Table 8.5 - Summary of Existing and Proposed Peak Flow Rates at Lambton Street Storm Sewer Inlet
| Return Period Event | Existing Peak Flow (m3/s) | Proposed Peak Flow (m3/s) |
|---|---|---|
| 2-Year | 0.86 | 0.73 |
| 5-Year | 1.13 | 1.12 |
| 10-Year | 1.36 | 1.36 |
| 25-Year | 1.62 | 1.59 |
| 50-Year | 1.82 | 1.77 |
| 100-Year | 2.09 | 1.98 |
Table 8.5 illustrates that post-development peak flow rates have been controlled to rates similar to, but less than those under existing conditions. Model outputs for both existing and future conditions are provided in Appendix D.
9 Stormwater Management Plan
9.1 Design Rationale
The PDR SWM plan identified a set of SWM design criteria (summarized to Section 8.1) to guide the development and implementation of The Parkway SWM plan. The set of criteria was established to mitigate potential development impacts in terms of water quality, in-stream erosion and peak flow control. To achieve these criteria, the PDR SWM plan screened several stormwater management practices (SWMPs) that could be utilized to mitigate potential development impacts of The Parkway. The screening process resulted in a number of preferred SWMPs that were developed as part of the preliminary design stage:
- Storage SWMPs to provide quality treatment, erosion control and quantity control
- Oil & grit separators to provide water quality treatment for small areas and pre-treatment for pumping stations
- Vegetative SWMPs such as grassed swales and buffers to provide passive water quality treatment and erosion control.
The PDR SWM plan also noted that a treatment train approach to quality treatment should be emphasized. This strategy is particularly conducive to this study given the extensive aesthetic and restoration landscapes proposed within The Parkway corridor. In particular, vegetative SWMPs are low cost, low maintenance practices that provide quality treatment through filtration, settlement and infiltration for small drainage areas. These linear features are well suited for highway roadside and table land areas, and can provide erosion protection with well placed rock check dams which serve to reduce overland flow velocities.
The PDR SWM plan has been further refined in support of The Parkway detailed design. Changes to the PDR SWM plan are a result of several design changes:
- Highway and tableland grading refinements that resulted in changes to the catchment plan
- Optimization of the storm sewer network and pumping stations
- Relocation and optimization of some SWMPs to suit detailed design changes, improve access, functionality and integration with other discipline design considerations.