December precipitation was only 51% of average across the Henry's Fork watershed. However, water year-to-date precipitation and snow-water-equivalent are at 87% and 89% of average, respectively. And, thanks to above-average precipitation during water year 2017, the upper Snake River reservoir system is 87% full, and winter streamflow is above average. Long-range forecasts call for average to above-average precipitation for the remainder of the winter, so the overall water-supply outlook remains good as we head into the New Year.
Each of the last two years at this time, I have reported on the resurrection of “fish of the month,” a tradition that Henry’s Fork Anglers guide Tom Grimes and I started many years ago. The goal is to catch at least one wild trout every month of the year, on a fly, in our local Idaho, Montana, and Wyoming waters. My longest fish-of-the-month streak lasted 55 months, from July 2004 through January 2009. On December 4, I added month 36 to the current streak.
Earlier in November, the Henry’s Fork Watershed Council hosted a satellite location of Safeguarding Idaho’s Economy in a Changing Climate, a two-day a summit held November 16th and 17th. Invited speakers represented a broad sample of private businesses, public agencies, tribes, and NGOs in Idaho from Simplot and HP to the EPA and Idaho Dept. of Lands to Trout Unlimited. See the complete list of speakers here.
The Henry’s Fork Foundation (HFF) officially moved its offices into the new HFF Community Campus in August, but this community project has been more than three years in the making! This building at 801 Main Street was originally built as the Ashton Hospital in 1950. In 1988, the hospital was converted into a nursing home and a few years later became storage units when the new senior living center was built across town. The building remained, used for storage, until June of 2016 when it was purchased by HFF as our new community campus.
Water year 2017 was above average in both precipitation and streamflow. Averaged over the whole watershed, precipitation was 138% of average, led by the Fall River watershed, at 144% of average. Due to the cumulative effect of four years of drought, especially in the groundwater-dominated subwatersheds, natural streamflow was only 109% of average, led by the Teton River at 134% of average. Streamflow in the upper Henry's Fork, which is dominated by groundwater, was only 91% of average.
Natural streamflow is still above average in Fall River and Teton River but below average in the upper Henry's Fork.
Total watershed natural flow is 3,400 cfs, right on average for this time of year. Total watershed diversion is also average, at 3,300 cfs.
Delivery of storage water from Island Park Reservoir began last week; current flow out of Island Park is 1,060 cfs, compared with the long-term average of 1,300 cfs for the date and last year's value of 1,420 cfs.
Island Park Reservoir is currently 96% full, compared with 49% full at this time last year.
Headlines: Water temperatures through the Ranch have been on the warm side. Temperature has climbed above 71˚F for a couple of hours each day over the last week. However, daily maximum temperatures have not been deadly for rainbow trout, and only a few daily averages have been at the lowest levels that would stress fish. This is the same pattern we saw in both 2015 and 2016, when streamflows were about 800 cfs higher than current flows. Thus, releasing additional water from IP dam does not result in significantly cooler summertime water temperatures, but we do know that increasing flow out of Island Park Dam decreases water clarity and will reduce winter flows, which reduces survival of juvenile trout next winter and hence recruitment of 2-year old fish into the population in 2019.