Characterizing Recharge to Fractured Bedrock in a Temperate Climate

Fractured bedrock aquifers can have large seasonal water table fluctuations due to their low storage capacity. This study uses a land surface – subsurface model, MIKE SHE, to investigate the spatial and seasonal rainfall-runoff-recharge dynamics on Gabriola Island, in a temperate region of British Columbia, Canada. The model results suggest that recharge averages 20% of the annual precipitation, occurring dominantly over 70% of the island, typically at higher elevation. Perennial seepage areas are simulated over 4% of the island, and are generally confined to breaks in slope in low topography areas. The high water table in late fall to early spring causes both seepage and saturated overland flow to contribute to more runoff. Increases in precipitation due to climate change leads to increased runoff (+36% to +40%) and recharge (+8% to +10%) relative to today. Recharge changes are most significant in winter (+13% to +16%), compared to summer (-3% to -4%).