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.