Laserfiche WebLink
<br />. <br /> <br />-0756 <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />sufficiently intense to produce appreciaole runoff. Therefore, it is <br /> <br />assumed that the 85 square miles of drainage area above this elevation <br /> <br />is non-contributing. On the basis of available climatological and <br /> <br />meteorological data, a storm of this magnitude might occur over the <br /> <br />Purgatoire River basin above Trinidad, but such an occurrence would be <br /> <br />rare. It is believed that such a storm would produce a flood of standard <br /> <br />project magnitude at Trinidad, Colorado. The selected storm as trans- <br /> <br />posed has an average precipitation of 7.02 inches in a 60-hour period <br /> <br />over the 710 square miles of the contributing drainage area above <br /> <br />Trinidad and 6.98 inches over the 613 square miles of contributing <br /> <br />drainage area above Trinidad dam site. <br /> <br />35. Initial losses,inf~ltration indices, and runoff factors. - <br /> <br />Several storms of record were studied in the basin aoove Trinidad in <br /> <br />order to determine initial losses, infiltration indices, and runoff <br /> <br />factors. An accurate determination of initial loss and of runoff pro- <br /> <br />ducing areas is precluded because of the sparse coverage by precipita- <br /> <br />tion stations of the area. For additional data, studies were made of <br /> <br />other watersheds in mountainous areas where basin characteristics were <br /> <br />similar and more detailed data were available. Based on the latter <br /> <br />studies, average percent-runoff curves were developed for 6-hour rain- <br /> <br />fall. Infiltration indices computed by the application of these runoff <br /> <br />curves to the precipitation indicated that 0.49 inch per hour would be <br /> <br />a reasonable minimum infiltration rate. Infiltration studies made of <br /> <br />. _ h ".,_._....- <br /> <br />'''---.. <br /> <br />other watersheds having similar characteristics, and studies conducted <br /> <br />by the Soil Conservation Service, United States Department of <br /> <br />Agriculture, using the North Fork type infiltrometer, indicated a <br /> <br /> <br />weighted mean of 0.49 inch per hour for medium and high areas. From <br /> <br />the analysis of these data, a minimum infiltration rate of 0~~9 inch <br /> <br />per hour "as adopted for. the total watershed above Trinidad d8,m site. <br /> <br />29 <br /> <br />APPENDIX B <br /> <br />;._c. <br /> <br />-~., " ; ". <br /> <br />.;,. ~.~ <br /> <br />