Top

Henry’s Fork

Jimmy's All Seasons Angler / Henry’s Fork (Page 14)

Henry’s Fork, October 30th, 2021

On the lower river, Box Canyon, Cardiac Canyon holes and runs deep, and the Tubs, presenting streamer patterns is the name of the game. If you favor top water fishing, BWO life cycle patterns provide the best action.

More information from Dr, Rob Van Kirk on Henry’s Fork drainage water status follows.

Headlines:  

  • Precipitation yesterday was moderate and widespread again yesterday, averaging 0.4 inches across the watershed.    
  • Natural flow has increased by 330 cfs (17%) since Friday and is 89% of average.
  • At a mean outflow of 124 cfs, Island Park Reservoir gained 781 ac-ft yesterday, 110 of which was due to direct precipitation on the reservoir surface. The reservoir is 55% full, compared with 53% full on average.

Details:

Moderate precipitation continued yesterday at all locations, averaging 0.4 inch across the watershed. Precipitation was uniformly distributed across the watershed, and even valley areas received 0.2-0.3 inch. This pushed the water-year total to date to 3.63 inches, compared with the long-term average of 2.75 inches for the whole month of October. Temperatures dropped yesterday to 2 degrees F below average, the coolest in 11 days. As a result, most of the SnoTel stations gained new snow water equivalent (SWE) yesterday. White Elephant, Black Bear, and Grand Targhee each have over 1 inch of SWE on the ground. Small chances of precipitation continue on and off over the next week, with temperatures staying near average.

Watershed-total natural flow has increased by 330 cfs (17%) since Friday, with most of that increase occurring Monday and yesterday. Although streamflow in headwater areas peaked yesterday, some of that is still making its way to the lower watershed this morning. Natural flow yesterday was 89% of average for the date, and cumulative natural flow for the water year to date has increased a percentage point to 75% of average. Diversion incidentally increased by around 30 cfs yesterday due to higher river stage and was 93% of average. Total diversion for the irrigation year to date—which ends on Sunday—is 92% of average.  

At an average outflow of 124 cfs, Island Park Reservoir gained 781 ac-ft yesterday. Around 110 ac-ft of that gain was due to direct precipitation on the reservoir surface. The reservoir is 55% full, compared with 53% full on average. Over the next day or two, fill rate will gradually drop back to around 550 ac-ft/day, where it was prior to the recent precipitation event.

Rob Van Kirk, Ph.D.

Senior Scientist

Henry’s Fork Foundation

P.O. Box 550

Ashton, ID 83420

208-652-3567 OFFICE

208-881-3407 CELL

208-652-3568 FAX

[email protected]

Share

Henry’s Fork, October 26th, 2021

As is our usual practice, excerpts from Dr. Rob Van Kirk’s Monday AM analysis of the Henry’s Fork drainage water status are given below.

REPORT NOTE: USBR data sites are down for maintenance this morning, so diversion, streamflow and reservoir data are current only through Saturday. I’ve filled in missing data for USBR weather stations with data from the nearest non-USBR stations.

Headlines:  

  • Precipitation during the much-anticipated atmospheric river event has so far been highly variable, ranging from a few hundredths in the valleys to over 1 inch in the Centennial Range.    
  • Diversion and natural flow were around 75% of average until rain increased natural flow in Fall River on Saturday.
  • At a mean outflow of 110 cfs, Island Park Reservoir gained 549 ac-ft/day for the week ending Saturday and is 54% full, compared with 52% on average.

Details:

Mean temperature last week was 3 degrees F above average. At 8 degrees F above average, Friday was the warmest day since October 6. Precipitation for the week-—most of which has fallen in the past two days—was highly variable across the watershed, ranging from a few hundredths in the valley locations to 1.3 inches at White Elephant. The Centennial Range and Yellowstone Plateau areas have received by far the highest totals thus far during the much-anticipated atmospheric river event that is bringing heavy precipitation to most areas of the West. Lewis Lake Divide, Black Bear, White Elephant and Crab Creek all received over 0.6 inch of water equivalent last week. Because of warm temperatures, new snow accumulation has been limited to the highest elevations, where Black Bear and Grand Targee have 1.7 inches and 2.5 inches, respectively, of snow water equivalent on the ground–around 80% of average for the date. Precipitation is expected to continue today and tomorrow, with somewhat cooler temperatures arriving this afternoon.

Watershed-total natural flow and diversion stayed around 75% of average until rain on Friday night and Saturday morning increased streamflow in Fall River by 40 cfs or so. Streamflow in the Teton River is also increasing a bit this morning.

We measured outflow from Island Park Reservoir at 114 cfs on Friday. For the week ending Saturday, mean outflow was 110 cfs, and the reservoir gained an average of 549 ac-ft/day. Projecting that gain through the end of yesterday, the reservoir is 54% full, compared with 52% full on average.   

Rob Van Kirk, Ph.D.

Senior Scientist

Henry’s Fork Foundation

P.O. Box 550

Ashton, ID 83420

208-652-3567 OFFICE

208-881-3407 CELL

208-652-3568 FAX

Share

Henry’s Fork, October 23rd, 2021

With the stormy weekend and first of next week predicted, brown trout will be active on the lower river, so break out those streamer patterns. Other than that BWO activity will be plentiful anywhere on the river. For the river in Island Park, the best news is that Highway 20 repaving between the Sheep Falls Road and Riverside Campground is complete, so no more flaggers and long lines of vehicles to slow down traffic.

Share

Henry’s Fork, October 19th, 2021

Aquatic weeds are breaking up everywhere giving better chances for landing larger fish especially on using finer tippets when presenting BWO, mahogany dun or midge life cycle patterns. Wherever you try the river, streamer patterns are a must. Brown trout are moving in the lower river, and locations in the upper river such as Box Canyon, Cardiac Canyon holes and runs, and The Tubs now host large foraging trout.

Below are excerpts from Dr. Rob Van Kirk’s summary of water conditions up to this morning in the Henry’s Fork drainage.

REPORT NOTE: I will be presenting a brief summary of water year 2021 at the Henry’s Fork Watershed Council meeting tomorrow, following a presentation on upper Snake River reservoir operations by the US Bureau of Reclamation. The meeting starts at 9:00 a.m., and you can join via Zoom at https://us02web.zoom.us/j/81474786741

Headlines:  

  • Last week was cool and wet, putting us in a good position to receive above-average precipitation for the first month of water year 2022.  
  • Natural flow has dropped a little from the effects of last week’s precipitation and is 75% of average.
  • At a mean outflow of 110 cfs, Island Park Reservoir gained 592 ac-ft/day last week and is 51% full, compared with 50% on average.

Details:

Mean temperature last week was 7 degrees F below average, and precipitation totaled over 1 inch for the watershed. All stations received precipitation over the week, ranging from 0.02 inch at Ashton to 2.6 inches at Lewis Lake Divide. Total watershed precipitation for the water year to date is 2.10 inches, and with more on the way, the first month of water year 2022 will very likely receive above-average precipitation. That happened in only four months during water year 2021. Precipitation this evening is now forecast to be lighter than anticipated a few days ago, with most areas receiving 0.1-0.2 inch. However, very heavy precipitation is expected next weekend and into the beginning of next week. Totals over the next week are expected to range from 0.75 inch at the western edge of the watershed to as much as 2.5 inches along the Teton crest. Temperatures will generally remain near to slightly above average over that time period, but snow will continue to accumulate at elevations above 7,500 feet.   

Natural flow has dropped a little from the effects of precipitation early last week and is 75% of average across the watershed and within a few percentage points of that in each of the three subwatersheds. Accumulated natural flow for the water year to date is 74% of average. Diversion is still on a generally downward trajectory with two weeks remaining in the administrative irrigation year. 

At a mean outflow of 110 cfs, Island Park Reservoir gained an average of 592 ac-ft/day last week and is 51% full, compared with 50% full on average. The upper Snake River reservoir system is at 14% of average and filling slowly.  

Rob Van Kirk, Ph.D.

Senior Scientist

Henry’s Fork Foundation

P.O. Box 550

Ashton, ID 83420

208-652-3567 OFFICE

208-881-3407 CELL

208-652-3568 FAX

Share

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

Henry’s Fork Foundation

P.O. Box 550

Ashton, ID 83420

208-652-3567 OFFICE

208-881-3407 CELL

208-652-3568 FAX

Share

Henry’s Fork, October 5th, 2021

BWOs and early in the day trico in small sizes (#18-22) and mahogany duns are making for good near-the-top or top water fishing almost anywhere on the river. While presenting hopper patterns will soon begin to diminish in being effective as cold weather settles in, consider that presenting streamer patterns will become increasingly effective in Box Canyon, the Tubs and anywhere on the lower river where brown trout are present.

Share

Henry’s Fork, September 21st, 2021

Here are excerpts from Dr. Rob Van Kirk’s Henry’s Fork drainage status report of today.

Headlines:  

  • Three-day precipitation totals ranged from 0.3 inch at Grassy Lake to 2.0 inches at Crab Creek, increasing the water year total to 82% of average.
  • Natural flow has increased by around 130 cfs since last Friday, while diversion has dropped by about the same amount.
  • At an average outflow of 236 cfs, Island Park Reservoir gained 415 ac-ft yesterday and is 42% full.

Details:

At 12 degrees F below average, yesterday’s mean temperature was the coldest since May 10. The daily minimum was the coldest since June 11. With complete data in hand, Saturday-Monday precipitation totals ranged from 0.3 inch at Grassy Lake to 2.0 inches at Crab Creek. Other stations receiving 1 inch or better were Grand Targhee, Pine Creek Pass, and Lewis Lake Divide. The watershed total was 0.86 inch for the three-day event. That was enough to move water-year total precipitation from 80% of average to 82% of average. If the forecast for dry weather holds for the next 10 days, total precipitation for the water year will end up 81% of average. That will rank 6th lowest since 1989, the lowest since 2007, and around 2.5 inches less than in 2016. Dry conditions and above-average temperatures are expected for the next week.

Natural flow continued to increase yesterday in response to the weekend rain but is still only 73% of average for the date. For the water year, total natural flow is76% of average, which is about where it will end up once the water year is in the books next week. Meanwhile, diversion has decreased by around 9% since last Thursday, although a few canals increased diversion a little yesterday. Streamflow in the lower Henry’s Fork peaked yesterday afternoon at around 400 cfs above its irrigation-season target and is dropping this morning. The effect of yesterday’s outflow decrease from Island Park Reservoir has not yet reached the lower watershed. After things settle out in another day or two, I expect streamflow in the lower Henry’s Fork to drop back closer to but still above the target flow.

At an average outflow of 236 ac-ft, Island Park Reservoir gained 415 ac-ft yesterday and is 42% full, compared with 46% full on average and 17% full in 2016. Although fill rate will decrease a little as the effect of the weekend rain subsides, I expect the reservoir to end the water year at around 60,000 ac-ft (45% full), which would be right at the 1978-2020 average, despite a water year with natural flow at only 76% of average.

Rob Van Kirk, Ph.D.

Senior Scientist

Henry’s Fork Foundation

P.O. Box 550

Ashton, ID 83420

208-652-3567 OFFICE

208-881-3407 CELL

208-652-3568 FAX

Share

Henry’s Fork, September 14th, 2021

The late summer mayfly activity peak is on going up and down the river. BWOs, mahogany duns, and tricos lead with respect to quantity and are accompanied by diminishing PMDs and speckled duns. Add a good number of terrestrial insects remaining streamside and a great time to be dry fly fishing here continues.

Below are excerpts from Dr. Rob Van Kirk’s analysis for today of Henry’s Fork drainage water status.

Headlines:  

  • Dry conditions continue, with only light precipitation forecast over the week.
  • Diversion decreased yesterday on the lower Henry’s Fork, increasing stream flow there by around 20 cfs.
  • At an average outflow of around 500 cfs, Island Park Reservoir dropped 205 ac-ft yesterday and is 41% full, compared with 46% full on average and 15% full in 2016.

Details:

Mean temperature yesterday was 1 degree F above average, and no precipitation was recorded. Updated precipitation data from SnoTel stations confirmed that water-year precipitation to date is 81% of average. With only 17 days remaining in the water year and no heavy precipitation in the forecast, precipitation for the water year will end up in the neighborhood of 80% of average. That will put 2021 somewhere in the range of 4th-7th driest since 1989. For reference, precipitation in 2016 was 88% of average. Temperatures over the remainder of the week are expected to stay around where they were yesterday. Precipitation is possible on Sunday and Monday, although amounts look light.

Diversion decreased by around 25 cfs yesterday, all of which occurred on the lower Henry’s Fork. Meanwhile, natural flow stayed roughly constant, although that in Fall River dropped by around 5 cfs from a small bump over the weekend resulting from rain on Friday night. The net result was an increase in stream flow of around 20 cfs on the lower Henry’s Fork. Otherwise, conditions in the lower watershed have been very stable for the past week.   

All measures of water quality remain very good in all river reaches. Turbidity at Island Park Dam continues to decrease on both sides of the dam.

Rob Van Kirk, Ph.D.

Senior Scientist

Henry’s Fork Foundation

P.O. Box 550

Ashton, ID 83420

208-652-3567 OFFICE

208-881-3407 CELL

208-652-3568 FAX

Share