AS4 – Broadway Drain Design Focus

Substantial reconstruction, realignment and enlargement of the Broadway Drain are needed to provide adequate drainage outlet for the new bridge plaza and adjacent lands that are tributary to the watercourse. Where channel realignment cannot be avoided, the realigned watercourse will be designed using natural design principles to create productive fish habitat. Due to the inherent hydrographic characteristics of the Detroit River that will dominate water levels within the improved Broadway Drain, it would be impractical and inappropriate to attempt to design the new channel using principally fluvial geomorphological channel design principles. Instead, it is proposed that the new Broadway Drain be designed as a canal or backwater coastal feature. Accordingly, in addition to sizing the channel to provide sufficient outlet capacity for the tributary lands, the design will focus on fitting out the drain with coastal features and structures that will be productive and sustainable for the aquatic communities. In the local environment, this approach seems more appropriate than attempting to design stream features that focus on the balance of natural erosion and depositional processes.

As a final point, the limited plan area and highly impervious nature of the watershed will cause large fluctuations in flow rates, resulting in very limited baseflow volumes and velocities. Therefore, less consideration will be given to fluvial morphological elements and greater consideration will be given to introducing features typically found in coastal backwater zones.

Final approval and clearances for construction of the proposed designs will be sought from all applicable agencies, including DFO.

AS5 – Stormwater Management Report

Final design of the bridge plaza will include the preparation of stormwater management (SWM) reports. Separate reports will be prepared for the perimeter access road and for the bridge plaza. SWM for this development will focus on quality control only. Quantity control for the purpose of attenuating peak flows is not warranted, due to the proximity of the site to the Detroit River, and the hydrographic characteristics of the River. Given the limited size of the drainage area that is tributary to the Broadway Drain, the percentage of the drainage area that has been designed to become impervious, and the channel geometry that will be needed to provide proper drainage outlet, the opportunity to significantly augment baseflow within the Broadway Drain does not exist.

AS6 – Base Flow Maintenance/Enhancement

Given the small tributary area that contributes flow to the Broadway Drain, there is a very low potential to implement measures that will significantly enhance baseflow. This factor, combined with the geometric channel properties (i.e., size and depth) that will be needed to provide sufficient drainage outlet for the plaza and adjacent tributary lands, will result in extremely low flow velocities (i.e., immeasurable) at all times – except for brief periods following rainfall