Phase 2 Flood Strategy Projects

Here's a look at work underway in the Lower Mainland Flood Management Strategy.

• Lower Fraser River 2D Flood Modelling & Mapping
• Digital Elevation Model of the Lower Fraser River
• Flood Risk Assessment
• Assessment of Flood Management Options
• Online Atlas on Flood and the Environment
• FloodWise Website

Also see summaries of related flood projects in Other Work:

• Seismic Guidelines for Dikes
• Assessment of Orphan Dikes
• BC Storm Surge Forecast Model

Lower Fraser River 2D Flood Modelling and Mapping Project

Completed: 2019

The Lower Mainland Flood Management Strategy has developed a Lower Fraser Floodplain Model. Following an RFP process, Northwest Hydraulic Consultants was retained for the work, initial runs underway in the fall of 2018, and the work completed in late 2019.

The floodplain model is based on a new digital elevation model that encompasses both the river channel and the floodplain.

The new modelling work provides a better understanding of how water moves down the river and across the floodplain under various flow scenarios. The model can also be used to analyze the effects of dike breaches; to create flood hazard maps that show the extent, depth and velocity of floodwaters; and to evaluate the effectiveness of proposed flood mitigation options.

Maps of a number of Lower Fraser flood scenarios (present day, 2050 and 2100) have been produced in the modelling project: see Lower Mainland Flood Maps.

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Digital Elevation Model of the Lower Fraser River

Completed: March, 2018

Photo: 2017 bathymetric survey of the Lower Fraser

In 2017, Northwest Hydraulic Consultants was retained to:

• conduct a bathymetric survey to collect data along the lower Fraser River from Hope to the river’s mouth at the Strait of Georgia, and
• combine the newly-collected data with existing bathymetric and topographic data to develop a digital elevation model.

The bathymetric survey measured the underwater depths of the river. It was conducted by boat using single (sonar) beam hydrographic equipment and software. The final elevation data from the survey was combined with data collected by Public Works & Government Services Canada in 2015, LiDAR topographic data commissioned by the Province of BC and other data.

A digital elevation model (DEM) has been derived using these datasets. The DEM provided a critical input for the development of the Lower Fraser Floodplain Model.

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Flood Risk Assessment

In Progress | Completion: March 2020

With funding from the National Disaster Mitigation Program, FBC and the LMFMS partners began work on the Lower Mainland Flood Risk Assessment in late summer 2019. The project is expected to be completed in March 2020.

Objectives

• To broaden and deepen understanding of flood risk in the Lower Mainland
• To support risk-based decision-making by identifying higher risk areas of regional priority for flood risk reduction

This assessment improves on the Regional Assessment of Flood Vulnerability by:

• Using more accurate flood maps
• Applying consistent, more complete, up-to-date asset data
• Capturing infrastructure interdependencies.

Key Elements of the Flood Risk Assessment Risk Areas

• Encompasses coastal and river floods
• Accounts for current and future risk
• Integrates new flood depth damage curves developed for the Lower Mainland
• Asset datasets and vulnerability indicators will be prepared for the criteria and considerations listed below
• Risk factors will be weighted through consultation and engagement.

Expected Outcomes

• A flood risk profile that accounts for a full range of impacts from flood events in the region
• A web portal to communicate risk profiles
• A key tool to inform regional priorities and recommendations.

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Assessment of Flood Management Options

In Progress | Flood Strategy Interim Report (Draft):2020

1) Regional Flood Mitigation Priorities

Lower Mainland local governments and other flood authorities were surveyed in the fall of 2017 about their short- and long-term priorities for flood mitigation, and what factors should be weighed when setting regional priorities.

Survey respondents identified factors of importance when setting flood mitigation priorities for the region. These include public safety and a number of other factors (in no specific order):

• Public safety
• Critical infrastructure and essential services
• Economic values
• Social and cultural values
• Environmental values
• Agriculture / food security.

Additional technical analysis, consultation and dialogue will be facilitated to further refine priorities for the Lower Mainland Flood Management Strategy.

2) Flood Mitigation Options

In consultation with the Joint Program Committee for Integrated Flood Hazard Management, FBC has identified a range of approaches to flood mitigation to consider in the context of a regional strategy.

An initial assessment of mitigation options for the Lower Mainland will be presented in a Flood Strategy Interim Report (Draft), expected for late spring 2019. These include:

• Hard- and soft- engineered flood mitigation works (e.g., dike upgrades, dike realignment, breakwaters, sediment management and water retention)
• Adjustments to land use policies
• Floodproofing requirements for new and existing development in floodplain.

In assessing mitigation options, FBC and project advisory committees will look at a range of considerations. In no specific order, these include:

• Effectiveness
• Technical feasibility
• Costs and benefits
• First Nations interests
• Environmental impacts
• Public and stakeholder interests
• Suitability of options for diverse local and sub-regional circumstances.

3) Funding and Decision-Making Models

An initial inventory and analysis is in progress to document past, present and emerging approaches on funding and decision-making related to flood risk. Examples from BC and other jurisdictions are being reviewed. Near-term funding opportunities are being explored, as well as the potential to establish a new funding program for longer-term strategy implementation. The business case for proactive investment and regional cost-sharing is also being developed.

The results of this work will be presented in a discussion paper and in the Flood Strategy Interim Report (Draft) for initial consideration by participants in the LMFMS and made available for public comment in late 2020.

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Online Atlas on Flood and the Environment

In Progress | Completed in 2019

An online map atlas and document library has been developed to identify environmental values and features along the lower Fraser River and coastal foreshore areas – in the context of flood hazards and flood management.

Visit the Lower Mainland Flood and Environment Atlas

The atlas can help identify potential environmental benefits and adverse impacts of flood mitigation works or policies. Decision-makers can use the atlas to flag issues likely to require review in regulatory processes and identify potential candidate sites for habitat protection, conservation, restoration or compensation.

The atlas is hosted on the Community Mapping Network. Thanks to several governmental and non- governmental agencies that have made data available, information will include:

• Estimated depth and extent of Fraser River and coastal flood scenarios
• Location and alignment of flood mitigation works
• Communities and land use
• Watercourses and wetlands
• Sensitive ecosystems
• Fish habitat.

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FloodWise Website

In Progress | Completion: March 2020

A first-stop flood education website is in development to support better awareness of flood hazards and the opportunities for flood risk reduction in the Lower Mainland.

The site will support the Lower Mainland Flood Management Strategy through information, story maps and a series of short videos. The site will also profile best-in-class flood information resources and case examples relevant to BC.

While the initial focus of the site will be on the Lower Mainland, the site may also be expanded in future to profile other flood initiatives in British Columbia.

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Flood Strategy Briefing

For a further look at the Phase 2 projects, see:

• Flood Strategy Briefing 3 (2019)
• Flood Strategy Briefing 2 (2018)
• Flood Strategy Briefing 1 (2017)