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<br />h. EM 1110-2-1410, Interio~ Drainage of Leveed U~ban A~eaB: <br />Hyd~ology, 3 May 1965, Corps of Engineers; <br /> <br />L CWI Project ES-180, Study of Runoff ftoom Bottom Land and <br />Hillside Te~rain, January 1966, Corps of Engineers; <br /> <br />j. CWI Project CW-151, Resel11'eh Note No.3, Ft>equeney Cu1"lJett <br />f~om Incomplete Samples, September 1959, Corps of Engineers; and <br /> <br />k. Engineering HydrauZies, edited by Rouse, published by <br />John Wiley and Sons. <br /> <br />II - CLIMATIC AND METEOROLOGICAL INFLUENCES <br /> <br />2-01. Gene~al.- This section presents climatic and meteorologic <br />discussions and data used as a basis for hydrologic considerations of <br />the Arkansas River at Las Animas. The climate of the area is semiarid <br />and marked with large daily temperature variations. Average annual <br />precipitation varies from about 10 inches in the valley and plains areas <br />to about 30 inches in the headwaters area. Afternoon temperatures are <br />frequently high during summer months but low humidities and continual <br />breezes have a moderating effect. Temperatures drop rapidly after sun- <br />set so that nighttime temperatures are seldom high. <br /> <br />2-02. Preeipitation. - The average annual precipitation at Las <br />Animas is 12.34 inches. Average monthly precipitation varies from 0.27 <br />inch in January to 2.10 inches in july. About 78 percent of the average <br />annual precipitation occurs during the 6-month period from April through <br />September. The intensity of summer storms in the area is illustrated by <br />the following list of maximum recorded 24-hour precipitation amounts: <br /> <br /> Rainfall <br />Station in Inches Date <br />Colorado Springs WB AP 4.27 Apr 1921 <br />Pueblo WB AP 3.77 Oct 1957 <br />Trinidad 3.73 Sep 1942 <br />Las Animas 1 N 3.60 Jul 1958 <br />Walsenburg Power Plant 3.37 Jul 1946 <br /> <br />Most of the summer precipitation results from thunderstorm activity. <br />Pueblo has an average of 44 thunderstorms per year. Thirty-eight of <br />these occur in the 4-month period, May through August. Average monthly <br />and annual precipitation data for selected stations in the area are <br />given in table 3. Detailed precipitation data for Las Animas are given <br />in table 4. Average annual isohyets are shown on plate 2. <br /> <br />2-03. Snowfall.- Heavy snowfall is general in the higher eleva- <br />tions of the watershed. The average annual snowfall at Pueblo is 31.8 <br />inches. The maximum monthly snowfall at Pueblo is 29.3 inches and oc- <br />curred in November 1946. The maximum 24-hour snowfall at Pueblo occurred <br /> <br />5 <br />