{"id":807431,"date":"2020-05-14T11:00:00","date_gmt":"2020-05-14T17:00:00","guid":{"rendered":"https:\/\/www.summitdaily.com\/?p=383290"},"modified":"2020-05-14T11:00:00","modified_gmt":"2020-05-14T17:00:00","slug":"the-delicate-dance-of-dillion-reservoir-during-spring-runoff","status":"publish","type":"post","link":"https:\/\/alwaysmountaintime.com\/ksmt\/local-news\/the-delicate-dance-of-dillion-reservoir-during-spring-runoff\/","title":{"rendered":"The delicate dance of Dillion Reservoir during spring runoff"},"content":{"rendered":"<div id=\"article-byline\">\n<div class=\"row\">\n<div class=\"col\">\n<address><strong>David O. Williams<br \/>Aspen Journalism<\/strong><\/address>\n<\/div><\/div>\n<\/div>\n<div class=\"p402_premium\" readability=\"95\">\n<figure class=\"wp-block-image p402_hide\">\n<div class=\"caption-container\">\n<p><img loading=\"lazy\" decoding=\"async\" width=\"780\" height=\"520\" src=\"https:\/\/cdn.summitdaily.com\/wp-content\/uploads\/sites\/2\/2020\/05\/Dillon-Reservoir.jpg\" class=\"attachment-large size-large wp-post-image\" alt srcset=\"https:\/\/cdn.summitdaily.com\/wp-content\/uploads\/sites\/2\/2020\/05\/Dillon-Reservoir.jpg 780w, https:\/\/cdn.summitdaily.com\/wp-content\/uploads\/sites\/2\/2020\/05\/Dillon-Reservoir-300x200.jpg 300w, https:\/\/cdn.summitdaily.com\/wp-content\/uploads\/sites\/2\/2020\/05\/Dillon-Reservoir-768x512.jpg 768w\" sizes=\"auto, (max-width: 780px) 100vw, 780px\"><\/p><figcaption><strong>Dillon Reservoir in Summit County is the largest reservoir in the Denver Water system, holding more than 257,000 acre-feet of water when it\u2019s full. With two outlets \u2014 the Blue River and Roberts Tunnel \u2014 Denver Water officials say it\u2019s complicated to operate.<\/strong><br \/><em>Denver Water<\/em><\/figcaption><\/div>\n<\/figure>\n<p>Denver Water officials late last week increased the release of water from Dillon Reservoir into the Blue River to about 400 cubic feet per second as inflow held steady at about 500 cfs through Monday. The latter number is expected to steadily rise this week as spring runoff picks up.<\/p>\n<p>The current forecast from the National Oceanic and Atmospheric Administration\u2019s Colorado River Basin Forecast Center estimates there is, as of Monday, 146,000 acre-feet of water \u2014 in the form of snowmelt \u2014 that will flow into Dillon Reservoir through July 31. There\u2019s currently 17,500 acre-feet of space in the reservoir, according to Denver Water, so about 128,500 acre-feet will flow out of the reservoir either to the Blue River or Roberts Tunnel by July 31, with an estimated 13,000 acre-feet through the tunnel.<\/p>\n<p>All of these complex calculations are the first steps in a delicate dance Denver Water performs each spring-runoff season to balance public safety with Denver\u2019s water needs, recreation, hydroelectric demands and obligations to downstream senior water-rights holders.<\/p>\n<p>\u201cDillon is our biggest reservoir and one of our more complicated to operate,\u201d said Nathan Elder, water resources manager for Denver Water. \u201cMost of our other reservoirs only have one outlet, but Dillon\u2019s got both the outlet to the Blue and the outlet to the Roberts Tunnel, which provides water to the East Slope and down the North Fork (of the South Platte River) to Strontia Springs Reservoir and then to our customers.\u201d<\/p>\n<div class=\"row\">\n<div class=\"col\" readability=\"6\">\n<div class=\"row sd-donation sd-donation-mobile p-0\" readability=\"7\">\n<div class=\"col-xl-4 p-2\">\n<div data-bg=\"url(https:\/\/cdn.summitdaily.com\/wp-content\/uploads\/sites\/2\/2020\/03\/SDN-logo-white-1.png)\" class=\"p-0 mt-2 mb-2 h-75 text-center rocket-lazyload\">\n<p><img decoding=\"async\" src=\"https:\/\/cdn.summitdaily.com\/wp-content\/uploads\/sites\/2\/2020\/03\/SDN-logo-white-1.png\" class=\"logo m-0 p-0 invisible\"><\/p>\n<\/div>\n<\/div>\n<p><h3 class=\"d-inline mr-3\">Support Local Journalism<\/h3>\n<p><button class=\"btn d-inline\" type=\"button\" onclick=\"handleDonationButtonClickMidArticle()\">Donate<\/button><\/p>\n<\/div>\n<p><\/div>\n<\/div>\n<p>The Roberts Tunnel, finished in 1962 about the same time the old town of Dillon was relocated to its current spot and the Dillon Dam was built to supply its current number of more than 1.4 million Denver Water customers, is a 23-mile concrete conduit that diverts water from the Blue River Basin on the Western Slope to the South Platte Basin on the Front Range.<\/p>\n<p>This system is what\u2019s known as a transmountain diversion \u2014 one of many that bring water from the Colorado River basin on the west side of the continental divide to the state\u2019s population center on the Front Range. What it\u2019s not, Elder said, is a way to avoid dangerous spring-runoff flooding.<\/p>\n<p>\u201cWe can\u2019t use Roberts Tunnel as a flood-control option,\u201d he said. \u201cSo we\u2019re very careful about the amount of water we take from the West Slope over to the East Slope. And when we use the Roberts Tunnel, we can only take it over to the East Slope if it\u2019s put towards the demand. We can\u2019t just dump it over there to prevent flooding or high flows below Dillon.\u201d<\/p>\n<p>The 2014 Colorado River Cooperative Agreement places a 400,000 acre-foot limit on Blue River water stored in existing or future Denver Water storage facilities on the Front Range.<\/p>\n<p>There are more than 1,000 properties in&nbsp;regulatory floodplains&nbsp;in Summit County, according to the&nbsp;Federal Emergency Management Agency, and quite a few of them are along the Blue as it makes its way northwest through Silverthorne and toward its confluence with the Colorado River near Kremmling.<\/p>\n<h3><strong>Snowpack melting<\/strong><\/h3>\n<p>This time of year, as snowpack begins to melt into local tributaries \u2014 the Blue, Snake River and Tenmile Creek all feed Dillon Reservoir from the south \u2014 Elder and his team closely monitor snowmelt forecasts and weather reports to coordinate with local officials to prevent flooding.<\/p>\n<p>\u201cDenver Water has worked with the town over the years to release water from Dillon Reservoir at rates between 50 cfs and 1,800 cfs,\u201d said Tom Daugherty, Silverthorne\u2019s director of public works. \u201cThey have done a very good job of doing that. Denver Water attends our local meetings concerning snowmelt runoff and inform us of what they expect.\u201d<\/p>\n<p>FEMA designates 2,500 cfs as a 10-year flood level just below Dillon Dam, while 3,350 cfs there would be 100-year-flood levels. The amount of runoff pouring into the reservoir varies widely, depending on weather conditions and snowpack, from a low inflow of 410 cfs in the drought year of 2012 to a high of 3,408 cfs in 1995.<\/p>\n<div class=\"p402_hide\">\n<figure class=\"wp-block-image size-large is-style-default\">\n<p><img decoding=\"async\" src=\"https:\/\/cdn.summitdaily.com\/wp-content\/uploads\/sites\/2\/2020\/05\/Roberts-Tunnel-1024x683.jpg\" alt class=\"wp-image-383293\" srcset=\"https:\/\/cdn.summitdaily.com\/wp-content\/uploads\/sites\/2\/2020\/05\/Roberts-Tunnel-1024x683.jpg 1024w, https:\/\/cdn.summitdaily.com\/wp-content\/uploads\/sites\/2\/2020\/05\/Roberts-Tunnel-300x200.jpg 300w, https:\/\/cdn.summitdaily.com\/wp-content\/uploads\/sites\/2\/2020\/05\/Roberts-Tunnel-768x512.jpg 768w, https:\/\/cdn.summitdaily.com\/wp-content\/uploads\/sites\/2\/2020\/05\/Roberts-Tunnel-1536x1024.jpg 1536w, https:\/\/cdn.summitdaily.com\/wp-content\/uploads\/sites\/2\/2020\/05\/Roberts-Tunnel-2048x1365.jpg 2048w\" sizes=\"(max-width: 1024px) 100vw, 1024px\"><\/p><figcaption><strong>An inspection team leaving the 23-mile Roberts Tunnel east portal in Park County in 2016. The tunnel, which diverts water from the Blue River to the Front Range is inspected every five years.<\/strong><br \/><em>Denver Water<\/em><\/figcaption><\/figure>\n<\/div>\n<\/div>\n<p>The amount of snowpack on the Front Range and rate of melting due to high temperatures or rain events also impacts when Denver Water turns on the Roberts Tunnel and how much water it takes out of Dillon Reservoir. The Blue River Decree dictates that Denver Water needs to keep as much water on the Western Slope as possible and can take water only to meet demand.<\/p>\n<p>\u201cLast year was a good example of that,\u201d Denver Water spokesman Todd Hartman said. \u201cWe had so much snowpack on the Front Range that we just didn\u2019t need the Roberts Tunnel water and couldn\u2019t take it because of that demand issue.\u201d<\/p>\n<p>That resulted in higher flows on the Blue below the dam last runoff season.<\/p>\n<p>\u201cIt got up to around 1,900 cfs, and we didn\u2019t actually turn on the Roberts Tunnel until the second week in August last year,\u201d Elder said. \u201cThat\u2019s after everything on the East Slope filled and we started dipping into that storage and streamflow dropped off on the East Slope.\u201d<\/p>\n<p>This year, there\u2019s a similarly healthy snowpack above the reservoir and also decent snowpack on the Front Range, but temperatures have been higher and the spring runoff season hasn\u2019t been nearly as wet and cool as last year.<\/p>\n<p>\u201cWe have a SNOTEL (snow telemetry) site on top of Hoosier Pass, which is extremely important for monitoring that basin and for forecasting, and it\u2019s still at 121% of normal right now,\u201d Natural Resources Conservation Service hydrologist Karl Wetlaufer said last week. \u201cIt looks like it did actually have a net accumulation through April and is just really just starting to turn around and melt out now over the last few days with this warm weather.\u201d<\/p>\n<p>The NRCS produces snowmelt forecasts used by Denver Water, which also taps into NOAA\u2019s forecast center.<\/p>\n<p>Based on information from SNOTEL sites, snowpack above Dillon Reservoir peaked at 127% of normal. The forecast center\u2019s inflow outlook for Dillon Reservoir is 104% of average, and the forecast from the NRCS was 107% of average.<\/p>\n<p>The first priority for Denver Water is to fill the reservoir to meet customer needs, but it also tries to minimize high flows out of the reservoir via the Blue River and maintain water levels so that the Frisco and Dillon marinas can operate from June through Labor Day. Elder said the minimum operating level for both Dillon and Frisco marinas is 9,012 feet in elevation.<\/p>\n<p>The goal, Elder said, is to get the reservoir to that level or higher by June 12, and on Monday afternoon the surface level of the water in the reservoir was at 9,010 feet. The reservoir is full when the elevation of the water, as measured on the dam, is 9,017 feet, which is 257,304 acre-feet of water. At 9,010 feet, the reservoir is holding around 236,232 acre-feet of water.<\/p>\n<p>Release too much and too early \u2014 to avoid high flows and flooding downstream \u2014 and Denver Water runs the risk of missing the chance to fill Dillon for use by its customers later in the summer season as well as keep the reservoir full for a long boating season. And then there are the downstream hydroelectric factors and calls by senior water-rights holders.<\/p>\n<h3><strong>Senior water rights<\/strong><\/h3>\n<p>While the Blue River Decree does not have a volumetric limit on how much water Denver Water can take out of Dillon Reservoir through the Roberts Tunnel to meet its customer needs, the Roberts Tunnel right is from 1946 and is junior to Green Mountain Reservoir and Shoshone Power Plant rights, which limit the ability of Denver Water to divert. The Roberts Tunnel right is for 788 cfs, which is not a storage right but instead a direct-flow right.<\/p>\n<p>So if Green Mountain gets toward the end of its fill season and hasn\u2019t filled and Dillon has diverted, then Denver Water owes water to Green Mountain. Green Mountain Reservoir, located on the Blue River in northern Summit County, was created specifically to compensate the Western Slope for diversions to the Front Range as part of the Colorado-Big Thompson Project.<\/p>\n<p>Then on the Colorado River in Glenwood Canyon, well downstream from where the Blue feeds the Colorado at Kremmling, there\u2019s Xcel Energy\u2019s Shoshone Generating Station hydroelectric plant \u2013 which has one of the most senior water rights on the main stem of the Colorado River. A 1902 right draws 1,250 cfs of water downstream to meet the plant\u2019s needs. During dry times of the year, such as late summer, the power plant often places a \u201ccall\u201d on the river, meaning junior diverters upstream \u2014 including Denver Water \u2014 must stop diverting so that Shoshone can get its full allocation of water.<\/p>\n<div class=\"p402_hide\">\n<figure class=\"wp-block-image size-large is-style-default\">\n<p><img decoding=\"async\" src=\"https:\/\/cdn.summitdaily.com\/wp-content\/uploads\/sites\/2\/2020\/05\/Blue-River.jpg\" alt class=\"wp-image-383295\" srcset=\"https:\/\/cdn.summitdaily.com\/wp-content\/uploads\/sites\/2\/2020\/05\/Blue-River.jpg 1024w, https:\/\/cdn.summitdaily.com\/wp-content\/uploads\/sites\/2\/2020\/05\/Blue-River-300x200.jpg 300w, https:\/\/cdn.summitdaily.com\/wp-content\/uploads\/sites\/2\/2020\/05\/Blue-River-768x512.jpg 768w\" sizes=\"(max-width: 1024px) 100vw, 1024px\"><\/p><figcaption><strong>The Blue River travels north-northwest through Dillon Reservoir to its confluence with the Colorado River near Kremmling. Each spring Denver Water performs a delicate balancing act to accommodate flows from snowpack runoff.<\/strong><br \/><em>Denver Water<\/em><\/figcaption><\/figure>\n<\/div>\n<p><a href=\"https:\/\/www.summitdaily.com\/news\/the-delicate-dance-of-dillion-reservoir-during-spring-runoff\/\" target=\"_blank\" rel=\"noopener noreferrer\">via:: Summit Daily<\/a><\/p>\n","protected":false},"excerpt":{"rendered":"<p>David O. WilliamsAspen Journalism Dillon Reservoir in Summit County is the largest reservoir in the Denver Water system, holding more than 257,000 acre-feet of water when it\u2019s full. With two outlets \u2014 the Blue River and Roberts Tunnel \u2014 Denver Water officials say it\u2019s complicated to operate.Denver Water Denver Water officials late last week increased [&hellip;]<\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[99],"tags":[],"class_list":{"0":"post-807431","1":"post","2":"type-post","3":"status-publish","4":"format-standard","6":"category-local-news"},"acf":[],"publishpress_future_action":{"enabled":false,"date":"2026-07-11 03:53:04","action":"change-status","newStatus":"draft","terms":[],"taxonomy":"category","extraData":[]},"publishpress_future_workflow_manual_trigger":{"enabledWorkflows":[]},"distributor_meta":false,"distributor_terms":false,"distributor_media":false,"distributor_original_site_name":"KSMT The Mountain","distributor_original_site_url":"https:\/\/alwaysmountaintime.com\/ksmt","push-errors":false,"_links":{"self":[{"href":"https:\/\/alwaysmountaintime.com\/ksmt\/wp-json\/wp\/v2\/posts\/807431","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/alwaysmountaintime.com\/ksmt\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/alwaysmountaintime.com\/ksmt\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/alwaysmountaintime.com\/ksmt\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/alwaysmountaintime.com\/ksmt\/wp-json\/wp\/v2\/comments?post=807431"}],"version-history":[{"count":0,"href":"https:\/\/alwaysmountaintime.com\/ksmt\/wp-json\/wp\/v2\/posts\/807431\/revisions"}],"wp:attachment":[{"href":"https:\/\/alwaysmountaintime.com\/ksmt\/wp-json\/wp\/v2\/media?parent=807431"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/alwaysmountaintime.com\/ksmt\/wp-json\/wp\/v2\/categories?post=807431"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/alwaysmountaintime.com\/ksmt\/wp-json\/wp\/v2\/tags?post=807431"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}