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<br />000122 <br /> <br />- 8 - <br /> <br />Little actual infonnation is available for the San Juan Basin <br />on consumptive use of water by irrigated crops on large irrigated <br />areas. <br />A brief description of each basin and its 9rop pattern and <br />method of water use is included. Present use practices such as <br />diversion rates, consumptive use, and irrigation efficiency are <br />given where records are available or could be estimated with <br />some degree of accuracy. A summary table of present irrigated <br />acreage and present depletions is given at the end of this <br />section. <br />1. San Juan River above Arboles, Colorado. (Upper San Juan Basin). <br />The irrigated crops in this basin are mainly pasture, hay, <br />and alfalfa used in support of the general ranching which is the <br />main agricultural enterprise of this area. Irrigated lands are <br />situated on the valley floors and nearby terraces which can be <br />served by direct diversion from the streams. Little storage is <br />available to conserve spring flood flows, from the melting snows, <br />for use in late season. This coupled with the short growing <br />season prohibits the growing of cash crops. <br />The source of the water supply is the rugged San Juan <br />Mount~ins to the north and east of the area. Most streams flow <br />south and west out of the basin.' Downstream the configuration <br />of the land changes to broader valley floors and the mountains <br />give way to long ridges and broken country. Diversion rates are <br />high, especially in the spring, but return flows are correspond- <br />ingly high. The rainfall during the growing season is about 10 <br />inches, reducing somewhat the crop requirement from stream flow. <br /> <br />--- -~ <br />