6.2 Existing Drain State and Condition

Based on our examinations of the drain, and our consideration of the various background reports and documents, we have summarized the current state and condition of the drain below. For convenience, we have presented our findings based on the delimited drain segments that exhibit similar characteristics. In addition to listing bounding landmarks, channel station locations are also provided. We have designated the outlet of the Marentette-Mangin Drain into the Grand Marais Drain as Station 0+000.

Drain Outlet at Grand Marais Drain to Sewer Inlet near Lambton Street (Sta. 0+000 to 0+650). The drain through this segment consists of an enclosed drain, comprised of the existing concrete trunk storm sewer system that services Huron Estates. During construction of the subdivision in the late 1980s, an open-channel segment of the Marentette-Mangin Drain was replaced with the enclosed drain system. A copy of Sheets 1, 2, 8, 9a, 10, and 18 of the as-built drawings that depict the former route of the open drain and the existing sewer system is presented as Appendix D.

The drain segment from Sta. 0+000 to Sta. 0+335 has a diameter of 1,350mm and a slope that ranges from 0.13 to 0.22% From Sta. 0+335 to 0+507, the drain has a diameter of 1,200mm and a slope in the range of 0.14 to 0.15%. A 6m long segment of the drain consists of twin 900mm diameter pipes immediately upstream of Sta. 0+507. From Sta. 0+514 to Sta. 0+650, the drain has a diameter of 1,200mm and a slope in the range of 0.07 to 0.15%.

The sewer system for Huron Estates discharges to the Grand Marais Drain via a concrete outlet structure that serves as the ultimate outlet for the Marentette-Mangin Drain. The structure consists of a 2.4 x 2.4 x 4.85 m high concrete box chamber. The outlet features a 1,350 mm diameter low-level discharge pipe, and a 1,800 x 1,440 mm (width x height) grated overflow spillway. The lower discharge pipe is fitted with a 600 mm diameter orifice through a brick bulkhead.

We observed a significant accumulation of gabion stone within the outlet chamber. The quantity of rock appears sufficient enough to partially obstruct low flows from the sewer system. The stone appears to have originated from erosion protection placed downstream of the structure during its original construction, and appears to have been hand bombed through openings in the safety grating.

The enclosed segment of the drain terminates at Sta. 0+654, west of the Lambton Street cul-de-sac, where it transitions to an open, earth-lined channel. Flows discharge from the open-channel segment and enter the sewer system via a daylighted 1200 mm diameter concrete sewer. The upstream sewer end is fitted with a vertical bar grating. We observed a significant accumulation of woody debris at the sewer inlet during our examinations, which is clearly restricting the inlet capacity.

Sewer Inlet near Lambton Street to Upstream limit near Lamont Street (Sta. 0+650 to 1+004). The drain through this segment consists of an open, earth-lined channel. Over its entire