high Figure 4.9. Groundwater seeps at tilVaiIuvium contact maintain saturation of bank and lead to progressive erosion of the surface (bend 030).

Figure 4.10. Cracks and lumps of clay broken away fiom clay-till bank. Note smoothed till 'pebbles' undenvater (bend D4 1). Figure 4.1 I . ExampIes of mass wasting of gIacial deposits in cutbanks dong Dingman Creek (A: bend D27, B: bend D 18) Figure 4.12. Exposed tree roots in the channe1 banks suggest planimenic adjustrnent (located upstream fiom bend 032). above the present channel both indicate downcutting and abandonment of former floodplain leveis. Short-term aggradation is also evident in sorne reaches through deposition of silts and sands at the base of tree roots, undercut sections, or at the margins in wider sections within the channel. Overbank deposits occur in al1 three study streams, indicating that floods are not confiined to the channel, even in deeply entrenched reaches. This is particularly significant in incised reaches of Dingman Creek where vertical banks up to 2 rn in height (width approximately 13 m) show sand, grave1 and organic debris collected around the base of trees and in numerous cutoff chutes in wooded areas above the channel, indicating an apparently active floodplain and exceedingly high flows. Al1 three study sites have abandoned channels indicating that lateral migration has taken place. An in-filled oxbow occurs on Nissouri Creek between bends N19 and N22 in an open section of the floodplain. -4 water-filled oxbow lake, between bends Dl 1 and D12, is entirely cut-off from the present channel, and a meander cut-off is in the process of being formed on Oxbow Creek @ends 033 to 036). The original channel now contains minimal discharge and resembles a senes of shallow ponds at low flow. The meander cut-off chute does not appear to be natural, yet the present owner claims no channel realignment has been carried out. The new channel is narrow and deep (width: depth is 4: 1) and conveys approximately two thirds of the discharge at low flow. It contains no pools and rifles except in its downstrearn-end where it rejoins the main channel. Shallow meander cutoffs are naturally occumng features that are occupied during periods of high 80w and serve to shorten the chamel. Cutoffs occur in al1 three sites. Dingman Creek has many sand-lined meander cutoff chutes located well above the level of the present channel. Many cutoffs on Nissouri Creek have led to the formation of small-vegetated islands or braided sections. Most cutoffs bisect the slip off dope, thereby shortening the channel length; however, several chutes are located parallel to the channel at the base of cutbanks. Oxbow Creek has several high-water meander cutoffs in its lower reaches; several contain gravel-size material, indicating substantial flow during high stage. 4.5 Bed material 4.5.1 Giacial till in the channel The presence or absence of till was determined firom bed matenal descriptions, photographie records, and field notes, then mapped in AutoCAD (figures 4.3,4.4, and 4.5). Through queries in AutoCAD, the length of channel formed in till was determined by adding the lengths of all chamel segments classed as occumng in till. The occurrence and extent of clay-till found in the channel bed and banks varies irregularly along al1 three streams and may be overlain by thin layers of alluvial material (table 4.2). Any location where till was observed in the bed or banks was recorded as till; till is discernable in patches between loose gravels, cobbles or boulders on the bed, while in the banks clear contacts are visible between lower till and upper alluvial terrace deposits. It is likely that the figures are underestimates of the actual proportions of till in the channel owing to alluvial and vegetative cover of the bed or banks that impeded observations. Neverthelesq many of the outcrops of glacial material occur at bends in the chamel where the Stream abuts the valley sides thereby continuously revealing till in the banks. Till occurs along nearly 50% of the surveyed channel on Dingman Creek. Eighty six percent of this till is then overlain by alluvial material. Less till is found along Oxbow and Nissouri Creeks, although a similar proportion is overlain by loose alluvium. The least arnount of till is found along Nissouri Creek such that it is apparently the closest to an alluvial state. However, the cobble-boulder bed material is derived fiom the local glacial deposits and restricts channel adjustment.

Table 4.2. Length of study site occumng in glacial sediments Dingman Creek OIcbow Creek Nissouri Creek

Total length of sweyed channel 4776 m 4910 m 3335 rn

Total Iength of channel uith e'iposed tiii in bed or banks Length of &ciai deposits in the bed overlain by alluvial materiai 86%' 82% 83%

Length of covered glacial deposit is underestimated for Dingman Creek 4.5.1.1 Micro-forms in glacial till Tills composed of stony clasts held within a clay and silt matrix dominate the glacial deposits found in the study area. The clay-till is easily shaped and sticky, such that the bed has many knobs, hollows and protmsions sculpted by the flow. These are most common in pools which are floored by clay-till (figure 4.13) and have been observed in other post-glacial environments (Andrle, 1994). The surface of the till itself is often dimpled by many circular holes which range in diameter from 1-2 mm to several centirnetres (figure 4.14A and B). These appear to be pockets lefi behind by pebbles eroded £iom the silt-ciay matrix.

4.5.2 Downstream bed material sequence As a consequence of the multiple sediment inputs along the channel, there is no systematic downstream trend in bed material size. Downstream changes in bed material were observed by recording the dominant bed material at each intersight using five size classes (clay, sand, gravel, cobble or boulder) with the adaptation of 'coarse' or 'fine7 if material fell between classes. Visual size limits set for this survey were silt/clay c0.052 mm; sand 0.052-2.0 mm; gravel 2.0-64 mm; cobble 64-256 mm; boulder> 256 mm. Each class was assigned a value eorn 1 to 5 (clay to boulder), with I 0.5 for coarse or fine. The results are given in figure 4.15. The bed matenal for al1 creeks shows an erratic distribution. Dingrnan Creek shows little downstream trend and a wide variety of bed material sizes along the chamel. The lower reaches of Nissoun Creek pass through cobble and gravel-rich glacial tills such that it is cobble-bedded along most of its length. Remnant boulders eroded from the bed (figure 4.16) dominate several reaches and remain in the channel as significant morphological features. Ifanything, the bed material appears to coarsen downstrearn along Oxbow Creek. This rnay be explained by the fact that the downstream reach of the creek is entrenched into till and glacio-fluvial sediment, while upstream the stream fl ows tkirough fine lacustrine deposits. A taIl bluff at the lower end of Oxbow Creek @end 0 1) contributes large quantities of coarse debris to the stream Figure 4.13. Clay-till sculpted by the flow of water (Dingman Creek bend D27). Figure 4.14. Pitted and sculpted ti11 microform (A, bend D29; between bends D36 and D37). Dingman Creek Bed Material Distribution i Boulder j rA clw I c. O Cobblei (No data)

Downstream Upstream

Oxbow Creek Bed Material Distribution

Boulder * 9 .+* 06 e*P- m . - Cobble2 -- *-&-** O - O ** N .CI w Grayel;* ** e* -0 Y---.--*O U .. O . Sand- 6 -OD~Y.Y 60-6 6 O .C - *e *- z cl~/tilI- O *** - *.aem *O 1 Downstrearn Upstr eam

Nissouri Creek Bed Material Distribution l

! Dominant bed ' materiai dong thalweg

Distance almg charme1

Figure 4.15. Downstream dominant bed material b y nominal class Figure 4.16. Remnant boulders eroded fiom glacial material in the channel along Nissourï Creek (view downstream towards bend N2 1). increasing the amount of boulder size material in the first 200 m of the survey. Downstream f?om the bluff, the channel is wider, shallower, and the bed material is coarser than the reach immediately upstream.

4.5.3 Sediment transport in semi-alluvial streams Most sediment transport functions are developed specifically for ailuvial sand or grave1 bed channels and assume hornogenous conditions that rarely exist in nature. The situation is fbrther complicated in southem Ontario where a variety of sediments, both alluvial and glacial, occur within any one watershed. Streams pas through pockets of sediment of varying size and cohesiveness along their course. Large bluffs control the downstream sediment distribution. The significance and quantities of non-alluvial sediment sources has been suggested in passing by a number of researchers, but few have addressed the issue directly (see Rice, 1998). An exception being Campo and Desloges (I994), who investigate the importance of non-alluvial sedirnent sources in cornparison with typical agricultural inputs and conclude that 64% of the total sediment outputs of the South Saugeen River in southem Ontario are nom glacial sources. Increasing bed roughness decreases the amount of energy available for transport of material and modification of the chamel boundary. It is lowest in flat till-lined reaches and increases with angularity and size of particles on the bed, thereby affecting in-stream flow processes. From an examination of common semi-alluvial Stream characteristics, one could hypothesise that the rolling mobility of particles may be increased where lone particles are found exposed on the till bed, conversely, it will be reduced where particles are lodged within a variety of coarse material at local supply locations. For a particle to move, the actual shear stress (r) (fictional force causing ff ow resistance along the chamel) applied to the particle must exceed the critical value (7, in ~rn-~),which, as a nile of thumb, is approximately the sarne as the particle's diameter in millimetres (Gordon et al., 1992). Rough calculations of shear stress for the sample streams can be made using the formula: where p is fiuid density (kgm"), g is acceleration due to gravity (ms"), h is bankfüll flow depth (m)and s is the dope of the energy line which is asnirned to equal the water surface dope (Allen, 1985). The average bankfull shear stresses calculated over the entire study reach are 35,43, and 33 ~m-'for Dingman, Oxbow and Nissouri Creeks, respectively. For Oxbow Creek, the shear stress is 88 for the steep lower 1500 m, and 21 ~m-~in the flatter upper reach. To determine the particle size that will be entrained by bankfill flow, one assumes the critical shear stress is equal to the particle size in rnillimetres. Bed material is generally in the gravel to cobble range (2-256 mm), such that critical shear stress is rady exceeded and very Me material is moved other than the fine clay, silt, sand and gravel range. Greater shear stresses are also required to initiate erosion of cohesive clay. Evidence of high flows existed at al1 three sites (matenal in overhanging branches and sediment and debns around tree roots), yet Iittle indication of recent transport was seen in the channel; the cobble bed was coated with algae and fine sediment and there were no chatter marks on larger in-strearn boulders. River morphology is determined in part by the energy available for the stream to modifi its boundary. Stream power (o)is the rate of energy expenditure and is often expressed as energy available per unit area of streambed (Ferguson, 198 1):

where Q is discharge and W is the channel width. Limited historical 80w data are available for Dingman and Nissouri Creeks. Accurate discharge measurements cannot be made from the data gathered in this study, however, an estimate of the maximum stream power attained for the period of record (Water Survey of Canada, 1998) can be made through use of the maximum instantaneous discharge (Q,,,) (table 4.3). The approximate maximum Stream power (hx)attained is therefore 1 1 1 and 1 17 ~rn'~for Dingman and Nissouri Creeks, respectively. Stream power for the 1.5-year retum interval flood event is 50 and 59 ~rn-~respectively, which places the streams in the range of inactive, underfit and irregular meandering streams (o= 1 - 60 ~m")observed in Britain (Ferguson, 198 1).

Table 4.3. Dingman and Nissouri Creek Stream power

aiax s W x Qi s 015, (rn3/s) (rn) (Wm") (m3/s) (Wm7

4.6 ChanneCscale bed topography Pools and rimes are found in the study streams; however, their rnorphology departs Born the traditional 'text-book' alluvial bedform model. Till outcrops in the channel bed and frequent coarse sediment inputs from the valley wall dismpt the expected rnorphology and sequence of pools in bends and riffles at crossovers such that the pool-riffle sequence in these creeks shows little discemible structure. The creeks possess a variety of pool morphologies, ranging from excessively long pools, multiple pools, and in some cases, the absence of pools in bends al! together.

4.6-1 Riffles and bars Riffles are often irregularly spaced, short or poorly formed. The riffle de-posits may be so thin that till is visible beneath (figure 4.17). In several cases, the channel bed is devoid of alluvial cover for distances greater than one channel width in length and the till may extend through the channel bed and across the entire channel (figure 4.18). The till is covered only at the margins by alluvial matenal collected into discrete bars that are approximately 0.3-0.6 m deep. Chutes at the edge of nffles are commonly scoured clear of alluvia1 material. The riffles are generally composed of coarser sediment than pools, yet the size of riffle sediment varies in size depending on location with respect to local sediment sources. Riffles located downstream from bluffs are generally coarser than those located away fiom the valley sides. There are also many long 'plane bed' (Montgomery and Figure 4.17. Riffle depleted of alluvial matenal in its upstream end. Note patches of paler till between alluvium in bed (upstream view towards bend D41 j.

Figure 4.1 8. Till exposed in stream bed. Note shallow depth of alluvial material in altemating bars (-70 m upstream from start of survey on Oxbow Creek, downstream view). Bufington, 1997) or '@idey reaches lacking obvious bed relief Plane bed sections occur in deep straight reaches in Dingman Creek and in shallow stretches along Nissouri Creek (figure 4.19). The occurrence of one unusuai rime composed entirely of till (figure 4.20) is particularly noteworthy. Iftill is exposed in rïffies, it is usually found in high velocity zones immediately above or beiow the rime crest; in this case, the till extends across the entire concave face of the nffle in a manner similar to a knick-point in the bed. ln alluvial streams, riffles are assumed to occur at the thalweg inflection point, which is taken to be rnid-way between consecutive bends (Leopold et. Al, 1964). In this study riffles are often closer to the entrance of bends (figure 4.21) or their upstream pool. This creates unusually steep riffle faces as the distance between riffle crest and downstrearn pool bottom is rninirnized. The nffïes on Nissouri Creek are poorly formed; they are structureless loose collections of cobbles with no defined crests. Well-developed point bars are found on Dingman and Oxbow Creeks, but are absent along Nissouri Creek. Media1 bars were found in Dingrnan Creek, but rarely dong Oxbow and Nissouri Creeks. These differences may be explained by presence of eroding bluffs and the incision of each creek; Nissouri is not incised to the sarne degree as Dingman and Oxbow Creeks and therefore has less sediment available for bar formation. Rather than showing a gradation of sediment size in the downstream direction, point bars or sidebars, if present, are comrnonly sorted into units of a particular sediment size. For example, in bends D 18 and D38, where bars are located adjacent to one another, the downstream bar is composed of cobbles while the bar immediately upstream is composed of sand or fine gravels. This peculiar sorting of adjacent bars into discrete sediment types is cornmon on Dingman Creek. A number of bends on Dingman Creek exhibit unusual deposition of material on the outside bank of meanders (for example, bend Dl). Bars extend down-channel frorn an upstrearn point bar and deflect the thalweg away from the apex of the next bend such that a back eddy is created between the bar and bank. The resuitant slaclrwater is an area of deposition and contnbutes to deposition in a location that would ordinariiy be expected to erode (see figure 4.22). Figure 4.19. Featureless plane-bed reach on Nissouri Creek (upstrearn view from bend 38).

Figure 4.20. Concave riffle face composed entirely of till (located between bends D36 and D3 7). Sketch not to scaIe - __-- entrance to

downstrean

direction

Fimwe4.2 1. RiMe at entrance to bend 023. Figure 4.22. Downstrearn view to bend Dl showing deflection of thalweg past bend by bar extending from bend D2. note sand deposits at base of outside bank of bend.

Figure 4.23. Scour pool fomed against resistant block of clay-till in channel bed (located in meander cut-off chute on Oxbow Creek) 4.6.2 Pools Pool amplitude and morphology Vary between the three channels. The deepest pools in Dingman and Oxbow Creeks are found adjacent to bank reinforcement structures, steep clay-till cutbanks or till in the lower banks in either bend or straight reaches. The till is somewhat more resistant to erosion than alluvial sections, such that 80w is focussed in a narrow cross-section and compensation through downcutting into the channei bed takes place, further deepening the pools. Nissouri Creek is distinct for its general lack of well-developed pools. Only in the lower reaches of the creek are pools of notable depth found.

4.6.2.1 Unusuai pool morphologies The 'normal' or expected pool geometry in bends may be distorted by the presence of large boulders or till knobs found in the centre of pools. Boulders derived from the glacial till, which are generally immobile once they enter the channel, serve to deflect the flow, causing scour of the bed at their base. Pools in alluvial channels would not ordinarily contain material of this size. Where channels contact the valley side, exceptionally long pools occur. This is particularly evident along Dingrnan Creek where pools are ofien formed at the base of till cut-banks (for example, bend D 18). Erosion of till produces hobby topography in the bottom of these pools, thereby dividing a single long pool into multiple smaller ones in any one bend. The shorter pools may be only one metre in length and are therefore not always detected by the interval used in the bed survey.

4.6.2.1.1 Scour pools As a result of local forcing, scour pools may occur in alluvial streams. A variety of obstructions, such as large woody debns (LWD), boulders, resistant bed material or in- Stream structures, rnay be responsible for the formation of scour pools. They occur randomly within the channel depending upon the location of the obstruction. Swur pools are often eroded at the base of trees that border the channel. Scour pools commonly occur in the study areas and are initiated by flow around boulders denved from the glacial deposits or LWD, and typically erode down to till. Of particular interest in the study strearns are scour pools forrned in proximity to resistant blocks of till in the channel bed (figure 4.23). Several such scour pools were noted on the upstream side of resistant till outcrops in the channel bed along Oxbow and Dingman Creeks. Two particularly unusual deep 'bathtub'-shaped scour pools are eroded into till on Dingman and Oxbow Creeks (figure 4.24). Both pools are deep (approximately 0.8 m) and are located downstream From the apex of inactive bends; bend 033 has recently experienced a meander cutoff, while bend D42 is found in a divided reach at the upstream end of the surveyed section. The bed material in bend 033 consists of a thin layer of cobble and grave1 covering a clay-till. The abrupt drop-off into the pool suggests that once erosion of the till is initiated, it abrades rapidly. The mechanics of the formation of such a feature are similar to those that form potholes: particles entrained within the flow are swirled around in the bottom of the pool, thereby enlarging it. The presence of a ridge of alluvial material immediately downstream firom the pool suggests that materiai may be transported easily through the deep pool.

4.6.2.1.2 Circular meander pool An unusually large circular pool is found at bend D27 at the base of a ta11 cutbank composed of glacial sediment on Dingman Creek (figure 4.25). The pool appears to be natural in origin, and is the only one of its type in the study area. At the location of the circular pool the channel forms a tight bend of approximately 90' as it impinges on the valley wall. The pool is larger (27 rn across) and deeper when cornpared to the reaches irnmediately upstream and downstream (average width is 13 m), and it lacks a point bar on the convex bank. Coarse cobble-boulder riffles are located at the entrance and exit of the bend. Several large boulders are found in the narrow channel at the base of the cutbank. The straight reach upstrearn from the circula. pool is deep and uniform, a result of ponding behind the nffle.

Measurement of the maximum pool depth was not possible owing to deep water and an unconsolidated pool bed; however, a depth of 1.6 rn was measured immediately below the entrance rime. The flow pattern through the bend is unusuai; the high velocity filament crosses to the rniddle of the pool and appears to divide into two counter-currents, without irnpinging on the cut back. The upstrearn current circulates into a slackwater are- while the downstream current moves over the downstream riffle face. Few researchers (Alford et al., 1982; Thompson, 1984; Andrle, 1994) have noted similar eniarged circula. pools located at the apices of extremely tight meander bends. Both Andrie ( 1994) and Thompson (1984, in Andrle, 1994) studied pools formed in mal1 strearns in previously glaciated terrain. Because circular pools have been found in both coastal and postglacial environments a simple explanation for their formation is not likely to develop without further study. The width, depth and diameter of the pool found in Dingman Creek fa11 between the values observed by Alford and Andrie (table 4.4). Andrle (1994) also noted a sirnilar flow pattern to that at bend D27 under a va.riety of flow conditions, and suggests that the bend is tightening over time as the bend entrance migrates downstream and is effectively closing the bend.

Table 4.4. Cornparison between dimensions of strearns containing circular rneander pools River Gradient Channel Pool Pool Stream Confinement Point Width diameter depth environment Bars (ml (ml (ml Coastai rivers none Coastal (Mord et al.. >0.0003 30-90 60-110 4-14 - (exensive None 1982) backs'vam~ aoodplain) Glacial Dingman Creek 0.0023 13 27 >1.6 siltsiciays confined(incisedl None

Mansfield Creek O.OO Glacial Iake confineci None 34 6 0.5 (Andrle, 1994) siltdciays (incised) 4.6.3 Other channel scale bed features - till ledges Ledges composed of till extend into the channel fiom the base of banks, and occur particularly through the outside (concave bank) of bends (for example, bends D3 8, D4 1, 028,03 1, N2) (figure 4.26). Deep pools commonly occur below these ledges; however, the Iedges have the effect of forcing the thalweg and pool doser towards the centre of the channel. A detailed bathymetric survey of bend D38 was conducted to illustrate the morphology of such a bend (figure 4.27). The bend was surveyed in October, during low flow, and tied-in to the long profile survey conducted eariier in July. This allowed observation of bed features that were not visible earlier in the summer when the water was too deep and turbid. The till bed in the bend contrasts with the cobble bed material upstrearn and downstream. Collections of cobbles are found lying loosely on a smoothed clay-till ledge that extends partway across the channel fiom the base of the undercut concave bank. At the deepest part of the channel, a clear contact is visible between the till fiom the concave bank and cobbles at the base of the point bar on the convex bank (figure 4.28). The ledge forces the pool closer to the convex bank. The pool is divided into several smaller pools, separated from one another by irregular ridges or knobs eroded in the till. The fack of alluvial deposits in the bottom of the pools indicates a shortage of sediment supply relative to the stream's carrying capacity.

4.7 Sumrnary Many of the features observed during field investigation along Dingman, Oxbow and Nissoun Creek differ considerably fiom the 'normal' alhvial condition. Frequent outcrops of glacial till along the charme1 are responsible for controlling the morphology of these semi-alluvial streams. Of particular note are several unusuaI pool morphologies, inhibited riffle development, fiequent non-alluvial sediment inputs, incision and confinement within old glacial spillways, a variety of bankfull width measurements, poor gradient adjustment, till ledges forcing pools away from the outside of bends and a highly erratic bed material sequence. The implications of the morphological differences from alluvial channels outlined above will be discussed in Chapter VI. Figure 4.26. Till ledge emending into channel fiom base of bank @end 031, downstream view).

Figure 4.28. Sharp contact between till in bed and alluvial material at base of point bar. Note pool is closer to the point bar than the outside bank of the meander (bend D38' 80w to top lefi of photograph). CEAPTER V POOL AND RIFFLE CHARACTERISITCS IN SEMI-ALLUVLAL STREAMS

5.1 introduction Using the location of pools and rimes identified by the bedform differencing technique, various aspects of the semi-alluvial channel morphology may be investigated. Pools and riffles are displayed aiong the bed profile and planform for each creek and examined to determine whether pools and riffles occur in anticipated locations. Cornparisons are made between bedform length, spacing and pool depth to determine if there are systematic differences between alluvial and till sections, or between bends and straight reaches. Investigation is made into how definition of channel width affects bedform spacing, how T value affects the spacing and placement of bedforms, and whether there are differences in spacing that arise from measurement between inter-pool spacing and twice the pool-rime spacing. Statistica and Microsoft Excel are used for statistical analysis. The bed profiles for al1 three creeks are presented in figure 5.1 which shows pools and riffles as detailed undulations in bed topography as the channel descends along its course. For purpose of cornparison the three creeks arrive at a cornmon datum. The scale is the same for al1 three creeks and the height of the bed features is exaggerated (Vertical exaggeration = 130x) to show clearly differences in pool-rime amplitude between the 3 creeks. Nissouri Creek was surveyed over 3335 m directly to its confluence with the Middle Tharnes River, while the surveys on Dingman (4776 m) and Oxbow Creeks (4910 m) stopped several hundred metres short of their downstream confluence with the Thames River owing tu inaccessible depth and channel modification, respectively. The study reach along Oxbow Creek is the steepest of the three, followed by Nissoun, then Dingman Creek. Oxbow Creek is clearly convex in profile, being steepest at its downstream end, while Dingman and Nissouri Creeks are dso somewhat convex in profile. Al1 three profiles have small breaks or concavities that occur within the overall pattern; on Oxbow Creek, one particular break at 3700 m occurs in a meander loop that is in the process of being cut-off by an apparently natural channel upstream. Dingman Creek has minor concavities at 500 m and 2100 m, and Nissoun Creek shows several

concavities at 1 100 m and 3000 m. A notable concavity at 2400 m, occurs where the channel has been artificially straightened upstream from the County Road 78 bridge on Nissouri Creek. Unevemess in the bed profile is often the result of an increase in the gradient where the channel haç been shortened in proximity to bridges, or, in the case of the downstream end of Oxbow Creek, a rnarked channel steepening where it flows into the Thames River valley. Irregularities in the channel gradient are also to be expected where the streams altemate contact between cohesive glacial deposits and alluvial material.

5.2 Characteristics of pools and rimes in the channel profile The individual bed profiles for the three study sites are shown in figures 5.2, 5.3, and 5.4. Each profile is broken into four sections for ease of presentation. The vertical scale is maintained between each of the profiles for individual creeks, however it differs between the creeks. Pool and nffle syrnbols are placed at the exact maximum or minimum elevation location identified by the bedform differencing technique. Every tenth riffle and specific bends are labeled to aid in discussion and for comparison with the associated planform maps (see figures 5.14, 5-16, and 5.17). Significant features along each charnel are identified on the profiles.

5.2.1 Dingrnan Creek The spacing of the 93 bedforms identified along Dingman Creek is quite irregular (figure 5.2). The range in amplitude is from 0.122 to 1.605 rn (mean 0.627 rn). There are several featureless reaches of up to 100 m long (see 30G - 3 75 m, 550 - 650 m, 2 100 - 2175 m,2925-3000 m, 3280-3480m,4000-4100m,and4400-4475 m),while other sections have well-defined regularly spaced bedforms (see 1000 - 1900 m and 3800 - 4000 m). Reaches of both high and low amplitude features occur such that deep pools are often interspersed with shallower ones (see for exampie 1900 m - 2300 m). Owing to the high amplitude of bed features, the pools and rimes appear to be the best defined of al1 the creeks. 97

1 Dingman Creek

205 60

E 1 m 203 'P 2;. 202 Bend 13 (d

z. . 130 1400 1500 lm 1700 1800 1900 2000 2100 2200 2300 2LKX) 3500 zw 210 -rt0 - Co ,' 209- Brigham Road - Bridge 2,- 2,- ,207 - 206 - 205 - 1 Circula. pool. bend 27 2w 1 I I I 1 1 I 1 I I 1 I

211 - 210 -

209 - A RiMe I Bend36 208 - Bathynetric Bend-tl Bend 42 pool Bend 35 207 - meyof bend 38 'IO Riffle

Distance along channei (m) Figure 5.2. Bed profiles of Dingman Creek, showing locations of fiesand pools identified by the bedfonn differencing technique using a T value of OS78(SD) = 0.175. Specific ben& numbered to aid discussion. 5.2.2 Oxbow Creek The range in amplitude of bedforms on Oxbow Creek (mean amplitude 0.421 m) is not as great as on Dingman Creek (figure 5.3). Few of the abrupt deep pools seen in the Dingman Creek profile are found on Oxbow Creek. in dl, 1 19 bedforms are identified. The bed profile in the lower 600 m is the steepest part of the channel and only a few widely-spaced bedforms are defined in this reach (see 50 - 125 m, 175 - 250 m, and 425 - 575). Ta11 bluffs eroding into glacial deposits at 690 m and 180 m contribute corne material to the channel and are responsible for a breakdown in the pool-riffle sequence downstream giving long featureless sections of chamel bed. Reaches downstream fiom other bluffs, confined or rnodified reaches also show inhibited development of bedforms (see 1375 - 1425 m7 2200 - 2275 m, and 2920 - 3000 m), although they are not as conspicuous as the downstream 600 m of the profile. Bedforms in the meander cutoff section (3300 - 3700 m) are tightly spaced compared with the reaches immediately up- and downstream (see figure 4.24). Owing to reduced discharge, as water is diverted through the cutoff chute upstream, the stream7s cornpetence to transport material is reduced and deposition occurs. The channel bed is therefore adjusted to the lower flow of recent years since the chute developed. The bed material upstream from the cutoff is composed of finer sands and gravels than further downstream. This may be responsible for the general reduction in bedfom amplitude between 4 100 rn and the upstream end of the survey. The reach is also accessible by grazing livestock whose trampling may have evened-out any bedforms.

5.2.3 Nissouri Creek Bedforms along Nissouri Creek show no regular spacing, large pools are absent along rnost of the channel length and there are long reaches of featureless bed (figure 5 -4). Bedforms tend to occur in tight clusters (see 13 50 - 1400 m) separated by plane bed sections (see 1300 - 1350 m and 1400 - 1500 m). Other plane bed sections occur at 175-210m,825-900m,975-1050rn7 1175-1250m,1425-l5OOm,1500-1625 m, and 2675 - 2775 m. Eighty bedforms are identified over 3337 m. The bedforms have the lowest amplitude of the study creeks (mean = 0.285 m), the smallest features rnay be I 1 I 1 I I I I I I 1 1 i i O LOO 200 300 400 500 600 700 800 900 1000 1100 1200

Vanneck Road Bridge

I

u c.- 1300 1400 1500 1600 1700 1800 1900 2000 2100 2200 2300 2400 2500 rn> O -O 224 - Cut-off section 3 Coldstream Road 0 223 - 30 LT 222 - 221 -

Bend 3 1 .Bathtub' pool 218 - Bend 33 Bend 27 217 T 1 , 1 1 1 r I I 1 1 I

Osbon. Drive Bridge

Bend 38 10 Rrme number- 1 1 I I 1 I 1 I I I I I

Distance along channtl (m)

Figure 5.3. Bed profile of Oxbow Creek, showing Iocations of riWes and pools identified by the bedform differencing technique using a T value of O.%(SD) = 0.118 . Ans of downstream reach increased to mairitain sale behiveen profiles. Specific bend numbered to aid in discussion. 9 1 Nissouri Creek - - - Middle Thames - River

- - Narrow uillow section

Bend 12

I 1 I I r I 4 1 I L L ,000 1100 1200 1300 1400 1500 1600 1700 1800 1900 2000

200 -

199 - A Riffle ! 198 - Pool 4 197 - 10 Rime number

196 1 1 i L r 1 1 1 1 3000 3100 3200 3300 3400 3500 3600 3700 3800 3900 4000

Distance dong channe1 (m) Figure 5.4. Bed profile of Nissouri Creek, showing Iocations of riffles and pools identified by the bedform differencing technique using a T value of O.E(SD) = 0.090. Specific ben& numbered to aid in discussion. as little as 0.065 m, which is close to the actual bed material grainsize. Minor undulations in the bed profile are thereby defined as bedforms, and it is only in the downstream end (O - 300 m) that pools of any great depth are observed. In fact, the bedform amplitude is so low that it is possible that if the measuring staff were placed on top of a cobble, the elevation change would be great enough to define a riftle. Naturall y, every effort was made during the survey to ensure that this did not occur A major concavity occurs in the profile between 2300 and 2550 m in the reach upstrearn fiom the Road 78 bridge. The reach was straightened in the 1960s during construction of the road bridge, thereby shortening the channel and increasing the gradient. Several short bedfms are located immediately upstrearn between 2550 and 2650 m.

5.3 Bedform spacing The spacing of pool-rime bedforms may be calculated in a variety of different ways. Field observation and examination of the profiles indicate that not al1 sections of the chamel bed fa11 into the mutually exclusive categories of 'pool' or 'riffle'. Some sections of the bed are better classified as plane bed, yet occur within the pool-rime system. Existing definition methods often ignore this reality. For this reason, spacing in this study is measured by two different procedures to determine if the choice of method influences the resultant spacing. These are method 4 the distance between adjacent pool bottoms, and method B, twice the length of each pool-riffle unit, on the basis that this is the fundamental scour and depositional unit (figure 5.5). The length of the bedform is doubled to obtain spacing between bedforms. If the bedforms are evenly spaced along the channel, there should be no difference in results between method A or B, however, if the distance between a pool and downstream riffle is greater than the distance between rime and downstream pool, irregularities will be revealed. In this way, the pool to pool method will include al1 of the profile, while the double-bedform-Iength method excludes sections of the bed between the riffle and next pool downstream that might othenvise be classified as piane bed. Figure 5.5. Definition diagram for methods of measunng bedform spacing; method A, the distance between adjacent pools; method B, twice the distance between pool and downaream rime - both measured along the thalweg.

5.3.1 Standardization of bedform spacing by channel width Following determination of bedform spacing in metres, the spacing was standardized by the bankfull channel width to enable cornparisons between the channels. Problems associated with standardizing spacing by the bankfbll channel width were discussed earlier in sections 2.3.2 and 4.4.1, and a graph showing changes in width with distance along each creek is given in figure 4.6. The range and mean banMull channel width in the creeks are given in table 5.1. It can be seen that the width varies considerably along each study reach, such that use of any one value for width is a generalization. Because the width was determined on average every 60 m, precise width measurements are not available for each bedform. Hence, bedform spacing using both a mean width for the entire study reach and a five period moving average width are investigated to detemine if the spacing is sensitive to the choice of width measure used. The actual distance between each bedform (in metres) is divided by the appropriate width measurement to give two standardized measures of the bedform spacing in channel widths . Table 5.1. Bankfull channel width dimensions for the study sites

DingmanCreek 76 14-11 2.37 8.62-21.70(13.08) OX~WC~reek 94 10.75 2.96 4.57 - 19.00 (14.43) Nissouri Creek 53 9.13 2.50 2.40 - 14-04 (1 1.64)

Determination of mean bedform spacing is required for most restoration work, where the mean spacing for alluvial streams is generally expected to be in the range of 5 to 7 widths. In the case of the study creeks, the means are 3 or 4 channel widths depending on which method is used (table 5.2). Even when standardized, the mean spacing of bedforms on Dingman Creek is greater than for Oxbow and Nissouri Creeks. In al1 cases, the modal fiequencies for bedform spacing (3 W and 1W) are less than the mean spacing, indicating a tendency for short bedforms in al1 the study creeks.

5.3.2 Frequency distribution of bedform spacing The fiequency distribution of bedform spacing is often more revealing than the often-quoted mean bedform spacing. Al1 three creeks are found to have unimodal positively skewed fiequency distributions for bedform spacing (figure 5.6, table 5.2) regardless of the method used for their definition. The Pearson's coefficient of skewness (Sk), which is norrnalized by the standard deviation, allows comparison between the degree of skew in the creeks (McGrew et al., 1993, p50). An Sk close to zero indicates there is little difference between the mean and the median, while relative increases in the Sk indicate increasing asymmetry. The least skewed distributions (0.37, 0.48) arise with use of either method A or B on Dingman Creek. The most skewed (Sk 1 .O) plots arise kom use of method B on Nissouri and Oxbow Creeks, meaning that riffles in these creeks fiequently occur very close to their upstream scour pools. Dingrnan Creek

O 3 6 9 12 15 18 21 24 27 O 3 6 9 12 15 18 21 24 27 O 3 0 9 12 15 18 21 24 27 O 3 6 9 12 15 18 21 21 27 Spacing (bankfull channcl width) Spi-cing(bankfuil channcl width) Spacing (bankfull channcl width) Spacing (bankfull channcl width)

42 4- 6'36- Oxbow Creek

- - O 3 6 9 12 15 18 21 24 27 3 6 3 12 15 18 21 24 27 O 3 G 9 12 15 18 21 24 27 Spacing (banklull channcl width) Spacing (bankfull channcl width) Spcing (bankfull chatincl widt h) Spacing (bankfull chrinncl width)

Nissouri Creek

O 3 6 9 t2 15 18 21 24 27 O 3 6 9 12 15 18 21 24 27 O 3 6 3 12 15 18 21 24 27 0 3 6 9 12 15 18 21 24 27 Spacing (bankfull channcl width) Spacing (hnkfull channel width) Spacing (hnkfull chaniicl widili) Spaciiig (bankfull clianncl widl h) Figure 5.6. Frequency distribution of bedform spacing in study reaches of Dingman, Oxbow and Nissouri Creeks. Bedforms identified using the bedform differencing technique. A variety of methods were used to calculale the spacing of bedforrns: Column A, twice the length of a pool and its downstrearn rime, and a moving average of the bankfull widtli; (Method B) Column B, twice the length of a pool and its downstream rime, and a site average bankfull width; (Method B) Column C, pool to pool distance, and a moving average of the bankfull widtli; (Method A) Column D, pool to pool distance, and a site average bankfull width. (Metliod A) Table 5.2. Summary statistics for bedform spacing frequency.

A: Pool to pot spacing* B: Tnhthe length of pool + rime* (moving alr.nidth E (m) x Mode 5 (m) z Mode S;k site ai;. width) Dingman Creek

Oxborv Creek 4 Nissouri 40.97 3 '-O4 25.46 3 1 0.99 Cr& 3 0.84 1 0.82 * Ail uidths given in banW channel widths unless othernise stated

The shape and mean of the frequency distribution differs depending on whether one uses method A or B, indicating a sensitivity to the method of definit ion chosen. The pool to pool spacing plots more closely resemble a normal distribution, the mode being closer to the mean, while twice bedform length gives greater skew with a modal class of 1 in al1 cases and indicates a tendency for riffles to occur close to their upstream pools rather than at crossovers equally spaced between pools. The range in spacing generally increases when method A is employed rather than method B. Method A is not affected by the tendency for short pool-riffle distances, and gives an accurate description of the actual spacing between pools but is biased by the assumption that al1 bed features are either pools or nffles. Even though there is large scatter in the bankfdl channel width measurements (figure 4.6), there is little change in the shape of the distribution when one uses different measures of the bankfùll width for standardization. The rnean and the mode do not change, however, the skew of the distributions is higher when a moving average width is used (except for method A on Dingman Creek) rather than the site average width.

5.3.3 Forced mean bedform spacing of seven tirnes the channel width Use of the chosen tolerances in the bedform differencing technique gives a mean spacing of 3 or 4 times the channel width. Changes in the tolerance value are reflected in the definition of fewer or greater numbers of bedforms, which modifies the mean spacing. To investigate how the identification of bedforms alters if fewer features are identified, a mean spacing of 7W (the upper limit of the expected range for alluvial charnels) is investigated. Using the average width for the entire reach, an approximation of the number of bedforms required to obtain a mean spacing of 7W for each creek (n) was determined as follows:

where L is survey length, W, is the study site average bankfûll channel width, and Sp is the required spacing. Forecast curves (figure 5.7) were generated to obtain the 'T' values necessary to obtain the required spacing. The T values that would result in a bedform spacing of 5 to 7W are shown in grey. T values that are slightly above or below those that are projected will also define spacing in the 5 to 7W range owing to rounding of the mean. Using these T values (table 5.3), the bedform differencing technique was once again applied to the data to define bedform location.

Table 5.3. Tolerance value and number of bedforms required to force spacing to 7W no. bedforms T value

Oxbow Creek 69 1.13 % = 0.2463

Nissouri Creek 52 1.20 SD = 0.1445

The pool and riffle locations are shown in the profile on figures 5.8, 5.9, and 5.10. By raising the tolerance value, the lowest amplitude features are Lost and the bedforms are thinned-out. In Dingman Creek, high amplitude features are identified, while highly irregular lower amplitude sections of the bed, that are known to have till or alluvial cover over till, are featureless (see Dl800 - 2075 m, D3300 - 3500 m, and D3950 - 4125 m). The main effect of reducing the number of bedforms identified in each creek, is the elongation of existing plane bed reaches (see D300 - 425 m, D3950 - 4125 m, 0425 - 600 m, and N1425 - 1625) or the creation new extremely long ones @articularly Dl 750 - 2075 m, 0 1700 -1 850 m, 0 1875 - 2000 m, 04650 - 4900 m, and N775 -1 150 m). This suggests that even though the number of bedforms identified depends on the tolerance value, there is still a tendency for low amplitude or plane bed reaches in these creeks. 1 Nissouri Creek /

0.4 0.6 0.8 1.O 1.2 1.4 1.6 1.8 T value

Figure 5.7. Forecast mesused to obtain T values required to give a mean spachg of 7 times the bankfiill channel width (5 to 7W shown in grey). Dingman Creek 1- Carriage Road - Bridgc I -

1 I 1 I I I 1 I i 1 1 I O 100 200 300 m 500 600 700 800 900 1000 1100 120

s20J 1 I I 1 I 1 1 1 I 1 1 e 1 ..a 1300 14ûO 1500 16ûO 1700 1800 1900 2000 210 2200 2300 2UX) 2500 C E V

E 210 7 L .4 -6 209- Brigham Road < 208 - ' 207 - 206 - 205 - Circular ph, bend 27

201 1 I I I 1 I 1 I 1 I I 1 2500 2600 2700 2500 2900 3000 3100 3200 3UX) 3400 3500 3600 3700

211 - Clay riffle 210 - 209 - A Riftle 208 - Bathjmetric swey POO^ of bend 38 IO ~im~ 207 - numbcr

Figure 5.8. Bed profiles of Dingrnan Creek, showing locations of rimes and pools ident ified b y the bedform differencing technique. A 'T' value of 1.4(SD) = 0.423 was used to obtain an average inter-pool soacine of 7 times the bankfull channel width. 220 - CN Railway 40 219 - bridge TT. . Vanneck'i Road 218 - Bridgetinage 217 - 50 216 - 215 -

h -E 224 t Cut-off section C oldstream Road

'Bathtub' pool 218 -

Oxbow Drive Bridge 225 - ! 224 - 223 - 222 - Pool

Distance dong channel (m )

Figure 5.9. Bed profile of Oxbow Creek showing locations of rimes and pools identified by the bedform differencing technique. A 'T' value of 1.13(SD) = 0.246 was used to obtain a mean spacinp of 7 times the bankfull channel width. kwis of downstrearn reach increased to maintain scale between profiles. 191 1 Nissouri Creek

198 - Road 78 bridge ~97- & stream muge

196 -

195 -

194 -

200

199 A Riffle 198 Pool 197 - 10 Rime nurnber 196 i 1 1 r i 1 1 1 1 1 i 3000 3100 3200 3300 3400 3500 3600 3700 3800 3900 4000

Distance dong chuinel (rn) Figure 5.10. Bed profile of Nissouri Creek, showing locations of rimes and pools identified by the bedform differencing technique. A 'T' value of 1.2(SD) = 0.144 was used to obtain a mean spacing of 7 times the bankfùll channe1 width. The grouping effect is ail1 evident on Nissoun Creek, while the spacing of feahires is somewhat more regular along Dingman Creek (see D2500 - 3300 m). Only three bedforms are loa in the meander cutoff section of Oxbow Creek such that they are still more tightly spaced here than in adjacent reaches. Examination of the location of bedforms in the planforrn is made in section 5.4. The frequency distributions of bedform spacing remain positively skewed (figure 5.11), however by removing some of the smaller features, the skewness is often reduced (see Sk in table 5.4). As a result of the method used to force the mean spacing to 7W, the mean spacing for method B remains at 3 or 4W. The least skewed distribution (0.08) occurs on Dingman Creek with use of rnethod B, where the skew was 0.55 under the previous spacing. The most skewed plots (1.44 and 1.57) still occur with use of method B on Oxbow Creek, indicating that riffles tmly occur close to their upstream scour pools and the effect is not a result of the chosen tolerance value in the definition method. The shape of the frequency distribution still differs between method A or B, the pool to pool spacing plots giving a distribution that is closer to normal. The modal class generally occurs at a higher spacing than before. The range in spacing is greatly increased, reflecting the elongation of plane bed reaches discussed above.

Table 5.4. Summary statistics for bedform spacing fkequency where mean spacing is forced to 7 channel widths. Pool to pool spacing Tnice the length of pool + de (moving av. widtk (m) E (m) s? Mode Sk site av. width) >z z Mode Sk Dingman Creek

Oxbow Creek

Nissowi Creek

5.3.4 Comparison between bedform spacing in tiU and alluvial reaches To determine if bedform spacing differs between open-till and partially-alluvial sections of the channel, the number and length of bedforms occumng in till and in alluvial sections of each creek (table 5.5) was detennined. Planform rnaps of till location 9 - a 36 Dingman Creek 30 - - - d- Fti O - ii !dm&-, 1 n ,-, C O 3 6 9 121518212427 O 3 6 9 12 15 18 21 24 27 O 3 6 9 12 15 18212427 O 3 G 9 12 15 18 21 24 27 Spacing (brinkfull chaimcl widths) Spacing (bankfull chaniicl widths) Spacing (bankfull channcl widtlis) Spacing (bankfull channcl widths)

Oxbow Creek 30

O 3 6 9 12 15 18 21 24 27 O 3 6 9 121518212427 O 3 G 9 121518212427 O 3 G 9 12 15 18 21 24 27 Spacing (bankfull channcl widths) Spacing (bankfull clianncl widths) Spacing (bankfull channcl M idths) Spacing (bankfull channcl widths) 1 Nissouri Creek - 30

O 3 G 9 12 15 18 21 24 27 O 3 6 9 12 15 18 21 24 27 O 4 8 12 16 20 24 28 32 36 O 4 8 12 16 20 24 28 32 36 Spacing (bankfiill channcl widths) Spacing (bankfull channcl vlidths) Spacing (bankfull cliaiincl widt1.i~) Spaciiig (bnnkfull cliaiincl widtlis) Figure 5.1 1. Frequency distributions of bedform spacing in study reaches of Dingman, Oxbow and Nissouri Creeks. Bedforms identified using the bedforrn differencing technique to give a mean spacing of approxiinatcly 7 times the bankfull cliannel width. A variety of methods were used to calculate the spacing of bedforms: Colurnn A, twice the distance between pool and downstream rime, and a nioving average of the bankfiill width; (Method B) Colunm B, twice the distance between pool and downstream riffle, and a site average baiikfull width; (Method B) Column C, pool to pool distance, and a rnoving average of the bankfùll widih; (Method A) Colurnn D, pool to pool distance, and a site average bankfull width. (Method A) Note, horizontal axis of columns C and D for Nissouri Creek differ from other plots. in the channel and pool-riffle locations (such as figures 4.3 and 5.14) were overlain in AutoCAD. Because only the maximum or minimum elevation is defined by the bedform differencing technique, pool and riffle lengths were obtained fiom the rnid-points between pool bottoms and rime crests. Pool to pool spacing was determined for sets of pools occumng cornpletely within a till or alluvium unit. Ifone pool uraslocated in till and the next in alluvium, both were discarded from the set. Calculations are made in metres rather than channel widths to avoid ambiguity introduced during standardization. Dingman Creek has a greater number of bed features formed in till than in alluvium, while Oxbow and Nissouri Creeks have the reverse. No pool to pool units were found in till on Nissouri Creek, although individual pools in till do exist. Using a Kolmogorov-Smimov test to examine the shape of the spacing distribution, al1 D datistics for bedform length, pool length, rifle Iength and inter-pool spacing were less than the critical values for D at P = 0.05, therefore one may conclude that the sample data are drawn f?om populations which do not differ significantly from a normal distribution. Consequently Student's t tests were used to determine if there were significant differences between the lengîh of bedforms, pools, nffles, and inter-pool spacing forrned in predominantly alluvial versus tiI1 sections in each creek. The results for al1 tests are shown in table 5.5. One-tailed t tests were canied out to determine if the mean length of bedforms, pools, rimes and pool to pool distance differed statistically in a particular direction; for example, whether bedforms that occur where till is visible in the channel are shorter than those formed in alluvial material. Although, the means of bedform length, pool to pool distance, pool length and riffle length in till are al1 less than the means for features in alluvium for Dingman and Oxbow Creeks, only the length of bedforms in alluvium on

Dingman Creek were found to be significantly larger than those formed in till, t = 2.382, P=O.O 193. Even though the mean lengths for bedforms in till and alluvium in Nissouri Creek differ by a substantial margin (1 1-74),the sample size for bedforms in till is only 5, reducing confidence in the interpretation of the results. Diflerences between pool-pool distance, pool length and nffle in till or alluvium were not found to be significant. Table 5.5. Cornparison between bedform length in alluvium and glacial till reaches.

- -- minium

Bedform length 44.92 0.149 U 56.56 33.68 0.088 2.382 Dingman Creek 48 (3.02) (2.87) Osbow Creek

Nissouri Creek . --, Pool-pool distance 28 37-65 62.80 0.206 26 ".O8 48.81 0.194 0.835 Dingman Creek (5.66) (5.18)

Osbow Creek

Nissouri Creek

Pool lcngth 24.00 62-50 0.158 45 27.3 1 Dingman Creek dg (2.17) (1.88) 46.06 0.210 1.148 Osbow Creek

Nissouri Creek

Rime Iength 24.59 58.80 0.148 44 (l.74)26-78 43.17 0.153 0.800 Dingman Creek 48 (2.09) O?rbow Creek

Nissotri Creek 5 21*03 65.57 0.140 0.895 (2.47) * Lengths in metres * Highlighted figure statistically significant at P=0.0 193

5.3.5 Bedform spacing in the downstream direction Ordinarily, relative pool depth and distance between pools can be expected to increase in the downstream direction, reflecting changes in energy expenditure with decreasing gradient, increasing discharge and erodibility (Wohi et al., 1993). However, the wide scatter and general absence of downstream trend in channel width measurernents, together with lack of tributaries in each creek, suggests little change in discharge downstream. Furthemore, gradients within the study reaches actually increase downstream in Oxbow and Dingman Creeks, while erodibility of the channel bed and banks is highly variable in response to the mix of bed material through which the creeks are flowing. The spacing of bedforms (in metres) with distance along the channel for the three study sites is given in figure 5.12. The regression line and ? values are shown, and both the pool to pool distance (method A) and twice pool to nffle distance (method B) are illustrated. No trend in bedform spacing in the downstream direction is found in the study creeks. The pool to pool method results in a wider range of bedfom spacing, while twice the bedform length shows a tendency for riffles to be located closer to upstream pools than adjacent bedforrns. The distribution of bedform spacing differs between the two methods; for example, method A on Oxbow Creek gives an inter-pool spacing of 180 rn at 500 m along the channei, while this long spacing is lost with use of method B. .4t P=0.05, the slope of the regression line is not significantly different from zero, indicating that neither method of determining the spacing shows a significant relationship between distance along the channel and bedform spacing. Clusters of bedforms with shorter-than-average spacing occur within the overall pattern. These are outlined in figure 5.12. To investigate other patterns that may exin, cumulative departure fiom the mean pool to pool spacing is plotted with distance along the channels (figure 5.13). The upstrearn end of the channel is show on the right of the figure, the downstream end on the left. Increasing bedform spacing is seen as a rise in the cumulative departure fiom the mean from the lefi to the right, while shorter spacing is indicated by fa11 in the line from left to right. None of the plots show consistent periodicity; however, there is a cycl ic pattern, particularly along Nissouri Creek, where breaks between shorter and longer bedforms occur approximately every 530 rn along the channel. On Dingman Creek, there is little pattern in bedforms spacing, although longer features are grouped in the upstrearn end of the survey. The shorter spacings outlined in tigure 5.12 are expressed as a continuous fa11 in the cumulative departure plot between 800 - 1200 m and 3000 - 4000 rn on Oxbow Creek (figure 5.13). The latter section of shorter spacing coincides with the meander cutoff reach noted earlier. Oxbow Creek

R'--o,oI

Nissouri Creek

I 1 O 1000 2000 3000 4000 5000 0 1000 2000 3000 4000 5000 Distance along channel (m) Distance along channel (m) Figure 5.12. Bedform spacing with distance along the channel (downstream end is at O). Column A shows pool to pool distance, columii + w B shows twice the distance between pool and downstream riffle. Ellipses identiS, grouyings of shorter bedforrns. QI 250 200 Dingman Creek

250 4 N~SSOU~Creek

O 1000 2000 3000 JO00 5000 Distance along channel (m) Figure 5.13. Cumulative depamire eorn mean pool spacing with distance dong the channel for study reaches along Dingrnan, Oxbow and Nissoun Creeks. 5.4 Pools and rimes in the channel planform Figures 5.14, 5.15, and 5.16 show the pool and riffle locations in the planform for each creek, as defined using the bedform differencing technique. Riffle number, bend number, and distance markers along the channel are also given to aid in location of features during discussion. Reference is made to the bed profile fiyres discussed earlier (figures 5.2, 5.3, and 5.4) and comparisons may be made by matching nffle number or distance along the charnel. Bends mentioned in the text are nurnbered on the Stream profiles. The semi-alluvial streams in the present study do not possess the 'text-book' pool- rime distribution with pools in each bend and riffles in the straisht sections joining bends. The amplitude and spacing of bedforms in semi-alluvial channels may be influenced by occurrence of more resistant glacial material in the channel boundary and by coarse sediment delivery where the strearn impinges upon the valley walls. Such influences are responsible for interruptions in the placement and replar spacing of bedforms in the long profile. In al1 three creeks, over twice as many pool-rime units are identified than bends in the planforms (table 5.6). Therefore, on average, there are over twice as many pools and riffles in each meander than expected. Ln ody a few sections of channel where the bed is predominantly alluvial, does the morphology follow the expected regular pattern of pool-riffle placement (see D3800 - 4000 rn, and 0180 - 400 m). Instead, long sections of chamel bed are featureless, riffles are ofien found in bends and, while pools may be absent in some bends, other bends have extrernely long pools or multiple pools.

Table 5.6. Number of bends and bedforms in study streams Number of Number of Nurnber of Nurnber of Number of pool-ae ben& with bends nithout ben& wth bends units pools pools rnultipIe pools* Dingman Creek 42 93 38 4 16

Osbon. Creek 5 1 120 46 5 1O

Nissouri Creek 39 80 32 7 8

121

Nissouri Creek

flow-

0 12 O, direction Il 0 I = 1OOOm 1O

A& A& Road 78 /-

- Riffle 30 O

Distance frorn 500m downstream end of study reach Confluence with Middle Thames River 14 Bend nurnber Stream gauge 02GD022 =: =: Riffle crest O Pool bottorn Figure 5.16. Map of Nissouri Creek study reach (icon size varies to showing location of pools and riffles identifled by allow bener fit) the bedform differencing technique, T=0.75(SD). 5.4.1 Bends with no pools Sixteen bends lack well-defined pools (table 5.6), particularly on Nissouri Creek, where bedform amplitude is the lowest of al1 the study streams. Bends with no pools occur in both till and alluvial reaches (those formed in till are in bold in the text for section 5.4.1). Bend D38 has no pool, even though the bathymetric survey showed several small scour pools in till. This may be the fault of a fixed survey interval that inevitably misses some of the smaller features that were later detected in the detailed bathymetric survey. The bed elevation through bends D35 and D36 is intermediate between pooI and nffle with a few minor unduIations eroded in till. Other bends that Iack pools are D20, 09, 015, 038, 045, 047, N10, N12, NT7, N19, N24, N32, and N33.

5.4.2 Bends with pools Even though the distribution of bedforms is confùsed by the fact that there are many more pools and riffles than in regular alluvial meanders, most bends do have pools located slightly downstream of the bend apex (see bends D4, D28,05, 014, N5 and N39). Bends that have pools tend to faIl into two categories: those with long deep pools that extend al1 the way around the bend (such as bends D13, pool 65; D28, pool 28; D42, pool 1; and 027, pool 59), and those with multiple small pools separated by till protxusions (see table 5.6, and bends D18, pools 52, 53,54; bend 027, pools 55, 56, 57, 58; and N15-16, pools 45, 46, 47). Approximately one quarter of al1 bends have more than one pool. There does not appear to be any physically predictable pattern to the distribution of either type of pool, long pools in till being followed by bends also in till with no pools at dl.

5.4.3 Rimes in bends Single or multiple riffles ofien occur in bends, see for example bends D 18, D4 1, 09, 034-35, 051 and N28. This may be a response to coarse sediment delivery from failure of cutbanks at bends daring meander migration. Excess sedirnent remains in the channel as the creek is not competent to transport the coarse glacial debris, thereby resulting in multiple shallow bars. Riffles formed entirely in till separate pools in bends, resulting in many multiple pools (see bend D 18). 5.4.4 Bedforms in straight reaches Both pools and nffies occur in straight reaches. Bedform spacing tends to increase in straight sections of the charnel owing to more stable banlis, thereby less sediment input for riffles and bars (see D2550 - 2750 m, and N2200 - 2500 m), and is also somewhat regular @ 150 - 250 m, nffles 86 - 90; and 01500 - 1700 m, rimes 84 - 87). Approximately one third of al1 pools occur in straight reaches (roughly 30, 38, and 30 pools on Dingman, Oxbow and Nissoun Creeks respectively).

5.4.5 Featureiess reaches Several sections of the study channels lack well-developed bedforms. Plane bed sections occur mainly in straight alluvial reaches (see D280-3 50 m, D550-650 m, and

0425 - 575 m, and in till: D29 15 - 3000 m). The longest plane bed reach between D3200-3475 m has till in the banks and alluvial material in its downstream end as it approaches bend D28. Many short plane bed reaches occur on Nissoun Creek, although they are mostly in bends (see bends NlO (below a till cutbank), NI9 , and N3 1 - 33).

5.4.6 Planform location of bedforms forced to a mean spacing of seven tirnes the channel width When the mean bedfonn spacing is forced to be consistent with that of the 'average' alluvial channel, discrepancies persist in the planform location of bedforms. Al1 three of the study streams have more bedforms than bends (table 5.7), such that there rernain too many bedforms to match the planforrn (figures 5.17, 5.18, and 5.19). In alluvial charnels, it is possible that altemate bars may occur in long straight reaches, thereby increasing the number of bedforms in the overall planform while maintaining the mean 5 - 7W spacing. In the semi-alluvial examples, bedforms are often lacking in the straight sections hile multipie pools and nffles occur through bends (see D200 - 425 m,

D4400 - 4700 m, and 0450 - 850 m).

126

Nissoun Creek

flow direction d3 Riffle IO-. ,O35 a 12 I I1 1OOOm 1 O

-8 Riffle 40-- Q'

A& A& Road 78 7

Rime 20

t

Distance from Confluence with Middle 500m downstream end Thames River of snidy reach 14 Bend number O 1O0 200 A Stream gauge Meurs 02GD022

Figure 5.19. Map of Nissouri Creek study reach O Pool bonom showing location of pools and rimes with mean spacing of 7 times the bankfull channel width (identified by (icon size varies to gbedfonn differencing technique. T=I .Z(SD)). allow bener fit) Table 5.7. Number of bends and bedforms in study streams when mean spacing is 7 times the channel width Number of Number of Number of Number of Nuber Of pl-nffle bends nith ben& \%-ichour brnds wïth lxnds uni& pools pools multiple pools* Dingman Creek 42 47 30 12

&bow Creek 51 69 42 9

Nissouri Creek 39 52 25 14

Although pools are fond on many bends, there is an increase in the number of bends without pools. Accordingly the number of pools in straight reaches and of bends with multiple pools decreases when mean spacing increases (table 5.7). The proporiion of channel for which no bed features are defined increases (see N800 - 1 150 m, NI425 - 1625 m, and Dl 750 - 2075 m). Most featureless sections occur in straight reaches (see

D300 - 425, D2600 - 2750 m, and D4400 - 4550 m) and are predominantly alluvial. Al1 the pools previously defined through bend D 18 are lost under the new definition, even though field observation suggests the multiple pools do exist.

5.5 Bedform amplitude A rough estimate of the amplitude of bedforms is calculated derremoving the downstream slope £tom each of the profiles. Amplitude is calculated by combining both the elevation difference between pool and downstream rime, and riffle to downstream pool. The amplitude differs between the three streams (table 5.8), the amplitude on

Dingman Creek (mean = 0.627 m) being the greatest of the three, and Nissouri Creek

(mean = 0.285)the least. This is to be expected as the Dingman Creek drainage basin is 5 times the size of Nissoun Creek and bedform size is related to properties of the flow such as discharge and strearn power that generally increase with drainage basin area. Table 5.8. Bedform amplitude (m) in study streams

- . - R. SE ma^ - min

Dingman Creek 1.605 O.122 (0.022) -

ûxbow Creek

Nissouri Creek

An examination of figure 5.1 reveals that the amplitude of bedforms is also seen to Vary within each channel; for example, the bedfoms in the lower 600 m of Oxbow Creek are subdued when compared to the remainder of the channel. This may be a result of changes in energy expenditure along the channel resulting fiom a combination of factors such as differences in bed material size, radius of curvature, location in the planform, proximity to valley wall, strearn power, reach gradient, or human modification. The causes for variation in amplitude are cornplex, such that it is next to impossibie to isolate individual influences upon the bedform amplitude with the data available in this study. Only limited inquiries may be conducted in order to identi+ potential causes for variations in amplitude.

5.5.1 Pool depth Water height is subject to fluctuation with discharge over tirne and is therefore not a reliable measure of pool depth. Pool depth is therefore calculated as the elevation change fkom pool bottom to downstrearn nffie crest. Even though the depth of water in the pools is usually greater than this value, it enables cornparisons of pool depth between and along the creeks as the influence of changing discharge domthe channel and over time is removed (table 5.9). Pools are significantly deeper in Dingman Creek @), followed by Oxbow (0) and Nissoun (N) Creeks @ > O t=3.8614, D > N t=6.0029, O > N ~3.1750,p=0.0022) (Table 5.9). Similady, the range, maximum, and minimum depths of pools follow the same order. Figure 5.20 shows the fiequency distribution of pool depths for each creek. Dingrnan Creek has a greater variability of pool depths, while the plots for Oxbow and Dingman Creek n = 93

Oxbow Creek n=119

Nissouri Creek n=80

Pool depth (m)

Figure 5 20. Frequency distributions of pool depth in study reaches of Dingman, Oxbow and Nissouri Creeks Nissouri Creeks are strongly positively skewed indicating they have a greater proportion of shallow pools. These findings follow the corresponding decrease in drainage basin area (table 3.2) and observations made in the field.

Table 5.9. Summary statistics for pool depth in the study channels

Pool depth (m)

n X, SE CV mg'= (m.min.) 0.580 1.15 Dingnun Creek 9 3 (0.031) ''." (1.334.18) 0.357 0.91 Osbow Creek (0.017) 53.22 (1.064.12) 0.326 0.59 Nissouî Creek 80 (0.015) 57-52 (0.68-0.09)

5.5.2 Pool depth with distance along the channel One would ordinarily expect to find increasing pool depth with increases in discharge and distance downstream. However, for the same reasons that no trend in bedform spacing is found in the downstrearn direction, when pool depth is regressed against distance along each channel, the dope of the regression line is not significantly diEerent fiom zero, indicating that there is not a signifiant relationship between distance along the channel and pool depth (P=0.05). Cumulative departure fkom the mean pool depth is plotted with distance along the channels (figure 5.21). Again, the upstrearn end of the channel is show on the right of the figure, the downstream end on the left. The plots also show that there is no downstream increase in bedform size, yet there are sume interesting patterns within each Creek. Dingman Creek shows three areas (2900 - 4000 m, 2050 - 2300 m, and 1500 - 1800 m) where pools are generally larger than 'average'. These coincide with reaches that are confined in till against the south valley wall. Pools along Oxbow Creek are generally deeper between 2000 - 4000 m, while there are more shallow pools in the downstream end. This agrees with observations made fhm the bed profile (figure 5.3) in 1 Nissouri Creek

1 Downstrearn Upstrearn

Distance dong channel (m) Figure 5.21. Cumulative depature from mean pool depth with distance dong the channel for study reaches of Dingman, Oxbow and Nissouri Creeks. which the lower portion of the nirveyed channel exhibits reduced amplitude of bedforms. There is little change in pool depth along Nissouri Creek. Pools are generally small until the lower 500 m of the survey where pool depth increases.

5.5.3 Comparison between pool depth in till and alluvial reaches To determine if bedform amplitude differs between till and alluvial sections of the channel, the number of pools occurring in till and in alluvial sections of each creek was determined (table 5.10) by overlaying planform maps of till location in the channel and pool-riffle locations in AutoCAD. Pool depth was determined as described above. Relative frequency distributions for pool depth in each substrate are shown in fiwre 5.72. Dingman Creek has more pools in till than in alluvium, while Oxbow and Nissouri Creeks have fewer pools in till than in alluvium. Using the Kolmogorov-Smirnov test to examine the shape of the pool depth distribution, D statistics for pool depth were found to be less than the cntical values for D at P = 0.05 for al1 three creeks. Therefore one may proceed with one-tailed Student's t tests to determine if the depth of pools scoured into till is significantly greater than pools formed in alluvium in each creek, as observed in the field. The results for al1 tests are shown in table 5.10.

Table 5.10. Comparison between pool depths in alluvial and glacial till reaches.

Glacial till Allinium

Dingman Creek 48 (O.O4T) 54.04 0.128 17.28 O.102 0.899 iU (0.039) 52.00 O. 177 54.18 0.140 0.751 Osbow Creek 'O (0.031) 79 (0.021) Creek 66.99 0.221 52-11 2.252 Nissouri l1 (0.062) 69 (0.013) 0.151 * Deph in rnetres * Highlighted figure statisticaiiy signiflcant at P=0.0271

Although the mean depths for pools in tiil exceed those in alluvial material for al1 creeks, only those pools occumng in till along Nissouri Creek were found to be significantly larger than those formed in alluvium, t = 2.252, P=0.0271. However, when one investigates the deepest pools (defined as those greater than one standard deviation Dingman Creek n = 93

Oxbow Creek tt:Q> 1

0.8 i Nissouri Creek 0.6 1I

Pools ui allu\iium 0.2

0.0 O .O 0.2 O -4 0.6 0.8 1.O 1.2 1.4 Pool depth (m)

Figure 5.22. Frequency distributions of pool depth in till and alluvial material in study reaches of Dhgman, Oxbow and Nissouri Creeks. from the mean), a disproportionately large number of deep pools occur in till (table 5.1 1). Using a Chi Square test, the number of deep pools found in each substrate for Dingman and Oxbow Creeks is not significantly different from that which we would expect considering the distribution of pools in each substrate in the entire channel (X2=3 245, x2=2. 183, for Dingman and Oxbow Creek respectively, P=û.OS). The distribution of deep pools on Nissouri Creek are significantly dif3erent fiom the proportions expected f?om the number of pools in each substrate for the entire channel (X2=30.436,P = 0.05). If one were to compare the number of deep pools of each substrate with the number of pools occumng in the entire chamel for each creek as a percentage however, more of the deep pools occur in till than in alluvial material. For example, 36% of a11 pools formed in till along Nissouri Creek are deep cornpared with 12% in alluvium.

Table 5.1 1. Proportion of deep pools formed in till and alluvium Number of *P Pools no. of Numkr of deep poo 1s as % Total pools of pools in (2 X+Sn)-, al1 each subsrate tiii ailuvium Total Tiil Aliwium Till AIlinium 48 45 11 7 16% Dingman Creek (52%) (48%) l8 (61%) (39%) 23% 40 79 9 13 O>

5.5.3.1 Pools in bends and straight reaches Pool depths in bends and straight reaches are compared to determine if pools are deeper in bends (Richards, 1978). The number and depth of pools in bends and straight reaches was determined and radius of curvature (Rc) of each bend was calculated by fitting circular arcs to each meander in the channel planform in AutoCAD. The radius of each arc was queried in AutoCAD and recorded. Pools located at the apex of each bend are recorded as pools in bends, while al1 other pools are considered to occur in straight sections of channel. Summary statistics for radius of curvature and pool depths in till and alluvium in bends and straight reaches are shown in tables 5.12 and 5.13. Frequency distributions of pool depth in bends and straight reaches are show in figures 5.23 and Buanbag pazpuuoN 1 Dingman Creek

Nissouri Creek a Pools in till n = 48 Pools in alluvium

rri 0.2 0.4 0.6 0.8 1.0 1.2 1.4 0.0 0.2 0.4 0-6 0.8 1.0 1.2 1.4 Pool depth (m) Pool depth (ni) Figure 5.24. Frequency distributions of pool depth in strright reaches of Dingman, Oxbow, and Nissoiiri Creeks. w Column A shows al1 pools in straight reaches, column B shows pool depths in straight reaches in glacial till or alluvial material. w O\ 5.24. Each distribution is then fùnher divided by substrate to show the relative frequency of pool depths occumng in till and alluvial material.

Table 5.12. Summary statistics for pool depth in bends

- Depth of ail pools Pools in till in Rc Pools in aliu\iurn in ben& (m) bends (m) in ben& (m) 2. SE n 3. SE n X. SE n 2. SE Dingman Creek 51.295 4o 0.648 23 0.670 0.619 (6.007) (0.052) (0.080) " (0.060) 23.191 46 0.414 0.446 0.399 Osbow Creek (2.284) (0.034) l5 (0.057) 31 (0.012) 36.700 32 0.266 Nissouri Creek 0.485 O.242 (6.221) (0.028) (0.169) 29 (0.024)

Table 5.13. Summary statistics for pool depth in straight reaches Depth of al1 pools Pools in tili in Pools in allinium in sîraights (m) straights (m) in straights (m) n R. SE n X. SE n X. SE 0.529 549 0.5 11 Dingman Creek 53 o. 25 (0.053) 28 (0.049) 0.32 1 0.333 0.3 14 Osbow Creek 73 (0.018) *' (0.033) (0.021) O. 199 0.239 0.191 Nissouri Creek 48 (O-O11) * (0.015) U, (0.014)

Pool depths in bends are significantly deeper than in straight reaches (Dingrnan Creek: t=1.9444, p=0.0549; Oxbow Creek: t2.6776, ~4.0085;and Nissouri Creek: t=2.2853, p=0.0250). Both Oxbow and Nissoun Creeks have a positively skewed distribution for pool depths in straight reaches, suggesting that more shallow pools occur in straights while the deeper pools occur through bends. The mean depths of pools formed in till in bends is greater than the mean depth of pools in till in straight sections of al1 channets. Similarly, the mean depth of pools formed in alluvial material is greater for those in bends than in straight reaches. For al1 three creeks, the mean depth of pools in bends is greater for those formed in till than in alluvial material, although only pools on Nissoun Creek are significantly deeper (t=2.7 160, p=0.0109). Of the pools in bends on Dingman Creek, more occur in till than in alluvial material. This is not an unexpected result as most bends appear to be migrating laterally into the valley side glacial deposits, thereby increasing the probability that pools occur in tilt. In Oxbow and Nissouri Creeks, fewer pools in bends are incised into till than alluvial material. Of the deepest pools in bends (those above one standard deviation from the mean), 7 are in till and 1 in alluvial material on Dingman Creek. More of the deep pools in bends are in till (5) than alluvial material (3) dong Oxbow Creek, the reverse is found in Nissouri Creek (2, 3). The mean depth of pools in straight reaches is greater for those formed in tills than in alluvial material for al1 three creeks. In al1 cases, fewer pools occur in till than alluvial material in straight reaches.

5.5.3.2 Radius of curvature and pool depth Radius of bend curvature (Rc) is frequently observed to be 2-3 times the channel width. Studies have shown that pool depth increases with tightening of radius of bend curvature up to 2-3W afler which flow patterns are disrupted owing to high 80w resistance (Thorne et al., 1997). Simple regression of pool depth against radius of curvature (figure 5.25A and B) does not give a regression line slope significantly different from zero, indicating that there is no significant relationship between pool depth and radius of bend curvature in the study streams. When pools are separated according to bed materiai in scatter plots showing the relationship between pool depth and radius of curvature (figure 5.25A) there is no apparent division between pools in alluvium and till. There is however a cluster of deep pools in till that occur in bends with a tight radius of curvature (<40 m) on Dingman Creek. Little information can be drawn &om Nissouri Creek because only three pools in bends occur in till, however, the scatter plot does illustrate the poor relation between pool depth and bend radius.

5.5.3.3 Pool depth and confinement Similarly, to investigate whether there is a relationship between pool depth, radius of curvature, and confinement, pools are separated by proxirnity to the valley wal1 (figure 5.2SB and table 5.14). For the purpose of this study, pools located against the valley wall . ;c , - P. a.; ! 4 are considered contined. Confinement does not seem to influence the distribution of pool depths; however, the mean radius of curvature is tighter (except Nissouri Creek) and mean pool depth is greater for bends that impinge upon the valley wall. It is interesting to note that al1 but one of the confined pools are formed in till for each creek.

Table 5.14. Radius of curvature and pool depth in confined and unconfined bends

- - - -- Radius of ~mature(m) Pool depth (m)

- -- confined unconfined confineci unconfuiai

46.036 29 53.290 0.699 29 Dingman Creek 1 1 (8. 1) 0.629 (7.680) (O. 12 1) (0.056)

Osbow Creek 20.856 23.759 0.455 0.404 (3.149) 37 (2.744) (0.073) 37 (0.038) 43.500 30 36.247 0.516 3o 0.249 Nissouri Creek 2 ( 8.900) (6.572) (0.162) (-027)

5.6 Summary Through an examination of the spacing, amplitude and location of pools and nffles in the Stream planform it cm be seen that pool-rime spacing is quite irregular and there are many featureless reaches. Mean bedform spacing is 3 or 4 times the channel width, whereas the most fiequent spacing is 1 or 3W. Erosion of ta11 bluffs supplies coarse sediment to the channel, which contributes towards a breakdown in the pool-riffle sequence such that there is no downstream trend in pool-riHe spacing or pool depth. However, clusters of pools and riffles with shorter-than-average spacing do occur in some locations down the chamel. Spacing is generally greater in straight reaches. Mean bedform length, pool to pool distance, pool length and riffle length are shorter when features are formed wbere till is visible in the channel boundary. The mean depth of pools is greater for those that occur in till. A large number of 'deep' pools occur in till. More than twice as many pool-riHe units are identified than bends. Riffles frequently occur in bends, thereby creating multiple pools, while other bends have extremely long pools that extend around the entire bend. Some bends lack pools altogether. Pool depths in bends are significantly deeper than in straight reaches. Sirnilarly, the mean depths of pools in till and alluvial material in bends are greater than those in till and alluvial material in straight sections. There is no significant relationship between pool depth and bend curvature, and no demarcation between pools formed in either substrate in tight bends. The mean radius of curvature and mean pool depth is greater for bends that are confined against the valley wall. By raising the toierance value used in the bedform differencing technique, fewer bedforms are identified. This increases the mean spacing between bedforms, and results in the elongation and addition of excessively long plane bed reaches that occur predominantly in straight alluvial reaches. The shape and mean of the fiequency distribution for bedform spacing differs when the method of defining the spacing is altered; pool to pool distances are generally greater than twice the distance between a pool and its downstream riffle. Use of a site average or moving average bankfull width does not appear to influence the standardization of bedform spacing. CHAPTlER VI DISCUSSION

6.1 Introduction Although Dingrnan, Oxbow and N~SSOU~Creeks have the superficial appearance of being 'alfuvial' in some reaches, it should be remembered that they are flowing through glacial material and have only a shallow layer of alluvial material between alluvium visible in the Stream bed and till at depth. This condition has not been recognized extensively in the literature except for channels formed in bedrock, which have varying quantities of unconsofidated dluvium sorted into bars within the channel (see figure 1 1, in Keller and Melhorn, 1978). This study shows that in many places the alluvial layer is so thin that glacial material is visible in the channel bed and banks, particularly at bends where lateral channel migration continually exposes till in ta11 bluffs. Similar conditions exist across much of southern Ontario and other areas with substantial glacial deposits blanketing bedrock, yet no consideration of the streams' semi- alluvial nature is made in current channel restoration and design practices (see Keller and Melhom, 1973; Church and Slayrnaker, 1989; Kellerhals and Church, 1989).

6.2 Pool-dl'le identification problems 6.2.1 Pool-rime definition techniques A variety of methods for identifjring pools and riffles were investigated. Linear and non-linear regression and the bedform differencing technique are the only quantitative methods for differentiating pools and riffles from the profile plot that have been proposed to-date. This study concurs with Milne (1982), O'Neill and Abrahams (1984), and Jurmu and Andrle (1997) who assert that while linear regression is useful over short reaches, once substantial irregularity occurs in the bed profile, significant numbers of bedforms are omitted and the method is unrefiable. To avoid this problem, Richards (1 976b) suggests using more complex curves for long data senes, yet even these prove inadequate for the highly irregular profiles of the present study. The bedform differencing technique overcomes these flaws since it is based on cumulative elevation change along the chamel and considers every irregularïty in the profile. However, the method is not entirely objective since the choice of tolerance value lies with the user. Pool-riffle spacing is quite sensitive to changes in tolerance value: figure 5.7 illustrates how alterations in the tolerance value (e.g. T=0.6So to 1SSD) cm Vary the mean spacing by 3 to 9W. There is no apriori rneans of determining the appropriate tolerance value. This is overlooked in previous use of the method.

6.2.2 Pool-rime spacing definition There are two problems in the definition of bedform length: the initial identification of features, and the choice of bed feature on which to base the measurement. Most bed profiles given in the literature show regular pools and riffles with an exaggerated vertical elevation (see Richards, 1976b, p75; O'Neill and Abrahams, 1984, p924-925; Jumu and Andrle, 1997, p93 1), which leave little question as tu which features are pools and rifles. The bed profiles of the study streams are not regular and pool-rime amplitude varies considerably within any one reach, such that simpte unambiguous definition of features is prob lematic.

6.2.2.1 Identification of features One could argue that tme pools and riffles do not exist in semi-alluvial streams. Riffles are invariably defined in the literature as depositional 'topographic high points' in the undulating long profile while pools are intervening 'low points' (Thome et al., 1997), however, where one begins and the other ends is a matter of interpretation (Gordon et al., 1992) and scale. Little work has focussed on this conundrum, yet it is important when management focuses on rigid boundaries between pool and nffle. Furthemore, al1 current techniques for defining bedforms require that feanires fa11 into mutually exclusive classes (pool or rime), however, in Nissouri Creek particularly, plane bed reaches dominate the morphology. Where a pool is found in the bed, a topographic high occurs by default between this and the next pool. Depending on the scale of the undulation, the higher section of the bed is automatically defhed as a rime. In an alluvial case, the 'high' is probably cornposed of alluvial material and would therefore be a 'rifTIey, however, while true 'rifflesy occur in semi-alluvial streams, a number of the topographic 'highs' between pools are sculpted entirely fiom clay-till and therefore cannot be classified as riffles under the conventional definition. Those that are formed from alluvial material are ofien ody one layer thick and are deposited directly over till. Whether pools and nffles occur in bedrock streams is also a matter of interpretation. Keller and Melhom (1978) examine strearns developed in sandstone and found pools and nffles both excavated entirely in bedrock, and formed from a loose veneer of alluvial material on top of the bedrock. They claim the morphology of the pool-riffle sequence is similar to that of an alluvial Stream, although some important differences occur that may be analogous to the present semi-alluvial example: long areas of shallow water flowing over exposed bedrock between pools, scour pools along bedding planes, and pools associated with depositional point bars in bends are comparable to plane bed reaches, scour pools in till and fiee formed pools, respectively, in semi-alluvial streams. They assert that the bedrock controI hinders the delineation between pool and riffle, making it somewhat subjective, although use of the water surface profile and flow depth do provide useful criteria for definition.

6.2.2.2 Choice of bed feature upon which to base measurement The distance between successive pools or riffle crests is most cornmody used to determine bedform spacing. Mechanically, the pool-nffle spacing used in this study (i-e. a single erosion-deposition unit) rnakes better sense as a definition criteria than pool to pool spacing because it is based on the processes responsible for the form itself. In the study streams, the distance between successive pools is consistently greater than twice the span between each pool and riffle unit (figure 6.1). The implications of this are twofold. Firstly, the difference between the two methods of determining spacing indicates riffles do not occur at mid-points between bends (Leopold et al., 1964) nor do they occur closer to downstream pools (Dietrich, 1987), instead riffles systematically occur immediately after their upstrearn pool and result in long featureless sections of the bed between the riffle and downstream pool. The twice pool-riffle length method of definition is not used elsewhere and as such, this condition does not appear to have been reported in the literature. Wohl et ai. (1993) recognized plane bed reaches (called 'mns') within the pool-riffle sequence of rivers in northem California, but did not investigate their effect on pool-riffle spacing. Plane bed reaches in this study occur predominantly downstream from rimes while WohI illustrates 'mns' following both pools and riffies. The rnechanics of pool-rBle genesis appear to differ in these semi-alluvial streams and will require further investigation. Secondly, spacing calculated by method A or B wiil give different results and affect management decisions. Cornparisons between streams cannot be made if the method of definition varies and subsequent management decisions based on regular spacing rnay be inappropriate.

Figure 6.1. Meander planform s howing placement of pools and riffles; (i) morphology suggested by Dietrich (1987), and (ii) morphology found in semi-alluvial study sites. Stippled area may be plane bed or contain another pool-riffle sequence. Methods of bedform spacing meanirement (A and B) illustrated. Twice the length between pool bottom and rime crest (B) is consistently shorter than inter-pool distance (A) in the study streams. 6.3 Variability in pooCnme spacing While no downstream trend in pool-riffle spacing was detected, distinct groupings of bedforms of similar spacing were found that do not seem to have been observed elsewhere. Perhaps the most significant result however, is the short mean spacing of pools and nffles in the range of 3-4W (range f?om 1-16W), while the most common spacing is consistently below the mean (1-3W) for dl three creeks, regardless of definition technique. This is considerably less than the comrnon observation of spacing in the range 5-7 widths. Even afier the mean spacing is forced to 5-7W, the modal spacing remains below 5 widths. Few previous studies have reported the frequency distribution of pool-nffle spacing, although those that do also show positively skewed distributions and a great range in spacing (1-23W) for both bedrock and alluvial streams. These conditions are largely overlooked. Figure 6.2 and table 6.1 show fiequency distributions for the study streams in cornparison with seven others taken from the literature (Keller, 1972; Keller and Melhorn, 1973; Roy and Abrahams, 1980; Hooke and Harvey, 1983; O'Neill and Abrahams, 1984). In al1 cases, the most frequently occumng bedform spacing is less than the mean (except for O'Neill and Abrahams, 1984). The mean spacing for those in the literature is between 5 and 7W. The shape of the ffequency distributions in this study are similar to others for pool to pool spacing, but show a rnarked difference when one compares others with the twice pool-riffle length distribution. Other studies do not report the distance between pool and riffle; thus further cornparisons camot be made. O'Neill and Abrahams (1984) report a 'bedform' spacing (figure 6.2)which on closer inspection results fiom adding all inter-pool and inter-riffle spacings rather than rneasuring only between individual bedform units. The shape of their inter-pool and inter-nffle spacing distributions differ (one is birnodal, while the other is norrnally distributed) even though they are drawn from the same population, indicating that pools and riffles are not necessarily evenly spaced along the channel. a 35 4 Dingrnan Creek Dingman Creek Bedrock streams Alluvial st reanis (Roy & Abrahiinis, 1980) 1(Kcllcr & Mc1 horn 1973)

O 3 6 9 12 15 18 21 24 O 3 6 9 12 15 18 21 24 O 3 6 9 12 15 18 21 24 2x pool to rifflc Icrigth (bfW) Pool spacing (bW) Pool spacing (bfW) Pool spacing (MW)

iri. - Oxbow Creek Oxbow Creek Alluvial streams Dry Creek, Ca. - (Roy & Abrahartis, 1980) (Kcllcr, 1972) - - 4 - - -t - - - O 3 6 3 12 15 18 21 24 O 3 6 3 12 15 18 21 24 O 3 6 9 12 15 18 21 24 2x pool to rifflc leiigth (MW) Pool spacing (bNV) Pool spacing (bfW) Pool qxicing (bfW)

42 i Nissouri Creek Nissouri Creek Mansfield Creek, NY Multiple riffle bends i (O'NcilI & Abrahams, 1984) (Hooke & Harvey, 1983)

O 3 6 9 12 15 18 21 24 O 3 6 9 12 15 18 21 24 0 3 6 9 12 15 18 21 24 O 3 6 9 12 15 18 21 24 2x pool to rimc lcngth (bW) Pool spacing (bfW) Bcdfonii spicing (bfW) Rimc spacing (bW) Rock coiitxolIcd bcnds Frcc bcnds

Figure 6.2. Cornparison of bedform spacing frequency distributions between study reaches and those in the literature. 148

Table 6.1. Simple statistics for bedform spacing fkequencies Bedform spacïng Note (in ùankfdl uidths) mean mode Duigman Creek 3 t 2x pool-rime length

Nissouri Creek

Dq Creek

--a-A -- Rock controlled multiple riffie ben& Free meandering multiple rifne ben&

Predorninance of a single low modal frequency for streams in the present study may indicate some systematic process that promotes short pool-riMe spacing. Hooke and Harvey (1 983) exarnined pool-riffle sequences in relation to channel morphology and rock bluff confinement and could not find a single preferred spacing within a wide range in pool-rime spacing (see figure 6.2 bottom-right pool-rime spacing frequency distribution). This compares with the distributions observed in this study for the pool- pool spacing when the mean spacing is 7W (figure 5.1 1 C and D). However, they also found multiple short riffles through bends and attributed their presence to a breakdown in secondary circulation after meander path 1engt.h exceeded a critical length (approximately 16W). The insertion of extra nffles then facilitated growth of a secondary lobe in the bend, and subsequent meander migration. This differs £tom Keller's (1972) mode1 in which the presence of extra pools and riffles is accounted for by insertion in the limbs of meanders, rather than in the apex region, to keep spacing constant during lengthening of the channel (Hooke and Harvey, 1983). Although no histoncal analysis of pool-riffle placement in relation to meander migration was conducted in Dingman, Oxbow or Nissouri Creek, it seems unlikely that pools and riffles are inserted in this way since the detailed functioning of the streams appear to be constrained more by multiple coarse sediment inputs at bluffs than secondary circulation leading to pool formation in meander bends. The spacing of pools and riffles was compared between predorninantly alluvial and semi-alluvial sections where till is exposed in the study creeks and was not found to be significantly different, although mean spacing was consistently shorter for pools and riffles in till than alluvium. This is opposite of the findings of Roy and Abrahams (1980) who re-analyzed Keller and Melhorn's (1978) data and found that mean pool spacing in bedrock streams (7W) was greater than in al Iuvial streams (6W). Considering the cohesive but erodible nature of the glacial deposits fonning the chamel bed in the semi- alluvial streams of the present study, we might have expected the spacing to fa11 somewhere between the alluvial and bedrock conditions. An explanation for this may rest in the fact that 'alluvial' reaches in this case are only a thin veneer of loose material covering till, and in potential differences between the formation of the pool-rime sequence in alluvial and semi-alluvial strearns.

6.4 The formation of pools and riffles in semi-alluvial channels The formation of pools and nffles in alluvial strearns is generally accepted to be related to the existence of large-scale eddy structures within the flow that cause local variations in shear stress at regular intervals down the channel. Scour occurs where eddies impinge on the bed and results in the formation of pools, while deposition of bars occurs where eddies rise from the bed (Clifford, 1993). The result is a regular sequence of pools and rifles altemating dong the channel. Riffles in semi-alluvial streams are not strictly depositional features and therefore cannot be fonned and maintained in the same way as in alluvial streams. Furthemore, the meander pattern is highly irreguiar and may not be able to support the flow structures required to maintain a regular pool-riffle sequence. Irregularities appear to be imposed on top of the regular sequence of pools and riffles. Pools generally occur in bends, but many more pools are found in reaches between bends. Thus sirnilar processes rnay be at work in semi-alluvial charnels, but are somewhat disrupted in reaches where multiple pools and 'riffles' occur in bends, or even in those areas where no pools ocwat dl. By definition, riffles and pools are altemate highs and lows deposited or eroded nom alluvial material on the channel bed, that may only develop where transport of bed material is possible (Miller, 1958). Two conditions appear to exist for pool-riffle development in these semi-alluvial streams that rnay explain irregularities found in the bedform sequence. Firstly, an abundance of coarse material supplied nom present day weathering of Wisconsin glacial deposits at somewhat random locations along the channel renders the formative flows powerless to modiS the bed matenal into bedforms, and secondly, many of the pools are eroded directly into cohesive clay-till. A large percentage of the material that is eroded from these pools is very fine and is easily removed nom the system rather than being deposited downstream as a rime. Coarse sediment, in this case, is limited and accounts for short riffles, patches of till visible in riffles through the thin 'alluvial' cover, and the occurrence of lengthy plane bed reaches. Many of the undulations seen in the bed profile are therefore not 'me' riffles, being merely high points sculpted in till between non-alluvial pools. Furthermore, for bedforms located in reaches where till is visible, une finds long or multiple pools with no downstream rime as the clay-size materiai is easily washed away. Plane bed reaches are common in al1 three streams, although they occur predorninantly with some form of alluvial cover. The streams are only marginally competent. Stream power limits the amount of energy available for the streams to manipulate the bed material. Estimates for the 1.5 year retum-interval event for Dingman and Nissouri Creeks (50 and 59 ~rn'~, respectively) place the streams in the range of inactive, underfit and irregular meandering streams with bankfull stream powers from 1 to 60 ~rn-'observed by Ferguson (198 1) for lowland British rivers. As a result of the abundance and large size of the glacial material and general lack of stream power, the flows are largely incapable of transport, such that the streams are not likely to change their form, even under flood conditions. Considering the geologically brkf period since ice retreat (-10 000 abp), it unlikely that there have been many flows capable of moving the largest boulders. This, together with the cohesive nature of the predorninantly clay tills, indicates the streams are adjusted to innequent flows and are not in equilibrium. The erosive requirements for glacial till are not known, such that it is difficult to speculate on pool-riffle formation from a process standpoint but one can postdate that the cohesive nature of the till is likely to aid in resistance to erosion, so retarding further changes in morphology. Wohl et al. (1993) note greater stream power is expended in overcorning boundary resistance in reaches with coarse bed material, reducing the energy available for bed scour and pool formation, and inhibits the development of pools and nffles; evidence for this can be seen in the lower 600 rn of Oxbow Creek.

6.5 State of channel adjustment Lateral confinement in the semi-alluvial strearns results in similar morphologies as those described in the Iiterature for alluvial or partially bedrock channels. The channel abuts the valley wall for substantial distances, there are restricted, box-shaped bends (Dl 3 and D18), and maximum channel curvature occurs at the valley wall@27). Al1 are indicative that the naturd lateral migration of meanders is being constrained by the valley walls (Ferguson, 198 1). The presence of valley-side bluffs suggests the streams possess the power to cut into the walls, yet coarse debris in the streambed reveals they are unable to remove the calibre of material being supplied. The long profile of a river is an expression of the degree to which the river is adjusted to discharge, sediment supply and imposed valley gradient. In reality, few profdes adhere to an exponential concave-upward form. Stream dynamics and morphology are such that responses will differ for streams in alluvium, glacial material or bedrock. Following deglaciation, a rapid drop in Great Lakes base level caused downcutting and continued exposure of glacial material in banks of streams in southern Ontario (Campo and Desloges, 1994). The convex downstream ends of Dingman and Oxbow Creeks are over-steepened as adjustment to the Thames River base level progresses. The rate of adjustment is slowed by a general lack of stream power as the channel degrades through cohesive tills and coarse matenal that make up the chamel boundary and account for the profile's convex shape. The profile of Nissouri Creek is straight, the creek is considerably smaller and does not possess the discharge or stream power required to adjust and to modie its coarse bed load and channel planform. None of the study streams are therefore in an equilibnum state. 6.6 Morphological relationships in semi-alluvial streams Hydraulic geometry relationships developed by Leopold and Maddock (1953) describe the way alluvial channel properties change with stream fiow (Gordon et al., 1992). Similarly, a number of empirical observations hold for meander geometry. A considerable body of literature exists for the estimation of meander wavelength, amplitude and belt width (Leopold and Wolman, 1960; Ferguson, 1975). However, such measurements were not considered in this study because the meanders are highly irregular and their discussion would distract hmthe emphasis placed on pool-rifle rnorphology. Fi,we 6.3 shows a number of channel relationships for the study streams in context with existing data gathered &om other streams in southem Ontario (Annable, 1995). The data for Dingrnan, Oxbow and Nissouri Creek fit well within the existing relationships for the area and are therefore quite representative; however, when compared to expected distributions for 'normal' alluvial rivers, streams in southem Ontario show unusual results.

6.6.1 Relationship between drainage basin area and bankfull width and depth Mean bankfull width and depth both increase with drainage basin area (figure 6.3A) and show similar regression slopes as previous studies (see Gordon et al., 1992, p3 1 1; Newbury et al., 1997, p 12-4), yet there is considerable variation around the regression line. Considering the variation in width measurement shown in figure 4.6, it is remarkable that the sbeams should fit so well into this distribution.

6.6.2 Relationship between pool spacing and width Over half of the streams investigated, including Dingman, Oxbow and Nissoun Creeks, show mean inter-pool spacing below the expected average spacing of 5-7 widths (figure 6.3B). The overall relationship is weak, where a close linear relationship is expected.

6.6.3 Relationship beîweea bend radius of curvature and bankf'ull width It has been suggested that the average radius of curvature is 2.3 times the channe1 width (Newbury et al., 1997). Such a relationship is observed for southem Ontario streams (figure 6.3C),but the relationship shows considerable scatter over an order of magnitude. Confineci irregular meanders and over-tightened bends are likely to account for some of this variability.

6.6.4 Relationship between stream sinuosity and bankfull width Sinuosity depends upon gradient and channel boundary matends, wirh the general expectation that greater sinuosity is observed in narrower channels. No such relationship is seen in southem Ontario (figure 6.3D), where channel width is highly variable and boundary material rnay change from one bend to the next.

6.7 Conclusion and impticadons for stream management Aquatic species require a diversity of habitats, which should include a variety of flow velocities, resting areas, sorted gravels, rearing ponds and suitable water temperatures (Goudie, 1990). The morphology of the three streams in this study indicate that while pool and riffle habitat exists, it rnay provide only limited habitat potential and is therefore detrimental to the fish population. Rifles are short and typically offer only a thin depth of material for cover, pool depths Vary depending on substrate and proximity to the valley wall, and presence of many plane bed reaches is likely to increase water temperatures owing to insuficient depth at low fiow. High rates of bank erosion, particularly dong Dingman Creek, result in an abundance of fine matenal being introduced into the channel, which can decrease fish habitat by reducing the arnount of oxygen available for developing embryos (Payne and Lapointe, 1997). There is a dangerous tendency to follow prescrîbed solutions for channel restoration. Rosgen (1994) devised a simple Stream classification system as a means for predicting river response from its appearance for use in engineering, fish habitat enhancement, restoration and general water resource management. The system has been extensively adopted by land management agencies throughout the United States and is used increasingly in Canada (Ontario Ministry of Naturai Resources, 1994); Natunl Channel Design (KD) also incorporates the Rosgen classification and is used in Ontario to restore or maintain long-term stability in charnels. The Quaternary legacy in southem Ontario has resulted in significantly altered present river channel fom on a variety of scales. A number of channel relationships differ fiom existing observations such that extreme care should be observed when rules- of-thumb, such as Stream 'type' (Myers and Swanson, 1997) in the Rosgen system and mean pool-riffle spacing, are used as guides during restoration endeavours without attention to the specific reach-scale morphology. It is apparent that there is no perfect objective method for determining pool-rime spacing and extreme caution should be exercised where policy makers require hard numbers in order to make management decisions. The identification of pools and riffles is subjective and imprecise in the first place, and where seemingly objective methods exist, the user cm still manipulate the spacing. It is important to recognize that variability exists around the mean pool-riffle spacing, while management decisions typically focus on mean conditions. To give Stream managers useable numbers, we must understand the source of this variability in the pool-rime sequence and thus in-stream habitat. In this study, as in others, the range of pool-nffle spacing is quite considerable, while the most fiequent spacing is consistently below the mean (see Table 2.1, and Keller and Melhom, 1978). It would therefore be most beneficial if the frequency distribution of pool-riffle spacing and modal pool-rime spacing were considered when management decisions regarding the placement of artificial structures are made. Although the study streams fit well within relationships gathered for southem Ontario, attention to their morphology at a smaller scale must be taken in to account. They clearly differ fiom the 'text-book' alluvial example. Estimates for pool-riffle or meander parameters based on 'characteristic' features (Amable, 1995) should be undertaken with considerable caution when such variability is evident. WhiIe many restoration techniques are successful, most of the 'solutions' to common erosion or restoration problems are derived for environments very different fiom the situation found in southem Ontario. The variability in pool-riffle spacing and apparent dependence of pool dimensions on substrate indicates that adherence to well- known equations or expectations based on classification should be avoided. We have no concept of how such charnels will respond to instability, although dl indications suggest that adjustments will take a long tirne. The findings suggest that channel designs based on classic 'textbook' cases need to be modified where non-alluvial conditions exist. Further study is required and development of a regional database of hydraulic relations for semi-alluvial steams should be a priority. CHAPTER VII SlJMMARY AND CONCLUSIONS

7.1 Introduction The purpose of this thesis was to examine pool-rifle sequences in three semi- alluvial streams in southem Ontario and to document morphological c haracteristics of those streams. Detailed longitudinal bed profiles were surveyed along the thalweg of approximately 5 km of Dingman, Oxbow and Nissoun Creeks. The bedform differencing technique was used to define the location of pools and riffles within the bed profile; their location was then matched with the planform. The results for these three strearns are likely to apply to many other channels in southern Ontario and other parts of Canada that are 'semi-alluvial' .

7.2 Surnmary of major research fiodings 7.2.1 Morphology of semi-alluvial streams The rnorphology of the study streams was examined at a number of scales, ranging fiom valley scale features down to micro-scale forms within the glacial till. The streams generally lack competence to rnodifi their boundary and adjust to the gradient imposed by the glacial material through which they are flowing, giving rise to convex long profiles. Al1 three streams are incised into glacial deposits, lack substantial alluvial floodplains, and have irregular confined meanders, which fiequently impinge on the valley walls and results in repeated coarse sediment inputs that disrupt the large scale downstream bed materid trend. Channel confinement gives rise to rectangular, over tightened, and flattened bends in the planform where the channel hugs the valley wall. The channel width is highly variable and generally does not widen downstream. Mean pool depth is greater for all creeks in confined bends than in bends away from the valley wafls. Pools and riffles are short, poorly formed and irregular. Rifles are not strictly depositional features, being formed from a thin veneer of alluvium, with fiequent patches of till visible in the bed. A number of unusual pool morphologies occur; including multiple pools in bends, an enfarged circular pool, a number of deep scour pools or potholes formed in till, and several pools forced closer to the inside banks of meanders by till ledges extending into the flow fiom the outside bank. Bends occasionally lack pools altogether and well-developed pools are lacking dong Nissourï Creek. Point bars are absent in many reaches and bends are &en wider than straight reaches in Dingman Creek. PIane bed reaches are frequent between pool-riffle forms and dorninate the bed topography of Nissouri Creek.

7.2.2 Pool-rime spacing and amplitude in semi-alluvial streams Mean pool-riffle spacing is 3-4 hesthe channel width, with a range in spacing of 1- 16 widths. The most frequent spacing, 1-3 widths, is less than the mean for al1 creeks and for all methods of definition, and may indicate some systematic process in which shorter bedforms are created to the exclusion of lengthier forms. Pool-riffle spacing is highly irregular and is forced by numerous obstructions in the 80w such as boulders, LWD and resistant blocks of till. Distinct groupings of bedforms of similar spacing occur down the channel. Pool-riffle spacing is generally greater in straight reaches between bends, akhough there are many reaches with feahireless beds. Mean bedform length is shorter where alluvial material is lacking. Pools in bends are deeper than in straight reaches. The mean depth of pools is greater for those formed in till rather than in alluvial rnaterial for both bends and straight reaches, although onIy those on Nissouri Creek are significantly deeper. No significant relationship is found between pool depth and radius of bend curvature. Multiple pools and rifles occur in bends. Pools are fiequently found between bends. When spacing is forced to a mean spacing of seven widths, discrepancies persist in the planform location of pools and riffles and there is an increase in the number of bends without pools. The irregularities in the planform location of features are naturally occuning in these streams rather than the result of the definition method. The extent to which pool-riffle morphology can be predicted fiom existing theory and observation is limited in these streams. Many of the regime and hydraulic geometry reIations do not hold. Theer is no downstream trend in bankfull channel width (except for Oxbow Creek), pool-rime spacing, or bed material fining. Erosion of ta11 bluffs in glacial sediment supplies abundant coarse matenal to the channel which disrupts the expected downstream bed material sequence, alters channel width and disrupts pool-riftle development. Pools are fiequently found in straight reaches and nffles in bends. Reliable predictions of pool-riffle spacing cannot be made from the wide range in bankfbll charnel width measurernents that were recordeci, while the pool-riffle spacing is approximately half that predicted fkom the mean bankfùll width. The fiequency distributions for bedform spacing are positively skewed for al1 streams, thus mean spacing is not a representative predictor of channel form. The presence of plane bed reaches further cornplicates the measurement of pool-rime spacing.

7.2.3 Pool-rime identification techniques A number of techniques for objectively defining bedforms were examined and bedform spacing is found to be sensitive to definition method. Linear and polynomial regression methods result in identification of excessively long or short bedforms. The bedform differencing technique, by considering the cumulative elevation change between successive bed elevations, was successfully used in pool-rime identification and provides the most redistic method of identification avaitable to date. However, there is no apriorz means of determining the correct tolerance value to apply, such that the user can ultimately manipulate spacing. The choice of feature upon which to base measurement affects bedform spacing. Inter-pool and inter-riffle distances are commonly used. This study proposes a new method, which is based on measurement of the pool-nffle unit itself The distance between each pool bonom and nffle crea is doubled to obtain a measure of spacing. In this study the use of the pool-riffle spacing consistently results in shorter bedform spacing than for inter-pool measurement. Rimes occur close to their upstream pools and there are long plane bed reaches between a riffle and downstream pool. This result differs fiom the proposition that riffles occur at midpoints between bends (Leopold et al., 1964) or closer to downstream pools pietrich, 1987). 7.3 Implications for effective stream management Many empirical observations developed for regularly meandenng active alluvial streams may not be applicable in the semi-alluvial environment where meanders are irregular and strearns are only partially alluvial. It has been shown that fiindamental morphological differences exist beîween alluvial and semi-alluvial streams, which may provide only limited in-strearn habitat, and should not be ignored in stream management. Most of the current 'solutions' to cornmon restoration problems are determined for alluvial rivers, however, the variability in pool-rifle spacing and apparent dependence of pool dimensions on substrate in these streams indicates that adherence to well-known equations or expectations based on simple classification should be avoided. The existence of pools and riffles is subjective at best, especidly in these semi- alluvial streams where riffles may be formed in till, such that reliance on 'hard numbers' and rules-of-thumb, such as regular mean spacing, may be inappropriate. Ernpliasis on mean pookiffle spacing is inadequate when one considers the ambiguity involved in pool-rime definition. The frequency distribution of bedforrn spacing and most frequently occuning bedform spacing should be considered where restoration decisions concerning the placement of artificial pool-rime structures are made. The findings suggest that channel designs based on classic 'textbook' cases should be modified where semi-alluvial conditions exist. Further sîudy is required and developrnent of a regional database of hydraulic relations for semi-alluvial steams is imperative.

7.4 Recommendations for future research Pnor to this project, the specific study of semi-alluvial streams had not been investigated in southern Ontario, or, to the author's knowledge, in any other area. The study, therefore, provides an initial investigation into pool-riHe morphology of semi- aliuvial streams. Recommendations for fùture research are as follows:

1. The examination of pool-riffle spacing and rnorphology necessitated detailed surveys over distances of up to five kilometres; consequently, the focus was on three streams known to differ in their morphology. Additional surveys of other serni-alluvial streams should be undertaken to supplement the findings of this report. Development of a regionai database of semi-alluvial Stream characteristics through surveys and photographic documentation of features is imperative.

2. While the description and statistics on pool-riffle spacing and amplitude were determined, it would be usefùl to return to the channels and match the pools and riffles defined in the bed profile with particular pools and nffles in the charnel for a number of reasons. Firstly, to determine whether specific &les defined in the profile are depositional or sculpted from till and consequently how they differ in their appearance in the bed profile. Secondly, it would enable assessment of the accuracy of the bedform differencing technique and chosen tolerance value.

3. Qualitative observations of river form indicate that flow and sediment transport dynamics may differ in these channels. An examination of sediment delivery mechanisms, sediment budgets (Campo and Desloges, 1994), and downstream trends in bed material for a number of semi-alluvial strearns may increase an understanding of sediment mechanics. An investigation of the depth of alluvial material covering glacial tilt on the floodplain may be beneficial. Small-scale investigations of flow processes and the rnechanics of riffle development shouId be conducted.

4. Given the morphological evidence, assessment of the habitat potential of the streams should be investigated. Where pool-riffle developrnent is inhibited, the variety of habitats available to the biotic comrnunity is likely to be reduced. The presence of deep pools in till and shallow plane bed reaches will affect water temperature and thus metabolic rate and development of organisms. A reduction in turbulence through plane bed reaches will also affect water temperatures and the concentration of dissolved oxygen in the water. An imbalance in the percentage of each habitat type may affect the number and species of organisms present in the strearns. 5. The potential exists for a number of smaller studies on Dingman Creek. a) Detailed measurement of 80w processes and morphology of the circular pool @end D27) in cornparison with previous studies conducted in similar environments in New York (Andrle, 1994) and Britain (Thompson, 1984) rnay contribute towards an understanding of the genesis of such features. b) Erosion continues to be a problem along Dingman Creek as upstream urbanization expands and increases its influence in the watershed. Further erosion monitoring and bank reinforcement is necessary. REFERENCES

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Beschta, R.L., and W.S. Platts. 1986. Morphological Features of Small Streams: Significance and Function. Water Resotrrces Bzrlleti~z.72(3): 369-379.

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Inter- Inter- Bed Distance Cumulative Water Water Bankfull Dominant Till sight sight elevation along dist. along height height + Width depth bed presence no. bearing (m) thalweg thalweg bed elev. material O = no (from N) (m) (m) (m) (rn) (m) (m) class 1 = yes APPENDIX 1, cont. Dingman Creek - field survey data (survey frorn downstream to upstrearn; daturn = 200 m)

Inter- Inter- Bed Distance Cumulative Water Water Bankfull Dominant Till sight sight elevation along dist. along height height + Width depth bed presence no. bearing (m) thaheg thaiweg bed elev. material O = no (from N) (m) (ml (m) (m) (m) (m) claçs 1 = yes APPENDIX 1, cont. Dingman Creek - fieid survey data (survey from downstream to upstream; daturn = 200 m)

Inter- Inter- Bed Distance Curnulatnre Water Water Bankfull Dominant Till sight sight elevatton along dist along height height + Width depth bed presence no. bearing (m) thaiweg thaiweg bed elev. material O = no (from N) (m) (ml (ml (m) (m) (m) ciass 1 = yes APPENDIX 1, cont. Dingman Creek - field survey data (swey from dowzlstrem to upstream; daturn = 200 m)

Inter- Inter- Bed Distance Cumulative Water Water Bankfull Dominant Tilt sight sight elevation along di&. along height height + Width depth bed presence no. bearing (m) thaiweg thalweg bed elev. material O = no (from N) (ml (m) (m) (m) (m) (m) class 1 =yes APPENDLX 1, cont, Dingrnan Creek - field survey data (survey fiorn downstream to upstream; datum = 200 m)

Inter- Inter- Bed Distance Cumulative Water Water Bankfull Dominant Till sight sight elevation along dîst. along height height + Width dapth bed presence no. bearing (m) thalweg thalweg bed elev. materiaf O = no (frorn N) (m) (M) (m) (m) (m) (rn) ciasç 1 =yes APPENDIX 1, cont. Dingman Creek - field survey data (survey from downstream to upstream; dam= 200 m)

Inter- Inter- Bed Distance Cumulative Water Water Bankfull Dominant Till sight sight elevation along dist. along height height + Width depth bed presence no. bearing (m) thahveg thaiweg bed elev. material O = no (from N) (m) (ml (ml (m) (m) (m) ciass 1 = yes Dingman Creek - fieid survey data (survey fkom downstream to upstrearn; dahrm = 200 m)

Inter- Inter- Bed Distance Cumulative Water Water Bankfull Dominant Ti11 sight sight elevation along di*. along height height + Width depth bed presence no. bearing (rn) thalweg thalweg bed elev. material O = no (frorn N) (m) (ml (m) (m) (rn) (m) class 1 = yes APPENDPX 1, cont. Dingman Creek - field survey data (survey from dowmtream to upstrearn; datum = 200 m)

Inter- Inter- Bed Distance Cumulative Water Water BankfulI Dominant Till sigM sight elevation along dist along height height + Width depth bed presence no. bearing (m) thatweg thaiweg bed eiev. material O = no (from N) (ml (ml (m) (m) (m) (m) ciass 1 =yes Dingman Creek - field survey data (survey from downstrearn to upstream; datum = 200 m)

Inter- Inter- Bed Distance Cumulative Water Water Bankfull Dominant Till sght sight elevation along dist. afong height height + Width depth bed presence no. bearing (m) thaiweg thalweg bed elev. material O = no (frorn hl) (ml (ml (m) (m) (m) (m) cfass 1 =yes APPENDIX 1, cont. Dingman Creek - field survey data (survey fiom downstream to upstrearn; datum = 200 m)

Inter- Inter- Bed Distance Cumulative Water Water Bankfull Dominant Till sight sight elevation along dist. along height height + Width depth bed presence no. bearing (m) thalweg thalweg bed elev. material O = no (from N) (m) (ml (m) (m) (m) (m) ciass 1 = yes Dingman Creek - field survey data (survey fiom downstream to upstream; datum = 200 m)

Inter- Inter- 8ed Distance Cumulative Water Water Bankfull Dominant Till sight sight elevation along dist- along height height + Width depth bed presence no. bearing (m) thaiweg thahiveg bed elev. material O = no (from N) (ml (m) (m) (m) (m) (m) class 1 =yes APPENDIX 1, cont. Dingmm Creek - field survey data (survey from downstream to upstrearn; datum = 200 rn)

Inter- Inter- Bed Distance Cumulative Water Water Bankfull Dominant Ti11 sight sight elevation along dist along height height + Width depth bed presence no. bearing (m) thahmg thaiweg bed elev. material O = no (from N) (m) (m) (m) (m) (m) (m) class 1 =yes APPENDIX 1, cont. Dingman Creek - field survey data (survey fiom dowmtream to upstrearn; dam= 200 rn)

Inter- Inter- Bed Distance Cumulative Water Water Bankfull Dominant Till sight sight elevation along dist. along height height + Width depth bed presence no. bearing (m) thaiweg thaheg bed elev. material O = no (from N) (m) (m) (m) (m) (m) (m) class 1 = yes APPENDIX II Oxbow Creek - field survey data (survey fiom downstream to upstream; dam= 200 m)

Inter- Inter- Sed Distance Cumulative Water Water Bankfull Dominant Till sight sight elevation along dist. along height height + Wiâth depth bed presence no. bearing (m) thaiweg thalweg bed elev. material O = no (from N) (m) (m) (m) (rn) (m) (m) ciass 1 = yes APPENDIX n, cont. Oxbow Creek - field survey data (survey fiom downstreah to upstream; datum = 200 m)

Inter- Inter- Bed Distance Cumulative Water Water Bankfulf Dominant T?II sight sight elevation along dist. along height height + WÏh depth bed presence no. bearing (m) thafweg thalweg bed elev. materiai O = no (from N) (m) (ml (m) (m) (m) (m) ciass 1 = yes Oxbow Creek - field survey data (survey fiom downstream to upstrearn; datum = 200 m)

Inter- Inter- Bed Distance Cumulative Water Water Bankfull Dominant Till sight sight elevation along dist. along height height + Width depth bed presence no. bearing (m) thalweg thalweg bed elev. material O = no (from N) (ml (m) (ml (m) (m) (m) ciass 1 = yes APPENDK II, cont. Oxbow Creek - field survey data (sumey from downstream to upstream; datum = 200 m)

Inter- Inter- Bed Distance Cumulative Water Water Bankfull Dominant Till sight sight devation along dist. along height height + Width depth bed presence no. bearing (m) thalweg thalweg bed elev. material O = no (from N) (m) (ni) (m) (rn) (m) (m) class 1 = yes Oxbow Creek - field survey data (survey from downstream to upstream; datum = 200 m)

Inter- Inter- Bed Distance Cumulative Water Water Sankfull Dominant Till sight sight elevation along distalong height height+ WMth depth bed presence no. bearing (m) thaiweg thaiweg bed elev. matenal O = no (from N) (m) (m) (m) (m) (m) (m) ciass 1=yes APPENDIX II, cont, Oxbow Creek - field survey data (nwey from downstream to upstrearn; datwn = 200 m)

Inter- Inter- Bed Distance Cumulative Water Water Bankfull Dominant Till sight sight elevation afong dist- along height height + Width depth bed presence no. beanng (m) thalweg thalweg bed elev. material O = no (from N) (m) (m) (m) (m) (m) (rn) ciass 1 = yes APPENDIX Iï, cont. Oxbow Creek - field survey data (survey fiom dowostream to upstream; damm = 200 m)

Inter- Inter- Bed Distance Cumulative Water Water Bankfull Dominant Till sight sight elevation along dist. along height height + Width depth bed presence no. bearing (m) thaiweg thafweg bed elev. material O = no (from N) (m) (m) (m) (m) (m) (m) ciass 1 = yes APPENDIX II, cont. Oxbow Creek - field survey data (survey fkom downstrearn to upstream; datum = 200 m)

Inter- Inter- Bed Distance Cumulative Water Water Bankfulf Dominant Till sight sight elevation along dist, along height height + Width depth bed presence no. beaRng (m) thaiweg thaiweg bed elev. material O = no (from hi) (m) (m) (m) (m) (m) (rn) ciass i=yes APPENDIX II, cont, Oxbow Creek - field survey data (survey fiom downstream to upmeam; daturn = 200 m)

Inter- Inter- Bed Distance Cumulative Water Water Bankfuil Dominant Ti11 sight sight elevation along dist dong height height + Width depth bed presence no. bearing (m) thaiweg thaiweg bed elev. material O = no (from N) (ml (m) (ml (m) (m) (m) class 1 =yes APPENDIX II, cont. Oxbow Creek - field survey data (survey fiom downstrearn to upstream; dam= 200 m)

Inter- Inter- Bed Distance Cumulative Water Water Bankfull Dominant Till sight sight elevation along dist along height heÏght + Width depth bed presence no. bearing (m) thalweg thalweg bed elev. material O = no (from N) (ml (m) (ml (m) (rn) (m) clas 1 =ves APPENDIX II, cont. Orbow Creek - field survey data (nirvey fiom downstream to upstream; datum = 200 rn)

Inter- Inter- Bed Distance Cumulative Water Water Bankfuli Dominant Till sight sight elevation along di& along height height + Width depth bed presence no. karing (m) thalweg thatweg bed elev. material O = no (from N) (m) (ml (ml (m) (m) (rn) class 1 = yes APPENDM. II, cont. Oxbow Creek - field survey data (survey fiom downstream to upstream; dam= 200 m)

Inter- Inter- Bed Distance Cumulative Water Water Bankfull Dominant Till sigM sight elevation along dist. along height height + Width depth bed presence no. bearing (m) thaheg thalweg bed elev. material O = no (from N) (m) (m) (ml (m) (m) (rn) class 1 = ves APPENDIX II, cont. Oxbow Creek - field suwey data (survey fiom downstream to upstream; datum = 200 m)

Inter- Inter- Bed Distance Cumufative Water Water Bankfull Dominant Till sight sight elevation along dist. along height height + Width depth bed presence no. bearing (m) thatweg thaiweg bed elev. material O = no (from N) (m) (ml (ml (m) (m) (rn) class 1 = yes APPENDIX il, cont. Oxbow Creek - field survey data (survey fiom downstream to upstrearn; datum = 200 m)

Inter- Inter- Bed Distance Cumulative Water Water Bankfull Dominant Till sight sight elevation along dist. along height height + Width depth bed presence no. bearing (m) thaiweg thafweg bed elev. material O = no (from N) (ml (ml (ml (m) (m) (m) ciass 1 = yes APPENDIX lI, cont. Oxbow Creek - field survey data (survey from downstream to upstrearn; datum = 200 m)

Inter- Inter- Bed Distance Cumulative Water Water Bankfull Dominant TRI sight sight elevation afong dist. along height height .t Width depth bed presence no. bearing (m) thalweg thaîweg bed elev. material O = no (from N) (m) (m) (ml (m) (m) (m) ciass 1 =yes APPENDIX II, cont. Oxbow Creek - field survey data (nirvey fiom downstream to upstrearn; datum = 200 m)

Inter- Inter- Bed Distance Cumulative Water Water Bankfull Dominant Till sight sight elevation along dist along height height + Wiih depth bed presence no. bean'ng (m) thalweg thalweg bed elev. material O = no (from N) (m) (ml (ml (m) (m) (m) class 1 =yes APPENDK nr Nissouri Creek - field survey data (survey fiom upstream to downstream; datum = 200 m) Inter- Inter- Bed Distance Cumulative Water Water Bankfull Dominant Till sight sight elevation along dist. along height height + Width depth bed presence no. bearing (m) thalweg thalweg bed elev. materiai O = no (frorn N) (m) (m) (m) (m) (m) (m) class 1 = yes ABPENDLX III, cont. Nissouri Creek - field survey data (survey firom upstrearn to downstream; datum = 200 m) Inter- Inter- Bed Distance Cumulative Water Water Bankfull Dominant Till sight sight elevation along dist. along height height + Width depth bed presence no. bearing (m) thalweg thalweg bed elev. material O = no (from N) (m) (m) (m) (m) (m) (m) class 1 = yes APPENDIX III, cont. Niuouri Creek - field survey data (survey fiom upstream to downstream; datum = 200 m) Inter- Inter- Bed Distance Cumulative Water Water Bankfull Dominant Till sight sight elevation along dist. along height height + Width depth bed presence no. bearing (m) thalweg thalweg bed elev. material O = no (from N) (m) (m) (m) (m) (m) (m) ciass 1 = yes APPENDIX III, cont. Nissouri Creek - field survey data (survey fiom upstream to downstream; daîum = 200 m) Inter- Inter- Bed Distance Cumulative Water Water Bankfull Dominant Till sight sight elevation along dist along height height + Width depth bed presence no. bearing (m) thalweg thalweg bed elw. material O = no (from N) (m) (ml (m) (m) (m) (m) class 1 = yes APPENDIX III, cont. Nissouri Creek - field survey data (survey fkom upstream to downstream; datum = 200 m) Inter- Inter- Bed Distance Cumulative Water Water Bankfull Dominant Till sight sight elevation along dist. aiong height height + Width depth bed presence no. bearing (m) thalweg thalweg bed elev. material O = no (from N) (m) (ml (ml (rn) (m) (m) class 1 = yes APf ENDIX IU, cont. Nissouri Creek - field survey data (survey fiom upstream to downstream; datum = 200 m) Inter- Inter- Bed Distance Cumulative Water Water Bankfull Dominant Till sight sight elevation along dist. along height height + Width depth bed presence no. bearing (m) thalweg thalweg bed elev. material O = no (from N) (m) (ml (m) (m) (m) (m) ciass 1 =yes APPENDK III, cont. Nissouri Creek - field survey data (survey from upstream to downstream; dahim = 200 m) Inter- Inter- Bed Distance Cumulative Water Water Bankfull Dominant Till sight sight elevation atong dist. along height height + Width depth bed presence no. bearing (m) thalweg thalweg bed efev. material O = no (from N) (m) (ml (m) (m) (m) (m) class 1 = yes APPENDIX III, cont. Nissouri Creek - field survey data (survey from upstream to downstream; datum = 200 m) Inter- Inter- Bed Distance Cumulative Water Water Bankfuli Dominant Till sight sight elevation along dist. along height height + Width depth bed presence no. bearing (m) thalweg thalweg bed elev. material O = no (from N) (m) (m) (m) (m) (rn) (m) class 1 = yes APPENDIX IU, cont. Nissouri Creek - field survey data (survey from upstream to downstrearn; datum = 200 m) Inter- Inter- Bed Distance Cumulative Water Water Bankfull Dominant Till sight sight elevation along dist along height height + Width depth bed presence no. bearing (m) thalweg thalweg bed elev. material O = no (frorn N) (m) (m) (m) (m) (m) (m) ciass 1 = yes Nissouri Creek - field survey data (survey fiom upstream to downstream; datum = 200 m) Inter- Inter- Bed Distance Cumulative Water Water Bankfull Dominant Till sight sight elevation along dist. along height height *. Width depth bed presence no. bearing (rn) thalweg thalweg bed elev. material O = no (from N) (m) (ml (ml (m) (m) (rn) ciass 1 = yes APPENDIX III, cont. Nissouri Creek - field survey data (survey fiom upstream to downstream; dm= 200 m) Inter- Inter- Bed Distance Cumulative Water Water Bankfull Dominant Till sight sight elevation along dist. along height height + Width depth bed presence no. bearing (m) thalweg thaiweg bed elev- material O = no (frorn N) (m) (ml (ml (m) (m) (m) ciass 1 = yes APPENDIX UI, cont. Nissouri Creek - field survey data (survey fiom upstream to downstream; datum = 200 m) Inter- Inter- Bed Distance Cumulative Water Water Bankfull Dominant Till sight sight elevation along dist. along height height + Wiâth depth bed presence no. bearing (m) thalweg thalweg bed elev. material O = no (from N) (ml (m) (ml (rn) (m) (m) class 1 = yes APPENDIX III, cont. Nissouri Creek - field survey data (survey fkom upstream to downstrearn; dahm = 200 m) Inter- Inter- Bed Distance Cumulative Water Water Bankfull Dominant Till sight sight elevation along dist along height height + Width depth bed presence no. bearing (m) thalweg thalweg bed elev. material O = no (from N) (ml (ml (ml (m) (m) (m) class 1 = yes APPENDIX m, cont. Nissouri Creek - field survey data (survey fiom upstream to downrtream; dahuii = 200 rn) Inter- Inter- Bed Distance Cumulative Water Water Bankfull Dominant Till sight sight eletion along dist. along height height + Width depth bed presence no. bearing (m) tnalweg thalweg bed elw. material O = no (from N) (m) (m) (ml (m) (m) (m) class 1 = yes APPENDIX IV

Concavity Index Calculation

Concavity Index = x / Ht where 'x' is the maximum iength of a line perpendicular to a straight line joining the headwaters and the downstrearn discharge point and that also joins the stream profile, and 'Ht' is the total elevation drop over the length of the profile, as illustrated below (Weeler, 1979; Overholt, 199 1)

Horizontal distance fiom headwaters to outlet Downstream discharge point

(Figure modified fkom Richards, 1982 and Overholt, 1991)

For further explanation, see Wheeler (1979), Richards (1982) and Overholt (199 1).