Kohn, Michael S. Mast, M. Alisa 20260422 tabular digital data Reston, VA U.S. Geological Survey data release https://doi.org/10.5066/P9Q5AMFV Michael S. Kohn M. Alisa Mast Tara A. Gross 2026 publication Scientific Investigations Report 2025-5047 Reston, VA U.S. Geological Survey Peak-, mean-, and low-streamflow regional-regression equations for natural streamflow in central and western Colorado, 2019 https://doi.org/10.3133/sir20255047 The U.S. Geological Survey (USGS), in cooperation with the Colorado Department of Transportation, developed peak-, mean-, and low-streamflow regional-regression equations for natural streamflow in central and western Colorado. This data release includes geographic information systems data and hydrologic data that were compiled, processed, and analyzed for this peak-, mean-, and low-streamflow study. The 7-day minimum and maximum streamflow for return periods of 2-, 10-, and 50-years at each streamgage were computed from daily mean streamflow data for streamgages operated by the USGS and the Colorado Division of Water Resources (CODWR) for the period of record through water year 2019. The 7-day minimum and maximum streamflows were computed using the USGS software program SWToolbox for the period of record that is representative of unregulated streamflow conditions. Streamgages without 10 years of non-zero daily mean streamflow were excluded from the 7-day minimum and maximum streamflow computations. This child page contains 2 output text files from SWToolbox, one with 7-day maximum estimates (7_day_high.txt) and one with the 7-day minimum estimates (7_day_low.txt). The purpose of this data release is to present data that were used to update regional-regression equations for estimating peak, mean, and low streamflows for use in central and western Colorado. The regional-regression equations relate peak, mean, and low streamflows to topographic and climatic attributes of the stream basins. These regressions can provide reliable estimates of streamflow for ungaged streams that can be used for water-resource management, stream-related structural design, stream-hazard identification, and water-quality management. 19101001 20190930 observed Complete None planned -109.7534 -105.0952 41.3603 36.3682 USGS Thesaurus hydrology streamflow mathematical modeling floods USGS Metadata Identifier USGS:6255fd6ad34e21f8276f4b1f Common geographic areas Colorado No access constraints. Please see 'Distribution Information' for details. These data are marked with a Creative Common CC0 1.0 Universal License. These data are in the public domain and do not have any use constraints. Users are advised to read the dataset's metadata thoroughly to understand appropriate use and data limitations. Michael S Kohn U.S. Geological Survey, ROCKY MOUNTAIN REGION Civil Engineer (Hydrologic) mailing address

Mail Stop 415, W 6th Ave Kipling St

Lakewood CO 80225 US 303-236-6924 303-236-4912 mkohn@usgs.gov Prepared in cooperation with the Colorado Department of Transportation. Colorado Division of Water Resources 2020 application/service Colorado Division of Water Resources [CODWR], 2020, Colorado Division of Water Resources Surface Water Stations: Colorado Division of Water Resources Web site, accessed May 21, 2020, https://dwr.state.co.us/Tools/Stations/. https://dwr.state.co.us/Tools/Stations/ U.S. Geological Survey 2020 application/service U.S. Geological Survey [USGS], 2020, USGS water data for the Nation: U.S. Geological Survey National Water Information System database, accessed May 21, 2020, at https://doi.org/10.5066/F7P55KJN. https://doi.org/10.5066/f7p55kjn Julie E. Kiang Kate Flynn Tong Zhai Paul Hummel Gregory Granato 2018 publication U.S. Geological Survey Techniques and Methods book 4, chapter A–11 Reston, VA US Geological Survey Kiang, J.E., Flynn, K.M., Zhai, Tong, Hummel, Paul, and Granato, Gregory, 2018, SWToolbox: A surface-water tool-box for statistical analysis of streamflow time series: U.S. Geological Survey Techniques and Methods, book 4, chap. A–11, 33 p., https://doi.org/10.3133/tm4A11. https://doi.org/10.3133/tm4A11 No formal attribute accuracy tests were conducted. Values were assumed to be reliable because they were computed from quality-assured streamflow records published by USGS and CODWR No formal logical accuracy tests were conducted. The dataset is considered complete. not applicable not applicable Daily mean streamflow values were downloaded from the USGS National Water Information System (NWIS) database (USGS, 2020) and the Colorado Division of Water Resources (CODWR) database (CODWR, 2020) through water year 2019 for each streamgage. For sites that had data collected by USGS only and had no period of stream regulation in the record, 7-day minimum and maximum streamflow values for return periods of 2-, 10-, and 50-years were computed for the entire period of record using the USGS software program SWToolbox version 1.0.5 (Kiang and others, 2018). The data were computed in nine iterations so the program would not crash due to the large number of sites. For sites that had data collected by USGS only but had some period of stream regulation during the period record, minimum and maximum streamflow values were determined for the unregulated period of record using SWToolbox version 1.0.5. For sites that had data collected only by CODWR or by both CODWR and USGS, daily mean values were compiled from the CODWR database into text files and minimum and maximum streamflow values were determined using the SWToolbox version 1.0.5. The outputs from all the SWToolbox runs are compiled in the "7_day_high.txt" and "7_day_low.txt" files. Regardless of the approach, streamgages without 10 years of daily mean streamflow were excluded from the computations. 20220331 0.0197487373 0.0256295797 Decimal seconds North_American_Datum_1983 Geodetic Reference System 1980 6378137.0 298.257222101 7_day_high.txt tab delimited text file with output from SWToolbox for calculating maximum 7-day streamflow values Producer Defined Identifier USGS or CODWR station number NWIS and CODWR database USGS or CODWR station number BegYear First year of record Producer Defined N/A No Data Producer defined 1891 2007 year EndYear Last year of record Producer Defined N/A No Data Producer defined 1909 2019 year NumZro Number of zero values Producer Defined N/A No Data Producer defined 0 2 count NonZro number of non-zero values Producer Defined N/A No Data Producer defined 3 114 count NumNeg Number of negative values Producer Defined N/A No Data Producer defined 0 91 count Ldist Type of frequency distribution fit to data Producer Defined N/A No Data Producer defined LP3 Log-Pearson Type III Distribution Producer defined Mean Log of mean streamflow in log cubic feet per second Producer Defined N/A No Data Producer defined -1.124 4.661 log of cubic feet per second Stdev Standard deviation of streamflow in log cubic feet per seconds Producer Defined N/A No Data Producer defined 0.024 1.002 log cubic feet per seconds Skw Skew of mean streamflow Producer Defined N/A No Data Producer defined -2.587 1.716 unitless Recur01 2-year recurrence interval Producer Defined N/A No Data Producer defined 2 2-year recurrence interval Producer defined Exceed01 Exceedance probability for 2-year recurrence interval in percent Producer Defined N/A No Data Producer defined 0.5 exceedance probability for 2-year recurrence interval Producer defined N-Day High01 7-day maximum streamflow with recurrence interval of 2 years (7Q2) in cubic feet per second Producer Defined N/A No Data Producer defined 0.0 47274.0 cubic feet per second K-Value01 K-value (frequency factor) for 7Q2 Producer Defined N/A No Data Producer defined -0.27 0.367 unitless Variance01 Variance of 7Q2 Producer Defined N/A No Data Producer defined 1.0 1.176 log cubic feet per second CL_Low01 Lower confidence level for 7Q2 in cubic feet per second Producer Defined N/A No Data Producer defined 0.079 36205.0 cubic feet per second CL_Up01 Upper confidence level for 7Q2 in cubic feet per second Producer Defined N/A No Data Producer defined 0.731 58984.0 cubic feet per second Recur02 10-year recurrence interval Producer Defined N/A No Data Producer defined 10 10 year recurrence interval Producer defined Exceed02 Exceedance probability for 10-year recurrence interval in percent Producer Defined N/A No Data Producer defined 0.1 exceedance probability for 10-year recurrence interval Producer defined N-Day High02 7-day maximum streamflow with recurrence interval of 10 years (7Q10) in cubic feet per second Producer Defined N/A No Data Producer defined 0.0 71302.0 cubic feet per second K-Value02 K-value (frequency factor) for 7Q10 Producer Defined N/A No Data Producer defined 0.75 1.341 unitless Variance02 Variance for 7Q10 Producer Defined N/A No Data Producer defined 0.966 1.007 log cubic feet per second CL_Low02 Lower confidence level for 7Q10 in cubic feet per second Producer Defined N/A No Data Producer defined 0.483 57996.0 cubic feet per second CL_Up02 Upper confidence level for 7Q10 in cubic feet per second Producer Defined N/A No Data Producer defined 6.18 101830.0 cubic feet per second Recur03 50-year recurrence interval Producer Defined N/A No Data Producer defined 50 50-year recurrence interval Producer defined Exceed03 Exceedance probability or 50-year recurrence interval in percent Producer Defined N/A No Data Producer defined 0.02 exceedance probability for 50-year recurrence interval Producer defined N-Day High03 7-day maximum streamflow with recurrence interval of 50 years (7Q50) in cubic feet per second Producer Defined N/A No Data Producer defined 0.0 87211.0 cubic feet per second K-Value03 K-value (frequency factor) for 7Q50 Producer Defined N/A No Data Producer defined 0.772 2.82 unitless Variance03 Variance for 7Q50 Producer Defined N/A No Data Producer defined 0.966 1.007 log cubic feet per second CL_Low03 Lower confidence level for 7Q50 in cubic feet per second Producer Defined N/A No Data Producer defined 0.923 69410.0 cubic feet per second CL_Up03 Upper confidence level for 7Q50 in cubic feet per second Producer Defined N/A No Data Producer defined 15.7 165800.0 cubic feet per second Note Note on processing Producer Defined << empty cell >> No Data Producer defined Note: Could not complete analysis. Review source data for missing or zero flows. 7_day_low.txt tab delimited text file with output from SWToolbox for calculating minimum 7-day streamflow values Producer Defined Identifier USGS or CODWR station number Producer Defined USGS or CODWR station number BegYear First year of record Producer Defined N/A No Data Producer defined 1891 2008 year EndYear Last year of record Producer Defined N/A No Data Producer defined 1909 2019 year NumZro Number of zero values Producer Defined N/A No Data Producer defined 0 63 count NonZro Number of non-zero values Producer Defined N/A No Data Producer defined 3 113 count NumNeg Number of negative values Producer Defined N/A No Data Producer defined 0 90 count Ldist Type of frequency distribution fit to data Producer Defined N/A No Data Producer defined LP3 Log-Pearson Type III distribution Producer defined Mean Mean streamflow in log cubic feet per second Producer Defined N/A No Data Producer defined -1.964 3.326 log cubic feet per second Stdev Standard deviation of streamfow in log cubic feet per seconds Producer Defined N/A No Data Producer defined 0.033 0.901 log cubic feet per second Skw Skew of mean streamflow Producer Defined N/A No Data Producer defined -4.508 2.0 unitless Recur01 2-year recurrence interval Producer Defined N/A No Data Producer defined 2 2-year recurrence interval Producer defined NonExc01 Exceedance probability for 2-year recurrence interval in percent Producer Defined N/A No Data Producer defined 0.5 exceedance probability for 2-year recurrence interval Producer defined N-Day Low01 7-day minimum streamflow with recurrence interval of 2 years (7Q2) in cubic feet per second Producer Defined N/A No Data Producer defined 0.0 2220.8 cubic feet per second K-Value01 K-value (frequency factor) for 7Q2 Producer Defined N/A No Data Producer defined -0.307 0.414 unitless Variance01 Variance for 7Q2 Producer Defined N/A No Data Producer defined 1.0 1.828 log cubic feet per second CL_Low01 Lower confidence level for 7Q2 in cubic feet per second Producer Defined N/A No Data Producer defined 0.039 1825.2 cubic feet per second CL_Up01 Upper confidence level for 7Q2 in cubic feet per second Producer Defined N/A No Data Producer defined 0.074 2498.1 cubic feet per second Recur02 10-year recurrence interval Producer Defined N/A No Data Producer defined 10 10-year recurrence interval Producer defined NonExc02 Exceedance probability for 10-year recurrence interval in percent Producer Defined N/A No Data Producer defined 0.1 exceedance probability for 10-year recurrence interval Producer defined N-Day Low02 7-day minimum streamflow with recurrence interval of 10 years (7Q10) in cubic feet per second Producer Defined N/A No Data Producer defined 0.0 1594.4 cubic feet per second K-Value02 K-value (frequency factor) for 7Q10 Producer Defined N/A No Data Producer defined -1.341 -0.895 unitless Variance02 Variance for 7Q10 Producer Defined N/A No Data Producer defined 1.0 1.499 log cubic feet per second CL_Low02 Lower confidence level for 7Q10 in cubic feet per second Producer Defined N/A No Data Producer defined 0.002 989.24 cubic feet per second CL_Up02 Upper confidence level for 7Q10 in cubic feet per second Producer Defined N/A No Data Producer defined 0.039 1902.5 cubic feet per second Recur03 50-year recurrence interval Producer Defined N/A No Data Producer defined 50 50-year recurrence interval Producer defined NonExc03 Exceedance probability for 50-year recurrence interval in percent Producer Defined N/A No Data Producer defined 0.02 exceedance probability for 50-year recurrence interval Producer defined N-Day Low03 7-day minimum streamflow with recurrence interval of 10 years (7Q50) in cubic feet per second Producer Defined N/A No Data Producer defined 0.0 1193.2 cubic feet per second K-Value03 K-value (frequency factor) for 7Q50 Producer Defined N/A No Data Producer defined -3.298 -0.98 unitless Variance03 Variance for 7Q50 Producer Defined N/A No Data Producer defined 1.0 1.331 log cubic feet per second CL_Low03 Lower confidence level for 7Q50 in cubic feet per second Producer Defined N/A No Data Producer defined 0.0 522.53 cubic feet per second CL_Up03 Upper confidence level for 7Q50 in cubic feet per second Producer Defined N/A No Data Producer defined 0.019 1554.6 cubic feet per second Note Note on processing Producer Defined << empty cell >> No Data Producer defined Note: Could not complete analysis. Review source data for missing or zero flows. GS ScienceBase U.S. Geological Survey mailing address

Denver Federal Center, Building 810, Mail Stop 302

Denver CO 80225 United States 1-888-275-8747 sciencebase@usgs.gov Unless otherwise stated, all data, metadata and related materials are considered to satisfy the quality standards relative to the purpose for which the data were collected. Although these data and associated metadata have been reviewed for accuracy and completeness and approved for release by the U.S. Geological Survey (USGS), no warranty expressed or implied is made regarding the display or utility of the data for other purposes, nor on all computer systems, nor shall the act of distribution constitute any such warranty. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Digital Data https://doi.org/10.5066/P9Q5AMFV none 20260422 Michael S Kohn U.S. Geological Survey, ROCKY MOUNTAIN REGION Civil Engineer (Hydrologic) mailing address

Mail Stop 415, W 6th Ave Kipling St

Lakewood CO 80225 US 303-236-6924 303-236-4912 mkohn@usgs.gov FGDC Content Standard for Digital Geospatial Metadata FGDC-STD-001-1998