• The potential for the accumulation of ice at the mouth of the Broadway Drain would be substantially reduced, as compared to the original infill design;
• The area of the Detroit River bottom that would be impacted by the combination of the outlet jetty construction and the infill on the BBA lands would be approximately 1,200 sq.m less than Alternative A, and approximately 175 sq.m less than the original design (when accounting for footprint of the training jetties and the original BBA infill); and,
• The usable land within the BBA property limits would remain unchanged from the original infill proposal.
The principal disadvantages to this strategy are:
• The embayment area would be effectively eliminated. However, the sustainability of the habitat that would otherwise be constructed within the embayment area is highly doubtful due to the effects of long-term sedimentation, as presented herein and in the Impact Assessment authored in October 2015.
D. Other Considerations
We understand that BBA was being provided the opportunity to locate some of its compensatory habitat within the water lot that fronts the Broadway Drain right-of-way. The implementation of either of the two outlet designs presented herein will impact the area of the embayment, and hence, the area of the habitat to be constructed on the Detroit River bottom within the proposed embayment area.
For the original outlet design, the training jetties would have occupied approximately 380 sq.m of the compensatory habitat area. If Alternative A is implemented, the area occupied by the training jetties would increase to approximately 1,220 sq.m. That said, the jetties will provide a desirable form of fish habitat - that associated with rock mound structures.
The sustainability of river bottom habitat constructed in the proposed embayment area is considered suspect, due to the likely long-term aggradation of the area due to the increased potential for sedimentation caused by the altered shoreline alignment. Therefore, we would expect that any habitat structure (rocks and logs) placed within the predicted eddy flow zone will be substantially covered/fouled with sediment (granular and organic) within a fairly short timeframe (i.e., probably less than 10 years based on our experience with similar undertakings). Consequently, the functional quality of the proposed nursery habitat (within the proposed embayment area as it is currently configured) may not be sustainable beyond the short-term.
As noted in the previous section, if Alternative C were adopted, the area of the Detroit River bottom that would be impacted by construction would be approximately 1,200 sq.m less than Alternative A, accounting for the combination of the outlet jetty construction that is associated with each option, and the infill quantity on the BBA lands that is
Design Summary for Broadway Drain Outlet – January 12, 2016
Gordie Howe International Bridge