Fishing Reports

Henry’s Fork, May 6th, 2023

Ground water flooding impacts access at the Vernon Bridge.

Headlines from Dr. Rob Van Kirk’s SWE Report Filed Yesterday for the Henry’s Fork Drainage

• The month of April was cooler and slightly drier than average.
• Watershed SWE peaked last Monday, at 119% of the average annual peak; 94% of this year’s peak SWE is still on the ground, compared with 87% on average.
• Natural flow is increasing in response to snowmelt; moderate rainfall is expected later in the week.
• Last week’s freshet exported 321 tons of sediment out of the Island Park to Pinehaven reach, compared with about 30 tons had the freshet not occurred.

Here is some interesting info from Dr. Van Kirk on the effects of the freshet performed for four days in late April.

Over the four days of the freshet operation, 321 tons of fine sediment were exported from the river reach between Island Park Dam and Pinehaven. Based on pre- and post-freshet numbers, we expect that about 30 tons would have been exported over those four days had the freshet not been done. For reference, the average annual net export of fine sediment from the reach over irrigation years 2016-2022 is 650 tons. So, the freshet moved half of the average annual sediment budget in three days. Freshet-related turbidity has dropped to near pre-freshet levels, but now increased stream flow from natural snow melt is increasing turbidity again, especially in the lower watershed.

Meanwhile, warmer water temperatures are accelerating aquatic insect development, although hatch timing remains later than average and even later than last year over the lower watershed. We expect rapidly warming conditions over the next few days, but the cooler forecast for late in the week could slow down progress toward average hatch timing ( His info on aquatic insect hatches helps explain the relatively slow recent fishing on the lower river).

Rob Van Kirk, Ph.D.

Senior Scientist

Henry’s Fork Foundation

P.O. Box 550

Ashton, ID 83420

208-881-3407 CELLG

Henry’s Fork, May 2nd, 2023

Headlines from Dr. Rob Van Kirk’s SWE report filed yesterday for the Henry’s Fork drainage.

Headlines
• Temperatures and snow melt were well above average yesterday, but current SWE is 10% above the average annual peak and 27% above average for the date.
• Natural stream flow has increased 22% in the past two days and is 72% of average for the date.
• Precipitation over the next week is now forecast to be heavy, with much cooler temperatures.
• My forecast for April-September total natural stream flow is 105% of average for the watershed: 102% in upper Henry’s Fork, 103% in Fall River, and 106% in Teton River.

Henry’s Fork, April 25th, 2023

Headlines from Dr. Rob Van Kirk’s SWE Report Filed Yesterday for the Henry’s Fork Drainage

• Precipitation overachieved yesterday, pushing SWE to yet another seasonal peak, at 119.2% of average.
• Dry weather and a warming trend start today, which will greatly increase snow melt across the watershed.
• Island Park Reservoir will start today’s freshet delivery at 91% full and just a few inches below the rubber spillway collar.
• Outflow from Island Park will be increased to 2,000 cfs in four hourly increments this morning.

Outflow will be increased to 2,000 cfs in four hourly increments this morning and held at 2,000 cfs until at least Thursday and most likely until Friday morning. Post-freshet outflow is tentatively planned to be set at 650 cfs, but the exact figure will be determined by inflow rate. Current inflow is around 500 cfs, but I expect that to jump quickly over the next few days to 800 cfs and likely to exceed 1,000 cfs by the weekend. This will impact flow downstream to Ashton Reservoir and has purpose of helping to flush silt from the river bed.

Rob Van Kirk, Ph.D.

Senior Scientist

Henry’s Fork Foundation

P.O. Box 550

Ashton, ID 83420

208-881-3407 CELL