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<br />LAKE POWELL MEASUREMENTS <br /> <br />The following data was collected from each of the three rafts; water sur- <br />face temperature, air temperature, and relative humidity. The wind was <br />measured by an anemometer placed two meters above the water surface. The <br />anemometers were read once each week. At each of the three rafts, water <br />surface temperature, air temperature, and relative humidity were recorded <br />on 7 day circular charts as shown in Figure 2. Wind was measured and <br />recorded by anemometers placed 2 meters above the water surface which were <br />read once each week. The data was manually read and recorded on the form <br />shown in Figure 3. <br /> <br />ADJUSTMENTS TO DATA <br /> <br />The wind run was required on a daily basis but the raft anemometers were <br />only read weekly on the rafts. Therefore, the daily wind run from anomeme- <br />ters at the Wahweap Marina and Page were used to pro rate the weekly raft <br />wind run readings for each day. <br /> <br />Some of the data was not recorded or was obviously wrong. Therefore, <br />methods were developed to estimate missing data either by interpolation, <br />observing trends before and after the missing data, or by correlation with <br />data from other rafts. Wind has a large effect on evaporation and is <br />highly variable. Therefore, a procedure was developed to estimate missing <br />wind data using a hierarchy of options starting with the most preferred <br />method. This procedure is explained in the files of the Water Operations <br />Branch. Other details and computer printouts are also available in these <br />files. <br /> <br />CALIBRATION OF COEFFICIENT <br /> <br />The evaporation rate as determined by the Lake Powell Research Project <br />(LPRP) was used to calibrate a mass-transfer coefficient. For those days <br />in 1974 when there was concurrent data as collected by the LPRP instruments <br />and Bureau instruments a regression analysis was made for each of the three <br />data stations. Thus there were 295 data sets at Wahweap Bay, 143 data sets <br />at Bullfrog Bay and 133 data sets at Padre Bay. The regression coef- <br />ficients were; .53 at Wahweap; .72 at Padre Bay, and .55 at Bu11frog Bay. <br />These coefficients are not very high mainly because of the determined <br />distribution of wind data. If the regression analysis were done for weekly <br />or longer periods, the regression coefficients would be much higher. A <br />comparison of month1y rates is shown in Tab1e 1. From the regression ana- <br />lysis a mass transfer coefficient of 3.27 was determined and used in <br />equation (3). <br /> <br />6 <br />