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7/28/2009 2:41:05 PM
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4/24/2008 2:57:32 PM
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Weather Modification
Title
Suitability of the Upper Colorado River Basin for Precipitation Management
Date
10/1/1969
Weather Modification - Doc Type
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<br />a common recording length. Three hundred m1d sixty- <br />five sets of these with greater than 0.90 correlation <br />coefficient were used for the calculation of the in- <br />crease in runoff and of the number of years needed for <br />evaluation (see Appendix B). <br /> <br />3. Increase of runoff. At the present stage, it <br />is impossible to assign scientifically a reasonable <br />value to the relative increase in precipitation, ki, <br /> <br />in equation (7), for each station. A uniform 10 per- <br />cent increase of winter precipitation over its natural <br />value is assumed for further computation. Then the <br />increase of spring runoff induced by an increase of <br />winter precipitation is, on the average, found from <br />equation (13) in Section 2 of Chapter III. <br /> <br />Here the Pwi were calculated, not for the common <br /> <br />recording length, which was used to find the regres- <br />sion line, but for the whole recording length of each <br />station (see Appendix B). <br /> <br />The computed value of 6Q for every station is <br />s <br />plotted on Fig. 9 and rough contour lines of equal in- <br />crease of spring runoff are shown there. <br /> <br />The names of the watersheds where the greatest <br />increase in runoff is expected follow: <br /> <br />(1) San Juan Mountains, <br /> <br />(2) Upper reach of the Yampa River and its <br />tributaries, <br /> <br />(3) Headwaters of the Green River, <br /> <br />(4) Upper basin of the Colorado River, <br /> <br />(5) Upper basins of Uinta River, Lake Fork, <br />and Rock Creek, and <br /> <br />(6) Headwaters of the Rafael River basin. <br /> <br />These watersheds also have a large amount of <br />natural precipitation and natural spring runoff. <br /> <br />4. Number of years needed for evaluation. Using <br />6Qs calculated in the previous section, the number of <br /> <br />years needed for evaluation was computed for each sta- <br />tion by equation (16) in Section 3 of Chapter III. <br /> <br />The results are shown in Appendix B and on Fig. 10. <br />The occurrence of aberrant values made it difficult to <br />draw more precise contour lines. This is caused mainly <br />by the fact that the cornman recording length was not <br />used, and the variability of the data affects the value <br />of N to the second power, compared to the case of <br />6Qs in equation (13). <br /> <br />In general, the value of N are smaller in the <br />high mountain watersheds where the large increase of <br />spring runoff is expected. However, when the size of <br />the watershed becomes quite small the trend sometimes <br />reverses. This seems to occur to the watersheds con- <br />sisting of sub-basins with different hydrological <br />features and with a smaller variance. The names of the <br />watersheds where the smaller number of years can be <br />expected follow: <br /> <br />(1) Upper reach of the Yampa River and its <br />tributaries, <br /> <br />(2) Headwaters of the Green River, <br /> <br />(3) Upper basin of the Colorado River, <br /> <br />(4) Upper basins of Uinta River, Lake Fork, and <br />Rock Creek, and <br /> <br />(5) San Juan Mountains. <br /> <br />5. Optimized selection of basins in the pilot area. <br /> <br />(a) Runoff stations in tr~~ area. Out of 53 <br />stations in the San Juan ~lountains and 49 stations in <br />the upper basin of the Colorado River, 15 and 14 sta- <br />tions, respectively, were selected faT the study. They <br />gage representative sub-basins and have relatively long <br />records. The locations of the stations and their char- <br />acteristics are found in Table 2, and on Figs. 6 and <br />11. The covariance matrix was computed and is shown in <br />Table 3. <br /> <br />(b) Optimized selection of basins. As discussed <br />in Section 3 of Chapter III an attempt was made to find <br />a combination of numbers of sub-basins giving the mini- <br />mum number of years for evaluation. This was accom- <br />plished by solving equation ~9) for all possible combina- <br />tions of two through six stations out of 15 in the San <br />Juan Mountains and out of 14 in the upper basin of the <br />Colorado River. The number of all possib Ie combina- <br />tions is so large that only those combinations which <br />yield the twenty lowest values of N* are plotted. In <br />Fig. 12, N* is plotted versus the increase of spring <br />runoff and also versus the drainage area. The minimum <br />value in the San Juan Mountains is six and in the upper <br />basin of the Colorado River it is three. <br /> <br />The same calculation was performed setting all the <br />ai'S equal to 1 in equation ~7)instead of optimizing the <br /> <br />parameters. The results are shown on Fig. 12. The <br />comparison of the results for the two cases demonstrate <br />that the method is effective. <br /> <br />The analysis of the results indicates that several <br />particular sub-basins play a particular important role <br />in making N* small. They are in: <br /> <br />(a) the San Juan Moantains <br /> <br />1077015 <br />1077250 <br />1371555 <br /> <br />Navajo River at Edith <br />Rio Blanco near Pagosa Springs <br />Uncompahgre River near Ridgway, <br /> <br />and in <br /> <br />(b) <br /> <br />the upper basin of the Colorado River <br /> <br />1762500 <br /> <br />East Fork Troublesome Creek near <br />Troublesome <br />Willow Creek below Willow Creek <br />Reservoir <br />North Inlet at Grand Lake. <br /> <br />1810000 <br /> <br />1930000 <br /> <br />These stations do not necessarily have a small value of <br />N in Tab Ie 2. Tab Ie 4 list the optimal combination <br />of gages for group sizes equal to 2, 3, 4, 5 and 6 <br />selected from 15 stations in the San Juan Mountains and <br />from 14 stations in the upper basin of the Colorado <br />Rive r. <br /> <br />The results are very encouraging for eval ua tion of <br />the pilot projects. The method of optimized grouping <br />of basins brings a very large reduction in the number <br />of years needed to establish significance. One may <br />nevertheless question the method. In other words how <br />sensitive is the method? Could a slight variation in <br />this or that parameter say doub Ie the calculated value <br />of N*, quadruple it .,. etc? <br /> <br />A complete theoretical answer to the question is not <br />easy. One can however obtain an idea by varying various <br /> <br />21 <br />
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