Chemainus River Sediment Study

Water Street and Westrek Geotechnical Services Ltd. were retained by the Ministry of Forests and Halalt First Nation to conduct a study of the sediment mechanisms within the Chemainus River, located on Vancouver Island. The Chemainus watershed has become increasingly prone to drought, flooding, significant erosion, and fluvial changes within the river network.

The purpose of this study was to identify sediment sources, improve understanding of sediment movement throughout the watershed, and provide recommendations to mitigate sedimentation issues and improve future watershed management.

The first phase of the study included a desktop review of previous studies, historical aerial photos, LiDAR, geology, watershed data, historical wildfire records, and historical logging information. A total of 658 sources of sediment were identified within the watershed, predominantly being caused by anthropogenic activities in the watershed and climate change. The sediment sources were categorized based on apparent cause.

During the second phase of the study, a helicopter field review was completed to verify the desktop analysis and assess key sediment sources and mitigation opportunities. Priority sites were identified based on erosion severity, proximity to the stream network, and access. Recommendations included in-stream sediment capture, rehabilitation of drainage diversions, and coordination with ongoing riverscape restoration efforts to reduce sediment loading in the lower Chemainus River.