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<br />001903 <br /> <br />Animas River at Durango (1929-1930), San Juan at Blanco (1931-1935), and San Juan at <br />Pagosa Springs (1936-1969) were combined to form a set of 1929-1969 key station values <br />for the gauges on the San Juan (pagosa Springs and Carracas), Rio Blanco, Navajo, and <br />Little Navajo. <br /> <br />2. Similarly the monthly flows for the Animas River at Durango (1929-1930), San Juan at <br />Blanco (1931-1935), and San Juan at pagosa Springs (1936-1969) were used as key <br />station values for gauges on the Piedra, Los Pinos, and Spring Creek. <br /> <br />3. The monthly flows for the Animas River at Durango (1929-1969) were used as key <br />station values for gauges on the Animas River at Durango, Cedar Hill, Farmington and <br />for the Florida near Lemon Reservoir. <br /> <br />4. The monthly flows of La Plata at Hesperus (1929-1969) were used as key station values <br />for gauges on the La Plata at Hesperus, CO-NM Stateline, Farmington, and for the <br />Mancos River, and McElmo Creek. <br /> <br />San Juan Gaaes below Navaio Reservoir <br /> <br />The monthly flows for the main stem gauges below Archuleta (San Juan River at Farmington, <br />Shiprock, and Four Corners) were estimated using the 1929-1969 CRSS natural flows for the San <br />Juan at Archuleta and the San Juan near Bluff as the key stations. These main stem flows were <br />calculated from gain/loss balances as discussed below. <br /> <br />Monthly natural flow balances by reach or gainlloss corrections have to be included in the Model to <br />account for unknown natural gains and losses that occur along any reach of the river. This same data <br />will also be used to back calculate the natural flows at Farmington, Shiprock, and Four Corners. <br />Determination of the individual reach natural flow balance is problematic in that the CRSS natural <br />flow estimates are available for Archuleta and Bluff for water years 1929 to 1969. However, USBR <br />natural flow estimates are available for all San Juan gages between Archuleta and Bluff for water <br />years 1970 to 1993. Using these sets of data the following procedure was used to create the natural <br />flow balances for each reach of the San Juan between Archuleta and Bluff for water years 1929 to <br />1993. <br /> <br />1. CRSS monthly natural flow balance. A monthly natural flow balance was used to <br />estimate the gains and losses for 1929 to 1969 for the Archuleta to Bluff reach based on <br />the following equation. <br /> <br />CRSSaluff - CRSSMb,'da - AnimasNP - LaPla!aNp - MancosNP - McElmoNP <br /> <br />The Animas, LaPlata, Mancos, and McElmo natural flow estimates, indicated by the <br />llNFll subscript in the equation, come from the extended monthly natural flow data <br />discussed previously. <br /> <br />2. USBR monthly natural flow balance and reach ratios. A reach by reach monthly <br />natural flow balance was used to estimate the gains and losses for 1970 to 1993 between <br />gages (Archuleta, Farmington, Shiprock, Four Corners and Bluff) using the USBR <br /> <br />DRAFT - SJRIP Hydrology Model Documentation <br />June 18, 1999 <br /> <br />30 <br />