–106°45' –107°00' –107°30' Steamboat Lake –107°15' Pearl Lake iver ins k R 40°45' ad Mounta El Elkhe ek MOFFAT re Park Range CONTINENTAL C ad DIVIDE khe El MOUNT ZIRKEL WILDERNESS k e e r Lake C Elbert n 11 o i t a ic Elkhead rtif Fo Reservoir 10 Craig pa River ROUTT Yam 8 Steamboat eek 40°30' Milner Springs Cr ish 12 Hayden 7 F JACKSON ek 6 re 9 Fish Creek C Reservoir ge 5 Sa Wi lliam reek e k s Fo Fish C re EXPLANATION rk C Mountains k Lake Oa GRAND Subbasin Catamount Gore Range Yampa River below Craig k Oak Stagecoach ree C Creek Reservoir Yampa River above Elkhead Creek, ut 3 4 GRAND ro T near Hayden 1 2 40°15' Yampa River at Milner Phippsburg SARVIS CREEK Y WILDERNESS am Elk River near Milner p a R i Yampa River at Steamboat Springs Allen Basin v e Reservoir Yampa r Yampa River below Oak Creek, near RIO BLANCO Flat Tops er Steamboat Springs iv r R Phillips ea Creek Yampa River above Stagecoach FLAT TOPS B Reservoir WILDERNESS Subbasin boundary GARFIELD 0 5 10 15 20 MILES 12 Streamflow and water-quality analysis 40°00' Yamcolo 0 5 10 15 20 KILOMETERS site and site number (table 1) Reservoir 11 Stillwater Streamflow only site and site number Reservoir (table 1) Upper Yampa River Basin 2 Water-quality only site and site number Base from U.S. Geological Survey digital data, 1:750,000, 2020 (table 1) Geographic Coordinate System North America 1983 projection DENVER Decimal degrees North American Datum of 1983 den21-0013-day/den21-0013_fig01.ai –106°45' –107°00' –107°30' –107°15' r Rive 40°45' Elk ek re C d hea Elk 11 10 pa River 8 Yam 40°30' 12 9 7 6 5 3 4 iver a R 2 EXPLANATION p 1 40°15' m a Cretaceous-age sandstones and shales Y Yampa coal field Upper Yampa River Basin boundary 12 USGS streamgage or water-quality site (table 1) 0 5 10 15 20 MILES Base from U.S. Geological Survey digital data, 1:750,000, 2020 40°00' 0 5 10 15 20 KILOMETERS Geographic Coordinate System North America 1983 projection Decimal degrees North American Datum of 1983 den21-0013-day/den21-0013_fig02.ai 4,000 3,000 2,000 in cubic feet per second 1,000 Mean monthly streamflow for water years 2013 through 2018, 0 April May June July March August JanuaryFebruary October September NovemberDecember Month EXPLANATION Site name Yampa River at Steamboat Springs, CO (site 7, table 1) Elk River near Milner, CO (site 8, table 1) Yampa River above Elkhead Creek near Hayden, CO (site 10, table 1) den21-0013_fig 03 1-day maximum Mean 7-day minimum 125 A. Yampa River above Stagecoach 100 Reservoir, CO 75 50 25 0 −25 −50 −75 125 B. Yampa River below Stagecoach 100 Reservoir, CO 75 50 25 0 −25 −50 −75 125 C. Yampa River at Steamboat 100 Springs, CO 75 50 25 0 −25 −50 −75 Change in streamflow, in percent per decade Change in streamflow, 125 D. Yampa River above Elkhead Creek 100 near Hayden, CO 75 50 25 0 −25 −50 −75 125 E. Yampa River below Craig, CO 100 75 50 25 0 −25 −50 −75 April May June July April May June July April May June July March August Annual March August Annual March August Annual JanuaryFebruary October JanuaryFebruary October JanuaryFebruary October September NovemberDecember September NovemberDecember September NovemberDecember Month EXPLANATION Estimated slope Significant downward trend 90 percent confidence interval den21-0013_fig 04 1-day maximum Mean 7-day minimum 125 A. Fish Creek near Steamboat 100 75 Springs, CO 50 25 0 −25 −50 −75 125 B. Elk River near Milner, CO 100 75 50 25 0 −25 −50 −75 125 C. Elkhead Creek above Long Gulch 100 near Hayden, CO 75 50 25 0 −25 Change in streamflow, in percent per decade Change in streamflow, −50 −75 10 D. Yampa River at Steamboat 5 Springs, CO 0 −5 −10 April May June July April May June July April May June July March August Annual March August Annual March August Annual JanuaryFebruary October JanuaryFebruary October JanuaryFebruary October September NovemberDecember September NovemberDecember September NovemberDecember EXPLANATION Month Estimated slope Significant downward trend Significant upward trend 90 percent confidence interval den21-0013_fig 05 40 ) y 20 0 –20 Deviation from mean peak streamflow date, in days ( y = −0.067x + 131.373, R2 = 0.024 –40 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 2010 2020 Year (x) EXPLANATION Annual deviation from mean peak streamflow date y = Equation describing linear regression Slope of linear regression den21-0013_fig 06 Yampa River above Stagecoach Reservoir, CO 100 EXPLANATION 75 Largest value within 1.5 times 50 interquartile range above 75th percentile 25 75th percentile 50th percentile Interquartile 0 (median) range 25th percentile Yampa River below Oak Creek near Steamboat Springs, CO Smallest value within 1.5 times 100 interquartile range below 25th percentile concentrations 75 Model estimated daily Outside concentration—Value is greater than 1.5 times or less than 3 times the 50 interquartile range beyond either end of the box 25 0 Discrete concentration Discrete (<) concentration Elk River near Milner, CO 100 75 50 25 0 Yampa River at Milner, CO 100 75 50 25 0 Yampa River above Elkhead Creek near Hayden, CO 400 300 200 Discrete concentrations and model-estimated daily mean of suspended sediment, in milligrams per liter 100 0 Jan. Feb. Mar. Apr. May June July Aug. Sept. Oct. Nov. Dec. Month den21-0013-day/den21-0013_fig07.ai Little Morrison Creek near Stagecoach, CO EXPLANATION 1.0 Largest value within 1.5 times 0.50 interquartile range above 75th percentile 0 75th percentile Yampa River above Stagecoach Reservoir, CO 50th percentile Interquartile (median) range 1.0 25th percentile Smallest value within 1.5 times interquartile range below 0.50 concentrations 25th percentile Outside concentration—Value is greater Model estimated daily 0 than 1.5 times or less than 3 times the interquartile range beyond either end Yampa River below Oak Creek near Steamboat Springs, CO of the box 1.0 CDPHE interim concentration standard (table 2) 0.50 Discrete concentration 0 Yampa River at Steamboat Springs, CO 1.0 0.50 0 Elk River near Milner, CO 1.0 0.50 0 Yampa River at Milner, CO 1.0 0.50 0 Yampa River above Elkhead Creek near Hayden, CO 1.50 2010 1.00 Discrete concentrations and model-estimated daily mean of Kjeldahl nitrogen, in milligrams per liter 0.50 0 Yampa River below Craig, CO 1.50 2002 2010 1.00 0.50 0 Jan. Feb. Mar. Apr. May June July Aug. Sept. Oct. Nov. Dec. Month den21-0013-day/den21-0013_fig08.ai 1.25 1.00 Little Morrison Creek near Stagecoach, CO 0.75 0.50 0.25 1.25 1.00 Yampa River above Stagecoach Reservoir, CO 0.75 0.50 0.25 1.25 Yampa River below Oak Creek near Steamboat Springs, CO 1.00 0.75 0.50 0.25 1.25 Yampa River at Steamboat Springs, CO 1.00 0.75 0.50 0.25 1.25 Elk River near Milner, CO 1.00 0.75 0.50 0.25 1.25 Discrete concentration of total nitrogen, in milligrams per liter 1.00 Yampa River at Milner, CO 0.75 0.50 0.25 Yampa River above Elkhead Creek near Hayden, CO 2.00 1.00 0 Yampa River below Craig, CO 2.00 1.00 0 April May June July March August January February October September November December EXPLANATION Month Discrete concentration Discrete (<) concentration Discrete (E) concentration CDPHE interim concentration standard (table 2) den21-0013_fig 09 0.20 Yampa River above Stagecoach Reservoir, CO 0.15 0.10 0.05 0 0 25 50 75 0.20 Yampa River below Oak Creek near Steamboat Springs, CO 0.15 0.10 0.05 0 0 25 50 75 0.20 Elk River near Milner, CO 0.15 0.10 0.05 0 0 25 50 75 0.20 Yampa River at Milner, CO Total phosphorus concentration, in millgrams per liter Total 0.15 0.10 0.05 0 0 25 50 75 0.45 Yampa River above Elkhead Creek near Hayden, CO 0.30 EXPLANATION 0.15 Discrete concentration Discrete (<) concentration 0 0 100 200 300 Suspended sediment concentration, in millgrams per liter den21-0013_fig 10 Little Morrison Creek near Stagecoach, CO EXPLANATION 0.20 0.15 Largest value within 1.5 times 0.10 interquartile range above 0.05 75th percentile 0 75th percentile Yampa River above Stagecoach Reservoir, CO 50th percentile Interquartile (median) range 0.20 25th percentile 0.15 Smallest value within 1.5 times interquartile range below 0.10 25th percentile concentrations 0.05 Outside concentration—Value is greater Model estimated daily 0 than 1.5 times or less than 3 times the interquartile range beyond either end Yampa River below Oak Creek near Steamboat Springs, CO of the box 0.20 CDPHE interim concentration 0.15 standard (table 2) 0.10 Discrete concentration 0.05 Discrete (<) concentration 0 Discrete (E) concentration Yampa River at Steamboat Springs, CO 0.20 0.15 0.10 0.05 0 Elk River near Milner, CO 0.20 0.15 0.10 0.05 0 Yampa River at Milner, CO 0.20 0.15 0.10 0.05 0 Yampa River above Elkhead Creek near Hayden, CO 0.45 0.30 Discrete concentrations and model-estimated daily mean of total phosphorus, in milligrams per liter 0.15 0 Yampa River below Craig, CO 0.45 0.30 0.15 0 Jan.