By IAN PEACE
In the June 4 article about the weir project, North Salt Spring Waterworks District (NSSWD) hopes to better protect beaver yet seeks to minimize an important environmental issue. Namely, how much the coho salmon, cutthroat trout, resident lake trout and other river species rely on 8.9 L/s minimum flow mandated for Duck Creek.
In a recent report about flow rates in the creek, hydrologist Dave Gooding wrote, “Both sea run and resident lake trout spawn in January/February when adequate flows are usual. Salmon fry emerge in May to out-migrate, trout later in June. Low flows during these times can limit the ability of fry to out-migrate to the ocean, and their health and size. Low flows during the period when fry are in the stream (a year for both coho salmon and lake run trout fry) results in lower oxygen levels, higher water temperatures and less food availability, with the result of reduced fry health or even mortalities. The lack of a consistent fresh water flow to the estuary affects the biologic function of that habitat, and therefore the size and health of smolts leaving to the ocean.”
NSSWD applications to reduce the minimum flow on Duck Creek began at least 10 years ago. For example, in 2015, NSSWD applied to the federal Department of Fisheries and Oceans for permission to reduce the minimum flow by about half. In September 2024, NSSWD published the Water Master Plan (WMP), which supports their effort to significantly increase water service connections. In it, the district questions whether Duck Creek requires 8.9 L/s and suggests 4.0 L/s instead.
The district has shared their plan to commission a study on the topic. The WMP relies on about 900 pages of studies NSSWD commissioned over the past 10 years. One of these directly addresses how low-flow conditions degrade aquatic habitat. In 2018, NSSWD paid Ecofish Research Ltd. to study environmental flow needs (EFN) in Duck Creek. The result is available on the NSSWD website. Written by Todd Hatfield, the 145-page study focuses on the commonly acknowledged relationship between flow rates and aquatic health.
In order to figure out EFN, environmental managers divide the mean annual discharge (MAD) by 10. The general acceptance of this “10 per cent of the MAD” to determine healthy fish flow extends across the continent. Table 7 of the Ecofish study shows that compared with 8.9 L/s, a 4.0 L/s flow rate degrades fish habitat quality by two thirds and at a 2.0 L/s flow rate, habitat is degraded by 90 per cent.
Since May 11, Duck Creek flow rates fell below 4.0 L/s at least eight times. On four of those incidents the flow rate measured less than 2.0 L/s. Sometimes, when the flow rate falls short of the mandated minimum, volunteers restore flow by removing some of the blockage. This takes about 10 minutes.
In the article, NSSWD board chair Brian Pyper states that on average, the total consumption of NSSWD customers is about 17 L/s. He then compares that consumption with Duck Creek EFN of 8.9 L/s and laments, “roughly half of our entire consumption is mandated for summer flow.”
More to the point, how does the volume of water leaking from the NSSWD distribution system compare with EFN? The NSSWD water audit showed that in 2016, unmetered losses added up to about 20 per cent of annual output, or about 4.0 L/s.
Another perspective is to look at how these withdrawals affect lake levels. The 2016 unmetered losses work out to about seven cm of St. Mary Lake depth. That is a lot more than the five cm of lake depth required to maintain EFN in the dry months. For comparison, during the four dry months, the total St. Mary Lake drawdown, including evaporation, human use and EFN, is about 60 cm.
Out of the blue 15 months ago, the province allocated $10 million to increase the water storage capacity of St. Mary Lake and allow for the required EFN in Duck Creek. In the WMP, NSSWD continues to ask nature to make do with less than half of EFN. Wouldn’t it be better to fix the leaks in the distribution system first?