Dam Fine Work, New $46 M spillway should keep EID members safe from future floods

By Tim Kalinowski

After three years of work, and $45.5 million spent, the Bassano Dam spillway project will finally have its grand opening on Oct. 25.

Earl Wilson, manager of special projects with the Eastern Irrigation District, oversaw the new spillway’s construction, and says he can rest easy and get set for retirement now that it has been completed.

It’s a much better emotion he is feeling in 2019, Wilson admits, than what he felt in 2013 when the flood of that year threatened disaster for the entire region.

“My blood pressure was pretty high during that flood, I can tell ya,” Wilson says. “The flood in 2013 exposed the fact our existing spillway was at its limit, and we did a dam safety review and decided we needed to add an additional spillway.

“The spillway capacity was originally designed to take about 2,800 cubic metres per second at its normal level on the upstream side,” he explains. “Then there is a fuse plug on the west end of the earth dam. If it gets above the normal operating level, at approximately 1.6 or 1.7 metres above that would wash out the fuse plug.”

“At that point, the capacity is at about 4,500-5,000 cubic metres per second,” Wilson explains.

“The flood in 2013 was 4,200 cubic metres per second. So we were within about 10 per cent of the water having to wash out the fuse plug. If it washes out the fuse plug then in the channel would divert to that location and potentially re-route the river; so it would be a very costly repair.”

And the consequences for the entire region if that ever happened wouldn’t just be limited to the immediate repair cost either, he says.

“All the water within the Eastern Irrigation District, including the City of Brooks, the Lakeside packing plant and numerous other industries comes from the Bassano Dam,” Wilson states.

“It would have been a huge economic loss if something like that happened, and it takes you a year or more to fix. I can’t even put a number to it. I have no idea what it would cost if you lost all the water in this region for a year or two. The bankruptcies to farms, and all the industries, would just be unthinkable.”

It was under this dire threat that the provincial government stepped forward and gave a grant of $30 million toward completion of the second spillway in 2014, and the reason why the EID was more-than-willing to chip in the rest to see the work completed; even though the 2013 flood was the first such event in the dam’s 100-year history, says Wilson.

“If we have another event at 2013 levels or higher, it will pay off in spades,” he states. “Now, at the normal operating level with the two spillways functioning, we can handle 4,500 cubic metres per second without being above the level at all. Altogether the system is now designed to take over 7,500 cubic metres of flood capacity before that fuse plug is triggered.

“So we’re in a very safe situation now in a flood event,” he adds. “We can pass a major flood without damaging anything within the Eastern Irrigation District.”

The construction of the project itself was very interesting, admits Wilson, and involved complex planning to carry out successfully.

On the political side, Wilson was grateful for the support of local governments, particularly the Siksika Nation whose land the new spillway must cross. The Siksika quickly and willingly signed a new easement agreement with the EID, he says, even though the dam would not help their community in the event of a major flood the scale of 2013 or higher, being located so far upstream from the dam.

The Nation did provide workers for the project though, he says, through construction firm Niitsitapi Graham LP; and that did benefit the local community in a measurable way.

On the construction side of things, the new spillway involved constructing a temporary coffer dam and other earthworks to allow the work to be completed. The new spillway is located beside the original spillway built between 1910-1914.

Wilson says working on the modern project gave him a strong appreciation for the original builders.

“The original concrete spillway is still there and still operating, “he states. “We built this new one beside it. But part of the original construction included a railway bridge across the river.

“When we were excavating out at the final part of the structure before we put the new one in and the coffer dam, we did hit remains of the pilings of that trestle bridge way down underneath, and that lumber still was in reasonably good shape— it had been buried there for 100 years.”

Wilson hopes 100 years from now future builders will look back on his crews’ efforts at the Bassano Dam, and have similar grounds to appreciate how well everything was done.

“The first one was built 100 years ago, and this new one should last at least that long also,” he says. “It makes me feel really good to see this completed.

“Prior to this project, I was the manager of the Irrigation District and re-built a lot of the infrastructure within the district over the last 35 years.

“But this was the biggest, and most critical, piece of infrastructure to have operating perfectly. It is kind of nice to know we are in very good shape going forward.”