As noted in the Impact Assessment, the proposed works on the BBA property will result in a westward (offshore) realignment of the shoreline in the order of 50 to 60 metres. The design drawings that we were provided illustrate that the new river bank/shoreline would abruptly revert back to its original alignment near the south limit of the BBA property, in very close proximity to the proposed drain outlet. We noted that a substantial eddy or recirculation zone would be created downstream of the Kennette property as a result of the proposed infilling. We predicted that the downstream extent of this eddy flow or recirculation zone would extend significantly south of the Broadway Drain right-of-way.

A particularly significant effect of the eddy flow would be the collection of sediment, flotsam and jetsam within the predicted eddy flow area.

The following diagram (reproduced from the Impact Assessment) illustrates the general extent of the BBA infill and the originally proposed training jetties at the outlet of the Broadway Drain. We estimated that at a minimum, the boundary of the eddy flow zone would extend from the offshore limit of the Kennette infill to the downstream shoreline at a 12 to 20 degree angle. The zone delineated by a 12 degree flow expansion angle is considered a more probable, albeit larger eddy zone. For the purpose of the assessment, and our design, we have adopted the smaller eddy zone that is associated with a 20 degree flow expansion angle.

We forecasted that if the BBA infill proceeds as originally proposed, that extensive amounts of sediment (granular and organic) may accumulate over time, within the eddy flow zone, causing the river bottom to aggrade. The resulting aggradation would change the river bottom sediment characteristics, as well as the nearshore bathymetry.

To be sustainable, the design of the Broadway Drain outlet would need to take this into consideration.

In order to mitigate the added potential for aggradation due to the effects of eddy flow, the outlet jetties would need to be substantially extended, so that the drain outlets closer to the predicted boundary of the eddy flow zone.

Design Summary for Broadway Drain Outlet – January 12, 2016

Gordie Howe International Bridge