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<br />The tributaries flowing into the Blue River are very steep and <br />shallow. The channels are approximately 1 foot deep, and the <br />slopes are approximately 150 feet per mile. The flood plains, <br />whicn are developed in the lower reaches, vary in width from 10 to <br />400 feet. They are covered with grass and willow and pine trees <br />in the upper reaches. <br /> <br />The climate of Breckenridge is cool, with an average yearly temperature <br />of 350F. Annual precipitation is 14 inches, with approximately <br />one-half of it occurring as snowfall (Reference 1). <br /> <br />The primary soil group in Breckenridge along the flood plain is <br />the Cryaquolls Association, which is cold, deep, and somewhat <br />poorly drained. Elsewhere, the soils are of the Cryoborolls-Rock <br />outcrop Association. These are cold, deep, and well drained. <br />These soils are found on the steep mountain slopes and high <br />reaches (Reference 2). <br /> <br />2.3 Principal Flood Problems <br /> <br />Flooding along the Blue River, Sawmill Gulch, Illinois Gulch, and <br />Lehman Gulch through Breckenridge occurs primarily in mid-June, <br />with the principa~ cause of flocxiflows being runoff from snowmelt <br />(Reference 1). According to stream gage records, approximately <br />97 percent of the annual peak flows in the Blue River basin have <br />been the result of melting winter snow accumulations (Reference 3). <br />spring runoff usually begins the first week in April, increases <br />to a peak by mid-June, and then returns to a normal flow by early <br />August. Rainfall occurs in the basin; however, this is primarily <br />after tqc peak snowmelt period. These summer rainstorms rarely <br />cause floodflows (Reference 4). <br /> <br />The largest discharge recorded during 64 years of record on the <br />Blu~ River near Dillon was 1250 cubic feet per second (cfs), which <br />occurred on June 17, 1965. The high discharge was a result of <br />snov-:melt and a high-intensity thunderstorm centerE~d on a tributary <br />above the Town of Breckenridge; it had a return period of 50 <br />years. Floodiny wit.hin the town was caused by backwater from <br />blocked culverts and bridges (Reference 1). Many of the culverts <br />have since been replaced; however, if these become blocked, they would <br />again cause flooding around the major crossings. Some shallow <br />flooding is caused by the culverts backing up and overland flow <br />from gulches. <br /> <br />The most recent flood occurred on July 23, 1965. This flood was <br />caused by a high-intensity storm over a tributary. As in the <br />storm earlier that year, the Blue River topped its banks; however, <br />damage was not as extensive. <br /> <br />3 <br />