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2.3 Principal Flood Problems Generally, severe floods are caused by rainfall in the Durango area; rainstorms usually OCCUr during the period from July through October. This type of flood resul ts from' prolonged heavy rainfall over the watershed and is characterized by high peak flows of moderate volume and duration. Flooding is more severe when antecedent rainfall has saturated the soils in the watershed. Flood potential also exists from the rapid melting of heavy snow cover in the late spring. Floodflows resulting from snowmelt are characterized by moderate peaks, large volume, and long durat ion. This type of flood is usually not as damaging as those resulting from rainstorms. Cloudburst storms generally cause flooding on the streams having small tributary areas, such as Dry Gulch Creek. These high- intensity short-duration type rainstorms usually occur during the summer months. Floodflows resulting from cloudburst storms are characterized by high peak flow, short duration of flow, and small volume of runoff. Information on flooding in the study area prior to the turn of the century is practically nonexistent. Detailed information on the earlier historical floods is very limited because streamflow records were not being kept, newspaper accounts were very sketchy, and eyewitness accounts are not available. Large floods occurred lfi 1896, 1909, 1911, 1927, 1937, 1941, 1946, 1949, 1970. and 1972. The flood of October 5, 1911, is considered the most severe flood known in Durango. During that flood, a peak flow of 25,000 cubic feet per second (cfs), which was estimated to be a flood of a 100- year recurrence interval, was recorded. High flows also occurred on Junction and Lightner Creeks. Major snowmel t floods have occurred on the Animas River in May 1941 and June 1949, A rainstorm falling on melting snow in June 1927 produced flows of 20,000 cfs. Cloudbursts have caused numerous floods in the areas near Durango from both Junction and Lightner Creeks. The largest flood on both Lightner and Junction Creeks occurred on October 20, 1972, with peak flows of 2,830 and 1,780 cfs, respectively (approximately a recurrence interval of 50 years), Floodflows for Dry Gulch Creek are not available. Past floods have disrupted highway and railroad traffic and communication services; drowned Livestock; and damaged and destroyed agricultural lands, roads, bridges, buildings, the sewage disposal plant, and the State Fish Hatchery. Several persons have drowned and many others have been injured. 5