length, the drain has a bottom width ranging from 1.5 to 3m, an approximate depth in the range of 1.5 to 2 m, and an average longitudinal slope in the order of 0.2%.

In general, the open-channel segment of the drain is well defined, and has sufficient size and adequate conveyance capacity to provide outlet for the upstream tributary lands. However, the channel traverses a mature woodlot and therefore exhibits a heavy growth of large trees over its length – along its channel banks and within the drain itself. There is an excessive amount of blowdown (large trees that have been blown over by the wind) throughout the drain segment. In some instances, the blowdown has dislodged large root balls that have disturbed the drain bottom. Some of the blowdown is crossing the drain and has the potential to induce clogging and impede flow as the trees decompose over time.

Portions of the open-channel segment of the drain border on, and in some locations, encroach within the east boundary of a provincially-designated Area of Natural and Scientific Interest (ANSI) known as the Spring Garden Natural Area. In addition, portion of the open-channel traverse areas that have been previously mapped as Provincially Significant Wetland (PSW) and Environmental Significant Area (ESA). Any works along the open channel will require approval of governing agencies and ministries.

6.3 Hydrologic and Hydraulic Assessment of Drain Capacity

In order to assess the capabilities of the drain to safely convey the anticipated flows, we constructed a PCSWMM model to represent the existing site condition within the Marentette-Mangin Drain watershed. Simulations were then undertaken to estimate the runoff rates that would be produced during a range of statistical runoff events.

A few notable aspects of the modelling are summarized below: