o Removal of brush along the channel banks within the lowerhalf of the channel.
e The downstream segment of drain that consists of the trunk municipal storm sewer through Huron Estates Subdivision is in good condition and has sufficient capacity to convey the 5-year storm flow. However, under the 100-year storm event, significant portions of the sewer system will surcharge severely. Ponding depthsnear the westlimit Lambton Street could achieve depths greater than 450mm. In order to mitigate the potential for flooding within the subdivision during a 1:100 year runoff event, a continuous overland spill corridor to the Grand Marais Drain would need to be established. The only practical route would be along the east border of the Spring Garden ANSI, immediately west of and adjacent to the lots along Amy Lynn Park Dr. The associated disruption to the natural environment would likely render the proposal impermissible.
Significant relief from flood potential during the 100-year event can be achieved by removing the orifice from within the outfall structure. Since our analysis revealed no significant impact to downstream lands, its removal is recommended. In combination with removal of the orifice, the gabion rock that has been placed within the chamber should be removed and openings in the safety grating repairs. The improvementsto the outlet structure shouldentail the following:
o Break out and remove concrete-parged, masonry bulkhead from within the outlet chamber;
o Removeand dispose of gabion rock from within outlet chamber; and,
o Repair damagedbar grate.
e Thecurrentdesign ofthe ditch inlet bar screen is prone to clogging with brush and other floating debris. We observed a significant accumulation of debris during our inspections. We recommendthat a more substantial cage be installed over the end of inlet sewer to mitigate the potential for future clogging. The work should be completed as depicted in the attached design drawings.
7.0 Allowances
In accordance with Sections 29 and 30 of the Drainage Act, we have assessed the warrants for allowances and compensation to the ownersof lands affected by the work for the following:
¢ loss of land and use ofland for rights-of-way e damagesto lands, fences, ornamentaltrees,etc.
The downstreamportion of the drain, from Sta. 0+000 to 0+654 is located completely with City- ownedroad rights-of-way. Lands ownedbythe City will be provided at no costto the drain.
Wealso evaluated the warrants for assessing allowances and compensation for lands taken for various reasonsas result of the drainage works, and concluded that a very nominal allowance wasin orderfor the following reasons: