While stormwater management ponds providing some quantity control have been integrated into the design of the GHIB plaza and the PAR, the idea of controlling peak flows to predevelopment rates was discarded early in the design process. Due to the proximity of the site to the Detroit River, and its limitless capacity to receive discharges from the subject drainage area, we determined that there are no warrants for achieving the level of quantity control that was proposed in the original EA document.

We further concluded that due to the highly impervious nature of the lands within the proposed watershed and the anticipated dominating influence of the Detroit River hydrograph on water levels and flows within the new drain, no significant impact on either baseflows or the erosion regime within the Broadway Drain could realistically be achieved via quantity control, without compromising the essential and most fundamental drainage needs of the project.

5.3 Outlet Design Constraints

Design of the drain outlet to the Detroit River from the Broadway Drain also posed some unusual challenges. Section 15 of the Drainage Act requires that all drainage works be extended to a sufficient outlet. A sufficient outlet is one that not only has sufficient capacity, but is also stable and sustainable for the long-term.

Where the Broadway Drain outlets to the Detroit River, the characteristic of the shoreline is unique from a coastal perspective. It consists of a natural, unprotected, actively eroding shoreline fronted by a narrow, dynamic, littoral transport zone. The predominant littoral transport direction is from south to north (i.e., in the upstream direction), due to prevailing winds and the resulting wave climate. Our initial examinations of the shoreline revealed that the immediate foreshore in the area of the proposed outlet consists of a narrow sand/gravel beach. During site examinations conducted in Spring 2015, a narrow barrier beach existed across the mouth of the existing drain. From this, we concluded that the drain improvements would need to include measures to protect the outlet against future fouling and infilling of the mouth of the drain by littoral sediments.

The outlet design for the Broadway Drain was further complicated by the site’s proximity to a separate project proposal, involving a substantial infill into the nearshore area along the Detroit River shoreline to the immediate north of the proposed outlet location. This project, proposed by Brighton Beach Aggregate (BBA), was under review by Fisheries and Oceans Canada when the subject drainage undertaking was commenced. The proposed infill was recognized as having the potential to significantly alter nearshore sediment transport and sediment deposition near the drain outlet. As discussed further in Section 6, Transport Canada and the WDBA required that design of the Broadway Drain improvements and outlet accommodate the potential effects of the proposed infill.