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14 <br /> These minimum flows are of special interest because of the reduced capacity <br /> for dilution of effluents to the stream. <br /> Notwithstanding occasional large flood discharges and substantial spring <br /> snowmelt, the 550 sq. mi . catchment above the Madrid gaging station would <br /> be classified as a low yield watershed. The 6 year mean annual runoff volume <br /> measured at Madrid is 28,980 ac-ft and represents an average yield of 1 in. <br /> I over the entire watershed. <br /> The width of the valley ranges from a few hundred to a few thousand <br /> feet. Where the geometry of the valley permits, limited flood irrigation <br /> is practiced. It is estimated that approximately 6000 ac-ft are diverted <br /> from the stream for irrigation above the Madrid station. Irrigated lands <br /> are, for the most part, located on the strath terraces. Irrigation on the <br /> lower alluvial terraces is also practiced but, apparently, the small size <br /> often precludes viable irrigated agriculture. Much more extensive irri- <br /> gation occurs in the valley downstream of Trinidad. The stream discharge <br /> in this reach is heavily influenced by the Trinidad Dam and Lake located <br /> immediately upstream from Trinidad. <br /> In addition to irrigation, water is used along the valley for domestic, <br /> stock, and municipal purposes. Numerous wells are known to exist in the <br /> vicinity of the study area. Powell (1952) characterizes the water bearing <br /> capacity of the Raton formation as poor and suggests that, even where an <br /> adequate discharge can be realized, the quality is likely to limit its <br /> usefulness. Measurements of the hydraulic properties and water quality in <br /> both the bedrock and alluvial terraces, conducted as a part of this study, <br /> j are in agreement with Powell 's conclusions. A more detailed discussion of <br /> i the ground-water hydrology is contained in a subsequent section. <br /> GROUND WATER <br /> The specific objectives of the ground-water investigation were to <br /> quAntify the hydraulic properties of both bedrock and alluvial water-bearing <br /> materials and to characterize the quality of waters encountered. These <br /> are the necessary first steps toward projecting the potential consequences <br /> of mining. Of particular interest was the extent and recovery time of the <br />