If the design objective is to meet and provide peak flow control for storm events, it is necessary to plan beyond the 1:100-year peak flow, and instead plan for the new norm of a 1:1000-year flood event. Planning for the appropriate peak flow is crucial to building climate resilience and meeting the demand over the full lifecycle of the infrastructure. If an inadequate peak flow formula is used it could result in significant additional costs to the City if it has to repair or tear up failing infrastructure to rebuild and increase capacity before it has reached its end-life. “Even a 1000-year return period has a 5% risk of being equalled or exceeded in a 50-year period.”