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