The Vancouver Flood Plain Map

Flood plain maps are an important part of the planning process. Whether for new development or existing property, they help determine where risks are likely to occur and what can be done to mitigate them.

There are a number of different types of flood plain maps used in BC. These include inundation maps, flood hazard and risk maps.

The Floodplain

A floodplain is a low-lying area that’s susceptible to flooding from an adjacent watercourse, ocean, lake or other body of water. It may also be vulnerable to other threats, like tsunamis.

The Vancouver Flood Plain Map illustrates the various flood hazard areas in the city and shows how many properties in those areas are at risk of being flooded in a major storm or series of storms. It’s a useful tool for community members, planners and developers to use when developing flood risk management plans or identifying flood prone areas in their own jurisdictions.

It’s important for people to understand the potential for flooding because it could impact their lives in a number of ways. It could cut off utilities and emergency services, cause a loss of property or business value and affect their access to transportation, among other things.

In Canada, more than 86 high-risk areas are federally designated as flood hazard zones. However, all of those areas’ flood maps are 25 years out of date, according to a new paper from scientists at the University of British Columbia and the University of Toronto.

Those old maps are based on satellite elevation data and climate projections that haven’t changed since they were created in the 1970s, but they don’t take into account major changes on the ground or new knowledge about climate change-related risk. Thistlethwaite and his colleagues spent six and a half weeks evaluating 86 flood maps across the country and found that BC’s maps didn’t meet a set of nine criteria they developed to determine what makes a good map.

He layered 17 new climate models on top of those, using the latest science from the UN’s International Panel on Climate Change to project how the country’s flood risk could change in worst-, mid- and best-case scenarios up to 80 years into the future. He found that by the end of the century, 30 per cent more of Canada will be flooded, with a flood depth increase of up to 60 per cent.

He says the maps will help insurers, engineers, homebuilders, conservation authorities and governments at every level plan better policies and stronger flood protection. They will also give residents a sense of their own risk and enable them to make informed decisions when buying or building a home, as well as when looking for a job or deciding where to live.

Coastal Floodplain

The coastal floodplain is an important part of the city’s environment. It provides critical habitat for sensitive ecosystems, such as sea lions, and supports coastal fisheries and tourism activities. Protecting and preserving these areas is essential for maintaining the quality of life in our community.

The Coastal Flood Plain Map is intended to provide an overview of potential flooding from future changes in climate and sea level. The maps are intended to be used by residents, businesses, and local governments to assess flood hazards and develop action plans that can help them become more resilient to the impacts of extreme weather events.

Increasing sea levels will cause a number of coastal communities to experience flooding, including Vancouver. As a result, the City has worked with a variety of stakeholders to develop a Coastal Flood Risk Assessment to identify flood hazards, vulnerabilities and consequences expected over the next century.

Based on these findings, the City of Vancouver has developed a new Flood Plain Map with new flood construction levels (FCLs). This was completed as part of the Coastal Flood Risk Assessment and is shown below.

The FCLs show flood construction levels based on ground conditions as they exist today in a Digital Elevation Model (DEM) that has been edited to remove buildings and temporary features. This model is based on the most current data available and any changes in ground elevations, land use or building structures will change the FCLs and render site-specific information obsolete.

It is recommended that the FCLs are reviewed periodically to ensure they still reflect the most current development conditions. They should also be compared with flood depth and velocity maps prepared for other jurisdictions.

Storm surges are an additional hazard that can significantly increase the frequency and severity of flooding. These storm surges combine with high tides, waves and/or river flows to generate an influx of water that can result in the inundation of a large area. In order to determine how to estimate storm surges, hydraulic modeling is required (KWL 2011).

Bank erosion can be a significant flood hazard. This is especially common in areas that are adjacent to mountain rivers. To mitigate this hazard, flood hazard maps should include appropriate setbacks from major rivers to indicate the areas that are susceptible to bank erosion.

Still Creek Floodplain

A floodplain is an area where a flood can occur and is often referred to as the “flood zone” or “flood plain”. This type of floodplain is vulnerable to flooding due to a river, ocean, lake, creek, pond or other body of water overflowing.

There are different types of flood maps used for a variety of purposes and can include inundation (flood extent) maps, risk and hazard maps and design flow maps. These maps are used for official designation of floodplains, establishing flood construction levels and designing dikes or other structures in the floodplain.

For example, the Lower Fraser River has designated floodplains along its banks and in certain areas of the river’s upper reaches. These are identified as Flood Hazard Areas and are mapped in the Lower Fraser River 2D Flood Model.

The flood hazard maps are based on the probability of a particular event happening, such as a 1% Annual Effective Percentage (AEP) flood or a 1:500-year storm. This means that if there were a flood of that type every year for the next 500 years, the level of risk would be very high.

Flood hazard maps also show areas where there is a potential for an increase in the frequency of flooding due to climate change, such as changes in peak river flows or sea level rise. This increased risk could result in the occurrence of larger and more severe flood events than those experienced today.

This can lead to a greater amount of damage to properties and infrastructure. It can also impact communities’ quality of life, cut off access to utilities and emergency services, cause loss of property value and affect the economic well-being of a community.

Various other types of flood hazard maps exist, including flood velocity and propagation maps, which document velocities of the flood water over time and can be used to determine how much groundwater flows through a region and where it may move. There are also evacuation maps, which can be used to help evacuate people in the event of a disaster.

The risk and hazard maps should be used in conjunction with the floodplain mapping to establish appropriate design flow. The QP is responsible for making the client aware of all potential flood-generating processes and making a recommendation as to the best flow to design to (i.e., 200-year or 2,500-year). The client should then make the final decision.

Map Details

Flooding maps are important tools that help community officials and residents make decisions about flood risk and land use. They can also be used to establish the correct flood insurance rates for homes and businesses.

A flood plain is a lowland area that is susceptible to flooding from an adjoining watercourse, ocean or lake. This is a risk that has been exacerbated by climate change.

The map details are provided by the City of Vancouver and can be found on their website (City of Vancouver). It includes the coastal floodplain, the Still Creek floodplain and other information that can help citizens understand the floodplain’s risks.

For the coastal floodplain, the data used to create the map is based on a combination of historical rainfall and snowmelt, hydrodynamic modeling and urbanization patterns. It also includes sea level rise and freeboard.

As a result of this data, the floodplain is divided into four zones, which are designated as the coastal floodplain, the Still Creek floodplain, the Pemberton valley and the Upper Squamish river valley.

During a storm, water can flow through the floodplain and cause damage to properties, as well as devastate entire communities. A flood can be caused by a combination of different factors, including rainstorms, windstorms, debris flows and landslide dam breaches.

In preparing the maps, it is important to consider flood hazards in all areas of the province where there is the potential for storms to cause damage. For example, in the Pemberton valley and the upper Squamish river valley, debris flows are a major source of flooding.

It is important to ensure that all changes in the topography are represented in the mapped flood elevations. This should be done through two-dimensional modelling, which can be a cost-effective and efficient way to prepare floodplain maps. Future road fills and other topographic changes can be included in the modelling to account for this transfer of risk.

The APEGBC Code of Ethics states that: “Engineers and geoscientists must determine whether they are qualified by training and/or experience to undertake and accept responsibility for the carrying out of flood mapping in BC” (APEGBC 2013a). Professional engineers and geoscientists who provide flood mapping services must seal all engineering or geoscience documents that they prepare and deliver in their professional capacity or have prepared and delivered under their direct supervision in any sector, in accordance with the APEGBC Quality Management Guidelines.