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Historical North Platte River calls reviewed for this task include records for 12 of the last 13 <br />years (1993 to 2005, excluding 1994). The available call data for the North Platte River basin in <br />Colorado (Water District 47) are summarized in Table 1 at the end of the memorandum. The <br />calls do not appear to exhibit any significant changes over the period of available record. <br />According to Division 6 Engineer Erin Light, changes in calls recorded over time are more likely <br />a response to variable hydrology and other factors related to operations of particular ranches in <br />the basin. <br />See SPDSS Task 3 -Water District 47 Meeting Notes memorandum for more information on <br />river administration and typical call scenarios in the North Platte River basin. <br />Comments and Concerns <br />An enhanced call record data set for the South Platte River main stem has been developed over <br />1950 to present and for the North Platte River basin in Colorado over 1993 to present. These data <br />are expected to be included in future versions of HydroBase with a disclaimer requested by <br />Division 1. The disclaimer will explain that the release dates developed for the pre-1981 South <br />Platte River calls are based upon information available to the State Engineer and believed to be <br />accurate, and that persons seeking to use the release dates in any legal proceedings are <br />responsible for verifying their accuracy. <br />The following are noted: <br />The absence of a call indicates free river conditions existed. However, free river <br />conditions do not automatically imply water is available for diversion by a junior <br />appropriation. For example, there are numerous instances from 1950 to 2005 when a <br />reservoir or ditch may not have made a call because there was no upstream user with a <br />junior right that could be called out or a user with a senior right decided it was not <br />necessary to call out a junior diverter. Additional diversions by a junior upstream <br />appropriation may have triggered a call during some of the historical instances of free <br />river conditions. While the development of an accurate historical call data set is <br />considered a valuable contribution to the South Platte and North Platte River basins, they <br />should only be used as one indication of historical water availability. Additional <br />knowledge of river administration and hydrology is required for complete analysis of <br />available water supply. <br />2. The 1950 to present call records are expected to be used in a Call Analysis Program to be <br />developed in Phase 4 of the SPDSS effort. This Call Analysis Program is expected to <br />compare the historical calls to auser-input water right administration number at a <br />location on the stream system to provide an indication of the number of days the input <br />water right would have historically been in and out of priority along with the daily calling <br />right affecting the input administration number. As discussed above, this output will <br />provide an indicator of historical water availability and knowledge of historical and <br />current river administration is recommended for further interpretation of historical call <br />data and available water supply for diversion by a junior right. <br />Page 10 of 14 <br />