Henry’s Fork, October 12th, 2021
The challenge now will be getting to the river to fish especially in the Island Park area! October storms like this has happened before, and after it passes a lot of good fishing will remain. BWO and midge activty will offer top water fishing and presenting streamer patterns will become increasingly effective. Another “plus” coming from this weather is that it will help clear aquatic vegetation ffom All waters.
Here are excerpts from Dr. Rob Van Kirk’s update for today on water conditions in the Henry’s Fork drainage. There is some welcome info here to begin the water storage year.
Headlines:
- The current winter storm over our area is over-achieving, producing 0.55 inch of water equivalent watershed-wide and the coldest temperatures since April.
- Natural flow dropped a little yesterday in response to colder temperatures, as yesterday’s precipitation fell as snow at all elevations.
- At an outflow of around 125 cfs, Island Park Reservoir gained 662 ac-ft yesterday, 100 of which was due to direct precipitation on the reservoir surface. The reservoir is 48% full and equal to the 1978-2021 average.
Details:
Precipitation yesterday exceeded expectations, with even more falling after midnight and continuing this morning. Through midnight, water-equivalent totals ranged from 0.02 inch at Ashton to 1.4 inches at Lewis Lake Divide, with a watershed average of 0.55 inch. Mean temperature yesterday was 32.8 degrees F, 6 degrees below average and the coldest since April 20. Precipitation fell as snow at all elevations, and all SnoTel stations are reporting snow on the ground this morning, ranging from 0.2 inch to 1.7 inches of water equivalent. Snow is expected to continue on and off through Thursday, with Friday morning’s low temperatures well down into the teens in most locations. Dry weather with a slow warming trend is expected over the weekend, which will melt most snow at the low and mid-elevations. Above-average temperatures are expected next week.
Natural flow dropped a little yesterday to 75% of average due to colder weather. Meanwhile, diversion dropped by nearly 100 cfs yesterday, so supply now exceeds demand by over 1100 cfs, the highest it has been since early June.
At an outflow of around 125 cfs, Island Park Reservoir gained 662 ac-ft yesterday, nearly 100 ac-ft of which was due to direct precipitation on the reservoir surface. The reservoir is 48% full and only 118 ac-ft below average for the date. However, the upper Snake River reservoir system as a whole continues to draft and is only 9% full.
As a final note this morning on streamflow at both Ashton and Island Park, which are critical to natural-flow calculations, I suspect that the current gaged flow at Ashton is lower than actual flow and that my estimate of Island Park flow based on our measurement last Friday is a little high. We will measure flow at both locations this Friday to get better estimates. Changes in the stream gage rating curves are large relative to actual flow in the river right now, as aquatic vegetation is decaying quickly and moving out of the stream channel.
Rob Van Kirk, Ph.D.
Senior Scientist
P.O. Box 550
Ashton, ID 83420
208-652-3567 OFFICE
208-881-3407 CELL
208-652-3568 FAX