Considerations Related to Equal Monthly Volumes

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I V. • The model results presented in January by GCMRC are intended to be a display of the modeling capabilities rather than a "test" of operational scenarios. One key assumption in the scenario presented is that Reclamation can implement equal monthly volumes as presented. In actuality, uncertainty in the hydrologic predictions will result in corrections in flow volumes throughout the year, resulting in trajectory that is step- wise. For example, in the 2006 "options" report, Reclamation modeled ten years of hydrologic conditions which took forecast error into account, and the result was un- equal monthly volumes. Thus, a realistic modeling scenario must incorporate forecast error (which the GCMRC analysis did not). • Here is an example year of the 10 -year study done by Reclamation for the "options" report (2006). The second column represents the SASF case (without HFEs) — an attempt to produce equal monthly volumes. The third column represents MLFF. While the water year in the two cases begins with a different philosophy regarding operations, when forecast error is taken into account, the monthly volumes end up being quite different than what was planned — in both cases. This year is not atypical. Most of the 10 years modeled for this analysis show significant differences from the planned monthly distribution to the one that actually would have occurredz. MONTH SASF MLFF Oct 600 615 Nov 600 595 Dec 800 615 Jan 978 793 Feb 901 876 Mar 770 785 Apr 816 1,297 May 872 1,133 Jun 1,122 1,305 Jul 1,481 1,246 Aug 1,537 1,252 Sep 1,488 1,453 Yr. Total 11,964 11,964 • Therefore, the available information does not support a conclusion that an equal monthly volume (EMV) operation at Glen Canyon Dam will result in significantly more sediment conservation over other scenarios (i.e., all scenarios result in near zero sediment retention after 1- year). Forecast error must be included as well as the error included in the model parameters and model output. 2 The following table is taken from the GCMRC evaluation of AMWG recommended options — prepared for the AMWG in 2006. These data related to model year 2012 2