A detailed draft plan for improved flood management within the Somass River watershed is available for public comment until March 24.
Developed over the last two years by a core team of about a dozen people through field surveys, flood level monitoring and hydraulic modelling, the plan provides a more complete picture of the watershed above and below the water line.
Consultants and ACRD staff shared the latest flood mapping results in a presentation Tuesday, March 10 at the Tseshaht First Nation administration building. A large flood-depth map was pieced together on the floor, indicating areas at greatest risk of flooding.
ACRD planning manager Mike Irg said previous mapping provided an incomplete picture of the area, which extends from Somass estuary to the shorelines of Sproat and Great Central lakes. New development since then, along with improved methods for predicting flood hazards, provide an up-to-date look at how the watershed functions. The plan also shows how it would react to extreme storm events, sea level rise and climate change to the year 2100.
“We’ve had events,” Irg said. “Some of the recent events have spurred us to look at what 200-year flood levels would look like.”
The Tseshaht community experiences flooding during heavy rain and high tides. There has been periodic flooding of other areas within the city as well. Rain events in 2016 and 2017 caused extensive flooding damage to properties along Sproat Lake. An extreme rain event in 2003 nearly overtopped the dam at Robertson Creek.
“It’s really starting a conversation about mitigation and where we go from here,” said Jana Zelenski of LANARC Consultants. “The more people we get studying and talking about it, the more it’s going to help us going forward.”
Hydrologist Faye Hirshfield of Northwest Hydraulic Consultants, the company that undertook the surveying and monitoring, said the plan represents riverine, coastal and lake flooding hazards but does not include tsunami flood hazards.
The climate change modelling was done with guidance from the provincial government, which uses global climate models, Hirshfield said.
“The Somass watershed will get a lot more rain by 2100, around 20 percent more,” she said. “If the rain increases 20 percent, the flow will increase 20 percent.”
The plan will serve as a tool for development and potential flood mitigation measures. The latter could include everything from alternative methods of construction, flood-proofing homes in certain areas, raising parts of Highway 4 or modifying the Sproat Lake outlet to cite a few examples.
“Engagement is really a key part of this,” Zelenski said, noting that community values may affect local decisions on flood prevention and mitigation.
After the public feedback period ends, the ACRD will share a summary of input along with finalized flood mapping and reporting. Documents supporting the plan can be viewed online at acrd.bc.ca/somass-flood. Maps can be viewed at the ACRD office by appointment. Questions and comments can be submitted via email at email@example.com or by phone at 250-720-2700.