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<br /> <br />A lag curve having the equation, <br /> <br />lag, hours = 1.2 <br /> <br />( }0.38 <br />LLCA <br />I"s <br /> <br />has been used in several Bureau studies for estimating lag times for <br /> <br />. basins. having rapid runoff cha!'ac teristics such as steep foothill-type <br /> <br />terrain. However, it was believed that lag times indicated by this <br /> <br />curve are two severe (short) for many of the mountainous subareas <br /> <br />delineated on Plate 6, main text. Therefore, the lag curves shown on <br /> <br />Plate 9, main. text, were selected for use in this study. The deriva- <br /> <br />tian of these curves is explained in the following paragraphs. <br /> <br />This Section has in progress as workload permits a research project <br /> <br />directed toward establishment of basic curves for estimating lag times <br /> <br />using the above method of plotting results of hydrograph analyses. <br /> <br />However, it has been postulated that in the equation, <br /> <br />. (LL )~. <br />lag, hours = C ~. <br />. . IS <br /> <br />7' . <br />tbe exponent'/~may have' a constant value and that the constant C, <br /> <br />wbich in effect is an index to runoff rate, may be estimated from <br /> <br />watershed topographical features, cover and soil characteristics. <br /> <br />Data available for the lag time research project for mountainous <br /> <br />terrain in western United States included results of 42 analyses from <br /> <br />Bureau-wide IDF studies and 61 points from a 1962 study of lag re1a- <br /> <br />tions by the Los Angeles District, Corps of Engineers. The Corps <br /> <br />data included 14 points from a Bureau IDF study for Glen Canyon <br /> <br />.- <br /> <br />7 <br /> <br />. . "_'''''_:''4.'~ , <br /> <br />.~" <br /> <br />...1.->.............., ............. <br /> <br />.w__- <br /> <br />. <br />