The 2013 flood of the Bow River basin has triggered a long-overdue conversation about the natural and man-made factors that caused or contributed to these types of events. Across society, people are now asking pointed questions that relate to mitigation, prevention, headwater management, overlapping landuses, floodplain infrastructure, climate change, and flood proofing.
The WaterSMART White Paper provides an excellent broad overview of the complexity of this watershed issue and makes clear that integrated solutions are required to meaningfully address this challenge. Appropriately, the WaterSMART report identifies that both engineering and landscape management approaches are required if watershed integrity of the Bow River basin is to be conserved and risk to infrastructure is to managed at an acceptable level.
As a resident of the Sunnyside community in Calgary, our neighborhood was extensively flooded and most families experienced serious damage to their basements, and in some cases, structural damage to their homes. In comparison to the residents of lower Benchlands, High River, and many other communities, we escaped relatively unscathed. In the aftermath of these events, we are told that those who have experienced flooding are expected to go through the emotions of anger, denial, depression and acceptance. For most affected by the flood, there is a basic need to understand what happened and what factors contributed to an event that so forcefully changed our lives. Over the next several months, more information will certainly come forward to help residents better understand the weather, landscape, and landuse dynamics that shaped this massive event, but a few thoughts are respectfully offered below to help put some of these dynamics into context.
During the past five years, the ALCES Group has completed two Bow River basin watershed studies examining the effects of land use (forestry, energy, agriculture, residential, transportation, recreation) and climate on watershed integrity. One of these studies (the Upper Bow Basin Cumulative Effects Study) examined the entire basin upstream of Calgary. The other study focused on the Ghost River watershed, an important headwater basin within the Bow River system. For those wanting to understand the detailed findings, these reports can be downloaded from the ALCES website (www.alces.ca).
These studies underscore the large amount of natural variation in environmental conditions that characterize the headwater landscapes of southwest Alberta. Year-to-year and decade-to-decade change in precipitation, temperature, and fire create a wide range of natural variation in levels of groundwater saturation, river flow, and water quality. The episodic nature of this natural variation is such that rare events (massive floods or sustained drought) are not commonly observed in any given year and may take multiple generations to witness the full variation of Mother Nature. But we must be careful not to confuse uncommon with unimportant, for it is these relatively rare events that define the form and function of the Bow River and its tributary basins. Many of us witnessed one of these infrequent events firsthand this June. The improbable combination of a large moisture-laden low-pressure system, stalled against a high-pressure ridge created by a fold in the jet stream, lead to a massive precipitation event that fell extensively throughout the Bow River basin, including the drainages of the Ghost, Elbow, Sheep and Highwood rivers. This hydrological event was made even more impressive because some of the rain fell directly on a deep snowpack (which melted rapidly) while in other areas the rain fell on frozen or saturated groundwater. With limited capacity of the landscape to absorb the billions of cubic meters of water flowing downhill under the force of gravity, the outcome was a foregone certainty. All watercourses, from the smallest of tributaries to the largest mainstem rivers, quickly swelled, overtopped their banks and spread waters across their floodplains in a fashion that has re-occurred hundreds of times since glacial ice sheets retreated several thousand years ago.
What made this 2013 event of immense interest (and anxiety) was the magnitude of physical and economic damage to infrastructure it caused. Longterm river flow records indicate the 2013 flood was about the largest recorded for the Ghost River and 5th largest flow on the Bow River – yet it caused, by far, the greatest economic loss. The obvious point here is that a vast amount of infrastructure (houses, roads, schools, business complexes, industrial facilities, recreational facilities) has been constructed on floodplains and riverside benches in the past several decades. As Alberta’s main economic urban engine, Calgary and its surrounding communities have converted vast investment dollars into physical infrastructure – much of which is located directly along waterways. As these communities have sprawled outward, much of this growth has occurred along the very mainstem rivers (Bow, Ghost, Elbow, Highwood) that originally attracted Alberta’s pioneers and gave birth to the initial settlements. It has been the inevitable collision between high floodwater volume and dense floodplain infrastructure that lead to this unprecedented economic disaster.
While one does not need to invoke climate change scenarios to explain a single large flood event (such as the 2013 flood), the science of climate change universally points to these types of events becoming more frequent and of greater magnitude. Ignoring the role of climate change in the dynamics of current and future water flow in the Ghost River and the Bow River basin has immense risk to all land uses and citizens. Perhaps the 2013 flood will catalyze a more mature and science-based conversation about, and appreciation for, the critical “driver” of climate change. We ignore this conversation at great peril.
The findings of the ALCES projects in the Bow River and Ghost River basins highlighted the importance of landuse in affecting the flow and performance of water quality, landscape integrity, and wildlife to the residents and users of these watersheds. Were these landuses responsible for the flood and the destruction it caused? Our analyses revealed that the portion of these basins allocated for logging, agriculture, transportation, residential, recreation, and the oil ad gas sector can profoundly alter surface and subsurface movement of water and the amounts of nutrients and sediment entering water. In addition, the extent to which best management practices are adopted can mitigate risks caused by land use and water. Key management practices that reduce flood risk include protecting riparian forests (including those along small tributaries), leaving more live trees within cutblocks, improved cattle grazing practices, and careful selection of road/trail networks for forestry, oil and gas, and recreation. When all of these best management practices are deployed collectively, headwater landscapes can provide Albertans with improved performance of ecosystem services and significantly reduce the frequency and cost of floods that cause economic disruption. Would these improved land use practices, if fully deployed, have prevented the events of June 2013? Not likely! The magnitude of this foothill and mountain rainfall event was so extreme that it would have likely generated extreme surface water and sediment runoff even under conditions of progressive land management. That said, society must not lose sight of the longterm importance of sustainable watershed management. It would be unwise to use the volatility of natural systems as an excuse for poor land management practices. In hindsight, the most relevant “best management practice” would have been to avoid construction of new infrastructure within flood plains and lower benches, and to relocate, where possible, existing infrastructure away from these features. The carnage observed by those who live and work in these basins can be viewed as a reminder of the raw power of natural ecosystems. It is also a wake-up call of how these “rare” events can become more frequent in a climate change world, especially if society continues its historical preference to building infrastructure so close to waterways.
During the extended periods of time, often measured in multiple decades, that occurs between flood events, it is all too easy for generations living in the “gentle times” to forget the lessons learned by past flood survivors. Societies in general, and governments specifically, have a responsibility to remember these lessons, and to build policies and infrastructure that intelligently reflect the force and destructive potential of natural systems.
As long as there has been people, they have been drawn to water for food, industry, recreation, and viewscapes. Our challenge is to balance these amazing benefits with the flood risks that inevitably accompany “living at the rivers edge”.
Submitted by Brad Stelfox, Landscape Ecologist, ALCES Group; bstelfox@alces.ca
