Calgary drinking water safe during floods

P. Kim Sturgess and Lindsay Kline of Alberta WaterSMART report

Originally published in World Water - September/October 2014

Calgary skyline after the devastating floods in June 2013
Calgary skyline after the devastating floods in June 2013. Photo Credit: Angela Alambets, Alberta WaterSMART

In June 2013, Southern Alberta, Canada, experienced its worst flood event in 80 years. Flood waters washed away homes, inundated buildings, severely eroded riverbanks, and devastated local parks. The Insurance Bureau of Canada (IBC) declared the 2013 flood as the costliest natural disaster in Canadian history.

Heavy rainfall and rapid snowmelt bloated rivers that raged down through the Rocky Mountains and into the foothills and prairie regions. Over the course of several hours, flood waters rose rapidly and swept into the Bow, Elbow, Highwood, and Sheep Rivers areas - the region's primary drinking water sources. These turbid waters posed significant health and safety threats to anyone or anything in their path.

Between the evening of June 20 and morning of June 21, flood waters approached the city of Calgary at high levels and carried silt, mud, and other organic debris. As flood waters impacted one municipality after another, many water treatment plants were unable to provide safe drinking water to residents. Alberta's health authority issued boil water advisories for communities after water treatment facilities experienced mechanical difficulties and were unable to cope with the turbidity of the water.

The city of Calgary is located at the confluence of two of the rivers affected by the flood - the Elbow and Bow Rivers. When the Bow River flooded on the morning of June 21, turbidity in the river was reportedly 4,000 Nephelometic Turbidity Units (NTU) - an amount well beyond the 10 NTUs typical of summer river conditions in southern Alberta. Additionally, the Bow River peak flows reached 1,750 cubic meters per second, while the Elbow River peaked at 700 cubic meters per second. Comparatively, normal river flow for the Bow is less than 500 cubic meters per second in June, while the Elbow River is typically 150 cubic meters per second.

Despite these incredibly challenging conditions, Calgary's two water treatment plants, the Bearspaw and Glenmore Reservoir, were able to remove sediment and treat river water from both rivers effectively, maintaing safe drinking water for the more than one million residents of Calgary and surround municipalities.

According to Dan Limacher, director of water services for the city of Calgary, the city avoided boil orders on the drinking water because of major improvements made to the city's two water treatment facilities since the 2005 flood. The key improvement was the implementation of the ACTIFLO® high-rate clarification technology from Veolia Water Technologies. Conventional water treatment technology typically removes sedimentation in approximately six hours. ACTIFLO is capable of treating turbid water in approximately fifteen minutes, which proved invaluable during the 2013 flood.

The ACTIFLO system quickly and efficiently treated highly turbid water from the rapidly fluctuating Elbow and Bow Rivers. Employees at the two water treatment plants had approximately 10 hours to prepare for the flood waters, which included priming the ACTIFLO system for treating the expected excessive amounts of turbid water. The system's sandballasted flocculation technology proved especially integral during treatment.

Some of the most damaging flooding occurred within the Calgary city limits. However, unlike during the 2005 flood, both of Calgary's water treatment plants continued providing safe drinking water during the entire flood event.

ACTIFLO Technology?

The ACTIFLO system is a compact water clarification technology that treats raw water with coagulant, micro-sand, and polymer agents to remove impurities. Raw water enters the system and moves through a series of coagulation and flocculation basins where coagulant, micro-sand, and polymer agents are added to the feed stream. The agents bind suspended solids, natural organic matter, pathogens, parasites, and other naturally occurring elements for easy removal.

In the final water treatment stage, flocculated water is sent to a clarification chamber where high-quality water and sand-ballasted flocculated matter are separated. Clean, high-quality settled water flows out of the ACTIFLO system through a series of water collection troughs, and is then filtered and disinfected before it is pumped into the city's drinking water network.

Installation in Alberta

Highly turbid waters breached bridges
throughout the City of Calgary
Photo Credit: Angela Alambets, Alberta WaterSMART

After routine reviews in 2001 and 2002, Calgary city officials determined that both water treatment plants were due for extensive upgrading and maintenance, which led to the city's first installation of Veolia's ACTIFLO technology.

In early 2004, the Bearspaw Water Treatment Plant began upgrades with the construction of a new pre-treatment facility using the ACTIFLO sand-ballasted clarification technology. At the time, this was the largest (a 586-million-liters-per-day capacity) water treatment plant in North America to install an ACTIFLO treatment system. The technology was selected primarily because of its ability to adjust to the unpredictable river conditions characteristic of the southern Alberta region. Subsequently, scheduled upgrades and maintenance to the Glenmore Reservoir Water Treatment Plant were accelerated after the 2005 flooding that impacted the city. Upon completion in 2011, Glenmore Reservoir was the second water treatment plant in Calgary to receive the ACTIFLO technology for improved clarification (at a 425-millionliters-per-day capacity).

Lessons Learned

Because the ACTIFLO technology effectively removed extremely high levels of silt and pathogens from contaminated water, Calgary residents had clean and safe drinking water without interruption during the recordbreaking 2013 flood. Calgary Mayor Naheed Nenshi agreed with Limacher when he identified the improvements in the city's water treatment plants as the reason why boil water advisories and water restrictions were not implemented.

Limacher, whose position helps him know the possibilities better than anyone else involved in the event, summed it up best.

"This disaster impacted 100,000 residents," he said. "If the water treatment plants had gone down, this disaster would have affected a million residents."

Alberta WaterSMART Founder and CEO P. Kim Sturgess and Researcher Lindsay Kline are based in Calgary, Canada.

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