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.
In January of 2015, I started a new run of "fish of the month," a tradition I started years ago with long-time friend Tom Grimes, who is a guide at Henry's Fork Anglers. The idea is to catch a wild trout or whitefish every month of the year in our local waters, the streams and lakes of Montana, Wyoming, and Idaho in the Yellowstone region. My previous record was 55 months, from July 2004 to January 2009. Five academic years spent in California broke that streak, but I'm four years into the current one. How did 2018 turn out?
Diversion from the Henry's Fork has decreased 30% over the past 40 years, yet consumptive use of water by crops has increased, there is less water in the river during the middle of irrigation season, and use of storage water has increased, all other things being equal. How could this be?
Water-year 2018 ended up close to average, at 102% of average precipitation and 105% of average streamflow.
Upper Henry's Fork subwatershed was below average in precipitation and streamflow, vs. above-average values in Fall and Teton rivers.
However, Upper Henry's Fork water supply improved from 70% of average in 2016 to 91% in 2017 and 94% in 2018, indicating recovery of deep aquifers from 2013-2016 drought.
May and June rain compensated for early snowmelt and resulted in below-average irrigation diversion.
Despite very dry conditions and below-average streamflow during July, August and September, Island Park Reservoir ended the water year at 73% full, compared with 43% full on average, thanks to careful and precise water management.