Grafton Lake Water Supply and Water Conservation Considerations

Key Findings

This memo updates the assessment of Grafton Lake as a sustainable water supply for the Cove Bay and Eagle Cliff Local Service Areas on Bowen Island. Key findings include: (1) Per capita water consumption has declined significantly from 342 L/c/d in 2010 to approximately 260 L/c/d by 2021, well below the MMCD standard of 300 L/c/d. (2) The Grafton Lake control structure was reconstructed in 2012-2013, increasing live storage to approximately 320,000 m3. (3) Water licences held by BIM (totalling 630,543 m3/year for consumption and 330,572 m3 for storage) are sufficient to meet projected future demands including connection of Eagle Cliff LSA. (4) The 2021 drought (approximately 6 weeks) caused lake levels to drop to 105.35 m, about 0.4 m lower than model predictions, indicating the need for model recalibration; however, even with projected future demands, the lake level under extreme drought conditions would remain approximately 0.55 m above the control structure invert. (5) Three water conservation actions are recommended: ongoing education and consumption reporting, revision of the water rate structure, and a universal rainwater capture requirement for new construction.