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<br />INTRODUCTION <br /> <br /> <br />This technical addendum is prepared to provide the technical <br /> <br /> <br />aspects of hydrologic analysis for the flood insurance studies <br /> <br /> <br />in the San Juan, Archuleta and La Plata Counties, Colorado. Study <br /> <br /> <br />areas, climatology, flood characteristics and flood history are <br /> <br /> <br />briefly described. Methodologies used for flood flow frequency <br /> <br /> <br />and regional frequency analyses are presented. Results are pre- <br /> <br /> <br />sented in tabulated and graphical forms. All applicable data are <br /> <br /> <br />also included. <br /> <br />DESCRIPTION OF STUDY AREAS <br /> <br /> <br />1. San Juan County <br /> <br /> <br />The study area, which includes the Town of silverton and the ad- <br /> <br /> <br />joining unincorporated areas is located in the southwestern part <br /> <br /> <br />of Colorado's mountain region in San Juan County. The approximate <br /> <br /> <br />limits of study areas are shown in figure 1. The Animas River <br /> <br /> <br />flows from San Juan Mountains in southwestern Colorado in generally <br /> <br /> <br />southerly direction and joins the San Juan River at about the <br />Colorado - New Mexico state line. <br /> <br />The drainage area of the Animas River is approximately 75 square <br /> <br /> <br />miles above Silverton. The Cement Creek watershed, which is a <br /> <br /> <br />tributary to the Animas River at Silverton, covers about 20 square <br /> <br /> <br />miles. The Mineral Creek watershed, which is also a tributary <br /> <br /> <br />to the Animas River at Silverton, approximates 50 square miles. <br /> <br /> <br />The topography of the study area in the San Juan County is primarily <br /> <br /> <br />high mountainous terrains with steep to moderately steep slopes. <br /> <br />-1- <br />