Updated Floodplain Mapping Report identifies changes to flood hazard in the Pemberton Valley

Dec 05, 2018
Electoral Area C, Village of Pemberton

Report recommends coordinated emergency response planning, enhanced forecasting, improved flood protection measures; Local authorities commit to working together to address flood risk

PEMBERTON, BC – Elected officials from the Líl’wat Nation, Pemberton Valley Dyking District (PVDD), Squamish-Lillooet Regional District (SLRD) and Village of Pemberton were briefed this week regarding the results and recommendations of the Lillooet River Floodplain Mapping Report (‘Report’), which identifies changes to the flood hazard in the Pemberton Valley resulting from river capacity changes, material from the 2010 Mount Meager landslide and climate change.

Commissioned by the PVDD and funded by the Province of BC through Emergency Management BC (EMBC), the study was conducted by Northwest Hydraulic Consultants Ltd. The Report’s findings provide insights into the increased flood hazard while sharing new tools and recommendations to support flood management in the Pemberton Valley.

The updated flood modelling shows that peak discharge flows correlating to 50-, 100-, and 200-year floods are higher than previously understood and, as a result, current dike infrastructure does not offer the level of protection as was previously understood.

In addition, sedimentation from the 2010 Mount Meager landslide and changes in the timing of flood events (floods are more likely to occur after rain-on-snow events in the fall, rather than at spring freshet) all contribute to the increased flood risk in the Pemberton Valley.

The likelihood of a 200-year flood occurring is once in every 200 years or a 0.5% chance in any given year; the likelihood of a 100-year flood event occurring is once in every 100 years or a 1% chance in any given year and the likelihood of a 50-year flood event is once in every 50 years or a 5% chance in any given year. However, the magnitude of these flood events has increased. The report findings indicate that what was once thought to be a 1-in-200-year flood event, is now more likely to be a 1-in-50-year flood event.

The report offers several recommendations, some of which have been completed or are in progress.

Recommendations include: informing local residents of the increased flood risks, updating the emergency response plans, designating the new floodplain maps for the Lillooet River, conducting additional modelling and mapping of the tributary flows including the Birkenhead River, notifying the provincial River Forecast Centre of the flood hazards in the Pemberton Valley (complete; the trigger points for high stream flow advisories, flood watch and flood warnings have been adjusted to reflect new data), increasing sediment removal and conducting critical dike upgrades (in progress; PVDD) and increasing monitoring with additional flow gauges on the Birkenhead River as well as tributaries.

These recommendations have implications for all levels of government and will influence land use planning as well as emergency flood response and recovery planning. Some of these measures will prove to be costly, but the jurisdictions involved will work together in an effort to secure funding sources for long-term mitigation measures.

A working group consisting of emergency management personnel from all four agencies has been established and is developing an interim Integrated Flood Response Plan (IFRP). A formal, public IFRP is expected to be complete before October 2019.

All jurisdictions will continue to share information and provide updates to the community, while working together to pursue funding support from the provincial and federal governments to help advance further flood mitigation in the Pemberton Valley.

The full report, supporting videos and FAQ are available on the SLRD website. As updates become available, they will also be shared on the website and through social media.

Residents with specific technical questions about the Report’s findings should contact the PVDD at trustees@pvdd.ca. Please note that the PVDD does not administer building permits or control flood construction levels, any questions regarding these matters should be directed to your respective jurisdiction as indicated below.

Residents with other questions or concerns including building permits and flood construction levels are asked to contact their respective jurisdiction:

Líl’wat Nation
604-894-6115
info@lilwat.ca

SLRD
604-894-6371
info@slrd.bc.ca

Village of Pemberton
604-894-6135
admin@pemberton.ca

Quotes:

“Accurate floodplain mapping is essential to managing flood preparedness in our valley. We need to establish baselines and identify risks to community safety. Through careful planning we can then safeguard our communities from the hazards associated with flooding. The last substantial update to floodplain mapping happened over 25 years ago. Fortunately, the Pemberton Valley Dyking District (PVDD) was provided with an opportunity to apply for and secure considerable funds from Emergency Management British Columbia (EMBC) to obtain thorough mapping of all rivers in our valley. We are grateful to the Province of BC for recognizing the needs in our valley, and for their efforts to commit to supporting our communities.

The Pemberton Valley Dyking District has worked diligently to ensure the careful completion of the flood mapping project. Thank you to PVDD Operations Manager and staff at the PVDD for coordinating this major project.The floodplain mapping report provides state of the art updated information that is critical to enhancing public safety and identifying weaknesses in current flood protection infrastructure.  Now that we have a clear and detailed understanding of the current flood protection situation in our valley the PVDD is eager and committed to working collaboratively with the Squamish-Lillooet Regional District, Lil’wat Nation and the Village of Pemberton to address weaknesses and to enhance and improve flood protection for the benefit of all those living and working within our valley and our communities.” – Brenda McLeod, Chair, Pemberton Valley Dyking District Board of Trustees

 “I would believe that we are all on the same understanding of living where we live and the risks attached from Nature. Risks have come from the rumblings of Ts’zil as a potential threat, we also have reacted to the landslides of the upper valley. We have the annual occurrence of the high water which now based on all the accumulative contributing factors  has  now majorly increased our threat level. We need to have very clear communication with our citizens on preparedness, what to expect as far in comparison to what we faced already (worst case scenario). We need to start as soon as possible on the communication of the needs from agencies that can provide financial support now to decrease the major threat that is impending. We need to communicate our state of proactive action needs and intentions rather than the reaction of the incident we foresee.” – Dean Nelson, Political Chief, Líl’wat Nation

 “There’s no question, the findings in the report are sobering. With this knowledge, however, we now have an opportunity to work collectively to address the risks. Our immediate priority is to make sure residents are aware of the report’s findings and have the tools they need to be prepared for floods and other emergencies. Moving forward, the SLRD is committed to working with our partners to develop an integrated flood response plan, identify priority mitigation projects and advocate for the funding needed to undertake the flood protection measures recommended in the report.”– Russell Mack, Electoral Area C Director, SLRD

“The Pemberton Valley is a naturally beautiful, yet dynamic environment. Natural disasters, such as flooding, are a reality of living in BC and within the Corridor. Understanding and quantifying the risks so we can plan, budget and mitigate is our best line of defense to enhance public safety and protect our infrastructure. We will continue to work with our partners, Líl’wat Nation, Pemberton Valley Dyking District and the Squamish-Lillooet Regional District to seek mitigation measures and develop collaborative emergency plans to address the risks identified in the Lillooet River Floodplain Mapping Study. As we undertake this process, we are committed to engaging the community through public education opportunities and updates.” – Mike Richman, Mayor, Village of Pemberton

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Media Contact: 

Administration Office
Pemberton Valley Dyking District
Email: trustees@pvdd.ca
Telephone: (604) 894-6632

Chief Dean Nelson
Líl’wat Nation
Email: dean.nelson@lilwat.ca
Telephone: (604) 894-6115

Patricia Westerholm
Communications Coordinator
Squamish-Lillooet Regional District
Email: pwesterholm@slrd.bc.ca
Telephone: (604) 894-6175 ext. 239

Jill Brooksbank
Senior Communications and Grants Coordinator
Village of Pemberton
Email: jbrooksbank@pemberton.ca
Telephone: (604) 894-6135 ext. 230

Inside the SLRD > News & Events > Updated Floodplain Mapping Report identifies changes to flood hazard in the Pemberton Valley