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 |
9.4 SWM Pond 5 Design Summary
SWM Pond 5 operating characteristics are summarized in Table 9.4. Only the 24-hour duration results have been summarized, since the 24-hour duration produced the most conservative storage requirements.
Table 9.4 – Summary of SWM Pond 5 Operating Characteristics
| Return Period (years) | Inflow (m3/s) | Outflow (m3/s) | Maximum Storage (m3) | WSEL (m) |
|---|---|---|---|---|
| Extended Detention | 0.94 | 0.06 | 2086 | 179.45 |
| 2-Year | 1.47 | 0.11 | 4117 | 179.82 |
| 5-Year | 1.91 | 0.29 | 5107 | 179.99 |
| 10-Year | 2.23 | 0.37 | 5867 | 180.12 |
| 25-Year | 2.60 | 0.40 | 6902 | 180.28 |
| 50-Year | 2.89 | 0.43 | 7779 | 180.42 |
| 100-Year | 3.18 | 0.45 | 8677 | 180.55 |
The detailed design of SWM Pond 5 is in accordance with the MOE Stormwater Management Planning and Design Manual (2003). Design features include:
- Permanent pool storage volume of 4202 m3 (required volume is 3717 m3) at an elevation of 177.50 m to achieve Enhanced level water quality treatment.
- Permanent pool depth of 1.5 m (minimum 1.0 m), a forebay length-to-width ratio of 2:1 and an overall length-to-width ration of 5:1.
- Approximately 65 hours of extended detention (minimum 24 hours extended detention) for the runoff generated from the 25 mm Event (4-hour Chicago distribution).
- Access road to the outlet control maintenance hole and access road extending into the sediment forebay (max slope 10%).
- Maximum side slopes of 6H:1V for 3 m on both sides of the permanent pool edge and maximum side slopes of 5H:1V elsewhere.
- Bottom draw low flow outlet pipe to mitigate potential thermal impacts.
- Orifice flow controls to attenuate the 2- through 100-year return period event pond outflows to pre-development rates:
- 230 mm diameter orifice plate to control frequent flows
- 450 mm diameter orifice plate to control high flows
- 25 m wide emergency spillway set at 0.05 m above the 100-year return period event water surface elevation to provide emergency relief flow in the event of an outlet blockage.
Supporting calculations for the sizing of Pond 5 are provided in Appendix E of this report. The 90% detailed design drawings for SWM Pond 5 are also provided in Appendix E; and include plan, section,