Henry’s Fork, February 24th, 2024
This weekend looks like a good time to enjoy midge activity on the lower river before another stormy week begins on Monday. A bonus could be the first, but minor appearance of BWOs on the lower river. Consider that the rainbow trout spawning season is beginning. So lets allow them to do so in peace. It is in our best interests if we want his event to replenish their population for years coming up.
Headlines From Dr. Rob Van Kirk’s Snow-Water Equivalent (SWE) Report Filed 2/24 for the Henry’s Fork Drainage
Light precipitation yesterday kept the water year total at 96% of average and SWE at 81% of average.
- A major winter storm is still expected on Monday and Tuesday, with additional precipitation later next week.
- At an average outflow of 451 cfs, Island Park Reservoir dropped by 112 ac-ft yesterday and is 90% full, compared with 78% full on average.
- The upper Snake River reservoir system is filling rapidly and is 81% full, compared with 62% full on average.
Details
Natural flow stayed fairly constant yesterday at 96% of average: 91% in upper Henry’s Fork, 110% in Fall River, and 92% in Teton River. This is the largest difference between this year and 2016. Cumulative natural streamflow so far this water year over the Henry’s Fork watershed is 97% of average, ranking 25th out of the last 47 years (48th percentile–pretty close to the middle of the pack). On the other hand, natural flow at this point in water year 2016 was only 81% of average, ranking 42nd out of the 47 years.
So, while we know that warm late-winter and early spring temperatures cause poor water quality in Island Park Reservoir, we also know that natural streamflow into the reservoir counteracts that effect. Higher inflow produces better water quality. So, while climatic factors so far this winter look very much like 2016, the watershed is in much better shape this year than it was in 2016, thanks to above-average snow last year and to above-average precipitation in the late summer and early fall. The solid February we are having will also help. Lastly, water conservation measures implemented in 2018 by our agricultural partners, Fremont-Madison Irrigation District, and US Bureau of Reclamation have greatly reduced irrigation-season drawdown of Island Park Reservoir over the last six years, which will also help limit the negative effects of warm temperatures and low snowpack on Island Park Reservoir this summer.
Rob Van Kirk, Ph.D.
Senior Scientist
P.O. Box 550
Ashton, ID 83420
208-881-3407 CELL