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<br />. <br /> <br />. <br /> <br />. <br /> <br />'- <br /> <br />0757 <br /> <br />The runoff computed for the standard project and spillway design storms <br /> <br /> <br />was determined by considering an initial loss of 1.20 inches and a mini- <br /> <br /> <br />mum infiltration rate of 0.49 inch per hour during the most intense period <br /> <br /> <br />of precipitation. The runoff precipitation relation curves were used to <br /> <br /> <br />determine the rainfall excess during the periods of lesser precipitation. <br /> <br /> <br />36. Unit h,ydrograEh. - The unit hydrograph for the watershed above <br /> <br /> <br />Trinidad dam site was der-l ved from stream flow records at Trinidad and <br /> <br /> <br />developed in accordance with methods set forth in Chapter 5 of the Engi- <br /> <br /> <br />neering Man\:.al, entitled "Flood-Hydrograph Analyses and Computations," <br /> <br /> <br />dated March 1948. A study was made of several storms and the resulting <br /> <br /> <br />discharge hydrographs of record for Trinidad gaging station. The recorded <br /> <br /> <br />hydro graph at the Trinidad gage for the April 23, 1942 storm WaS consid- <br /> <br /> <br />ered typical of flow produced by total area runoff. A I-hour unit hydro- <br /> <br /> <br />graph was developed from this flood hydrograph. From the above studies, <br /> <br /> <br />the I-hour synthetic unit hydrographs were developed at Trinidad dam site <br /> <br /> <br />using the coefficients from the Trinidad unit hydro graph. The synthetic <br /> <br /> <br />unit hydrograph developed for Trinidad dam site (drainage area 698 square <br /> <br /> <br />miles) was routed to Trinidad gage. The routed hydro graph was then added <br />to the synthetic unit hydro graph for the intervening area (97 square <br />miles). The resulting combined hydro graph reproduced the adopted Trinidad <br />unit hydrograph. In addition, a synthetic unit hydro graph was developed <br />for the portion of the watershed above Trinidad dam site (613 square <br />miles), and above Trinidad gage (710 square miles), which would contri- <br />bute runoff during the standard project storm. Basic data for the adopted <br />I-hour unit hydro graph developed for Trinidad gage and the I-hour syn- <br />thetic unit hydro graphs at the gage and at the Trinidad dam site are shown <br />in table 13. The unit hydrograph ordinates for the 613 square miles area <br />and the 698 square miles area are shown on plates 5 and 7, respectively. <br /> <br />30 <br /> <br />APPENDIX B <br /> <br />. <br /> <br />.': <br /> <br />, .....'z'.,., "_ ~""'c",,~<<-.<__;'~ --;, < ,'~.;".., _,,"'0 0 <br /> <br />. <br /> <br />h. . <br /> <br />