Introduction 1 Description of study area 4 Physiography and drainage 4 General geology 4 Climate 4 Monitoring network 5 Streamflow characteristics 6 Average streamflow 6 Major rivers 6 Intra-area streams 7 Low flows 12 Major rivers 12 Flow duration 12 Low-flow frequency 14 Storage requirements 18 Intra-area streams 19 Flow duration 20 Low-flow frequency 21 Storage requirements 21 High flows 24 Major rivers 24 Peak-flow frequencies 24 Annual flood volumes 25 Intra-area streams 25 Peak-flow frequencies 25 Annual flood volumes 35 Water-quality characteristics 35 Water-quality criteria 36 Flow and general water-quality characteristics 36 Flow variability in relation to water quality 37 Specific conductance 39 Hydrogen-ion concentration (pH) 40 Water temperature 41 Dissolved oxygen 41 Alkalinity 43 Hardness 43 Oil and grease 47 Sediment characteristics 48 Major dissolved constituents 48 Major rivers 48 Intra-area streams 55 Trace elements 58 Nutrients 62 Biological characteristics 62 Contents III Water-quality characteristics Continued Organic characteristics 62 Pesticides 62 Radiochemical characteristics 62 Need for future monitoring 68 Data for current use 68 Data for planning and design 68 Data to define long-term trends 68 Data to determine effect on the stream environment 68 Summary 69 References cited 69 Conversion factors 72 FIGURES 1-2. Maps showing: 1. Location of study area within Upper Colorado Region 2 2. Location of streamflow-monitoring stations 3 3-45. Graphs showing: 3. Relation of annual flow at station 09307000, Green River near Ouray, to that at station 09315000, Green River at Green River, water years 1948-55, 1957-66 11 4. Relation of annual flow at station 09306900, White River at mouth, near Ouray, to that at station 09306500, White River near Watson, water years 1975-79 11 5. Frequency curve of annual mean flow at station 09315000, Green River at Green River, water years 1965-79 11 6. Frequency curve of annual mean flow at station 09306500, White River near Watson, water years 1924-79 12 7. Annual mean flow for station 09315000, Green River at Green River 13 8. Annual mean flow for station 09306500, White River near Watson 14 9. Average, maximum, and minimum monthly mean flows at stations 09306500 and 09306900 on the White River, water years 1975-79 15 10. Average, maximum, and minimum monthly mean flows at station 09315000, Green River at Green River, water years 1965-79 15 11. Relation of average annual precipitation measured during 1975-79 to normal annual precipitation published for 1941-70 for eight long-term National Oceanic and Atmospheric Administration stations near the study area 15 12. Relation of average annual runoff to mean altitude 15 13. Variance in average annual runoff 16 14. Relation of average annual flow in Evacuation Creek to distance upstream from mouth 17 15. Relation of average annual flow in Bitter Creek to distance upstream from mouth 17 16. Relation of average annual flow in Willow Creek to distance upstream from mouth 18 17. Relation of average annual flow in Hill C...