It turns out that a wayward boot is behind the series of construction mishaps that caused the Stoney Creek culvert failure last month.
During the rehabilitation of a culvert on a Stoney Creek tributary, an A.C. Paving employee who was maintaining a filter screen on a pump at the construction site got his boot sucked into the inlet hose of the pump.
The boot incident led to a cascading set of events that eventually forced a large amount of sediment into the creek and put the fish habitat in the waterway at risk.
The details of the mishap are part of a staff report presented to Burnaby city council that provides a post mortem of the entire project.
The city report explained in absence of the bypass after the boot got stuck, the upstream drainage flows overtopped the cofferdam and water flowed through the construction area sending debris to the No. 2 bypass pump discharge hoses at the Ash Grove inlet. This caused the bypass pumps and storm sewer plug at the No. 2 bypass pump to be compromised. The report noted at this point, the construction area was taking on full drainage flows and caused the newly placed slope to fail with a rush of water which transported the sediment from the site downstream.
It was several hours after when construction crews re-established control of the upstream flows and the slope erosion.
The city had undertaken the project in the first place after crews and Stoney Creek streamkeeper members noticed the beginning of some creek bank erosion near the outlet of the Stoney Creek Tributary 3A culvert under Gaglardi Way in the fall of 2014.
By spring 2015, the city said monitoring showed increase erosion to the bank. The decision was made to complete the rehabilitation before the winter.
In August, A.C. Paving was awarded the contract for the project, with work starting in September.
City staff had originally suggested heavy rains prior to the original incident on Oct. 30 were the cause of the failure and subsequent sediment damage. Several stream keepers have been critical of the city’s timing for the project, suggesting the work should have begun in the summer before the fall storm season.
The staff reportacknowledged the proposed work was being initiated toward the end of the fisheries window but noted it was deemed important enough to complete the work.
City staff have also suggested the creek is still passable and can support spawning activity.
As for remediation, earlier this month crews removed sediment at a couple locations to minimize further downstream impacts. The report noted city engineers will follow up with AC Paving on potential mid to long-term mitigation.
