Natural Hazards

Extended heavy rainfall during an ‘atmospheric river’ or a ‘pineapple express’ event can raise water levels and flood shoreline areas quickly and unexpectedly. Cowichan Lake and Shawnigan Lake have flood construction levels to ensure that housing surrounding the lakes are protected. But many houses, roads and infrastructure are already built within these areas.

• Do I live in a floodplain?
• Do I know the flood elevation below which things might get wet?
• Do I store valuables or contaminants like solvents in that zone? If so, are they raised off the floor?
• Is my septic field below the water line?

Rivers and streams often spill over their banks onto the surrounding floodplain. Low-lying areas adjacent to these streams flood regularly and are unsuitable for certain types of development. Increasing intensity of winter storms due to climate change may lead to higher flood levels in the future.

• Do I live along a river or water course?
• Do I have a way to get out in an emergency

In some developed areas across the Cowichan region, some form of organized drainage system is in place to manage stormwater flow due to increased density and impermeable (paved) surfaces. Drainage may be managed by a simple road side or more formal stormwater catch basins and pump station. Occasionally these systems may be overwhelmed or backed up due to the volume of rain or associated flooding.

• Do I live in such an area?
• Do I have a backflow protection system in place to protect my home?
• Have I done a quick check of the catchment basins around my house to make sure they are clear?
• Have I reviewed and upgraded my own drainage system around my home?

In 2004, the responsibility for flood mapping was turned over to local governments. The CVRD has completed updated flood mapping for the Lower Cowichan / Koksilah River, Chemainus River, Shawnigan Lake, and the Cowichan River – Riverbottom Road Area, which replaces the outdated provincial flood maps for these areas.

The current flood mapping within the CVRD is listed below for use in development applications.

• Lower Cowichan / Koksilah River Integrated Flood Management Plan
• Lower Cowichan / Koksilah River Flood Mapping Report (2021)
• Lower Cowichan / Koksilah River Floodplain Maps (2021)
• Lower Cowichan / Koksilah River Flood Mapping Report Appendices (2021)
• Memo: Use of Flood Construction Levels (2021)

• Shawnigan Flood Mapping Report
• Shawnigan Flood Maps (2020)

• Riverbottom Road Flood and Erosion Hazard Mapping Report
• Riverbottom Road Flood and Erosion Hazard Maps (2020)

• Provincial Flood Maps – Cowichan Lake (1984)

• Lower Chemainus Watershed Floodplain Management Plan (2023)
• Chemainus River Flood Mapping Report (2022)
• Chemainus River Geomorphic Atlas (2022)
• Chemainus River Floodplain Maps (2022)
• Chemainus River Flood Hazard Maps (2022)
• Chemainus River Geomorphic Hazard Map (2022)

Much of the region is forested land and subject to wildfires. Interface fires, where a wildfire threatens residential areas or infrastructure, pose a risk in rural and semi-rural areas and on the fringes of village and urban centres. FireSmart planning can protect your property from wildfire. Based on recent large wildfires elsewhere in British Columbia, all portions of the community are likely to be at risk or affected by smoke.

Ask Yourself:

• Have I made sure my property is FireSmart?
• Can I reduce my exposure?

• I want a free home assessment.
• Learn how to be prepared for a wildfire today.

Even a slight increase in wind speed can cause significant damage to many homes. Windstorms can damage and disrupt infrastructure, bringing down wires and blocking roads. Damage from high winds can happen anywhere in the region.

• Was I affected by a windstorm in the past?
• Have I looked at ways to improve safety in my home?
• Do I have supplies to carry me through if I lost power and/or phone service for an extended period?
• How do I or will I deal with damage and debris?
• Could I have done something before the storm to lessen the impacts?

• Be prepared for a power outage now.

Our mountainous terrain has many steep drainages which, when super-saturated, are prone to mudslides, landslides, debris collection and wash-outs. More intense storm events are projected with a changing climate, and could cross a critical threshold that will lead to more frequent events of this kind. Development activities on unstable slopes must be done with care to avoid increasing instability.

• Do I live along a ravine or natural drainage area?
• Are the culverts clear and able to pass water and other materials if necessary?
• Even if I don’t live below a steep slope, do I rely on power lines or roads that are in these susceptible areas?
• Could my property be putting a downslope neighbor at risk?
• Do I have an emergency kit or supplies in case I am cut off for a few days?

Landslide hazards exist in mountainous areas throughout the world. Wherever there are steep slopes, there is a risk of material falling or sliding down the slopes. Heavy rains can often cause instability as soils become overly saturated. As climate change increases the intensity and frequency of rainstorms in the Cowichan region, the CVRD has been studying what this means to the region’s existing natural hazards including (including flooding and landslides). The steep slopes above Cowichan Lake are prone to landslides, so the CVRD has been investigating these hazards.

There are many types of landslides, varying by the amount of water mixed with the sliding material. In the Youbou area, debris slides, debris flows, and debris floods are all potential hazards. Click here for more information on types of landslides.

It is the responsibility of local governments to identify hazards affecting or with potential to affect the community and to use that information to inform and guide land use decisions. Building inspectors must also ensure that all buildings under permit are safe for their intended use.

The CVRD has completed an initial study into landslide risk in the Youbou area. This study identified significant risks and led to follow-up studies.

Initial Study – based on existing air photos and provincial base mapping accurate at 1:15,000 scale

Ebbwater / Palmer (2019) analyzed historical air photos and provincial geological and topographical mapping to establish the landslide hazard on the slopes above Cowichan Lake from Cottonwood Creek to Hill 60. The landscape was divided into large polygons, each with hazard score based on the likelihood of a landslide impacting that polygon. This mapping is accurate at the 1:15,000 scale, but the hazard varies within each polygon; generally the hazard is greater closer to the base of the slope and within gullies. The mapping serves as a flag that further investigation at the site level may be required to determine the actual risk to an individual property. In cases where properties were found to be within the high hazard areas, notification letters were sent to the property owners. A public meeting was held in May, 2019 to share the results of the risk assessment with the community.

Follow-up: Debris Flow Modelling – based on new specially flown high-resolution data accurate at 1:5,000 scale

Palmer / Stantec (2020) conducted refined debris flow runout modelling for much of the same study area as the 2019 study. This project involved the acquisition of high-resolution LiDAR for the study area. Stantec then modelled over 68,000 hypothetical landslides and established a line beyond which no landslides travelled. This mapping is accurate at 1:5,000 scale and identifies areas where the hazard from a debris flow is very low. Previously-notified property owners will receive an update about the new mapping, and the results are being shared with the community.

Follow-up: Rock Slope Deformations – LiDAR and field investigations by CVRD & Mosaic

The initial study identified several rock slope deformation features on the slopes above Cowichan Lake. Both the CVRD and Mosaic Forests (the landowner) conducted additional investigations into these features and found that they were stable and presented an extremely low risk.

Learn more about how to be prepared for a landslide in British Columbia.