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<br />. <br /> <br />n ,r, ('.....! S <br />('j ., ~ (~ ~ -, . <br />'" "..1 ..'- <br /> <br />. <br /> <br />PART L SUMMARY <br /> <br />. <br /> <br />The San Juan River within Colorado drains a 1,230 square mile area in <br /> <br /> <br />Southwestern Colorado and discharges into Navajo Reservoir near its confluence <br /> <br /> <br />with the Piedra River immediately above the Colorado-New Mexico State line. <br /> <br /> <br />The river flows generally from the northeast to the southwest, with its headwaters <br /> <br /> <br />originating in the San Juan Mountains near Wolf Creek Fass. A major tributary <br /> <br /> <br />of the San Juan River is the Navajo River, which flows in a generally westward <br /> <br /> <br />direction to its confluence with the San Juan River approximately nine miles <br /> <br /> <br />upstream (east) of Navajo Reservoir. Elevations within the basin range from <br /> <br /> <br />over 13,000 feet to about 6100 feet at Navajo Reservoir. Annual precipitation <br /> <br /> <br />varies from over 50 inches in the San Juan Mountains northeast of Pagosa Springs <br /> <br /> <br />to about 15 inches at Navajo Reservoir. The general location of the San Juan <br /> <br /> <br />River basin is shown on Figure I. <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />The San Juan River and its tributaries above Navajo Reservoir provide <br /> <br /> <br />a water supply for irrigation of about 13,100 acres. Maximum river flow generally <br /> <br /> <br />occurs in April, May, and June, resulting primarily from snowmelt runoff. <br /> <br /> <br />Typically, about two-thirds of the annual runoff occurs during the three month <br /> <br /> <br />period. Minimum river flows can generally occur from August through February. <br /> <br /> <br />Flows on the mainstem of the San Juan and Navajo rivers have historically been <br /> <br /> <br />in excess of irrigation water requirements for the irrigated lands along the <br /> <br /> <br />rivers. hrigation water shortages occasionally occur on several tributaries <br /> <br />when available streamflow in the summer is insufficient to meet full irrigation <br /> <br /> <br />requirements. <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />Long-term streamflow gaging records are available on the San Juan River <br /> <br />and its major tributaries as shown on Figure I. Historic river flows at the San <br /> <br /> <br />Juan River inlet to Navajo Reservoir near Carracas have averaged about 440,000 <br /> <br /> <br />acre-feet per year. Historic flows at the confluence of the Navajo and the <br /> <br /> <br />San Juan rivers have averaged about 109,000 acre-feet per year on the Navajo <br /> <br /> <br />and about 325,000 acre-feet per year on the San Juan. Flows of the Navajo <br /> <br />. <br /> <br />-1- <br /> <br />. <br />