CREWS from the District of North Vancouver will start to lay the groundwork this month for a debris net that aims to protect homes from potentially deadly slides in Mosquito Creek.
The work, which involves cutting trees and scraping away loose soil and rock from the canyon about 200 metres above the Baden Powell Trail footbridge crossing, will allow the installation of the large metal net in the creek later this summer.
The $240,000 structure will function as a giant sieve, trapping logs, roots and branches if they are ever washed down the creek as part of a "debris flow" - essentially a liquid landslide.
Once the net is in place, it will cost $10,000 a year to maintain.
That money will pay for the process of unbolting one side from the canyon wall to clean it out - possibly with the assistance of helicopters.
For residents of Del Rio Drive, however, the debris net could be priceless.
"It'll be worth it if it saves someone's house from being hit by a debris flow," said Michelle Weston, public safety manager for the District of North Vancouver.
A study of risks from debris flow finished three years ago showed without it, several homes on Del Rio Drive and Fairmont Road exceed what's been deemed an "acceptable risk," defined as a one-in-10,000 chance of somebody dying in the event a liquid landslide comes thundering down the creek.
Models created by engineers showed if the worst occurred, landslide debris in the upper watershed would be washed down to the main creek channel, forming a dam behind which a small lake would form.
Eventually, that dam would burst, releasing a wall of water and debris that would surge down the hill.
The debris net is meant to reduce the risk of that happening, although it won't eliminate the risk entirely. "They're still living in a spot that has a hazard," said Weston.
Before the net can be installed, immediately upstream from an old wooden dam, crews will have to take down six trees on the steep bank above the stream - to eliminate the possibility of their falling into the net - and will drill into the canyon walls to install rock anchors.
The net will later be connected to the anchors with cables.
Work on the net's installation is expected to wrap up before next winter's rainy season starts.
Mosquito Creek isn't the only watercourse in the district to present possible hazards.
A risk analysis study commissioned by the municipality five years ago found that 22 buildings in the district had a greater than one-in-10,000 risk of fatality from debris flow landslides.
Those buildings included part of a children's summer camp up Indian Arm as well as residential homes, cabins and cottages located on eight creek fans.
Besides Mosquito Creek, Mackay Creek presents one of the biggest hazards.
In 1995, a debris flow from Mackay Creek spilt approximately 7,000 cubic metres of boulders, organic matter and soil onto the Ranger Avenue area, damaging homes and property.
Three years later, a debris flow barrier was constructed in the creek to reduce risks to homes in the Grousewoods area.
This year, Metro Vancouver - whose jurisdiction the headwaters of Mackay Creek falls into - has earmarked $1 million for further hazard modeling and mitigation planning.
Earlier reports put the cost of mitigation measures on Mackay Creek at more than $7 million.
The province has provided $2 million towards that.
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