November 9, 2016 Front Range Water Council c/o James S. Lochhead 1600 West 12th Avenue Denver, CO 80204-3412 RE: WSBRT Risk Assessment Dear Council Members: We have participated in the review of the Phase I Risk Assessment sponsored by the West Slope Basin Roundtables (WSBRT’s), and have also reviewed the proposed scope of work for the next phase of the study (Phase II). We offer the following observations for your consideration. Phase I Study The Phase I study was directed by the Colorado River Water Conservation District, Southwestern Water Conservation District, Hydros Consulting and the West Slope Roundtables. This investigation modeled various assumptions regarding the possibility of Lake Powell dropping below elevation 3,525’. The study also investigated how much water users in Colorado and other Upper Basin States may have to reduce consumptive water use in order to maintain a Lake Powell elevation at 3,525’ for several future scenarios. These future scenarios were based on multi-State operational and hydrologic assumptions specified by the west slope participants in the study. Technical representatives from the three East Slope roundtables were given three briefings on the study and an opportunity to provide questions and comments. Documentation of the Phase I study is primarily comprised of graphs and bullet points from several powerpoint presentations, and a brief overview document. We understand that the budget for the study was not adequate to prepare detailed documentation of the modeling assumptions used in the study, nor the study results. Front Range Water Council November 9, 2016 Page 2 Based on the information available for review, we understand that the primary study assumptions that influence modeling results are: The hydrologic conditions of the last 25 years would be repeated and repeated to represent the long-term future hydrology of the basin (i.e. stress test hydrology). The naturalized inflow to Lake Powell over this 25 year period was over 1.5 million acre feet per year less than the long-term naturalized inflow. The existing 2007 Interim Guidelines that balance Lake Powell and Lake Mead storage levels would remain in place permanently. The Upper Basin would experience a slow growth in demand. A Lower Basin drought contingency plan and the optimized use of Upper Basin CRSP storage would be implemented when storage levels are low. Initial storage levels for Lake Powell and Lake Mead modeling are similar to the existing storage conditions that have been resulting from the recent drought cycle and from the “structural deficit” in the lower basin. The West Slope participants selected a Lake Powell target minimum operating elevation of 3,525’, which is the lower end of the “Mid-Elevation Release Tier” associated with the 2007 Interim Guidelines. Reservoir capacity at this elevation is about 6 million acre-feet above reservoir dead pool and about 2 million acre-feet above minimum power pool. We have several important observations as shown on the attached study graph that was provided by Hydros: 1. There were no study years in which “compact curtailment” would be required in the Upper Basin. 2. There were few, if any, study years in which Lake Powell would fall to 3,490’ in elevation, which is the minimum power pool elevation. 3. Lake Powell elevations dropped below 3,525’ in approximately 6% of the study years, without upper basin demand reductions. 4. The upper basin demand reduction program that was studied could potentially lower the percent of study years falling below 3,525’ to about 4%. When reviewing the report, we advise keeping the following considerations in mind: In assessing our collective risk as a State and Upper Basin, additional consideration should be given to what the appropriate target elevations are at Lake Powell, what other potential triggers and basin conditions should be considered, and potential structural solutions that permit the full use of storage water in Powell. The MidElevation Release Tier is approximately 1.9 million acre-feet above minimum power pool. In pointing out this difference in elevation, we are not advocating that Lake Powell be allowed to fall to an elevation of 3,490 feet. Rather, we question whether the Front Range Water Council November 9, 2016 Page 3 elevation 3,525 feet is the only target or condition we should be concerned about, and whether we can tolerate some risk of Lake Powell falling below 3,525’. The Phase I Study does not address the question of how much Colorado River water remains available for development of either new West Slope or East Slope water supplies. A long-range evaluation with a full suite of potential supply and demand conditions (like the Colorado River Basin Study) should be performed to understand the plausible range of future water supply conditions. Phase II Study The WSBRT Group now propose to initiate the first portion of a multi-phase Phase II modeling effort to further quantify perceived risks to Upper Basin Colorado River water users by evaluating several proposed scenarios that could be imposed to increase water levels in Powell. The WSBRT Group proposes to use StateMod and Colorado’s Decision Support Systems (“CDSS”) to model water right administrative scenarios within Colorado and examine whether these tools can be used in parallel with the CRSS model. These scenarios evaluate the effect of compact curtailment on transbasin storage and deliveries, selective curtailment by individual sub-basins, and the impact of east-slope storage and water supply conditions on Colorado River Basin curtailment risk. We have several concerns with the WSBRT Group’s proposed Phase II(a) modeling effort as summarized below: 1. The State of Colorado, including the CWCB and State Engineer’s Office, should be leading modeling efforts on Colorado River issues; not one particular region or tributary basin. Allowing the WSBRT Group to lead a state-financed modeling effort creates confusion as to the State’s position on Colorado River issues and undermines State and Upper Basin unity on the Colorado River Compact. 2. To the extent Phase II(a) seeks to build off of Phase I, we question whether the results from Phase I are an appropriate place to start given the narrow range of hydrology and demand assumptions used in Phase I. Before moving forward with additional phases of the study, greater discussion needs to be devoted to whether 3,525’ is an appropriate trigger level as discussed above, and to other important considerations and modeling assumptions. 3. As part of Phase II, the WSBRT Group proposes to model several compact curtailment administration scenarios that could be adverse to the Front Range and not in the best interest of the State as a whole. The WSBRT Group’s proposed administrative operations to assure compact compliance could place a disproportionate burden on Colorado River water supply systems essential for meeting demands on the East Slope. Front Range Water Council November 9, 2016 Page 4 We hope these observations are helpful. Please do not hesitate to contact if you have questions or wish to discuss these observations in additional detail. Sincerely, Kerry D. Sundeen Hydrologist Graph from Hydros, July 11, 2016: