Lower Chemainus Watershed Flood Management Plan
We wanted to extend our appreciation to everyone who came together to share knowledge about the Chemainus River floodplain. It was educational to hear stories, questions, and recommendations from community members, many of whom experienced flooding in recent winters. If you were unable to attend or have more to share, online input can be provided through the mapping activity and comment form until August 2. Thank you for helping create the Lower Watershed River Flood Management Plan.
We are preparing a flood management plan for the Lower Chemainus watershed.
The Lower Chemainus River is a floodplain, which means it is prone to periodic flooding. Flooding can impact properties, infrastructure, businesses, and the environment. While floodplains are more susceptible to flooding, we are seeing even greater impacts in recent years. To prepare for the future, the Cowichan Valley Regional District, in partnership with Municipality of North Cowichan, Halalt First Nation, and Penelakut Tribe, has developed updated floodplain mapping for the Lower Chemainus Watershed. Mapping will help the communities better understand watershed processes and identify potential options to help manage future flooding. Through summer 2022, we are engaging with local First Nations, government agencies, stakeholders, interest groups, and the community to share what we've learned so far, and hear ideas and values that could inform future flood management planning.
Quick Links
View a Context Map | Read a Backgrounder Brief | Attend a Community Info Session | Map Your Knowledge | Complete a Comment Form | View Floodplain Maps | Read Technical Reports |
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We wanted to extend our appreciation to everyone who came together to share knowledge about the Chemainus River floodplain. It was educational to hear stories, questions, and recommendations from community members, many of whom experienced flooding in recent winters. If you were unable to attend or have more to share, online input can be provided through the mapping activity and comment form until August 2. Thank you for helping create the Lower Watershed River Flood Management Plan.
We are preparing a flood management plan for the Lower Chemainus watershed.
The Lower Chemainus River is a floodplain, which means it is prone to periodic flooding. Flooding can impact properties, infrastructure, businesses, and the environment. While floodplains are more susceptible to flooding, we are seeing even greater impacts in recent years. To prepare for the future, the Cowichan Valley Regional District, in partnership with Municipality of North Cowichan, Halalt First Nation, and Penelakut Tribe, has developed updated floodplain mapping for the Lower Chemainus Watershed. Mapping will help the communities better understand watershed processes and identify potential options to help manage future flooding. Through summer 2022, we are engaging with local First Nations, government agencies, stakeholders, interest groups, and the community to share what we've learned so far, and hear ideas and values that could inform future flood management planning.
Quick Links
View a Context Map | Read a Backgrounder Brief | Attend a Community Info Session | Map Your Knowledge | Complete a Comment Form | View Floodplain Maps | Read Technical Reports |
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Engagement Opportunities
Share on Facebook Share on Twitter Share on Linkedin Email this linkCommunity Information Sessions were held at the Halalt Gymnasium on Monday, July 18 and the Crofton Community Centre on Wednesday, July 20. Thank you to all who attended and shared valuable information about your experiences and recommendations for flood management.
If you could not make it to the sessions, you can still learn about the process and provide your comments.
- We recommend first reviewing a short Project Backgrounder.
- You can also view posters from the Community Information Sessions.
- If you'd like to dig deeper, review the Technical Reports and Floodplain Maps.
You can provide your comments in two ways:
- Use the Interactive Map to share your knowledge of and ideas about flooding in the Lower Chemainus Watershed.
- Share your comments and questions using the Online Comment Form.
Please share your feedback by August 2, 2022.
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About the Study Area
Share on Facebook Share on Twitter Share on Linkedin Email this linkThe study area (shown in the yellow dashed line below) is the Lower Chemainus River floodplain. The floodplain’s headwaters originate in the CVRD, and the lower floodplain includes portions of the Municipality of North Cowichan, Halalt First Nation, Tsussie (Penelakut Tribe), and Say-la-quas and Squaw-hay-one (Stz'uminus First Nation). The study area begins about 1 km upstream of the Highway 1 Chemainus River bridge and extends to the Chemainus Estuary. It includes Bonsall Creek and Whitehouse Creek where they are next to the Chemainus River.
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Floodplain Maps
Share on Facebook Share on Twitter Share on Linkedin Email this linkThe outcome of Part 1 of the Flood Management Plan process is updated floodplain mapping. The maps demonstrate flood conditions under a major flood event on the Chemainus River combined with a significant coastal flooding event. Two types of maps have been created:
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Flood Depth & Velocity Hazard Maps (1 large map or 5 maps)
These maps show a combination of flood depth (how deep waters get in different areas) and flood velocity (how fast the water is moving) during a major flood event. This information helps illustrate the impacts of the flood event, which can support community understanding and emergency preparedness.- Flood Hazard Map - Entire Floodplain (85MB) - this map shows the entire floodplain but can be slow to download due to size. If it is too large, the maps below divide the floodplain into four areas and are smaller to download.
- Flood Hazard Map - Index Sheet
- Flood Hazard Map - Sheet 1
- Flood Hazard Map - Sheet 2
- Flood Hazard Map - Sheet 3
- Flood Hazard Map - Sheet 4
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Designated Floodplain Maps (5 maps)
These maps show the full extents of the floodplain along with Flood Construction Levels (FCLs). FCLs indicate the minimum elevation that new inhabited buildings should be built at within the floodplain (how high they need to be). This information is used in regulatory planning for land use and new development.
How to use the maps:
- Both types of maps provide important information about the floodplain. The Flood Hazard Maps are often of more interest to community members.
- Start with the Index Sheet of the maps you'd like to view for an overview of the floodplain and to read the notes that explain the maps.
- Based on the Index Sheet, select the map for the area you are most interested in viewing (Sheets 1 - 4) and open that map.
- Use the legend to interpret the flood event outputs in your area of interest. You can zoom in and pan around the map.
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Flood Depth & Velocity Hazard Maps (1 large map or 5 maps)
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Technical Reports
Share on Facebook Share on Twitter Share on Linkedin Email this linkThe technical report and its appendices summarize the analyses and input used to create the floodplain maps. Watershed modelling is a technical exercise, and therefore these reports are technical in nature. Reports marked with an asterisk (*) may be of most interest to community members.
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Chemainus River Flood Mapping Program, Part 1 - Floodplain Mapping Report* (22 pages)
An overview of the study, process used to create floodplain mapping, and recommended next steps. -
Appendix A: Surveys and Water Level Measurements (11 pages)
Describes the survey data used to create the floodplain model. -
Appendix B: Hydrology (15 pages)
Describes how water flows through the watershed and the scenarios used to develop flood mapping for the study area. -
Appendix C: Chemainus River Geomorphic Atlas* (43 pages)
While we often think of rivers as unchanging, historical records show us that watercourses shift over time due to processes like flooding, sedimentation, blockages, and erosion. The geomorphic atlas summarizes landforms that affect how water flows through the Chemainus River floodplain. It includes hazard mapping that identifies where there is risk of physical changes to the river channel, providing important information for land use planning and hazard management. -
Appendix D: Hydraulic Modelling (29 pages)
Describes how a hydraulic model that simulates flood events was created and the results of the modelling process. The hydraulic model can be used to predict potential future flooding impacts in the area. -
Appendix E: Coastal Modelling (32 pages)
Because the Lower Chemainus River watershed meets the ocean at the Chemainus Estuary, the study includes coastal flood considerations as part of floodplain mapping. This report describes the process for integration of coastal considerations. -
Appendix F: Flood Mapping Methodology (10 pages)
Describes the two mapping outputs created for the Lower Chemainus River.
The outcome of the technical work described above is updated flood mapping for the Lower Chemainus Watershed. Click here to view the maps.
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Chemainus River Flood Mapping Program, Part 1 - Floodplain Mapping Report* (22 pages)
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Videos
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Click here to play video Chemainus Floodplain - Flood Event Animation The following animation captures a 200-year flood event for the Lower Chemainus River floodplain. Depths shown in the animation range on a scale from 0 to 2m. It illustrates potential water inundation areas during a major flood event. Please read the Chemainus Floodplain Mapping 2022 Report prepared by NHC (2022) for Cowichan Valley Regional District (CVRD) for more details on the hydraulic modelling. All model limitations are described within the report. DISCLAIMER These videos have been prepared by Northwest Hydraulic Consultants Ltd. for the benefit of Cowichan Valley Regional District for specific application to the Chemainus River Flood Mapping. The information and data contained herein represent Northwest Hydraulic Consultants Ltd. best professional judgment in light of the knowledge and information available to Northwest Hydraulic Consultants Ltd. at the time of preparation, and was prepared in accordance with generally accepted engineering practices. Except as required by law, the videos and figures and the information and data contained herein are to be relied upon only by Cowichan Valley Regional District, its officers and employees. Northwest Hydraulic Consultants Ltd. denies any liability whatsoever to other parties who may obtain access to this information for any injury, loss or damage suffered by such parties arising from their use of, or reliance upon, these videos or any of its contents.
Documents
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Overview Documents
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Floodplain Maps
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Flood Depth & Velocity Hazard Map - Entire Floodplain (85 MB) (85.4 MB) (pdf)
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Flood Hazard Map - Index (2.16 MB) (jpg)
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Flood Hazard Map - Sheet 1 (2.79 MB) (jpg)
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Flood Hazard Map - Sheet 2 (4.82 MB) (jpg)
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Flood Hazard Map - Sheet 3 (3.61 MB) (jpg)
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Flood Hazard Map - Sheet 4 (4.81 MB) (jpg)
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Designated Floodplain Map - Index Sheet (2.21 MB) (jpg)
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Designated Floodplain Map - Sheet 1 (2.55 MB) (jpg)
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Designated Floodplain Map - Sheet 2 (4.48 MB) (jpg)
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Designated Floodplain Map - Sheet 3 (3.01 MB) (jpg)
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Designated Floodplain Map - Sheet 4 (4.81 MB) (jpg)
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Lower Chemainus River Watershed - Flood Hazard Maps (complied PDF - large file) (24.6 MB) (pdf)
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Lower Chemainus River Watershed - Designated Floodplain Maps (complied PDF - large file) (23 MB) (pdf)
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Technical Report Documents
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Chemainus River Flood Mapping Program Part 1 - Floodplain Mapping Report (3.12 MB) (pdf)
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Appendix A: Surveys and Water Level Measurements (764 KB) (pdf)
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Appendix B: Hydrology (1.04 MB) (pdf)
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Appendix C: Chemainus River Geomorphic Atlas (16.2 MB) (pdf)
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Appendix D: Hydraulic Modelling (2.84 MB) (pdf)
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Appendix E: Coastal Modelling (2.74 MB) (pdf)
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Appendix F: Flood Mapping Methodology (765 KB) (pdf)
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Key Dates
Who's Listening
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Manager, Environmental Services Division
Email Kate.Miller@cvrd.bc.ca -
Email Jeff.Moore@cvrd.bc.ca -
Partner
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Partner
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Partner