Designing for Safety

GEI Consultants completed the Semi-Quantitative Risk Analysis (SQRA) process for the northern two dams, which resulted in a recommended inflow design flood (IDF) for both dams. The recommendation will allow the dams to safely pass a 10,000-year storm event, which corresponds to a 1 in 10,000-year Annual Exceedance Probability (0.01% AEP). AEP is the chance or probability of a natural hazard event (usually a rainfall or flooding event) occurring annually and is usually expressed as a percentage. It should be noted that the May 2020 floods for the Secord and Smallwood dams were estimated to be between the 100- to 200-year flood (1% to 0.5% AEP).

Summary
Secord Dam: The 60% design spillway for Secord was sized to safely pass the IDF of 17,515 cubic feet per second (cfs). The current Secord Dam gate spillway discharge capacity is approximately 7,740 cfs.

Smallwood Dam: The Smallwood 60% design spillway was sized for an IDF of 25,500 cfs. The current Smallwood Dam gate spillway discharge capacity is approximately 10,145 cfs.
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Overall, dam safety will be improved by significantly increasing spillway capacity from what historically existed. 

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