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<br />G~~ '~3 <br />I iI ~ >-) 'J ' <br />:..1.:-','(. . <br /> <br />period of the data base uses average monthly values calculated from <br />the 1935 to present data. <br /> <br />This use of average values is based on the assumption that the reach <br />gains and losses that historically occurred before the closure of <br />Glen Canyon Dam and Hoover Dam do not describe the present and pro- <br />jected river conditions below these dams. The nature of the mean- <br />dering river flowing through the Lower Basin that existed before the <br />closure of these dams has undergone significant changes. The results <br />of these changes and the expected behavior of the river system below <br />these dams can only be described by data recorded subsequent to their <br />closure. <br /> <br />Three of the four actual flow stations in the Lower Basin also use <br />average values for portions of their record sets. For these sta- <br />tions, average values of the existing portions of the record sets <br />were used to fill in gaps in the early years of the records. Average <br />values were used because of a lack of historical data and poor rela- <br />tionships between available data at gauging stations. This prevented <br />extension of the data using multiple regression or other techniques. <br />Average values were used at the Little Colorado River station from <br />1906-1925, at the Virgin River station froll1 1906-1909, and the Bill <br />Williams River station from 1906-1913. <br /> <br />~ <br />i <br /> <br />The hydrology data base presently extends only to Imperial Dam. This <br />in effect assumes that the sum of gains and losses between Imperial <br />Dam and the Southern International Boundary is. zero. Work lS pre- <br />sently underway to extend the hydrology data base from Imperial Dam <br />to Mexico. This work is expected to be completed and documented by <br />the end of 1985. <br /> <br />~ <br />fi <br />[, <br /> <br />5.4 Hydr~~_~ta Output <br /> <br />The MHYDRD program can generate statistical and graphical output data in <br />addition to creating the hydrology data input file for input to the <br />model. The output data summarizes the data contained in the hydrology <br />data base. The output data that are available are listed below along <br />with the MHYDRO command associ ated with it. <br /> <br />CHECKSUM - Sums monthly flow and salt values to obtain total values <br />of flow and salt for the entire period of record at one <br />or more stations. <br /> <br />INDEX - Prints an index of stations in the data base. <br /> <br />k <br />, <br />I <br />i <br />r <br />I <br />. <br />I <br /> <br />CORRELATE - Computes correlation coefficients between specified <br />stati ons. <br /> <br />PLOT - <br /> <br />Creates plots (with the help of another program) of <br />annual values of flow and salt versus time, a double <br />mass plot of accumulated flow or salt, accumulated <br />values of flow and salt versus time, or flow versus <br />salt. <br /> <br />23 <br />