2.3 Construction of Rt. Hon. Herb Gray Parkway

As noted previously, construction of the Parkway resulted in modification of the upstream 190 m long segment of the drain as well as the drainage area boundary. Parkway construction also significantly changed the hydrologic characteristics of the lands that it occupies, some of which outlet to the Marentette-Mangin Drain and other municipal drains in the region. The Parkway Infrastructure Engineers (PIE) undertook an independent hydrologic modelling exercise to calculate peak flood flows generated by the Parkway, and more relevantly, the flows that would be outlet to the respective receiving watercourses. PIE documented their independent hydrologic analysis and findings in various stormwater management reports, which formed the basis for sizing of the parkway drainage infrastructure and modification of the affected municipal drains through the parkway corridor.

Prior to construction of the works that impacted the drains, reports were prepared pursuant to Section 77 of the Drainage Act by Tom H. Marentette, P.Eng. of Dillon Consulting. The report entitled “Drain Improvements to the Marentette-Mangin Drain as Part of the Windsor-Essex Parkway” dated April 12, 2013, addressed the impact of the Parkway drainage improvement on the subject drain.

The most relevant aspects of the aforementioned reports that were relied on for this report are summarized below.

2.3.1 Stormwater Management Report (SWM Report)

The flows that were calculated by the PIE were used to design the new Parkway drainage infrastructure including a stormwater management pond known as Pond#5, which discharges into the existing open-channel portion of the Drain. Modification of the watershed boundary and upstream portion of the drain by WEMG prompted the need for a new report under the provisions of the Drainage Act to ensure a secure outlet for Pond#5 and to ensure that the risk of flooding of downstream lands was not worsened. The following paragraphs summarize the information provided in the SWM report that we consider most relevant to this undertaking. This information was relied on for the purpose of completing our assessment of the drain.

The detailed SWM plan for the Parkway includes five pumping stations and seven SWM ponds to service all new sections of Highway 401 and the majority of Highway 3.

Pond 5 is the only stormwater management pond associated with the Marentette-Mangin Drain and will receive flows from PS-1. Pond 5 has been designed to provide water quality and quantity treatment in accordance with the Ontario Ministry of the Environment (MOE) Stormwater Management Planning and Design Manual (2003) to meet Ministry and project specific design criteria

Stormwater Conveyance – The roadway drainage system for Highway 401 and roadways below grade will be constructed to convey the 100-year design event. The drainage system will be designed to prevent flooding of the travelled Highway 401 lanes. For sections of Highway 3