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TO: Platte River Water Advisory Committee <br />FROM: Don Anderson, U.S. Fish and Wildlife Service <br />DATE: 3 July 2007 <br />RE: Comments on Colorado's `Cumulative Effect Report for Colorado's <br />Plan for Future Depletions' memo of March 29, 2007 <br />As background, note that Colorado's Illustrative Tool has always had options for a`Wet', <br />`Average', or `Dry' hydrologic year analysis. The only difference between these <br />scenarios is that each assumes a different mix of water-supply sources by sub-region. <br />Figures 1-2007 and 1-2008 in Colorado's March 29 memo were generated using the <br />`average hydrologic year' scenario. As Colorado notes, conditions in the basin since <br />2000 have been unusually dry. If Colorado is obligated under the Program to replace/re- <br />regulate water each year relative to `average' conditions (rather than varying with the <br />occurrence of wet, average, or dry conditions), then it makes sense to evaluate these <br />`average year' Illustrative Tool results as they have in their 3/29 memo.l <br />Where the logic gets a little fuzzy is Colorado's proposal to adjust the `average year' <br />scenario to account for drought conditions in the basin. It is almost certainly true that <br />recent drought has reduced the availability and use of native water supply sources in the <br />South Platte basin, and increased water re-use. The question is whether that justifies <br />changing the assumed mix of water-supply sources in the basin under average year <br />condition, as they have proposed. The Illustrative Tool already includes a`dry year' <br />scenario in which water supplies from native flows in the North, Central, and South <br />regions of the South Platte Basin are assumed to be just 5%, 10%, and 5% respectively - <br />very similar to the 6%-9%-6% settings suggested by Colorado in their memo. <br />Therefore, it seems to me that if the revised numbers used to generate Figures 2-2007 and <br />2-2008 do not reflect a change in water-development strategies in the South Platte basin, <br />but rather simply reflect the recent occurrence of drought, then the justification for <br />changing these figures for the `average year' in the Illustrative Tool is doubtful. To <br />phrase this differently: do Colorado's revised percentages reflect a lack of developed <br />capacity for new native water supplies, or simply the unavaidability of new (junior) native <br />water? <br />Alternatively, if these numbers do reflect an actual change in water development trends <br />(for example, if decisions have been made along Colorado's Front Range since the initial <br />development of this Illustrative Tool not to implement measures which would capture <br />more native flows), then Colorado's adjustments may be appropriate. However, if this is <br />` Note that under the `dry hydrologic year' scenario, Colorado has no replacement obligations to keep the <br />river whole at the state line. According to the 1997 Illustrative Tool, no new depletions are generated in <br />dry years due to the basin's heavy reliance on trans-basin imports and non-tributary water sources.