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<br />. -_ <br />c <br />=_= TUTTLE APPLEGATE, INC. <br />Consultants for Land and Resource Development <br />Dr. .Jeris A. Danielson <br />State Engineer <br />July 16, 1990 <br />Page 2 <br /> <br />The NOAA Technical Report NWS 33, 'Evaporation Atlas for the <br />Contiguous 48 United States', published by the U.S Department of <br />Commerce was used to determine the amount of evaporation. The <br />following values were found for the Koenig Gravel Pit location: <br />NWS Class A Pan Evaporation 42.00 inches/year <br />NWS Class A Pan Coefficient 0.73 <br />Gross Lake Evaporation 30.70 inches/year <br />These values are for the period of May-October. The annual gross <br />evaporation was then estimated by comparing this data with the <br />data from a NWS station which measures annual pan evaporation. <br />The nearest station, Cherry Creek Reservoir, has a 17 year record <br />indicating that 80°s of the annual evaporation occurs during the <br />months of May-October. Using this ratio it is estimated the <br />annual amount of evaporation at the mine site is 38,3 <br />inches/year. The monthly evaporation was then calculated by <br />using the monthly percentages as suggested by the Office of the <br />State Engineer in their criteria for these reports (See Table No. <br />1). <br />The precipitation at the site was found by using data from the <br />publication, 'Climatography of the United States No. 81'. The <br />precipitation at the mine site is estimated to be the same as <br />that found at the nearest weather station which is located in <br />Windsor. The annual mean precipitation is 12.13 inches/year. <br />The breakdown of monthly averages is found in Table No. 1. <br />Effective precipitation was determined in order to compute the <br />net lake evaporation (See Table No. 1). Effective precipitation <br />was computed as 70% of the total precipitation for the months <br />April-October. A value of 85% was used for the winter months of <br />November-March. This 85% figure differs from the value suggested <br />by t:he State Engineer of 70%. Infiltration increases during the <br />cooler months of the year due to a lack of high intensity storms. <br />In addition, the first 0.5 inches of precipitation during the <br />winger months should be considered fully as effective <br />precipitation. This can be supported by the fact that these <br />properties are highly permeable gravel deposits in a floodplain. <br />