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1. Introduction The Canadian oil sands in northeastern Alberta contain approximately 10% of the proven global oil reserves (Natural Resources Canada 2019), with development expanding substantially since 1980 and oil [...], Oil sands development in the lower Athabasca River watershed has raised considerable public and scientific concerns regarding perceived effects on environmental health. To address this issue for tributaries and the mainstem of the Athabasca River in the Athabasca Oil Sands Region, the Water Component of the Joint Oil Sands Monitoring (JOSM) plan produced monitoring assessments for seven integrated themes: atmospheric deposition, tributary water quality, river mainstem water quality, groundwater quality and quantity, water quality and quantity modelling, benthic invertebrate condition, and fish health. Our review integrates and synthesizes the large and diverse datasets assembled in the seven JOSM theme assessments to (i) evaluate possible environmental effects based on known sources and candidate proximal causes and (it) determine the importance of cause-and-effect pathways related to contaminant, sediment, and nutrient inputs. Although JOSM research identified ecological effects that appear to be associated with contaminant exposure, the source of this exposure is confounded by co-location of, and inability to differentiate between, oil sands operations (principally released by atmospheric emission) and inputs from the natural bitumen outcrops (e.g., erosional material transported by surface and groundwater flows). Nutrient enrichment from treated municipal sewage effluent was the dominant ecological effect observed for the mainstem Athabasca River, associated with increased fish size and changes in invertebrate assemblages, likely because this pollution source is discharged directly into the river. If the direct release of treated oil sands process water occurs in the future, then the potential ecological impact of these direct industry releases will need to be evaluated carefully. The ecological causal assessment method proved to be a useful tool for better understanding how stressor sources relate to ecological effects through candidate proximate causes. Factors that confound our ability to assess the ecological effects of oil sands development focus on our inability to adequately differentiate between contaminants supplied from natural and anthropogenic contaminant sources. Our causal synthesis identifies options for changes in future monitoring to better anticipate and detect degradation in the ecosystem health of the lower Athabasca River and its tributaries. Key words: oil sands, biomonitoring, cumulative effects, sediments, contaminants, nutrient enrichment. L'exploitation des sables bitumineux dans le cours inferieur du bassin versant de la riviere Athabasca a suscite une grande inquietude chez le public et les scientifiques quant aux effets percus sur la sante environnementale. Afin d'aborder cette question pour les affluents et le cours principal de la riviere Athabasca dans la region des sables bitumineux de l'Athabasca, la composante eau du programme de surveillance conjointe des sables bitumineux (SCSB) a produit des evaluations des surveillances pour sept themes integres : le depot atmospherique, la qualite de l'eau des affluents, la qualite de l'eau du cours principal de la riviere, la qualite et la quantite des eaux souterraines, la modelisation de la qualite et de la quantite de l'eau, la condition des invertebres benthiques et la sante des poissons. La synthese realisee par les auteurs integre et resume les vastes et divers ensembles de donnees rassembles dans les sept evaluations thematiques du programme de SCSB pour (i) evaluer les effets environnementaux possibles sur la base des sources connues et des causes proximales candidates et (it) determiner l'importance des voies de causalite liees aux apports de contaminants, de sediments et de nutriments. Bien que les recherches du programme de SCSB aient identifie des effets ecologiques qui semblent etre associes a l'exposition aux contaminants, la source de cette exposition est confondue par la co-localisation et l'incapacite a differencier entre les operations d'exploitation des sables bitumineux (principalement rejetes par emission atmospherique) et les apports provenant des affleurements naturels de bitume (par exemple, les materiaux formes par 1'erosion transported par le flux des eaux de surface et souterraines). L'enrichissement en nutriments des effluents d'eaux usees municipales traitees a ete l'effet ecologique dominant observe pour le cours principal de la riviere Athabasca, associe a l'augmentation de la taille des poissons et aux changements dans les assemblages d'invertebres, probablement parce que cette source de pollution est rejetee directement dans la riviere. Si le rejet direct des eaux de traitement des sables bitumineux se produit a l'avenir, l'impact ecologique potentiel de ces rejets directs de l'industrie devra alors etre soigneusement evalue. La methode d'evaluation des causes ecologiques s'est averee constituer un outil utile pour mieux comprendre comment les sources de stress sont liees aux effets ecologiques par des causes immediates candidates. Les facteurs qui confondent notre capacite a evaluer les effets ecologiques de l'exploitation des sables bitumineux se concentrent sur notre incapacite a differencier de maniere adequate les contaminants provenant de sources naturelles et anthropiques. Cette synthese sur les voies de causalite identifie des options de changements dans la surveillance future afm de mieux anticiper et detecter la degradation de la sante de l'ecosysteme du cours inferieur de la riviere Athabasca et de ses affluents. [Traduit par la Redaction] Mots-cles: sables bitumineux, biosurveillance, effets cumulatifs, sediments, contaminants, enrichissement en nutriments.

Downstream impacts of large hydropower dams are often neglected or underestimated, especially for areas situated at long distances from a dam. Naturalization of the flow hydrograph is an important step in assessing hydro‐ecological and socio‐economic impacts of regulation. Using reservoir inflows, a recently developed, lagged‐flow naturalization method is applied to the lower portion of the regulated Peace River, which forms the northern boundary of the Peace‐Athabasca Delta (PAD). The PAD is a Ramsar wetland of international importance that depends on overland flooding for recharge of its high‐elevation or "perched" basins. Such flooding can be caused by ice jams during the spring breakup of the ice cover or by exceptionally high runoff during open‐water flow conditions. Herein, the focus is on the latter type of event and the resulting recharge of basins located within the Peace sector of the PAD. For the period 1972–2017, regulation has reduced open‐water flow peaks by ~4100 m3/s on average, while limiting the possibility of overbank flooding from the Peace River during the summer. Consistent with earlier findings on spring breakup flows, naturalized open‐water peaks do not exhibit a temporal trend. Recharge of non‐perched basins can also occur with moderately high flows that cause no overland flooding but generate flow reversals in Peace River tributaries. In turn, this mechanism can deliver river water to various basins either directly or via connecting channels. Our results show that flow‐based variables that index the hydrological sustenance of non‐perched basins have been significantly reduced by regulation. [ABSTRACT FROM AUTHOR]

Bridge infrastructure assets should be planned, designed, constructed, and operated to account for the physical processes that may occur over their service lives. In ice-affected rivers, this includes the interaction of bridge infrastructure with river ice. Advancements in river-ice science and modelling of ice processes in ice-covered rivers have enhanced the abilities of civil/hydrotechnical engineers to plan, design, and construct bridges in and along rivers with seasonal ice covers. In this paper, an overview is presented of ice-related considerations with respect to bridges. The bottom-chord elevation of the bridge superstructure with respect to water and ice levels, pier design to withstand ice forces, the waterway opening for ice passage, ice-induced scour, and research needs are discussed. However, as outlined in the paper, research on ice loads and passage at bridge sites and on hydroclimatic and ice conditions that led to bridge damage and failure remains needed. [ABSTRACT FROM AUTHOR]

A recent study of dynamic ice breakup processes and their erosional potential in the Lower Athabasca River concluded that breakup can result in very large sediment loads, which cannot be predicted at present. As a first step towards building suitable modelling capability, a user-friendly, public-domain, ice jam model is calibrated and validated using 2013 and 2014 water level measurements as well as historical data sets by others. The calibrated model is shown to reliably compute the profiles of different ice jams occurring in a 60 km reach that extends both above and below Fort McMurray. The model also enabled development of an ice jam stage-flow relationship for the city of Fort McMurray, which can help assess present and future, climate-modified, flood risk. Key words: climate, flood risk, HEC-RAS model, historical data, pressure loggers. Une etude recente sur les processus de poussee dynamique de rupture des glaces et leur potentiel d'erosion dans le cours inferieur de la riviere Athabasca a conclu que la rupture peut entrainer des charges de sediments tres importantes, ce qui ne peut etre predit a l'heure actuelle. Comme premiere etape vers l'etablissement d'une capacite de modelisation convenable, un modele d'embacle de glace convivial dans le domaine public est calibre et valide a l'aide de mesures du niveau d'eau de 2013 et de 2014, ainsi que d'ensembles de donnees historiques par d'autres. Il est demontre que le modele calibre calcule de facon fiable les profils des differents embacles qui se produisent dans un rayon de 60 km qui s'etend au-dessus et au-dessous de Fort McMurray. Le modele a egalement permis l'etablissement d'une relation etape de l'embacle - ecoulement pour la ville de Fort McMurray, ce qui peut aider a evaluer les risques d'inondation actuels et futurs, modifies par le climat. [Traduit par la Redaction] Mots-cles : climat, risque d'inondation, modele HEC-RAS, donnees historiques, enregistreur chronologique de pression., Introduction In 2011, the Governments of Canada and Alberta established a monitoring program for surface water quality and quantity, air quality, and biodiversity of the Lower Athabasca River between Fort [...]

The writer systematically refutes all of the discussers' criticisms and supplies more details on the rigour of his "slope-based" frequency analysis. He also identifies key flaws of alternative and conflicting statistical interpretations proposed by the two discussion teams; and provides detailed documentation of the large uncertainty associated with paleolimnological assessments of ice-jam flood frequency. Key words: climate, flood frequency, historical record, ice jam, proxy-record uncertainty, regulation, slope-based method. L'auteur refute systematiquement toutes les critiques des discuteurs et donne plus de details sur la rigueur de son analyse de frequence <>. Il degage egalement les principales lacunes des differentes interpretations statistiques contradictoires proposees par les deux equipes de discussion; et fournit une documentation detaillee sur les grandes incertitudes associees aux evaluations paleolimnologiques de la frequence des crues causees par les embacles. [Traduit par la Redaction] Mots-cles: climat, frequence des crues, releve historique, embacle, incertitude relative aux releves substitutifs, regularisation, methode fondee sur les pentes., 1. Introduction Though relentlessly critical, the discussers' comments have engendered an opportunity to scrutinize and elucidate conflicting perspectives on the frequency of flooding caused by ice jams in the Lower [...]

Major ice jams that occasionally form in lower Peace River generate extensive flooding, which helps replenish the perched basins of Peace-Athabasca Delta, a Ramsar wetland of international importance and a UNESCO World Heritage Site. This complex and dynamic ecosystem has experienced prolonged dry periods since the late 1960s, coincident with the construction of the W.A.C. Bennett hydroelectric dam in British Columbia. Physically-based and paleolimnological studies differ with respect to the impact of regulation on flood frequency. This issue is examined herein, based entirely on the historical record of observed ice-jam flood events. Key words: climate, flood, frequency change, ice jam, historical record, Peace River, regulation. Les embacles majeurs qui a l'occasion se forment en aval de la riviere de la Paix produisent d'importantes inondations qui aident a renflouer les bassins perches du delta des rivieres de la Paix et Athabasca, une zone humide d'importance internationale selon la Convention de Ramsar et un site du patrimoine mondial de l'UNESCO. Cet ecosysteme complexe et dynamique a connu des periodes seches prolongees depuis la fin des annees 1960, ce qui coincide avec la construction du barrage hydroelectrique W.A.C. Bennett en Colombie-Britannique. Des etudes basees sur des caracteristiques physiques et de paleolimnologie different en ce qui concerne l'impact de la regularisation sur la frequence des inondations. Cette question est examinee ici, se fondant entierement sur les documents historiques portant sur les observations d'evenements d'inondation causee par des embacles. [Traduit par la Redaction] Mots-cles: climat, inondation, changement de frequence, embacle glaciaire, document historique, riviere de la Paix, regularisation., Introduction The Peace-Athabasca Delta (PAD) in northern Alberta (Fig. 1) is one of the world's largest inland freshwater deltas, home to large populations of waterfowl, muskrat, beaver, and free-ranging wood [...]

In a river with seasonal ice covers, river ice effects must be considered in the design and operation of water control structures such as dams, barrages, and spillways. The regulation of flow and the water levels of rivers and reservoirs have several hydrological, socio-economic, and ecological effects. Regulation alters river-ice regimes by modifying the temporal and spatial characteristics of flow, water level, and thermal regimes in a watercourse. Removal of a water control structure and reservoir can eliminate some problems, but create new problems in areas where environmental or development conditions have changed. Therefore, thorough review of proposals to regulate (or remove regulation on) a river with seasonal ice covers is necessary. The effects of regulation on ice conditions and vice-versa are reviewed in this paper. Although considerable progress has been made during recent years, adequate understanding of the effects of river-ice interaction with structures and the effect of regulation on geomorphology, people, and aquatic habitat requires additional research. [ABSTRACT FROM AUTHOR]

The spring flow of the Mackenzie River into its delta drives the breakup ice jamming and consequent flooding and replenishment of the thousands of lakes on the delta plain. Daily flows for related studies are presently furnished by Water Survey of Canada, based on the records of a hydrometric station located close to the delta entrance. The relative proximity of the Beaufort Sea affects the local water surface slope, amplifying uncertainties that are normally associated with under-ice flow estimates. It is shown that gauge-derived spring flows often do not agree with other evidence, such as past discharge measurements, flows at the next upstream gauge, and hydraulic computations for the 2008 event. This appears to result in inconsistencies between spring flow hydrograph and observed severity of ice breakup. Options for improving spring flow estimates are discussed and installation of an auxiliary water-level gauge near Point Separation is recommended as a practical choice. Key words: flow, gauge, hydroecology, ice breakup, Mackenzie delta, spring, uncertainty. Au printemps, le debit du fleuve Mackenzie dans son delta engendre la formation d'embacles et les inondations qui en decoulent permettent le remplissage de milliers de lacs dans la plaine deltaique. Les debits quotidiens provenant d'etudes associees sont presentement fournis par la division des releves hydrologiques du Canada; ils sont bases sur les registres d'une station hydrometrique situee a l'entree du delta. La proximite relative de la mer de Beaufort affecte la pente locale de la ligne d'eau, amplifiant les incertitudes normalement associees aux estimations des debits sous la glace. Il est demontre que les debits printaniers obtenus des jauges ne concordent souvent pas aux autres donnees, telles que les mesures anterieures de decharge, les debits a la prochaine jauge amont et les calculs hydrauliques de l'evenement de 2008. Cela semble engendrer des discordances entre l'hydrographe du debit printanier et la severite observee de la debacle. Les options pour ameliorer les estimations des debits printaniers sont abordees et il est recommande d'installer une jauge auxiliaire du niveau d'eau pres de Point Separation comme choix pratique. Mots-cles : debit, jauge, hydroecologie, debacle, delta du Mackenzie, printemps, incertitude. [Traduit par la Redaction], Introduction In most Canadian rivers, spring runoff drives the breakup of the winter ice cover and the ensuing ice jams and ice runs. At moderate latitudes, breakup events may also [...]

Ice processes in general, and ice jams in particular, play a dominant role in the hydrologic regime of Canadian rivers, often causing extreme floods and affecting the life cycle of many aquatic, terrestrial, and avian species. Various numerical models have been developed to help simulate the formation and consequences of these very dynamic and often destructive jam events. To test and compare the performance of existing models, a series of three tests have been devised and coordinated by a task force appointed by the Committee on River Ice Processes and the Environment (CRIPE). The results indicate that the overall performance of the models is good when calibration data are available, but considerably more varied when the models are applied in uncalibrated or 'blind' mode. However, the diversity of results in the blind mode may be attributed more to the variations in perceptions of the physical processes by the users, as compared to the mechanics of the numerical computations. Key words: Calibration, case study, field data, ice jam, model testing, numerical model, river. Les processus de glaces en general, et les embacles en particulier, ont un role predominant dans le regime hydrologique des rivieres canadiennes, causant souvent des inondations extremes et touchant le cycle de vie de plusieurs especes aquatiques, terrestres et aviaires. Plusieurs modeles numeriques ont ete developpes pour aider a simuler la formation et les consequences de ces evenements d'embacle tres dynamiques et souvent destructeurs. Pour verifier et comparer le rendement des modeles existants, une serie de trois essais a ete concue et coordonnee par un groupe de travail assigne par le CRIPE (Committee on River IceProcesses and the Environment). Les resultats indiquent que le rendement general des modeles est bon lorsque les donnees d' etalonnage sont disponibles, mais varie considerablement lorsque les modeles sont appliques en mode << aveugle >> ou non etalonne. Toutefois, la diversite des resultats en mode << aveugle >> peut etre attribuee plus aux variations dans les perceptions des procedes physiques par les utilisateurs, que par la mecanique des calculs numeriques. Mots-cles : etalonnage, etude de cas, donnees de terrain, embacle, essai de modele, modele numerique, riviere. [Traduit par la Redaction], 1. Introduction Ice processes play a dominant role in the hydrologic regime of Canadian rivers and are intimately related to the life cycle of many aquatic, terrestrial, and avian species. [...]

A unique feature that has been detected in the course of past morphological studies of Mackenzie delta channels, and which is of particular concern to the design of pipeline crossings, is the frequent occurrence of very deep scour holes. A recent survey along East Channel revealed many additional holes, with maximum depths ranging from 13 to 37 m. Using the results of recent and past surveys, an inventory of known scour holes and associated morphological parameters is developed. Most holes occur near bends, and often next to recesses in the channel boundaries, known as scour bays. It is shown that presence of scour bays indicates deeper-than-expected holes while repeat surveys of three holes indicate stability. Previously postulated formative mechanisms of bay-associated holes are critically examined; scour under ice jams is eliminated while lake capture is considered likely. Practical implications of the present findings are discussed and research needs outlined. Key words: bankfull depth, bathymetry, distributary channel, fluvial processes, ice jam, lake capture, scour, scour bay, stability. Une caracteristique unique decouverte dans le cours d'etudes morphologiques anterieures des canaux du delta du Mackenzie est l'occurrence frequente de fosses d'affouillement tres profondes, ce qui pose un probleme particulier pour la conception de traverses de pipelines. Un recent releve le long du canal Est a revele plusieurs fosses additionnelles dont la profondeur variait entre 13 et 37 m. L'utilisation de resultats de releves recents et anterieurs a permis de creer un inventaire des fosses d'affouillement connues ainsi que les parametres morphologiques associes. La plupart des fosses etaient situees pres de coudes, souvent a cote de renfoncements dans les bords des canaux, lesquels sont connus sous le nom de baie d'affouillement. Il est demontre que la presence de baies d'affouillement indique des fosses plus creuses que prevues alors que de multiples releves sur trois fosses indiquent une stabilite. Les mecanismes hypothetiques anterieurs de formation des fosses associees aux baies sont examines attentivement. L'affouillement sous embacle est elimine alors que la capture de lacs est consideree probable. Des applications pratiques des presentes conclusions sont abordees et les besoins de recherche sont soulignes. Mots-cles : profondeur a plein bord, bathymetrie, canal effluent, processus fluviaux, embacle de glace, capture, affouillement, baie d'affouillement, stabilite. [Traduit par la Redaction], Introduction Environmental and industrial concerns associated with oil and gas resource development in the Mackenzie Delta, NWT, Canada, have motivated several studies of the morphology and fluvial processes of the [...]