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