WSP10425 - Laserfiche WebLink

Home Browse Search

on~296 Climate, Weather, and Water The climate of the Southern San Juan Mountains is typical of the Colorado Rockies. The area usually experiences low relative humidity, abundant sunshine, cool summers with frequent showers, heavy winter snows, and wide daily temperature fluctuations. Average annual precipitation varies from 12-50 inches per year, depending on elevation. Approximately 65 percent of the precipitation occurs as snow with the balance from summer showers. Temperatures generally decrease with elevation except for occasional winter inversions in mountain valleys. West of the Continental Divide the unit drains into the San Juan River, while east of the divide the streams flow into the Rio Grande River. The Chama-San Juan Water Diversion project is a man-made "exception" and annually diverts a maximum of 270,000 acre feet of water from the San Juan River drainage to the Rio Grande Basin. However, the average is 135,000 acre feet yearly. Water from this project is used for domestic, recreation, and irrigation purposes. l Major streams and rivers in the western portion of the unit include Wolf and Mill Creeks, East Fork of the San Juan, Rito Blanco, Rio Blanco, little Navajo, and the Navajo Rivers. The streams yield about 360,000 acre feet per year (an acre foot is the quantity of water required to cover one acre one foot deep.) ~ The Rio Chama, Rio de los Pinos, Conejos, La Jara, and Alamosa Rivers are the major waterways east of the Continental Divide. These watersheds provide approximately 464,000 acre feet of water yearly, but downstream water needs generally exceed this flow. The bulk of the runoff occurs in late spring from the melting snows. The amount and timing varies from year to year due to changes in snow accummulation, water content in the snow, and weather conditions. The water from the plann.ing unit is used for recreation, domestic, irrigation, and fish and wildlife purposes. The chemical and physical qualities of the water are generally excellent, with the exception of the Alamosa River from Iron Creek to Terrace Reservoir. Here, some pollution occurs from exposed natural oxides and hard metals on lookout and South Mountain. Mines and mine tailing ponds on Iron Creek and Wightman Fork also contribute to the problem.