Groundwater-surface water interactions reflect the variation in geology, climate and land characteristics that the Xwulqw’selu Sta’lo’ (Koksilah River) experiences. We can work towards a healthier watershed by monitoring how these connections change and by understanding why.
When we know about groundwater connections throughout the watershed, we can set realistic expectations and goals of water yield from tributaries to maintain critical flows. There are seasonal transitions to the timing and volume of water flows. Both of these transitions are critical. Information we gain from monitoring these seasonal transitions is useful to people who develop and implement low flow water management strategies.
Preliminary results from the 2021-2022 field seasons indicate that volunteer streamflow monitors are producing large amounts of quality data that are consistent with data gathered by experts and gathered mechanically with data loggers. Future work will focus on short- and long-term applications of the monitoring program.
The data show that discharge is sustained during low flows by the higher elevation, fractured bedrock found in the upper watershed. The 12 tributaries measured above the Water Survey of Canada (WSC) gauge in mid-August 2022 accounts for 50-60% of mainstem streamflow.
In our Pacific Northwest coastal climate, aquifers naturally recharge in high precipitation winter months and then slowly drain throughout the summer. The volume of flow and timing when this transition happens are determined by how much winter precipitation was able to recharge the aquifers, people’s use of water and to what extent evapotranspiration occurs during the summer.
Streams that are losing or disconnected from groundwater for the low flow season may have been connected earlier in the spring or winter. However, exploring that possibility has so far been outside the scope of the community monitoring program. Streams gaining over the whole summer are sustained by groundwater and they are more resilient to drought conditions. Streams with consistent baseflow values have reliable source water, regardless of gaining or losing conditions.
Curious to learn more? Read the preliminary report here:
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