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Somass Watershed Flood Management Plan

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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?
We have draft flood mapping to share!

Through 2019, the project team has been capturing data, modelling the Somass Watershed, and preparing draft flood mapping.

Flood mapping is an important step in watershed management planning. It provides a baseline of anticipated flood risks if no actions are taken. This information will help communities in the watershed take a collaborative and informed approach to identifying and evaluating mitigation and adaptation options to reduce future risks.

Thank you to all those who attended the Somass Watershed Management Plan Public Event Tuesday, March 10. We greatly value your input into the process.

It's not too late to review draft flood mapping and information and provide you comments for the project. We're building our collective knowledge about the Somass Watershed and your input will provide valuable insights for next steps in mitigation and adaptation planning.

ONLINE FEEDBACK FORM - March 10 to March 24, 2020
Please take a few minutes to review the displays for the project, then complete an online feedback form to record your comments.

Click here to view the public event displays

Click here to view the public event presentation slides

Click here to launch the online questionnaire

Provide your comments by Tuesday, March 24, 2020.

The draft flood maps may be viewed at the ACRD Office

How was the flood mapping developed?

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.
  • Using the model to develop maps that show predicted flood impact areas.
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 model is being used to develop draft floodplain maps that show predicted flood impact areas. This is an important first step in watershed management planning that provides a baseline of anticipated flood risks if no actions are taken. This information will help communities in the watershed take a collaborative and science-based approach in evaluating options to reduce future risks.

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.

February 26, 2020 - Media Release

January 14, 2019 - Project Start Letter

February 7, 2019 - Media Release

ABOUT THE STUDY
This 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:
how

TIMELINE
The 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.

Timeline March2020

QUESTIONS?
Please contact:
Alberni-Clayoquot Regional District
Planning and Development
250-720-2700
planning@acrd.bc.ca