Preface to the Special Issue on Floods in Canada

Abstract

Floods are widely recognized as a common and largely distributed natural hazard with potential for causing loss of life, property damage, disruption of the economy and environmental damages. All geographic regions of Canada are susceptible to the deleterious impacts of floods. Recent flood events in Canada and elsewhere have contributed to the common perception that floods and associated damages have been increasing in recent years. Given the ubiquitous nature of this hazard, a thorough examination of the many complex and interrelated aspects of natural and man-made floods in Canada is long overdue. This special issue contains 27 papers dealing with a variety of different aspects of floods in Canada. The first 16 papers deal with physical aspects of floods and include a collection of case study papers that present recent flood events in Canada, following a common format to allow readers to compare and contrast recent flood events in different regions of Canada. The last 11 papers focus on ecological, social and management aspects of floods. The papers included in this special issue present topical information on flooding and also challenge common perceptions of floods and flood processes in Canada.

Les inondations sont largement reconnues comme étant un danger naturel courant et à grande échelle, susceptible de causer des pertes de vie, des dommages matériels, et la perturbation de l’économie ainsi que des dommages écologiques. Toutes les régions géographiques du Canada peuvent être touchées par les incidences nocives des inondations. Les crues récentes au Canada et ailleurs dans le monde ont contribué à la perception courante que les inondations et les dommages connexes ont connu une hausse ces dernières années. Étant donné la nature omniprésente de ce danger, il y a belle lurette que nous aurions dû mener un examen en profondeur des nombreux aspects complexes et interdépendants des inondations naturelles et d’origine humaine au Canada. Le présent numéro spécial contient 27 communications qui traitent de diverses facettes des inondations au Canada. Les 16 premiers articles portent sur les dimensions physiques des inondations et comprennent un recueil d’études de cas qui présentent des événements récents d’inondation au Canada, selon un format commun afin de permettre aux lecteurs de comparer et de mettre en contraste les inondations récentes dans différentes régions du Canada. Les 11 derniers articles mettent l’accent sur les aspects écologiques et sociaux des inondations ainsi que sur la gestion des inondations. Les communications que comporte le présent numéro spécial présentent des données topiques sur les inondations et nous obligent aussi à revisiter nos perceptions courantes entourant les inondations au Canada et leurs processus connexes.

Physical aspects of floods

Buttle et al. (2016, this issue) provide the context for flooding in Canada including a description of the different flood-producing processes and the unique flood characteristics of different regions of Canada. This paper sets the scene for the papers that follow, particularly the case study papers describing recent Canadian flood events. The paper suggests directions for future flood research to address the many unresolved issues surrounding flooding and flood management in Canada, such as groundwater and urban flooding, and modifications to flood processes in a changing climate.

The next ten papers are case studies of recent flood events in Canada. These articles were prepared following the form used by Engel (2004) and differ from typical papers; this structure will allow readers to more easily make direct comparisons between events. Blais Clark et al. (2016, this issue) provide an overview of flooding and flood control infrastructure for the Red and Assiniboine Rivers in Manitoba. This paper provides both an historical background on flooding conditions in this flood-prone part of Canada as well as a comprehensive description of the various flood control works that have been built, and subsequently expanded, within the Red and Assiniboine River system. The background provided in this paper helps to set the context for the five case study papers that deal with flood events for the Red and/or Assiniboine Rivers.

Rannie (2016, this issue) describes the 1997 Red River flood, which the media dubbed the “Flood of the Century.” Heavy autumn rainfall, a large snowpack and a late spring blizzard all contributed to this extensive flood event that has an estimated return period of 100 to 140 years. Rannie documents the considerable damages from the event and describes the flood-fighting efforts that prevented even larger flood damages. Wazney and Clark (2016, this issue) describe the 2009 Red River flood event. This flood event also resulted from unfavourable antecedent conditions, particularly heavy rainfall in autumn that preceded the event. Although the flow magnitudes were less than for the 1997 flood event, flood damages still occurred largely as a result of ice-jam formation at several locations within the basin. This event illustrates the importance of the melt timing and duration for the formation of high water levels. Stadnyk et al. (2016, this issue) document the 2011 Red River flood, which resulted from a combination of well-above-normal soil moisture from heavy precipitation in the summer and fall of 2010, above-normal snowfall and colder-than-normal winter temperatures. The 2011 flood event was not as severe as it might have been as a result of warm temperatures and below-normal precipitation in the spring. The 2011 flood was noteworthy for the very long duration of the event, with the Red River Floodway in operation for almost 55 days. The wet antecedent conditions in late 2010 also led to major flooding in 2011 on the Assiniboine River (Blais Greshuk & Stadnyk 2016, this issue). This flood event was also exceptional for its long duration that resulted from the very high soil moisture, the melting of the winter snowpack and numerous high-precipitation events during the spring. For parts of the Assiniboine River Basin, estimates for the return period of the 2011 event are as high as 500 years. The Assiniboine River was again subjected to severe flooding in the spring and summer of 2014 (Ahmari et al. 2016, this issue). The 2014 flood event was unique in that it resulted from a series of significant consecutive rainfall events in late June and early July over a large proportion of the river basin, as opposed to the more traditional flood-generation processes of snowmelt and spring rains. The 2014 flood event was comparable to the 2011 event in magnitude and spatial scale, but was of a shorter duration.

Shook (2016, this issue) presents the 2005 flood events on the Saskatchewan River Basin. The flood events were caused by three large precipitation events in June and resulted in record-setting high flows and water levels for several locations. At least four deaths were attributed to the flood event, with property damages in excess of CAN $400 million. Pomeroy et al. (2016, this issue) describe the 2013 flood event in the Bow and Oldman River Basins in Alberta. The flood event was caused by a combination of a June rainfall episode in excess of 200 mm and snowmelt contributions from alpine areas. The 2013 flood was a long-duration event with a large spatial extent. Flood damages were on the order of CAD $6 billion, and there were five deaths that resulted from the flood.

Newton and Burrell (2016, this issue) describe flooding on the Saint John River in New Brunswick in April and May of 2005. The flood resulted from the melting of an above-normal snowpack combined with rain-on-snow events and a heavy rainfall event at the end of April. While there was no loss of life attributed to the flood event, extensive property damage occurred along the length of the Saint John River and its tributaries.

Saad et al. (2016, this issue) present the 2011 flood on the Richelieu River in Quebec. This flood resulted from a combination of heavy snow accumulation during the winter, a late onset of the spring freshet resulting in rapid snowmelt, and heavy and sustained spring rainfall. The flood event had a long duration with a return period for the flood magnitude of around 90 years.

Burn and Whitfield (2016, this issue) found that changes are occurring in flood regimes for watersheds across Canada, but that the nature of the changes depends on the watershed’s hydrologic regime. They also found that when attempting to attribute changes in hydrologic records, it is important to base the analysis on data drawn from a reference hydrologic network to facilitate the distinction between climatic and anthropogenic impacts on floods.

Nolde and Jakob (2016, this issue) challenge the standard approach of using a specified dike freeboard. This study calculated confidence intervals of river stage using an extension of the classical peaks-over-threshold approach to estimate freeboard. As such, they suggest that uncertainty should be incorporated into the calculation of allowable freeboard.

The physical process of flooding is reasonably well understood; however, rare and dangerous events can occur particularly in steep watercourses where potentially highly mobile beds are present. Jakob et al. (2016, this issue) address some of these issues in a Canadian context. Hydrogeomorphic processes such as debris floods and debris flows in mobilized channel bed sediments can lead to massive erosion of channel bed and banks. Also discussed are outburst floods that can be many times larger than normal floods and are often related to failure of landslide, glacier, moraine, beaver or constructed dams. This paper is dedicated towards bridging science and practice by highlighting some of the most threatening hydrogeomorphic hazards to which people and infrastructure in mountain regions are exposed. It provides suggestions on how current practice can be improved to properly diagnose and analyze the potential for such unusual floods.

Riboust and Brissette (2016, this issue) provide a detailed analysis of the 2011 flood in the Richelieu River. Spring rainfall was an important mechanism in this flood event, and they consider how extreme rainfall would have resulted in different flood magnitudes in winters with different snowpack conditions. Also related to linking precipitation to floods, McKee and Binns (2016, this issue) provide an analysis of the potential for improving forecasts of rainfall-generated floods using gauges and weather radar.

Floods and society

The first three papers in this section deal with issues related to the economic impacts of floods, flood insurance and human health. As such, they take as given the climatological, hydrologic and other physical processes that cause floods. These papers focus on the human dimensions of flooding: the policies that have been put in place to reduce flood risks and to mitigate flood impacts, the features of the insurance market and government policies related to that market, and finally the ways in which we may think about the dimensions of floods that affect society.

The paper by Davies (2016, this issue) identifies the major categories of economic losses arising from flooding, and distinguishes between losses that are pecuniary (measured in dollars) such as damages to structures and output losses and non-pecuniary (not measured in dollars in today’s markets) such as losses of services from one’s home, and lost recreation. This study also discusses alternative methods and approaches for modelling the economic consequences of floods. An important consideration in choosing amongst these is their relative data requirements. An additional topic addressed by Davies (2016, this issue) is the potential relationship between flood-damage assistance provided by governments and the workings of the private insurance market. Given the apparent shortcomings identified in this paper, the analysis is quite valuable.

The second paper focuses on the interrelated issues of flood-damage assistance and flood insurance (Sandink et al. 2016, this issue). An important set of issues concern the role of government regulation in shaping the coverage offered by insurance firms, and also the potential for government flood-damage assistance programs to “crowd out” (i.e. negatively impact) the provision of flood insurance by private insurance firms. The paper concludes by assessing alternative configurations of the future roles of the public and private sectors related to flood losses.

While loss of life dominates the media during a flood event, Burton et al. (2016, this issue) provide a review of the literature regarding the health impacts of floods on society. They identify gaps that should be addressed, and vulnerable populations within society that need further attention.

Not all floods that occur are the result of natural processes. For example, Albers et al. (2016, this issue) describe an alternative approach to modelling floods in a regulated basin. They use a random forest approach and apply the method to the Nechako basin in British Columbia. Indeed, flow regulation can play an important role in flood processes. Shook and Pomeroy (2016, this issue) describe floods that have occurred downstream of Lake Diefenbaker as a result of operational decisions.

Despite their different approaches and perspectives, there are several themes that are common to the above papers. These include a need to understand processes and incentives (intended or not) that may be contained in flood-related policies and programs, and to understand how private decision-makers (households and businesses) may respond to these incentives. Another common feature across the papers is a recognition of the shifting focus from engineering/structural approaches to flood management towards “softer” perspectives that incorporate, for example, a deeper understanding of the formation of risk perceptions by households, and that require new types of data to be collected and new forms of analysis to be carried out in support of efficient and sustainable flood programs and policies. Other papers show the need to estimate the risk of flooding through physical/statistical approaches; however, the operation of dams (i.e. flow regulation) also plays an important role in determining flood magnitude. Finally, the papers have demonstrated the utility of social science-based approaches by building on their understanding of the social and economic dimensions of floods to present and critically assess proposals for improved flood-related programs and policies.

Ecological aspects of floods

The influences of floods on river ecology, both instream and on the adjacent floodplain, play a major role in determining productivity as well as the distribution of species. St. Hilaire et al. (2016, this issue) describe how floods influence water quality, as well as the interactions of flooding with urbanization, agriculture and forestry that affect water quality. For each land use, a brief summary of the dominant processes linking runoff to water quality is provided and recent findings are summarized. For instance, with respect to urbanized watersheds, the relatively large proportion of impervious areas, lower vegetation cover and the presence of high-density drainage systems alter surface water routing and timing of peak flows. Peters et al. (2016, this issue) emphasize the ecological impacts and benefits of floods that are highly dependent on flood-generation processes as well as on their magnitude and timing. In Canada, floods can occur under open-water or ice-influenced river conditions. Ice-jam floods are generally associated with higher water levels and suspended sediment concentrations that can be detrimental to instream aquatic habitat, but beneficial to floodplain hydroecology. Given the potential alterations to the timing and magnitude of floods resulting from climate change, it is recommended that future research efforts should focus on enhancing our understanding of the ecological aspects of floods, especially under ice-jam conditions.

Changing climate and flood risks

It is widely recognized that climate change will have an impact on floods and the design of hydraulic structures in the future. Thiémonge and Clavet-Gaumont (2016, this issue) addresses the prediction of future floods within the province of Quebec. The analysis is carried out by simulating flows for nine drainage basins within the mostly naturally flowing Quebec North Shore using a hydrological model. The calibrated hydrological model is forced to climate scenarios (scenarios B1, A1B and A2) from global climate models and regional climate models. This study shows that changes in future spring flood volumes are site specific (between −6% and 13%); however, an increase of 9% is observed for 2-year return floods whereas an increase of 4% is observed for 100-year return floods, suggesting that lower return floods will increase at a slightly higher rate.

A related study is carried out by El-Jabi et al. (2016, this issue), where floods under current and future climate (scenarios B1 and A2 from the Canadian GCM) are compared at 56 hydrometric stations across the province of New Brunswick. Flood-frequency analysis shows that regional flood estimates have not changed significantly from the late 1970s and late 1980s; however, when predicting future floods under climate change, increases of between 15 and 30% are obtained. Similar to the above study by Thiémonge and Clavet-Gaumont, greater increases are predicted for low-return floods (about 30% for 2-year floods) compared to higher return floods (about 15% for 100-year floods).

How climate change is expected to affect the frequency distribution of floods in the Red River Basin is described in a paper by Rasmussen (2016, this issue). This study suggests that future snow packs will be smaller, but precipitation increases during the active snowmelt period should impact the distribution of floods. In the final paper, Lyle and Mills (2016, this issue) assess future flood risks by examining the rate of sea-level rise and the potential for storm surges in Vancouver.

In Canada, floods are a common hazard. This collection of papers reports on specific flood events from the past two decades, provides a recent perspective on both the physical and social aspects of flooding, and also challenges some common misconceptions about flooding in Canada.