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. , . . . . . . . . . ~ ~ ~ I , , , I . . , , , . I evaluations in its winter precipitation augmentation projects. See, for example. Griffith et al (1991) and Griffith and Solak (2002). These evaluations have been well received by the water management community, and a few have undergone independent review and verification (e.g., Stauffer and Williams, 2000). NAWC recommended the historical targeUcontrol technique for evaluations of this project and Denver Water agreed to this approach. Evaluation Unit and Measurements The seeding project is scheduled for operations during the period of November 1, 2002 through March 31, 2003. NAWC has selected that five-month period as the evaluation unit. Our experience in other similar project evaluations indicates that evaluation attempts at durations less than four-five months using winter precipitation measurements can suffer from greater "noise", where natural precipitation variability or a few storms can dominate the statistics, and where instrument error can further confound the analysis. Data from numerous sites over longer periods of time exhibit much less skew, requiring little or no transformation for normalization. For this project evaluation, snowpack, i.e., snowcourse and snow pillow data, based on the April 1 snow water equivalent values, are well suited. These data are available from published manual snow surveys and automated Natural Resources Conservation Service SNOTEL (snow telemetry) sites. The manual snow surveys are typically conducted monthly on site, as close in time as possible to the first of each month (Dec or Jan - Apr or May), providing a snapshot of the depth and water content of the snowpack at the time of the survey. SNOTEL data from various sensors at a given site are available on an automated data communication basis, including snow water equivalent from snow pillows, A reasonably dense array of twenty-three such measurement sites, consisting of sixteen snowcourses and seven SNOTEL sites, are located within or immediately adjacent the target area. Precipitation (water equivalent) data, as measured by a precipitation storage gage, are also well suited, offering the advantage of finer temporal resolution which allows analysis specific to the November 1 - March 31 period. The seven SNOTEL sites within the target area provide these observations in addition to snowpack information. TarQeUControl Evaluation Method for Denver Water NAWC has adopted the evaluation technique for the Denver Water project area as follows. . An historical targeUcontrol method is adopted. . Snowpack data (snow water equivalent) as of April 1 are used for a o