Phase 2 Flood Strategy Projects
Phase 2 Projects
In 2019 the Lower Mainland Flood Management Strategy (LMFMS) initiative completed new modelling and mapping for the Lower Fraser region. The work was carried out for the LMFMS partners by Northwest Hydraulic Consultants.
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 partners in the work 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.
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.
The Lower Mainland Flood and Environment Atlas was developed as part of the Lower Mainland Flood Management Strategy. This atlas contains flood extents for the Lower Mainland for select flood scenarios along with a range of environmental values and features along the lower Fraser River and coastal foreshore areas. The atlas is a resource when decision makers are considering potential environmental benefits (and adverse impacts) of floods as well as flood risk reduction projects or policies. The flood levels shown on this portal are based on the 2015 Analysis of Flood Scenarios and mapping from the 2016 Lower Mainland Flood Vulnerability Assessment.
Completed | Results to be included in draft Strategy Report
The Lower Mainland Flood Management Strategy initiative is focused on flood risk reduction in the BC Lower Mainland. In 2020 a Lower Mainland Flood Risk Assessment was completed to support the strategy development. The risk assessment spans BC’s South Coast — from Lions Bay to White Rock — and covers the lower Fraser River — from Hope to Richmond. It evaluates the potential impacts of flood hazards in the region on people and vulnerable assets (buildings, infrastructure and other things of value) to develop a regional baseline profile of flood risk. Through this risk profile, the LMFMS partners and decision makers will gain a better understanding for future flood risk management across the region.
Objectives of the Risk Assessment
- Broaden and deepen the understanding of flood risk in BC’s Lower Mainland; and
- Support risk-based decision-making for the broader Lower Mainland Flood Management Strategy, in particular by identifying higher risk areas of regional priority for flood risk reduction.
Components of the Risk Assessment
Flood Scenario Analysis
The risk assessment evaluated 16 different flood scenarios of different magnitude and likelihood. There were eight scenarios for each of two types of flood:
- Spring freshet flooding on the Fraser River and
- Winter storm surge flooding along the coast and Fraser delta.
Based on these flood scenarios, a vulnerability analysis was undertaken to estimate potential flood impacts across the Lower Mainland, based on best available and accessible data within the project timeline and budget.
Five consequence categories were assessed:
- Tangible direct damages to buildings, contents and infrastructure
- Intangible community consequences
- Social vulnerability
- Environmental consequences and
- Lifeline disruptions.
The results of this assessment will be included in a draft LMFMS report in summer 2020.
Challenges and Limitations
Assessing flood risk is extremely complex. The consequences from flooding are highly dependent on:
- size of the flood, how far it will spread and how deep it will be
- the location, elevation and resilience of buildings and infrastructure, and
- how prepared a community is for floods of different magnitudes.
A flood risk assessment cannot therefore predict with precision all impacts of a specific flood event. Moreover, many flood consequences cannot be easily measured – such as impacts to human health and well-being; loss of cultural, archaeological and traditional use sites; and contamination of the environment. Finally, limitations on time, budget and available data limit the level of analysis – it is anticipated that more work will be done over time.
Value of the Assessment
The risk assessment is an important step in understanding the value of assets at risk in the Lower Mainland.
The flood hazard model, flood damage model and risk profile tool that have been developed can all be refined with additional data and analysis, including additional flood scenarios, to continue to improve our understanding about flood risk across the Lower Mainland and inform risk reduction policies and actions.
In Progress | Results to be included in draft Strategy Report
Regional Flood Risk Reduction Priorities
Lower Mainland local governments and other flood authorities need to consider short-, medium- and long-term priorities for flood risk reduction, and what factors should be weighed when setting regional priorities. These include such factors as:
- Public safety
- Critical infrastructure and essential services
- Economic values
- Social and cultural values
- Environmental values
- Agriculture / food security.
Technical analysis, consultation and dialogue will be facilitated to refine priorities for the Lower Mainland Flood Management Strategy.
Flood Risk Reduction Options
In consultation with LMFMS partners and participants, a range of approaches to flood risk reduction options will be considered for the regional strategy.
An initial assessment of the options will be included as part of the draft Strategy Report, with input from LMFMS partners in the fall of 2020. 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 flood risk reduction options, it will be necessary to consider such issues as:
- Suitability of options for diverse locations and circumstances
- Technical feasibility
- Costs and benefits
- First Nations interests
- Environmental impacts
- Public and stakeholder interests.
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 reduction. 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 work on regional priorities, flood risk reduction options and funding and governance options will be considered by LMFMS partners and participants in the Fall of 2020.
A draft report will be available for public comment in early 2021.
Other Flood Projects
Here are some current flood projects relevant to the Lower Mainland, though not part of the Lower Mainland Flood Management Strategy initiative.
The Province introduced seismic guidelines for new and existing high-consequence dikes in 2011 (updated in 2014). The aim was to better protect the diking system from earthquake damage. Local authorities and design professionals in the Lower Mainland have found the standards are technically challenging to implement in many locations and/or cost-prohibitive.
The Province of BC has provided funding to:
- fill information gaps about the seismic vulnerability of flood protection dikes through geotechnical investigations and engineering analysis
- review the seismic guidelines and implementation challenges and propose changes/updates
- work with local governments and design professionals to develop a program that balances:
- a level of seismic resilience that is financially achievable, and
- continued improvement of flood infrastructure for current and future conditions
- develop professional practice guidelines for effective and consistent application of seismic risk assessment and design.
This initiative is expected to improve understanding of seismic vulnerabilities and to develop and implement a well-defined and regionally accepted program to improve the seismic resilience of Lower Mainland dikes.
In BC there are 101 orphan dikes and erosion protection works, which total more than 85 km in length. These works were either constructed or funded by the Province of British Columbia over the past 50 years to respond to emergency flooding situations or were built by others and abandoned. These works generally lack adequate planning and engineering design due to the emergency conditions under which most were constructed. They are not typically maintained or inspected by a diking authority.
The Fraser Basin Council, which oversees the project, retained a consultant to review risk assessment methodologies and recommend a methodology that would be suitable to assess orphan dikes in BC. A second phase of work involves an assessment of the orphan dikes using the recommended methodology, including field assessments. The project is evaluating the condition of the orphan dikes, the associated risks of failure, and what is needed to bring each up to provincial standards and into a state of readiness to establish a local authority. While only a small number of these orphan dikes are in the Lower Mainland, the project will help identify any significant risks associated with those that are.
The project is funded by the Province of BC with the aim of helping local governments, the public and provincial officials to quantify and understand the risks that these structures pose to BC communities. The project will also assist interested local governments that wish to mitigate these risks by assuming the role of diking authority, if warranted.
The BC Storm Surge Forecast model provides important 5-day forecasts of coastal flood conditions in the Georgia Strait. Coastal partners in the LMFMS and the Province of BC have cost-shared the operation of the BC Storm Surge Forecast Model over the 2016-17 and 2017-18 storm seasons (October through March). Funds for continued operation and enhancement of the forecast model were secured from Emergency Management BC for the 2018-19 and 2019-20 storm seasons.
Visit the StormSurge BC website.