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3.3.2.1 Spatial Coverage. As shown in Table B-2, HydroBase includes records for <br />7,121 surface water diversion structures in the South Platte River basin and 931 structures in the <br />North Platte River basin (including 135 structures in the Laramie River basin), thereby providing <br />good coverage for basins in Division 1 and Water District 47. <br />3.3.2.2 Period of Records. Record lengths vary as shown in Table 3-2, with the period <br />of digital records available generally dating back to 1950 and continuing through the present. <br />This period of record should be adequate for water resources planning purposes. As shown in <br />Table 3-2, however, some Water Districts do not include data for significant portions of the <br />1950-present period of record. <br />3.3.2.3 Completeness of Records. About 76 percent of the structures in Division 1 and <br />Water District 47 show infrequent records and only 530 structures show recorded diversions <br />exceeding 1,000 acre-feet annually. This 1,000 acre-feet limit was used to provide an indication of <br />the number of larger structures. Of the 7,121 structures in Division 1 and Water District 47, <br />approximately 319 structures have annual diversions of 2,000 acre-feet or greater, representing <br />about 85 percent of the total average annual diversion in Division 1. Approximately <br />210 structures have annual diversions exceeding 5,000 acre-feet, representing about 75 percent <br />of annual diversions in the Division. <br />Many of the smaller ditches in the Water Districts have infrequent measurements, especially <br />prior to the 1980s. As shown in Table 3-2, many of the incomplete diversion records exist in the <br />upper South Platte and North Platte River basins. <br />3.3.2.4 Reliability of Records. Most of the diversion structures are currently equipped <br />with reliable measuring devices such as Parshall flumes. Many of the ditches with diversions in <br />excess of 2,000 acre-feet in the basin have been equipped with continuous recording devices <br />since the early 1960s. In recent years, Division 1 has made an intense effort to require reliable <br />measuring devices on diversion structures. The accuracy of most permanently installed <br />measurement devices is considered good. The accuracy of the records for structures without <br />recording equipment is dependent on the number and timing of spot observations by the Water <br />Commissioner for that District. <br />For those structures without continuous recorders, the DWR's policy is to record changes inflow <br />only. For example if a diversion of 5 cfs was recorded on June 10th and the next reading was <br />3 cfs on June 20th, the DWR enter data on June 10th and June 20th. To determine the diversion <br />for the period June 11th through June 19th, the June 10th value of 5 cfs is carried forward. This <br />procedure of carrying data forward is an efficient database practice that has been accepted in <br />numerous Water Court transfers. It is generally acknowledged in the water community as being <br />a reasonable procedure for developing a complete diversion record. <br />It is assumed that the diversion records have undergone the normal quality control review by the <br />DWR during the process of transcribing records from Water Commissioner field books to the <br />electronic database and are considered sufficiently accurate for water resources planning <br />purposes. On the basis of this review, data for the total water diverted through a given structure <br />are considered reliable. Data for water use are also reasonably reliable. The primary exception <br />p:data\gen\spdss~final report\chapter 3.doc 3-c~ <br />October 31, 2001 <br />