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14 <br />I~ These minimum flows are of special interest because of the reducE:d capacity <br />for dilution of effluents to the stream. ~ <br />II Notwithstanding occasional large flood discharges and substantial spring <br />snowmelt, the 550 sq. mi. catchment above the Madrid gaging station would <br />be classifre as a low yield watershed. The 6 year mean annual runoff volume <br />measured at Madrid is 23,980 ac-ft and represents an average yield of 1 in. <br />~i over the entire watershed. <br />1! 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~rrigatinp <br />1 is practiced. It is estimated that approximately 6000 ac-ft are diverted <br />J from the stream for irrigation above the Madrid station. Irrigated lands <br />1 are, for the most part, located on the strath terraces. Irrigation an the <br />lower alluvial terraces is also practiced but, apparently, the small size <br />often precludes viable irrigated agricuiture. Much more extensive irri- <br />I 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 />r 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 su Bests that, even wr~ere 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 />are in agreement with Powell's conclusions. Amore detailed discussion of <br />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 />qudntify 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 />