Capilano Probable Maximum Flood Update

Project Highlights

Constructed in 1954, the spillway at Cleveland Dam was designed to pass the 1,000-year return period inflow design flood.  Subsequent downstream development and more stringent standards have resulted in the facility being reclassified as having “Extreme” downstream consequences.

KWL was retained by Metro Vancouver to update the Probable Maximum Flood in accordance with new Canadian Dam Association Dam Safety Guidelines and Probable Maximum Precipitation estimation techniques.  The study involved:

• Updating the Probable Maximum Precipitation estimate for Capilano Watershed,
• Estimating Probable Maximum Flood antecedent conditions to representative of coastal mountainous watersheds, and
• Developing, calibrating and validating two separate hydrologic models (UBC-WM and HBC-EC models)to cross check the results of the Probably Maximum Flood analysis.

By using start-of-the-art hydrological modelling and making across-comparison between the two modelling techniques, KWL was able to decrease the uncertainty in the Probable Maximum Flood estimate, enabling more robust design criteria for the dam.  This reduced the need to be overly conservative in the Probable Maximum Flood estimate, which translated into reduced costs for potential upgrades to the dam.