Diversion from the Henry's Fork has decreased 30% over the past 40 years, yet consumptive use of water by crops has increased, there is less water in the river during the middle of irrigation season, and use of storage water has increased, all other things being equal. How could this be? In Idaho, administration of irrigation water takes place over the "irrigation year," which runs from November 1 to October 31, lagging the more common October 1 to September 30 "water year" by a month. In most areas of the upper Snake River basin, irrigation water rights can be used from April 1 to October 31. Water for other uses, such as managed aquifer recharge and livestock watering, can occur during the winter. Irrigation year 2018 ended just a little over one month ago, allowing me a little time to summarize data from the 2018 irrigation season. This blog starts out with that summary but quickly moves into a discussion of long-term trends in irrigation practices, and the unintended and counterintuitive consequences of those trends. Data Sources The data reported here come from the Idaho Department of Water Resources (IDWR) water-rights accounting database. These data include all all points of
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As of December 10, water-year precipitation is 87% of average, and snow-water-equivalent is only 75% of average. Precipitation deficit since July 1 is over 5 inches. Natural streamflow has been around 95% of average since early October. Outflow from Island Park Dam has averaged 502 cfs since December 1, 143% of average. Water year 2019 has started out the same way 2018 ended, dry and with slightly below-average streamflow. Through December 9, accumulated water-year precipitation is 87% of average, and snow-water-equivalent (SWE) at the watershed's nine SnoTel stations is only 75% of average. So far this winter, precipitation has favored the southern half of the watershed, including the Teton headwater areas and the valleys. Upper Henry's Fork lags the other subwatersheds by quite a bit. In addition to the current water-year precipitaiton deficit of around one inch, the four-inch deficit accumulated during July, August and September puts us over five inches down over the past five months. The winter will have to be much wetter than average to make up the deficit. Graph of accumulated water-year precipitation as a percent of average. Graph of snow-water-equivalent (SWE) across all SnoTel sites in the watershed. Below-average SWE is not the result of
Many of us, on our adventures in Henry’s Fork country, have also traveled south to explore the South Fork of the Snake River (SFSR). However, during your travels you might not have realized how interconnected flows and management of the Henry’s Fork was to SFSR The SFSR from Palisades Dam to the Henry’s Fork confluence is roughly 60 miles long, supports robust populations of Yellowstone Cutthroat Trout, Rainbow Trout, and Brown Trout, and flows through cottonwood stands, canyons, and a braided flood plain. Management of the SFSR system, especially in regards to water management, can directly affect streamflow in the Henry’s Fork. So, when a group of SFSR outfitters and concerned citizens approached HFF and asked us to expand our brand of research and collaboration to the SFSR, we took note. They expressed concerns about how fluctuations in SFSR flows might be affecting macroinvertebrates and fish populations, about summer water temperatures and fish habitat, and if restoration projects could boost trout populations and the fishing experience, while still meeting irrigation demand. If we look back five, ten, or twenty years, these same questions were being asked about the Henry’s Fork. In fact, understanding the answers to these questions were a
Water-year 2018 ended up close to average, at 102% of average precipitation and 105% of average streamflow. Upper Henry's Fork subwatershed was below average in precipitation and streamflow, vs. above-average values in Fall and Teton rivers. However, Upper Henry's Fork water supply improved from 70% of average in 2016 to 91% in 2017 and 94% in 2018, indicating recovery of deep aquifers from 2013-2016 drought. May and June rain compensated for early snowmelt and resulted in below-average irrigation diversion. Despite very dry conditions and below-average streamflow during July, August and September, Island Park Reservoir ended the water year at 73% full, compared with 43% full on average, thanks to careful and precise water management. This blog is even longer and more detailed than my usual long, detailed blogs, but there was a lot to learn from water-year 2018. This blog is a slightly edited compilation of the four daily water reports I wrote during the first week of the new water year. The four reports appear in four different sections in this blog: Climate Natural flow and diversion Streamflow and water management in lower watershed Streamflow and reservoir management in upper watershed Tables and graphs appear at the end of
Temperatures and rainfall were near average in August. Natural streamflow and diversion were both around 90% of average for the month. As of September 10, Island Park Reservoir is 73% full, compared with 46% full on average. August Weather Near Average August provided a little reprieve in the middle of what has otherwise been a warm, dry summer. Temperatures were warm during the beginning of the month and cool at the end, resulting in a monthly mean about 1 degree F below average. Graph of watershed mean temperature, relative to long-term average. A very deep autumn-like trough of low pressure brought substantial rain and near-freezing temperature to the whole watershed on August 27, adding to lighter showers that fell at scattered locations earlier in the month. The result was near-average precipitation at most stations for the month. Precipitation favored Teton Valley and the Fall River watershed; the upper Henry's Fork and most valley locations recieved below-average precipitation. Ashton was an exception, receiving nearly one inch for the month. Temperatures during the late-August storm were cold enough that snow fell above 7,000 feet and stayed on the ground for a few days at the highest elevations. Water-year precipitation ended the month
The month of July was a little warmer than average but very dry. Natural flow and diversion were both around 90% of average for most of the month. Moisture from May and June rain has kept total diversion for the season about 100,000 ac-ft below average. As of August 3, Island Park Reservoir is still 82% full, compared with an average of 70% full at this time of year. Above-average Temperatures Continue through July Temperature over the month of July was 2 degrees F above average in the Henry’s Fork watershed, continuing the pattern of above-average temperatures. Mean April-June temperature was also 2 degrees above average. Cool nights throughout July offset very warm afternoon highs to keep daily means close to average. As of August 2, Pocatello had set a new record of 30 consecutive days with high temperature at or above 90 degrees. According to the National Weather Service, the current heat wave in southeastern Idaho is record-setting in persistence and duration but not extremes. Graph above sows temperature relative to average. Note consistently above-average temperature since early July. Spring Rain Keeps Irrigation Demand Low, Despite Dry July After abundant rain in May and June, July was very dry.
Main message: The great spring sediment flush we observed earlier this year not only impacted fishing during Memorial Day weekend—by contributing to high flows and turbidity—but has continued to impact the fishing experience from Box Canyon through Riverside this season in two plainly obvious ways: depressed hatches and higher than average amounts of uprooted floating plant material. In addition, the rainy and cloudy weather that contributed to the spring flush may also have contributed to later hatch timing of some species earlier this summer. Recall my blog from June 8 where we quantified the amount of sediment that was flushed out of each reach of the Henry’s Fork, from Island Park Dam to Ashton Dam, during the major runoff events we experienced during April and May. These spring rains brought the highest spring runoff flows in 7 years to the upper Henry’s Fork watershed! Our network of water quality monitors showed that these flows were strong enough to provide a major springtime sediment flush—a natural rhythm of our local hydrology that provides significant benefit to trout and aquatic insect habitat. We’ve seen much higher summertime flows than these in the last 7 years, but what was significant about this spring’s
Prepared by Melissa Muradian and Jack McLaren What happened? Due to warm water temperatures and low dissolved oxygen in the water at the intake to the Island Park hydroelectric plant, the plant’s aerators have been unable to maintain dissolved oxygen in power plant outflow above the level required by their operating license. Thus, the plant shut down yesterday morning (July 15), and all outflow from Island Park Reservoir was shifted to the bottom-withdrawal gates on the west side of the dam. How does this affect the river’s water quality? Temperature: Water delivered through the dam gates is from the bottom of the reservoir and as long as thermal stratification remains in the reservoir, the gates will deliver cooler water than the power plant. However, the response we saw in temperature was about 1 ˚C (approx. 2 ˚F) at our IP East sonde. We saw no discernable difference in water temperature by the time that water made it to Pinehaven. Thus the cooler water temps that result from total flow coming out of the gates only last until some point upstream of Pinehaven, and most likely only last until part-way through Box Canyon. Dissolved Oxygen (DO): DO was hovering at
Watershed temperature over the month of June was 1 degree F above average. June precipitation was 135% of average, but average natural streamflow at Island Park for the month of June was only 92% of average. As of July 6, watershed-wide natural flow has dropped to 89% of average. Delivery of Island Park Reservoir storage water began on July 3. Watershed temperature over the April-June period was 2 degrees F above average, continuing the 40-year trend of increasing springtime temperature. April-June precipitation was 134% of average. Precipitation 135% of average in June After a warm May, very little snowpack remained across the Henry's Fork watershed, leaving rain as the only mechanism to keep streamflow high. Fortunately, that happened, as watershed-total precipitation was 135% of average during June. Monthly climate summary for June, 2018 is given in this table. Moreover, precipitation in the agricultural areas of the watershed was 183% of average in June. In fact, the valleys received more precipitation during June than the high-elevation areas of the Teton subwatershed. As a result, irrigation demand was lower than average over the month. Total diversion in the Henry's Fork watershed so far in irrigation year 2018, compared with average and 2017.
Every year the Idaho Department of Fish and Game (IDFG) conducts fish population surveys on various river reaches in the Upper Snake River region. In the spring of 2018, surveys were conducted on the Chester to Fun Farm, Vernon to Chester, and Box Canyon, reaches of the Henry’s Fork River. These surveys provide valuable information on abundance, age-class structure, fish size, and species composition within the fishery. IDFG recently published the results in their annual brochure and this blog will highlight and explain some of those results. Largest Rainbow Trout sampled during the 2018 population survey in th Box Canyon reach. Highlights Box Canyon Abundance estimate for fish greater than 6 inches in length: 2,796 Rainbow Trout per mile 2017 abundance estimate: 2,913 Rainbow Trout per mile Average length 10.1 inches 2017 average length: 11.5 inches Max length: 22 inches Abundance estimate of age-2 class fish was higher than predicted for a second year in a row (see below for more details) Chester to Fun Farm 1,225 trout per mile (727 Rainbow Trout and 498 Brown Trout) Average length Brown Trout: 15 inches Rainbow Trout: 14 inches Max length Brown Trout: 23 inches Rainbow Trout: 20.5 inches Vernon to Chester 1,612 trout per mile (1,071 Rainbow Trout and