Flooding

Lake Flooding

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. 

Ask Yourself:

  • 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?
lake flooding
river flooding

River Flooding

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. 

Ask Yourself:

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

Stormwater and Urban Flooding

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. 

Ask Yourself:

  • 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?
stormwater

Flood Mapping

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/ Koksilah River, Chemainus River, Shawnigan Lake, and the Cowichan River - Riverbottom Road Area, which replaces the outdated provincial flood maps for these areas.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

Shawnigan Lake

Cowichan River - Riverbottom Road Area

Cowichan Lake

Chemainus River