UPPER COLORADO RIVER COMMISSION FIRST ANNUAL REPORT I- MARCH 20, 1950 I (b) Water Supply Forecasts. The Treasurer of the Commission is bonded to the amount of $40,000 and the Commission's depository has deposited securities It is contemplated that forecasts of streamflow and water with the Federal Reserve Bank of Denver to the amount of $50,000 supply conditions will be made by the Secretary's office as fre- to secure the Commission's funds. quently as necessary to provide information for administration of the Compact. At the present time several agencies publish fore- The Commission's budget for the fiscal year ending June 30, casts of streamflow for the Colorado River and its tributaries above 1951 is attached as Appendix K. Lake Mead. These agencies are the United States Weather Bureau, Soil Conservation Service, Colorado River Water Conservation Dis- V. HYDROLOGY trict, and the Bureau of Reclamation. Forecasts are usually made by these agencies asof the first of each month January through May for the subsequent run-off season. These forecasts Refinement of hydrologic data hereinafter contained can be are made for periods of time, and points on the Colorado River or expected as a result of detailed investigations now known to be its tributaries specific to the needs or functions of the agency underway. forecasting. (a) Inflow-Outflow Manual. The techniques and hydrologic data used in the forecasts by other agencies, and their forecasts, are of interest to the Com- One of the assignments carried out by the Engineering Ad- mission and will continue to be. However, it is believed that fore- visory Committee was the preparation of the Inflow-Outflow casting techniques and procedures must be developed to provide Manual which is included in full as Appendix L of this report. information specific to the administrative needs of the Commission. It is planned that the engineering staff of the Secretary's office The Inflow-Outflow Method of determining stream depletions will initiate the study of streamflow forecasting problems during was adopted by the Upper Colorado River Commission as stated in Fiscal Year 1951. Article VI of the Compact. The Manual was submitted at the meeting of the Compact Commission held at Salt Lake City, (c) Average Annual Flows at State Lines. Utah, on August 5, 1949. It was adopted by that Commission and was recommended to and adopted by the Upper Colorado River Average annual flows at State Lines were found, for the period Commission as "the basis for the commencement of administrative 1914 to 1945, to be as follows : calculations on the Upper Colorado River." AVERAGE ANNUAL HISTORIC FLOWS The Engineering Advisory Committee, in its Final Report to AT STATE LINES (1914-1945, incl.) the Upper Colorado River Compact Commission, stated the most Arizona important factors influencing depletion to be (1) "the areas using (1000 A.F.) water as a result of a man-made irrigation" ; (2) "the unit rates of - consumptive use of irrigation water"; (3) "stream depletion at Ungaged area tributary to Ran Juan River 86.5 sites of use"; (4) "channel losses between sites of use and Lee Ungaged area tributary to Colorado River Ferry"; and (5) "stream depletions above certain key gages, at 46.8 Arizona share of main stem channel losses within state boundaries, and at Lee Ferry." State -0.1 The effects of all these numerous factors are automatically integrated as additional development, by irrigation, industrial, or Net flow at State Line other enterprises, takes place in the Upper Basin causing man-made Colorado depletion of stream flow. The net effect of such depletion can be - determined by the application of the inflow-outflow method and the Little Snake River (at mouth) 226.9 Manual presents examples and procedures for the determination Yampa River (exclusive of Little Snake River) of results. 1,172.5 I Colorado (continued) ( TTtah (continued) (1000 A.F.) White River Paria River 18.1 Ungaged area tributary to Green River Ungaged area tributary to Colorado River Colorado River including Gunnison River below Green River, Bluff and Cisco 777.3 Dolores River Ungaged area tributary to San Juan River at Bluff 29.3 San Juan River above Rosa Utah share of main stem channel losses Pine River within State -50.6 Animas River Net Flow at State Line LaPlata River Mancos River Wyoming McElmo Creek Green River above Linwood 1,364.4 Ungaged area tributary to San Juan River Little Snake River (at State Line) 249.8 Colorado share of main stem channel losses Ungaged area tributary to Green River within State below Linwood 15.1 Net Flow at State Line Wyoming share of main stem channel losses New Mexico within State -18.7 Ungaged area tributary to San Juan River Net Flow at State Line 1,610.6 New Mexico share of main stem channel losses Sum of Flows at State Lines 14,361.1 within State (d) Historic Contributions at Lee Ferry. Net Flow at State Line (Average 1914-1945, inel.) Utah Historic Flow Out of State Historic Contribution to - State at State Lines Losses Flow at Lee Ferry Tributaries of Green River above Linwood Acre-Feet Acre-Feet Acre-Feet % of Total Arizona 133,200 1,000 132,200 0.96 Henry's Fork Colorado 10,408,400 455,600 9,952,800 72.18 Brush Creek near Jensen New Mexico 186,100 7,700 178,400 1.29 Ashley Creek near Vernal Utah 2,022,800 6,000 2,016,800 14.63 Duchesne River near Randlett Wyoming 1,610,600 102,200 1,508,400 10.94 Price River at Mouth Total 14,361,100 13,788,600 100.00 Ungaged area tributary to Green River (e) Irrigated Areas. Dolores River The following tabulations show the average irrigated areas for Ungaged area tributary to Colorado River the study period, 1914-1945, inclusive, and the present irrigated above Cisco areas adopted by the Engineering Committee. IRRIGATED AREAS ing tabulation shows the virgin contributions at State Lines and Lee Ferry and also the out-of-state channel losses which were State Average Present estimated for average undepleted flow conditions. Arizona 3,770 9,840 Colorado 790,606 790,600* VIRGIN FLOW AT LEE FERRY New Mexico 39,000 43,620 Virgin Flow Out of State Contribution to Virgin Utah 288,520 303,977 State at State Lines Losses Flow at Lee Ferry Wyoming 228,700 236,675 Acre-Feet Acre-Feet Acre-Feet 9% of Total Arizona 137,200 1,000 136,200 0.87 Total 1,350,596 1,384,712 Colorado 11,451,200 482,300 10,968,900 70.14 New Mexico 257,400 9,500 247,900 1.58 *Assumed to be same as average for period, 1914-1945. Utah 2,567,600 6,500 2,561,100 16.38 (f) Incidental Areas. Wyoming 1,837,000 112,600 1,724,400 11.03 The areas of non-cropped land adjacent to and consuming irri- Total 16,250,400 611,900 15,638,500 100.00 gation water incidental to the irrigation of the crop lands were estimated by inspection of the Bureau of Reclamation land classi- (i) Historic flows at Key Gaging Stations. cation sheets, field inspection, available aerial surveys and other detail and general maps of the irrigated areas. The incidental areas The average annual discharges for the years 1914-1945 and the adopted by the Committee are as follows: annual discharges for the water years 1946, 1947, 1948, and 1949 (Average for Study Period, 1914-1945, Incl.) at selected stream flow stations are as shown in the table following Arizona Negligible this page. Colorado 106,812 Acres (j) Main Stem Reservoir Operations. New Mexico 6,482 " Utah 48,625 " The flow of the Colorado River is not uniform but varies from Wyoming 28,600 " year to year. At Lee Ferry the historic flow has ranged between a Total 190,519 Acres minimum of about 4,400,000 acre-feet in 1934 to a maximum of about 21,900,000 acre-feet in 1917. The average historic flow for (g) Man-Made Depletions at State Lines and at Lee Ferry 1914-1945, inclusive, was 13,788,600 acre-feet. In the 10-year period Averages for 1914-1945, Incl. of lowest historic flow, 1931-1940, inclusive, the average annual (Acre feet) flow at Lee Ferry was 10,151,000 acre-feet. State At Sites of Use At State Lines At Lee Ferry Arizona 4,000 4,000 4,000 Reservoir operation studies were made to determine the extent Colorado 1,062,800 1,042,800 1,016,100 to which the Upper Basin can make its apportioned water uses New Mexico 72,200 71,300 69,500 during drought cycles and still meet its compact obligations at Lee Utah 556,500 544,800 544,300 Ferry, as it is quite evident that holdover reservoirs must be con- Wyoming 227,700 226,400 216,000 structed in the Upper Colorado River Basin to impound waters in Years of high runoff, and to release such stored water in critical Total 1,923,200 1,889,300 1,849,900 periods of low runoff, such as 1931-1940, to help meet the Upper Division obligation at Lee Ferry. (h) Virgin Flow at Lee Ferry. Virgin stream flow contributions at State Lines and at Lee Such reservoirs will deplete the flow at Lee Ferry by reason Ferry were obtained by adding to the historic contributions the of evaporation losses in excess of present stream channel losses. man-made stream depletions estimated at these sites. The follow- However, such losses, and the holdover storage capacity required UPPER COLORADO RIVER BASIN KEY GAGING STATIONS Mean Drainage Historic Runoff In Runoff in Runoff In Runoff In Area Flow- Water Year Water Year Water Year Water Year 1947 1948 1949 Streamflow Station Square Water Years 1946 1000 Miles 1914-45 1000 1000 1000 1000 Acre Feet Acre Feet Acre Feet Acre, Feet Acre Feet Provisional Provisional 1.