You've likely noticed how the Fraser River is particularly high and muddy these days.
Freshet is here.
The springtime phenomenon that sees the Fraser swell from melted snow and ice well up-river has been in full swing for the last few weeks and will continue to the end of June or so. With one quarter of all the streams, creeks and rivers in B.C. draining into the Fraser, the water level and velocity of the Fraser increases dramatically during this time.
In a previous article, I discussed how the powerful current carries with it millions of tonnes of sediment in a tumultuous journey from headwaters through the upper and middle Fraser regions and then through the Fraser Canyon. Until that point, the river's course is defined and restricted.
But emerging from the canyon, the river is no longer constrained by the mountains and spreads out and slows down. As it does, it drops the sediment it has been carrying.
Over thousands of years, this sediment has built up to form the estuary and landscape we are now familiar with, creating a vast flood plain.
To keep above water in this region, society has chosen to create a sophisticated infrastructure to guide and restrict the river.
Human settlement and agriculture in the Lower Fraser Region is possible thanks to approximately 600 km of diking that keeps the river within its banks.
But with the construction of dikes, the sediment once deposited on the adjacent wetlands of the river is entrained and must be dealt with as it settles in new locations within the dikes. Left unattended, this accumulation would quickly build up in key shipping channels to the point where they would become much too shallow to allow for commercial vessels to safely access port terminals along the river.
Also, these deposits could well drive the river to find new channels that would damage habitat and infrastructure along and behind the dikes.
Year-round navigation on the river relies on a complex and extensive infrastructure of training walls and dredged channels, most of it inconspicuous, hidden or submerged. Training walls are carefully designed and placed to keep the Fraser River moving fast enough during freshet to keep the sedimentation in the New Westminster harbour to a minimum.
Next time you take a walk along the Quay boardwalk, take note. One can see a number of training walls from the New Westminster riverfront. This infrastructure plays a crucial role in the proper functioning of the working river.
An hydraulic modelling program conducted at UBC between 1948 and 1963 did much to determine the power and benefits of training the river and helped shape an early vision of a fully trained lower Fraser River requiring minimum dredging. But at the time, the $40 million or so required to implement a full program was considered too costly.
Today, the cost of dredging the main shipping channel alone is approximately $20 million annually.
Freshet will continue to bring silt in vast quantity year after year. That will never change.
How we deal with it? That is for us to decide.
Catherine Ouellet-Martin is executive director of the Fraser River Discovery Centre.
