Letter Regarding Cumulative Effect Report for Colorado's Plan for Future Depletions

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Native South Platte Flows In Colorado's first report to the GC dated March 29, 2007, it was noted that throughout the Platte Basin, there has been an extended drought beginning in 2000 and that has continued. The availability of native South Platte flows with a priority date junior to July 1, 1997 (baseline date for new water related activities per PRRIP) has been less during this drought. In that first report, Colorado proposed a procedure which was accepted for reducing the percent water supply from native South Platte flow development based on the frequency of river calls at the Kersey river gage on the South Platte River in Colorado. That procedure is again used and is detailed in Table 3. The results of Table 3 are incorporated in Table I (far right column G) to determine the amount of new (i.e., water rights junior to July 1, 1997) South Platte native flows available to meet water deliveries for increased population growth. The Kersey river gage is just east of Greeley 145 miles upstream of the Colorado- Nebraska Stateline. This gage is downstream of the Denver metro area and downstream from where all the major tributaries enter the South Platte River so it represents a good location to analyze calls from senior Colorado downstream irrigation and reservoir rights that will effect upstream junior water right development by the front range municipalities. The call records used in Table 3 are from the records of the Colorado State Engineer's Office. The first section of Table 3 lists the monthly percents for April through July that a July 1, 1997 priority date would be out -of- priority at the Kersey river gage for the period 1993 through 2008 base on actual daily call records. A call scenario is also estimated for 2009 where the call scenario for the relatively wetter year of 2007 is used for 2009. With the good spring snow storm received near the end of April 2009 raising South Platte snow packs to about 110% of average, with plains reservoirs full and with fairly good soil moisture for irrigated ground on the South Platte, it is predicted that the snowmelt runoff and subsequent call scenario for 2009 could be similar to 2007. The April through July period is the spring runoff period from snowmelt and is the time when South Platte flow development would take place under junior water rights as assumed in the CPFD (i.e., South Platte flow development assumed to occur at 5% in April, 40% in May, 50% in June and 5% in July). This percent diversion pattern for April through July is used in "fable 3 to compute a weighted in- priority percent amount for April through July. At the Kersey gage as shown in the lower section of Table 3, the weighted in- priority for a 1993 -1997 baseline period is an average of 59.7% of the time a water right junior to July 1, 1997 would be in- priority. For a 1998 -2002 (initial CPFD period), this percent has dropped to an average of 49.6 %. For a recent 2004 -2008 period, this percent has further dropped to 19.4 %. This drop through the 2000 decade is the consequence of the long -term drought. Table 3 computes a 5 -year average in- priority percent for a 2005 -2009 period at the Kersey gage of 32.7% where as noted above the call scenario for 2009 is made to be that of 2007 because of the expected higher snowmelt runoff in 2009. The values for the 1998 -2002 initial CPFD period and the 2005 -2009 period are inserted in table 1 A in the far right column G. These inserted values in Table I for percent in- priority of a junior July 1, 1997 water right are multiplied times the acre -feet reported in the questionnaires for total use of native South Platte flows. Columns A and B of Table 1 A list the breakdown of utilized native South Platte flows that are post -1997 and pre -1997 (Le, pre - 1997 is part of baseline). The 5 -year average call scenario for 2005 -2009 will be used by Colorado in the CPFD analysis since the start of the Program on January 1, 2007. Future annual reports by Colorado to the GC may adjust this call scenario up or down if warranted by changing snowmelt runoff. Results of CPFD Analysis with Revised % Mix of Water Sources Table 1 B computes the revised % mix of water sources by adding to the original % mix (i.e., which was for the 1998 -2002 initial CPFD period) the % change (+ or -) between the initial and recent/current period of 2004 -2008 computed in Table IA. Colorado will use the revised % mix of water sources, which is representative of current conditions for CPFD accretion /depletion analysis for the initial reporting period of 2007 and 2008 and for the next reporting period of 2009 -2013. The revised % mix shows a large increase in water conservation as a source, which illustrates Colorado's efforts to respond to the extended drought by saving water. For the Northern region the percent of water from water conservation has increased from 5% to 18.9 %, for the Central region from 15% to 29.4 %, and for the Southern region from 10% to 18.8 %. The percent of water from reuse activities as also gone up with the largest increase for the Central region changing from 25% to 28.7 %. One would expect reuse to increase in response to drought but it