5.2 Design Criteria & Constraints

In addition to establishing overall drainage needs and objectives, the EA for DRIC (and the numerous studies and reports that were prepared in support of the EA) established the expectations of various review and approval agencies – particularly those agencies responsible for natural habitat. The recommendations from these studies formed the basis for many of the habitat enhancement measures that were integrated into the final design of the drain improvements. However, some of the recommendations provided in these reports (and the review protocols established by the Bridge To Strengthen Trade Act) significantly complicated the design, review and approval process - particularly in connection with fulfilling the intention of the Fisheries Act.

Aside from the usual hydrologic and hydraulic design criteria associated with drainage projects, the integration of appropriate fish habitat enhancement and mitigation measures posed the most significant technical challenge to satisfactorily completing the drain improvement designs. Two particular commitments/expectations that were established during the EA became very problematic over the course of the design process. These are described in detail below.

a) Natural Channel Design

Planning documents for the DRIC project expressed that where the Broadway Drain required relocation, the realigned channel would be designed to maintain natural geomorphic processes, based on natural channel design principles by fluvial geomorphologists with input from hydrologists, fish biologists and landscape architects. Upon review of the actual site conditions, however, we concluded that the planning documents did not take into consideration the inherent hydrographic characteristics of the Detroit River.

The impracticality and inappropriateness of attempting to design a new channel on the subject site using fluvial geomorphological channel design principles became very evident during the initial stages of final design. We noted that the hydrographic characteristics of the Detroit River would dominate water levels within the improved Broadway Drain - which would preclude the development of sustainable pool/riffle complexes and the balancing of erosive and sediment transport processes, as had been originally envisioned in the EA.

After considerable effort to explain this phenomenon, the decision was eventually made to design the new Broadway Drain as a canal or backwater coastal feature - in lieu of the originally proposed design approach. Nevertheless, significant fish habitat enhancement features were integrated into the new drain design, as presented in Section 6 of this report.

b) Flow Rates for Design

Prior planning documents expressed that the stormwater management design would achieve two objectives, namely:

provide quantity storage to control peak flows from the Plaza to pre-development rates; and,