PERMFILE68353 - Laserfiche WebLink

Home Browse Search

Spring runoff is the principal contributor to flow during April, May and June with individual events during the summer months adding to theoverallflow. Groundwateralsocontributestothestream baseflow during the summer months. The San Miguel River at Naturita, Colorado has a drainage area of 1,080 square miles. lorns et a1. (1965a) presents aflow-duration curve developed for the San Miguel River at Naturita based on historic streamflow records. The curve indicates that 90 percent of the time, discharge exceeds 60 cfs, and that flows larger than 1000 cfs occur only 10 percent of the time. The mean discharge of the San Miguel River at Naturita is 351 cfs. Regional Surface Water Quality. The geologic formations and soils overwhich the water flows greatly influences the chemical quality ofsurfacewater. In the Grand Division ofthe UpperColorado River Basin, and more proximate, within the subdivision between the Gunnison and Green Rivers, this statement has been demonstrated by lorns et a1. (1965a}. The San Miguel River Basin, into which Tuttle and Calamity Draws flow, originates in the San Juan Mountains which are principally composed of tertiary volcanic rocks. The lower altitude, interior portions of this basin are chiefly • underlain by the Dakota Sandstone, the Morrison Formation and the Mancos Shale. Ofthese rocks, the Morrison Formation and the Mancos Shale have the greatest potential for influencing water chemistry through solution of readily available minerals. According to lorns (et a1. 1965a), at times of high flow generated largely by snowmelt runoff from the upland areas underlain by volcanic rocks, the water is ofthe calcium bicarbonate sulfate type. During low flow, the water contains less bicarbonate and greater amounts of calcium and sulfate. As Flow progresses downstream, the waterquality will feature higherpercentages of magnesium, potassium, sulfate and chloride. Generally, Total Dissolved Solids (TDS) varies inversely with discharge, and also increases in the downstream direction. lorns et a1. (1965a) mentions that streams flowing from the Uncompaghre Plateau and entering the Dolores River between the San Miguel River and the mouth of the Dolores commonly exhibit a calcium bicarbonate water type with an average TDS of less than 300 ppm. These streams flow IargelyovertheGlenCanyonGroupandtheDakotaFormation. Historicwaterqualitysamplestaken at Naturita, Colorado indicate that the San Miguel River has a weighted average TDS of 316 ppm • (REVISED6/28/07) 2.04.7-21