Somass Watershed Flood Management Plan
Rivers, lakes, and the inlet form the landscape of our region. We are studying flood management for the Somass River System so we can plan effectively for its future.
WHAT'S NEW?Through 2019, the project team has been capturing data and developing a hydaulic model of the rivers, lakes, and coastal areas within the Somass Watershed. Key steps have included:
- Surveying the rivers, surrounding land areas, and structures that affect how the rivers flow.
- An assessment to chart how the river channels have changed over time and how that affects flows today and potentially in the future.
- A hydrology assessment to confirm what happens to the rivers under different conditions, including extreme weather.
- A coastal assessment to consider how local winds, tide water levels in Alberni Inlet, and lake levels may affect flooding now and in the future with consideration of climate change effects on precipitation and sea levels.
- Creation of a hydraulic model of the study area that predicts how flooding could occur in a defined weather event. The model was tested and validated to confirm it is able to reflect actual flood conditions.
The draft floodplain mapping is now being reviewed, and these maps will be introduced to members of the community at a public event coming this March. Watch here for an announcement with details about the event!
Since November, the Study team has been capturing data about the Somass Watershed:
- Water sensors installed at five locations in the Study area have been capturing water level measurements, including during the high water event that occurred in mid-December. This information will help track how water levels change through different times and conditions.
- A survey team has been out on the rivers completing a bathymetric river survey to chart the form of the river bed. This data is being compared to surveys from 1997 to understand how the rivers have changed in the past 20+ years.
- Hydrology analysis has been started to estimate 200-year flood levels and assess the effects of climate change on the system.
- Geomorphic assessment is underway to chart how the river channels have changed over time as sediment accumulates in different areas.
The collected data is being prepared for use in creating a Hydraulic Model of the rivers, lakes, and coastal areas within the Study area. Hydraulic modelling will begin this spring. As the Study continues we will provide updates on this webpage - please check back regularly.
ABOUT THE STUDYThis project will prepare up-to-date flood mapping for the Somass watershed - including portions of shoreline along Great Central and Sproat Lakes; the Ash, Sproat, Stamp and Somass Rivers; the Somass River estuary; and, the tip of the Alberni Inlet.
This mapping will provide important information about how the river system works today and how it could be affected by changing climate, extreme storm events, and sea level rise. This will provide more certainty around potential flooding events and impacts.
Why is updated flood mapping important?Flood mapping for this area was last completed in the mid-1990s. Since that time, there have been many changes including new development, changes in the landscape, changes in climate, as well as improved methods and accuracy for predicting potential flood hazard. Recent flood events have impacted both private properties and public resources - including a partial closure of Highway 4 in 2017. Public input has indicated a strong interest in better understanding potential flood impacts and mitigation options.
How Flood Mapping Helps Communities:
TIMELINEThe Study was initiated in November 2018 and is anticipated to continue to early 2020. During 2019, the focus will be on gathering technical data and developing a hydraulic model for the watershed. Once data analysis and updated floodplain mapping is complete, community members will be invited to review the results and initiate discussions on potential mitigation options.
Alberni-Clayoquot Regional District
Planning and Development