Millions in damages averted with new diking
If the province and the city hadn’t agreed to install a $160,000 dike, and if two property owners hadn’t agreed to permit access for its construction this spring, there could have been millions of dollars in property damage along Lakeshore Road south of Mission Creek earlier this year.
A combination of snowmelt and rain that swelled Mission Creek and lake levels above the normal operating range caused a backwater affect on the creek, which would have flooded both residential and commercial properties to the south of the creek four separate times, according to senior water engineer Don Dobson with Urban Systems.
With decades of experience monitoring the Okanagan’s watershed, Dobson said he’s never seen that combination of circumstances, and it could have been devastating without the timely construction of a permanent, higher dike along the south side of Mission Creek at Lakeshore Road in March.
Okanagan Lake was 11.2 centimetres above the normal full level on July 3, two days following one of the four peak runoff events on Mission Creek this spring on July 1, when the creek was measured flowing at 92.6 cubic metres per second, he reports.
It also peaked on June 9, at 93.3 cms, June 13, at 87.5 cms and June 24, at 93.03 cms and Dobson figures without the new, permanent flood protection works in that section of the creek, there would have been, “significant overbank flow, which would have flooded many residences south of Mission Creek.”
Dobson was retained by the City of Kelowna to come up with a dike design and oversee the construction of that floodproofing work.
John Vos, general manager, community services for the City of Kelowna, said historically, the city has frequently had to throw up a temporary dike there during runoff and the province pays for it, because the provincial government is responsible for diking along the creek.
However, when it came time to remove the temporary one put up last year, the city approached the province to look at construction of a permanent solution to the problem instead of just removing it, he said.
Ken Cunningham, resource manager for the forests, lands and natural resource operations ministry in Penticton, agreed it was needed, and he “got creative,” and found the funds, said Vos.
That allowed the city to construct a 170-metre long, 3.5 metre high dike, raising the dike more than a metre in height and using 3,750 metric tonnes of gravel and rocks.
The project was completed at the end of March.
“That took a huge burden off everyone. We’d have had to babysit that section of the creek all spring,” commented Vos.
As it was, there were spots on the creek upstream where the water was up to the top of the dike during this year’s runoff.
In his 20 years with the city, Vos said he’s never seen flows like this year.
There was some flooding of lakefront properties as well, particularly near the creek, he added.
“This year’s runoff was pretty spectacular,” he said.
“Monster trees slammed into the Lakeshore Road bridge over Mission Creek, giving it a pretty good shaking, and the water level rose to the steel beams under the roadway,” he noted.
Replacement of that bridge with a higher structure is the city’s top bridge replacement priority, he said.
Work also needs to be done on Priest Creek, upstream on Crown lands, to reduce erosion and keep tonnes of gravel from washing down it, he said.