Island groundwater picture shared in study
Salt Springers got a closer look at the island’s groundwater at a presentation on Friday afternoon.
The presentation discussed the findings of Golder Associates’ Groundwater Budget Analysis for Aquifers on Salt Spring Island. Environmental scientist Nick Gorski presented the group’s findings to a packed Lions Hall, giving an overview of the capacity for groundwater retention, accessibility of groundwater and the overall budget for the four main aquifers on the island.
Gorski explained that these are mainly made up of cracks in solid bedrock, a complex system that makes well drilling unreliable and varied across the island. Complexity is added thanks to an unpredictable water table that varies depending on elevation.
The study used existing knowledge of the island’s geology along with knowledge of existing wells to create a 3D visualization of the aquifers on the island. It discusses the water budgets for these aquifers and how communities can use this information to plan for the future.
According to Gorski, there is “no free water” on the island. Since no water comes from outside of the island’s watershed, all of the water that gets used needs to come from a different part of the closed system. Though the population has been increasing and the summers have been drier in recent years, the study did not see any long-term declines in the amount of water available on a yearly basis.
Salt Spring has approximately 180 million cubic metres of water available each year. The majority of the water on the island arrives from October until March. Out of that volume, only about 0.6 per cent is actually used by people on the island. The rest is either difficult to access, or is lost due to runoff or used by the forests.
Another finding of the study was that generally, aquifers and wells refill and actually overflow during the wet season. Gorski likened the effect to a bathtub with water that spills over the sides when it becomes too full. This was illustrated using a graph that showed annual highs and lows over a 10-year period. However, audience members were concerned that the analysis of the data did not include the lower end of the graph, which dropped year after year.
Community member Jane Squier asked about the lower end of that graph, saying that “That the recovery time is much slower . . . It doesn’t seem right to just look at that top level.”
Gorski explained that the recovery time for a well is affected by the nearby areas. Water is drawn from a network of cracks that can take more time to refill.
Though the water table consistently refills each year, Gorski explained that annual stresses on the groundwater and shortages present a real problem. Recommendations from the study include working to manage groundwater storage and infrastructure on the island. Other recommendations included mapping the faults that Salt Spring lies on, doing a survey of the springs on the island, monitoring streams during the wet season and other monitoring of various water sources.
The presentation was a draft version of the report, and Golder will be finalizing the report over the next few weeks. A final version is expected in the new year.