2012-12-26_HYDROLOGY - M2003091 - Laserfiche WebLink

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Dave Bailey, Esq. November 12, 2010 Page 3 Irrigated Lands and Crops Aerial photography taken in 1953, 1975, 1980, and 1998 was obtained and reviewed to confirm the historic use on this property. The 1953 photograph indicates the existence of a small pond but no structures or buildings. The irrigated acreage in 1953 was approximately 68.9 acres. Based upon interviews with Rosie Heaton, the small pond was enlarged in the 1950's or 1960's. A groundwater right was filed for the enlarged pond in Case No. W -3660, claiming a priority date of September 1, 1960. The 1975 aerial photograph indicated the larger pond and some surrounding development had removed about 16.9 irrigated acres. Additionally, in 1970 or so the Heaton's sold the five acres which had been irrigated in the south east corner of the property. Therefore, we used 68.9 irrigated acres from 1911 to 1961; 52 acres from 1962 to 1969 and 47 acres from 1970 to 1998 in our historic use analysis. The 47 irrigated acres show up on the three later photos. This is a conservative approach since more acres may have been irrigated prior to 1953, depending on the date of construction of the first pond. According to Mr. Adams, they did not attempt to re- irrigate with any of the tailwater. The tailwater typically ran along the road (Hwy 119) and back to the river. Based on conversations with Mr. Adams, we assumed that all of the ditch diversions have historically been used to flood irrigate the property with roughly the following crop distribution: 50 percent silage corn and 50 percent alfalfa. Although Mr. Adams stated that in some years they grew all of one crop or the other, and in some years they grew more alfalfa than corn, we believe this is a conservative estimate for the study period. For this analysis we have assumed that although the number of irrigated acres has varied throughout the study period, the 50/50 percentages of corn and alfalfa have remained constant. There is a decree for two wells, including the pond located on the property. Although the pond was decreed for 1.11 cfs for irrigation use, we have been told by Mrs. Heaton and Mr. Adams that it was not used for irrigation purposes historically. The second well was decreed for domestic uses. Therefore, no other sources of irrigation water have been considered in this analysis. Potential Consumptive Irrigation Requirement A maximum farm efficiency of between 40% and 70% is typical for fields that are flood irrigated. For this property, we estimated that a maximum efficiency of 65% was attainable. Based on average annual pro rata diversions, the potential consumptive irrigation requirement (CIR) for the crop mix described above, a 20% conveyance loss, 65% farm efficiency, and varying irrigated acres, the Heaton irrigated fields were often water long (especially in recent years); that is, they often had an adequate supply to fully meet potential consumptive use requirements. Because of the adequate supply, actual efficiencies were often less that 65 %. The CIR was calculated using a modified Blaney - Criddle analysis to determine monthly values for the entire study period utilizing the Longmont 2ESE weather station data which was available for the 1948 through 1998 period for both crops. The 1911 through 1947 period and the few months of missing climate data were filled in with the study period monthly average climate data. The yearly growing season for silage corn was based on the season defined in the Colorado Irrigation Guide for Longmont (May 5th to September 10 ). The yearly growing season for alfalfa varied throughout the study period based on the beginning and ending average 45 degree mean temperature. Crop coefficients for alfalfa and silage corn were determined based on SCS TR -21 growth curves. The average annual CIR values were found to be equal to 1.28 acre -feet per acre and 2.05 acre -feet per acre for silage corn and alfalfa, respectively, as shown in Tables 3 and 4. The average crop irrigation requirements were compared to the Colorado