A depth sounding survey was also carried out on 15 May 2015 to establish the nearshore bathymetry of the Detroit River along the frontage of the drain outlet corridor. This information was used to evaluate and design the drain outlet.

Preliminary planning reports and studies for DRIC also included substantial natural heritage assessments aimed at establishing the degree to which significant terrestrial and aquatic habitats could be impacted by the proposed bridge project. The report prepared by Morrison Hershfield (hereafter MoHe) entitled: Fish and Fish Habitat Existing Conditions Impact Assessment Report for the Broadway Drain and Healy Drain (dated 1 February 2011) assessed the impacts of the proposed plaza construction and operation on existing fish and fish habitat in the subject drains. The study identified project-specific impacts and recommended a scope of construction mitigation measures with respect to the anticipated realignment of the Broadway Drain and the infilling of the upstream segment of the Healy Drain. A table that summarizes the mitigating measures recommended by MoHe is attached as Appendix C. Further discussion on the topic of fish and fish habitat is also provided in Sections 5 and 6 of this report.

A detailed hydrologic analysis of the entire Broadway Drain tributary area was performed by Stantec for the purpose of sizing the components of the internal drainage system for the new bridge plaza, PAR and surrounding lands. This analysis also estimated the 1:100 year flood flow resulting from full development of the plaza and bridge, which was deemed to be the most appropriate design standard for the sizing of the new drain. Based on Stantec’s analysis (and additional calculations performed by Landmark), the 1:100 year peak flow for the new Broadway Drain was calculated to be 12.5 m3/s.

5.0 Design Considerations

5.1 Purpose & Scope

The purpose and scope of the project were substantially established during the preliminary planning stages of DRIC - during preparation of its Environmental Assessment (EA), in particular. It was during this stage that the needs and objectives for improvement of the Broadway Drain and abandonment of the Healy Drain were established.

In summary, the following drainage needs and objectives were identified:

• Provide sufficient outlet and capacity to serve the drainage needs of the proposed GHIB and associated site development works;

• Redirect runoff generated on the property occupied by Nemak of Canada, from the Healy Drain to the Broadway Drain;

• Improve and partially realign the Broadway Drain from its current upstream limit (near the intersection of Broadway Street and the ETR) to a sufficient outlet at the Detroit River, in order to:

  • provide adequate drainage to existing tributary lands,

  • accommodate the added runoff generated by the new bridge plaza and perimeter access road; and,

• Abandon the Healy Drain, if appropriate.