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. . I. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I. . . . . . . . . . drainage area of the Florida at its confluence point with the Animas River is approximately 221 sq mI. The La Plata River originates in the La Plata Mountains in the western portion of the county. It generally flows from north to south following the alignment of State Road 140 from its headwaters area south into New Mexico. The La Plata River is the largest stream system within the county for which no floodplain information (either detailed or approximate) has been developed. At the Colorado-New Mexico state line, the drainage area to the La Plata is approximately 331 sq mi. La Plata County is primarily a rural community with the only significant urbanization being the Durango area. Landuse within the major river basins of the county consists mainly of undeveloped mountain areas and agricultural uses in valley and lower elevation areas. Floodi"!!: Problems a"d Floodi"!!: History Generally, severe floods on the major streams of La Plata County such as the Pine, Florida, Animas and La Plata Rivers are the result of general storms occurring between July and October. General storms are characterized by prolonged, heavy rainfall over a large area and result in peak flows of moderate volume and duration. High-intensity, short duration cloudburst-type rainstorms, which are typical during the summer months, cause flooding only on streams with smaller drainage areas. Flooding potential on the larger streams though, also exists from the rapid melting of snow in the late spring. Snowmelt flood flows are characterized by moderate peaks, large volumes and long durations. Snowmelt floods are generally less damaging than those resulting from general rainstorms. Flooding information for La Plata County prior to the turn of the century is practically non- existent. On the Animas River, large floods are known to have occurred in 1896, 1909, 1911, 1927, 1937, 1941, 1946, 1949, 1970 and 1972. The largest of these events occurred on October 5, 1911. During that storm, a peak discharge of 25,000 cfs was recorded on the Animas River. This is the worst flood event on record for the entire San Juan River Basin and major flooding also occurred in other river valleys. Major snowmelt floods occurred on the Animas River in June 1927, May 1941 and June 1949, The flood of June 1927 was the result of rainfall on melting snow and produced a peak flow of approximately 20,000 cfs, On the Los Pinos River major flooding occurred in 1911, 1927, 1957 and 1970. In 1957, Vallecito Reservoir was filted to capacity and floodgates were opened releasing approximately 13,000 cfs. In 1970, a thunderstorm event produced approximately 4.5 inches of rain within a 6- to 12-hour time period and a number of vehicles and homes above Vallecito Reservoir were damaged. Previous Studies The original floodplain information for unincorporated La Plata County was a Flood Hazard Boundary Map published by the Federal Insurance Administration in 1977. The first PIS for the County was subsequently issued on December 15, 1981. The first revision to that PIS was dated March 16, 1995 and was carried out to incorporate intermittent channelization and more detailed 3