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The following account of flooding from Plum Creek basin in Douglas County is representative of typical floods in the area for which information is available. High-intensity, heavy rains occurred in the Plum Creek basin on the afternoon of June 16, 1965. Over 12 inches fell near Castle Rock, and over 14 inches fell near Palmer Lake and near Larkspur in approximately 4 hours. East and West Plum Creeks crested at 126,000 and 36,800 cubic feet per second (cfs), respectively, during the afternoon. The unit runoff above the site on East Plum Creek just downstream from Castle Rock was 1,170 cfs per square mile for a drainage area of approximately 108 square miles. Western tributaries of West Plum Creek and all tribu- taries of Plum Creek downstream from Sedalia were not in the high rainfall areas and contributed little or no runoff during the flood. The combination of steep slopes, sand and gravel streambed, and relatively open and straight reaches of Plum Creek near Louviers was conducive to high velocities and standing waves. The computed mean velocities in seven cross sections surveyed after the flood were near 15 feet per second, which implies maximum velocities of approximately 20 to 22 feet per second. The amount of scour and fill, the size of the cottonwood trees that were uprooted or bent over, and the matted condition of the debris on trees are physical indications that confirm the computed velocities. The damage in rural areas of the Plum Creek basin was extensive. The heavy runoff deposited a variety of debris, from sand to huge boulders and trees, on fields and pastures. Road embankments were severely eroded, and bridges on county, State, and interstate roads were destroyed. Large cut banks, particularly along East Plum Creek, were left after land had been washed away. Much of the Town of Castle Rock was inundated, and telephone service to approxi- mately 100 phones in the town was disrupted. Seven homes, a church, the Grange Hall, and the lower part of the main street in Sedalia vanished during the flood. The Denver and Rio Grande Western Railroad between Denver and Palmer Lake, built in l871-72, had never been damaged as extensively as it was in 1965. Five bridges, many culverts, and approximately 4 miles of track were damaged. The track was out of service for approximately 6 weeks after the flood. Repairs to the facilities cost $468,000. The Atchison, TOpeka, and Santa Fe Railway also follows the South Platte River and Plum Creek, and repairs, primarily to one bridge, cost approximately $500,000. Although the Plum Creek gaging station near Louviers was destroyed, observations indicated that the flow increased from approximately l50 to 154,000 cfs in less than 3 hours. The recurrence interval of this flood was estimated at greater than 500 years. Prior to the 1965 event, the maximum discharge was 7,700 cfs, in August 1945 (Reference 5). s