Within the past 5 years, it was discovered that the flow rate portion of the historic gauge data was unreliable, due to an issue with its rating curve. Consequently, any hydrologic models that had been calibrated against the historic hydrographs may also be considered unreliable. A new hydrologic model developed by Landmark for the Grand Marais Drain was calibrated against the new gauge and then used to calculate design flows. The new model forecasted peak runoff rates that were 50 to 70% higher than the historic estimates.
Given the foregoing, we deemed it appropriate to undertake an independent hydrologic and hydraulic evaluation of the subject drain as part of this report, in order to confirm the drains capabilities to receive and safely convey flows to a sufficient outlet.
3.0 On-site Meeting
The on-site meeting required under Section 9 of the Drainage Act was held on 28 August 2018 at the Capri Pizza Recreation Complex at 2555 Pulford Street. A copy of the Notice of On-Site Meeting that was issued by the City Clerk is attached herein as Appendix C. All property owners that would potentially be impacted by the drainage improvement works were invited to attend the meeting.
The meeting opened by introducing the attendees and highlighting the purpose of the meeting. With the aid of a PowerPoint presentation, the purpose of the meeting was highlighted, some brief history status of the Marentette-Mangin Drain was provided, the Drainage Act process was explained and opportunities for input by interested members of the public were identified. Specific needs for drainage improvements and the known issues with the drain were reviewed. At the end of the formal presentation, the meeting was opened up for questions and discussion.
A resident queried whether the Parkway construction resulted in removal of any pumps along the Grand Marais Drain. We noted that the Grand Marais Drain always has, and continues to, function as a gravity open drain.
Another resident from Lambton Street expressed their opinion that the existing sewer was too small to handle flow from the drain. We advised that the drain capacity and sewer capacity would be assessed as part of the exercise.
A resident presented some history of land expropriation in the area and referenced a letter that they received in 2004. We confirmed that there was no intention to expropriate land or address future land development issues as part of the assessment of the drain. In regard to the matter of future land development, we noted that some of the land in the area may be undevelopable due to environmental constraints and that it would not be possible to resolve these issues through the Drainage Act process.
A resident asked if the drain was connected to pump stations along the Parkway. It was noted that the assessment will determine what portions of the Parkway drainage are contributing flow to the drain, including pump stations. The resident asked if the drain had more than one outlet