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Sunnyside Flood Barrier - FAQ

 

Barrier terminology

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The height of a flood barrier is often described in terms of what river flow it is designed to protect against. This is often expressed in two ways:

  1. River flow rate: The amount of water travelling past a point, which is measured in cubic metres per second. For example: In 2013, the flow rates along the Bow River in Calgary reached 1,840 m3/s. Learn more about river flows.
  2. Percentage chance of a river flow rate occurring: The calculated odds associated with a certain flow rate occurring each year. For example: A river flow rate of 1,840 m3/s, like we saw on the Bow River in 2013, is considered to be a 1:75 flood (75-year flood). This translates to a 1.3 per cent chance of this flow rate occurring annually.

The City’s Flood Mitigation Strategy is aimed at achieving – at a minimum – protection against a 2013-level flood. This will be achieved through a combination of efforts including community-level flood barriers, the construction of additional upstream storage on the Bow River and modified operations of TransAlta’s Ghost Reservoir.

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Freeboard refers to the additional increase in height or “buffer” that’s commonly incorporated into the design of a flood barrier. Freeboard protects against uncertainty while reducing the risk that the barrier would be overtopped by the river flow that it was designed to protect against. This safety measure compensates for unknown factors like tree debris, potential waves or stormwater coming in.

Mitigation strategy

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There is not a ‘proposed height’ currently for the flood barrier in Sunnyside. During the preliminary design stage of the project, a variety of barrier heights are being studied and considered, including the 1:20 height, but options all the way up to 1:200 are being explored.

The Triple Bottom Line (economic) assessments completed to date were based on a conceptual design that looked only at Sunnyside’s flood barrier and did not take into consideration The City’s larger multi-pronged approach for flood mitigation. As studies are completed, the triple bottom line assessment for this project will be updated and will take into consideration The City’s multi-pronged approach for flood mitigation.

Before a decision is made on the height of the barrier, a new Triple Bottom Line assessment will be completed that looks at all the options being considered.

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Currently, land use and building regulations are not eliminated once barriers are built, and no communities in Calgary are currently exempt from the regulations set out in the Land Use Bylaw with respect to flood risk.

The City is working with The Province to clarify what future provincial and municipal policies may look like for our changing risk. Any potential changes to regulation will be brought to the public for engagement before being taken to Council.

Design process

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Understanding the impact of groundwater has a significant influence on the design of the barrier. A groundwater study is being done during the preliminary stage to better understand how groundwater moves from and to the river. Groundwater monitoring will continue through to the detailed stage (2020).

The results from the study will help inform how the new barrier will be designed to take groundwater into account.

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Yes, before any work commencing, a thorough assessment of the trees along the pathway will take place. This includes counting all the trees along the pathway and assessing the health and age of the trees.

From there, a tree protection plan will be implemented as required during the life of the project. The City will do its best to conserve as many trees as possible so as long as they do not pose a risk to the integrity of the barrier or to pathway users.

Trees that are removed or are at the end of their natural lifecycle will be salvaged, reused for other city river projects such as fish habitat projects, and replaced where possible.

Barrier height

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As part of the preliminary design process, The City will be exploring various flood barrier heights to understand the merits along with the trade-offs of proceeding with any option.

That being said, the community flood barrier in Sunnyside is just one mitigation solution that will work together with upstream storage on the Bow River and modified operations of TransAlta’s Ghost reservoir to protect the community from a minimum 2013-level flood.

We will be engaging with Sunnyside residents in late summer 2019 and presenting details on the various heights of the barrier being explored and their related trade-offs.

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The City’s flood mitigation strategy aims to achieve, at a minimum, 2013-level flood protection for all communities in Calgary. There isn’t one single project (i.e. community flood barrier) that will provide adequate protection on its own. The community flood barrier in Sunnyside is just one mitigation solution that will work together with upstream storage on the Bow River and modified operations of TransAlta’s Ghost reservoir to protect the community from another 2013-level flood.

All community flood barriers cannot be created equal. Each location that requires a barrier comes with its own unique set of circumstances that need to be considered.

At the Calgary Zoo, a large portion of the zoo is located on St. George’s Island. From the 2013 flood, we learned that evacuation options are very limited and it’s technically very challenging to evacuate zoo animals safely. That’s why City Council made the decision to build a higher barrier for this location.

As the economic engine of the region, the Downtown has high damage potential, which drives a large investment in mitigation and prevention.

In Sunnyside, The City has made significant investments in the community to address various sources of flooding in the community, including river, storm and sanitary flooding.

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The City is working with The Province to improve clarity around flood protection standards for Alberta communities and consideration of “layering” mitigation measures for increased resilience.

The multi-pronged approach of Calgary’s flood mitigation strategy is intended to work together to provide flood protection to Sunnyside and other at risk communities along the Bow River from, at a minimum, a 2013-level flood (~1:200-year flood).

That said, as part of the preliminary design process, The City will be exploring various flood barrier heights to understand the merits along with the trade-offs of proceeding with any option.

 

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