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1977 SF = 1976 total SF - 1987 GF parcels assigned to wells permitted in 1977 <br />1977 GS = 1976 total GS + 1987 GS parcels assigned to wells permitted in 1977 <br />1977 SS = 1976 total SS - 1987 SS parcels assigned to wells permitted in 1977 <br />If 1977 S S < 0, SF= 1977 SF + 1977 S S, and 1977 S S = 0 <br />Acreage subsets for 1978 would follow the same algorithm, starting with the acreage subsets <br />determined for 1977, and so on through 1986. This procedure was used for filling acreage <br />forward between each of the coverages (1957 through 1975, 1977 through 1986, 1988 through <br />2000, and 2002 through 2004). <br />A similar procedure was used to fill back to 1950 through 1955 acreage under each subset based <br />on 1956, as demonstrated in the following example: <br />1955 GF = 1956 total GF - 1956 GF parcels assigned to wells permitted in 1956 <br />1955 SF = 1956 total SF + 1956 GF parcels assigned to wells permitted in 1956 <br />Acreage subsets for 1954 would follow the same algorithm, starting with the acreage categories <br />determined for 1955, and so on back to 1950. <br />Acreage under each subset from after 2005 will estimated to be the same as in the 2005 <br />coverage. <br />Lands Irrigated with Ground Water Only <br />Lands served only by ground water generally were not irrigated prior to well development, <br />therefore as new sole-source wells were added, irrigated acreage increased. As a result, the total <br />acreage for ground water may change year to year. <br />The following serves as an example of how the categorized acreage served by wells would <br />change for the year 1977, based on both the 1976 and 1987 GIS acreage, and well information: <br />1977 GF = 1976 total GF + 1987 GF parcels assigned to wells permitted in 1977 <br />1977 GS = 1976 total GS + 1987 GS parcels assigned to wells permitted in 1977 <br />Note that total ground water only acreage in 1977 does not equal total acreage in 1976, instead <br />total 1977 acreage is the sum of 1977 flood irrigated acreage and 1977 sprinkler irrigated <br />acreage. Acreage subsets for 1978 would follow the same algorithm, starting with the acreage <br />subsets determined for 1977, and so on through 1986. This procedure was used for filling <br />acreage forward between each of the coverages (1957 through 1975, 1977 through 1986, 1988 <br />through 2000, and 2002 through 2004). <br />A similar procedure was used to fill ground water only lands back between 1950 and 1955 under <br />each subset based on 1956, as demonstrated in the following example. It is estimated that earliest <br />sprinklers were installed in the South Platte River basin around 1969, based on discussions with <br />water users and review of historical water use studies. The first snapshot to include sprinkler <br />