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<br />4.1 <br /> <br />IV. HYDROLOGY <br />4.1 Climate <br />Annual precipitation in the Telluride area totals approximately 27 inches. <br />Seventeen inches of precipitation generally f~lls as snow from October through <br />April, the remainder occurs as summer showers and thunderstorms. The annual mean <br />temperature is approximately 400F varying from 200F in January to 600Fin July. <br />Humidity is generally quite low, allowing for rapid evaporation. <br /> <br />4.2 DrainaQe Area <br />The drainage area of Cornet Creek is approximately 2.4 square miles at <br />its confluence with the San Miguel River. The drainage area at the mouth of the <br />Cornet Creek canyon, at the northern boundary of the town, is approximately 2.2 <br />square miles. The mouth of the canyon is the approximate apex of the alluvial <br />fan on which the town of Telluride is located. <br /> <br />4.3 PrinciDal Flood Problems <br />Fl oodi ng I n the town of Te 11 uri de can occur from two sources, the San <br />Mi gue 1 Ri ver and Cornet Creek. Flood i ng of the San Mi gue 1 Ri ver generally occurs <br />during late spring snowmelt runoff. Precipitation alone is usually insufficient <br />to cause severe flooding in the large drainages of the region. <br />Past records indicate that a summertime cloudburst thunderstorm over the <br />small drainage area of Cornet Creek, has the greatest potential for severe <br />flooding. A flood resulting from a cloudburst generally has a peak duration of <br />on ly a few mi nutes, followed by a rap i d decrease in flow rate. Due to its <br />position on the alluvial fan of Cornet Creek, flood hazards in the town of Tel- <br />luride are mainly associated with that stream. Specifically, flood hazards <br />associated with mud flows are of concern. Historically, the two largest recorded <br />mud flow events in Telluride occurred between noon and early evening during the <br />last week of July and the first week of August. <br />Mud flow events in Telluride are usually -initiated by brief, very intense <br />thunderstorms, generally lasting less than 30 minutes, followed by rainfall of <br />decreasing intensity. The thunderstorms may be relatively localized, engulfing <br />only the Cornet Creek drainage. In fact, during the 1969 mud flow event, rain <br />did not occur in the town prior to the flood. It is estimated that the frontal <br />wave of a mud flow will arrive at the Cornet Creek canyon mouth approximately <br />10 to 20 minutes after the onset of intense rainfall. The peak discharge arrives <br />