This week the Transportation ministry hopes to complete work that it hopes will prevent Highway 37 South being cut by the Kitimat River.
Skeena district manager Don Ramsay said the impending problem immediately north of Nalbeelah Creek was spotted in 2005-2006.
“There was a section of the river that appeared to be moving towards the highway,” he recalled.
At the time the ministry brought in a hydrologist who dug out some old aerial photos of that section of the river.
They showed that in the mid-1960s the river was more than 300 metres (1,000ft) from the highway.
Over the next two decades that gap closed to 200m and the river continued to close in on the highway through the 1990s.
Ramsay said that in 2005-2006 federal Fisheries didn’t want them putting rip rap along the bank to hold back the river’s progress, but were agreeable to a trench being dug between the river and highway and filled with rip-rap.
That work was done at a cost of about $75,000.
The department kept checking on that stretch and in May of this year the gap was down to 30m and by July 27.5m.
Then came the torrential rains of September.
Ramsay said when they did the regular check in mid-September they discovered there was less than a metre gap between the river and the highway.
“Conditions were such that the highway would have been lost in days without an immediate response,” he pointed out. “There was quite an urgency to get out there and address it with a large amount of rock.”
As to why the gap had reduced by only two-and-a-metres between May and July was all but wiped out in the following two months, Ramsay said that with the high flows in September the river had changed channels and therefore was hitting the highway bank much more directly than before.
To underscore that point, he noted flows measured by the Hirsch Creek gauge used by the department were the fourth highest ever seen.
“It had never recorded any kind of a high level in September, it’s usually been in October, November, he added.
The high flows also explained why the rock-filled trench didn’t work.
The theory was that when the river washed away the bank all the way to the trench, the rock in that trench would drop into place and protect the remainder.
Unfortunately, the flows were so strong they swept some of the rip-rap away allowing the river to cut almost to the highway.
Again a hydrologist was brought in and he recommended extending the rock work both upstream and downstream of the river’s point of attack, “keying in” the large rocks.
Ramsay explained that meant that instead of just dumping them in, the large rocks had to be placed in such a way that they locked into each other, rather like a jigsaw puzzle.
“It was a bit of a tricky job for an excavator operator.”
The hydrologist also recommended, with Fisheries agreement, that the rocks be installed “in a kind of a scalloped pattern so as not to create a straight line bank.”
Part of the work included excavation a trench just to the north of the main erosion point and filling it with large rock.
While that trench has been dug, the “armouring” hadn’t been completed as of last week because the department had run out of large rock at the quarry it used.
And before it could blast new rock, it had to go through Energy and Mines ministry permitting and consultation with the Kitselas First Nation.
All that had been done when the Northern Sentinel interviewed Ramsay last Thursday and he therefore expected work to be completed this week
By the time it is completed, he estimated the cost at $300,000.
However, Ramsay pointed out, that’s a lot cheaper than having to replace a section of highway, and a lot less inconvenient for travellers – when the first emergency work was done the highway was still open, albeit to single lane traffic.
As for Nalbeelah Creek bridge, he emphasized that was quite safe.
They had rip-rapped an area close to the bridge abutments as a precaution, but he pointed out that with the channel switch, the main force of the river was now bouncing off the bank further up from the creek “and is not putting any particularly stressful forces in the direction of the bridge.”
That said, the department would continue to monitor the area very closely.