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<br />rainfall are not possible in the Yampa River basin. Flooding <br />from rainfall is characterized by high peak flows and moderate <br />duration of floodflows. <br /> <br />Flooding from convective-type cloudburst storms is characterized <br />by high peak flows, short durations of flow, and small volume <br />of runoff. Because cloudburst storms are small in areal extent <br />and short in duration, they do not constitute a flood threat on <br />streams as large as Yampa River. <br /> <br />Ice jams have constituted a significant debris problem, particularly <br />along Fortification Creek where, historically, ice jams at the <br />highway and railroad bridges have caused substantial flood damage. <br />However, channel improvement work, largely accomplished on an <br />emergency basis in 1949, and improvement of the bridges appear <br />to have reduced the occurrence of ice jams at these locations. <br />Ice in Yampa River and the anabranch channel that carries Fortifica- <br />tion Creek flow to the main stem can also create flood conditions <br />in the lower portion of Fortification Creek. A special significance <br />of ice jams is that the locations of their occurrence and their <br />impacts are indeterminate. Not only is it impossible to predict <br />where an ice jam will occur, the area that could be affected by <br />overflow and the resultant depth of flooding are also elusive. <br />Flow that would not otherwise be damaging could, if associated <br />with an ice jam, flood areas ordinarily considered flood free. <br />Ice jams were not considered in this study. <br /> <br />Historical references to floods on Fortification Creek extend <br />back to 1879, when a major flood inundated the entire area where <br />Craig is now located. A minor flood occurred in 1896, and the <br />fi rst maj or flood since the town was established occurred in Apr il <br />1897. Agricultural areas that are now part of the city and residen- <br />tial properties east of Fortification Creek were severely damaged. <br />Floodflows cut new channels through rich agricultural lands in <br />and around the town. Irrigation ditches and head gates were washed <br />out. <br /> <br />Seven major flood events (1904, 1911, 1914, 1916, 1917, 1921, <br />and 1947) and five less damaging flood events (1902, 1906, 1922, <br />1923, and 1926) have occurred in Fortification Creek since the <br />turn of the century. Six flood events (1914, 1917, 1920, 1921, <br />1957, and 1974) occurred in Yampa River during that period. Of <br />these, the 1914, 1917, 1920, and 1957 floods were caused by rapidly <br />mel ti ng snow. <br /> <br />Yampa River snowmelt flows in the 1974 flood were augmented by <br />rainfall, primarily on snowless areas between Steamboat Springs <br />and Craig. The 1921 event was part of widespread rapid snowmelt <br />and rainfall in many parts of Colorado that year. Flood conditions <br />on Fortification Creek at that time also resulted from snowmelt <br />augmented by rain and were intensified by ice jams near the mouth <br />of the creek. <br /> <br />8 <br />