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<br />La Junta Local Protection Project <br />La Junta, Colorado <br />Hydrology <br /> <br />1. Purpose. The purpose of this report is to present <br />the basis and results of the hydrologic analysis required for <br />the La Junta Local Protection Project, The recommended plan. 9f <br />improvement consists of channel improvement projects on King <br />and Anderson Arroyos and or the Arkansas River. Presented is an <br />updated regional freql1ency study for development of frequency <br />curves on tributaries of the Arkansas River, a discharge- <br />frequency curve for the Arkansas River at La Junta, and standard <br />project floods at three locations. Plate 1 is a watershed map <br />and shows the location of the project. <br /> <br />( <br />\ <br /> <br />.. <br />2. Unit Hydrographs. Unit hydrographs.were developed by <br />synthetic methods because of lack of rainfall-discharge data to <br />substantiate natural unit hydrographs. The synthetic unit hydro- <br />graphs were determined by use of the fOYQulas presented in <br />paragraph 31 of the main report, Pertinent unit hydrograph <br />data for Anderson and Xing Arroyos are tabulated in Table 1. <br />Unit hydrograph data for the Arkansas River are presented on <br />Plate 15 of the main report. <br /> <br />~.L. <br /> <br />3. Initial Losses and Infiltration Indices. Rainfall <br />losses were obtained from previous studies done for the Arkan- <br />sas River basin. These are contained in the minutes of a <br />conference held in the Albuquerque District on 29-30 September <br />and 1 October 1969. The purpose of that conference was to <br />discuss the hydrology for the Arkansas River subbasin above <br />Great Bend, Kansas, and was attended by District, Division, and <br />OCE personnel. Table 2 is a sUIDQary of the initial and average <br />hourly losses presented at the conference. For the La Junta, <br />Colorado study, ar initial loss of 1.1 inches and an average <br />hourly .loss of 0.26 inch were adopted for use and are average <br />values from Table 2. <br /> <br />4. Standard Project Storm. Standard project rainfall <br />amounts were obtained from Draft llydrometeorological Report <br />(HHR) No, 51 as recommended in letter SHDED-:m (SHAED-P 10 Hay <br />1977) 1st Ind, dated 11. June 1977, subject: "Design lJemorandum <br />No. 1 - Fountain Dam and Reservoir, Arlcansas River Basin, <br />o Fountain Lake, Colorado. An isohyetal storm pattern .,as pre- <br />pared and centered critically above La Junta to obtain rainfall <br />amounts for the Arkansas River above La Junta. Standard project <br />rainfall amounts .rere taken as 50 percent of the I'llI'. An isohyetal <br />pattern was not used for Anderson and King Arroyos since their <br /> <br />1 <br />