Climate: Record-breaking February snow, springtime temperature 2 degrees below average, and heavy precipitation in September. Mean temperature for water year 2019 was equal to the 1989-2018 average, but mean April-June temperature was 2 degrees F below average.
Natural streamflow: 98% of average: 97% in upper Henry’s, 103% in Fall River, and 96% in Teton River. Snowmelt in Fall and Teton rivers lasted into July. Upper Henry’s Fork water supply was above the 1930-2019 average for the first time since 2012.
Irrigation Management: Draft of Island Park Reservoir started 9 days later than average and ended 4 days earlier than average. Over the period of draft, streamflow in the Henry’s Fork at St. Anthony averaged 1,070 cfs, compared with this year’s target of 1,000 cfs.
Island Park Reservoir: Ended the water year 73% full, compared with 46% full on average. Outflow during the upcoming winter is expected to be 500-550 cfs for the third consecutive year.
Predictive Model Performance: Based only on April 1 conditions, my predictions for most key hydrologic parameters were within 10% of actual values except those directly affected by spring and summer weather. The model over-predicted natural flow by 8.1% and Island Park Reservoir carryover by 6.8%.
February 2019, we began our long-term monitoring of aquatic macroinvertebrates (insects and other creatures that live in the river bottom) in the South Fork Snake River by sampling sites representative of the Upper South Fork, South Fork Canyon, and Lower South Fork.
Abundance of macroinvertebrates averaged roughly 134,000 individuals per square meter across all sites.
Mayflies, stoneflies, and caddisflies composed roughly 10-35% of all individuals within South Fork samples.
The HFF interns arrived this weekend excited for the upcoming roles they will play in the organization. One of these interns was born and raised in Ashton and has received the Don C. Byers Memorial Scholarship.
In the following paragraphs Rob Van Kirk tells us about the life of Don Byers and the generosity of the Byers family which led to a yearly intern scholarship:
Record precipitation in February moved snowpack from 80% of average on February 1 to 110% of average on April 1.
Watershed-wide natural streamflow for April through September is forecast to be 105% of average, compared with 104% of average in 2018.
Delivery of water from Island Park Reservoir is predicted to begin around July 1 and remain in the range of 800-1200 cfs during July and August.
Because of very good inflow, the reservoir is expected to end the irrigation season around 80% full, compared with 72% full in 2018.
Higher water levels in Island Park Reservoir have numerous, scientifically documented benefits to the Henry's Fork fishery, prompting HFF to continue to expand the number of methods we use to limit delivery of water from the reservoir.
Many already have a sense that Island Park Reservoir plays a significant role in water quality, streamflows, and the fishing experience downstream, but here are 4 key lessons learned about the reservoir since HFF's founding in 1984: