Loading...
HomeMy WebLinkAboutagenda.council.worksession.20170724 CITY COUNCIL WORK SESSION July 24, 2017 6:00 PM, City Council Chambers MEETING AGENDA I. Water Demand Study Results Presentation P1 ASPEN CITY COUNCIL WORK SESSION MEMORANDUM TO: Mayor and City Council FROM: Margaret Medellin, Utilities Portfolio Manager THRU: Scott Miller, Director of Public Works; Dave Hornbacher, Director, Utilities and Environmental Initiatives; DATE OF MEMO: July 21, 2017 MEETING DATE: July 24, 2017 RE: Risk Assessment of Aspen’s Water System - Work Session Part Two SUMMARY: On October 10, 2016, Council passed Resolution #141, Series of 2016 directing staff to implement certain water management measures to improve resiliency against future climate change impacts and other system changes while continuing efforts to maintain diligence for two conditional water storage rights on Castle and Maroon Creeks. Included in this Resolution was direction to further refine Aspen’s future water supply and demand. To this end, Aspen contracted with Headwaters Corporation to perform a risk assessment of Aspen’s Water System, now and through 2065. PREVIOUS COUNCIL ACTION: · March 20, 2017 Council work session: Dr. George Oamek, consultant with Headwaters Corporation, was introduced to City Council and discussed the risk analysis that he is conducting for the City on its water supply and demand projections. · July 11, 2017 Council work session: Dr. Oamek and staff provided Council a status report on development of the risk assessment tool, current findings, and sought input from Council to further refine this analysis. · July 24, 2017 Council work session: At tonight’s session, Dr. Oamek will present the results of the risk assessment based on input from the July 11th work session. Three risk scenarios have been developed that incorporate a continuum of shortage risk. Council will be asked to provide direction about where on the risk continuum they would like to project the future water supply and demand. DISCUSSION: Water shortages are projected by comparing how much water our community needs to how much water supply is available. Periods during which water supplies are unable to meet the community’s water demands are termed ‘water shortages’. These projections contain considerable uncertainty, especially when we are contemplating 50 years into the future and projecting how Aspen may use water and how the environment might change. These are uncertainties that every community must grapple with and projections can only be made with the best data available, and then refined as the future becomes more clear. In recognition of the inherent uncertainty in supply and demand projections, the City contracted with Headwaters Corporation to perform a risk analysis. Rather than providing one projection P2 I. for the year 2065, Headwaters Corp. range of potential scenarios for Aspen’s The goal of this effort is to provide an estimate of the performance of Aspen’s incorporating known variables and reasonable assumptions about the probability of key variable. Results of this analysis are meant to frame the level of risk that is appropriate for the City’s long-range water planning. This analysis does not intend to prescribe how the City should develop, but rather to inform current leaders and future. In addition, this effort is not intended to describe the best alte best management practices to reduce this Year 2065 Potential Water Supply Key variables and assumptions that went into the risk model were discussed during the July 11 work session and summarized in the Headwater’s memo dated July 9, 2017. indicates that the percentage contribution of these key variables Based on input from Council, three scenarios discussion around risk. These scenarios assume the same climate impacts, but vary the amount of demand that may be put on the water system. stream flows for each of the three scenarios. Summaries of impacts are discussed below. 1) Worst-case Scenario (See Attachment A) The importance of estimating a worst how Aspen’s Water System can be expected to perform during the most extreme, yet probable, critical period. The model probability of occurring, meaning there is approximately 1 chance in 10 assumptions will coincide. Headwaters Corp. used currently available data and statistical techniques to Aspen’s water system. effort is to provide an estimate of the performance of Aspen’s water incorporating known variables and reasonable assumptions about the probability of magnitude key variable. Results of this analysis are meant to frame the level of risk that is appropriate for the City’s is analysis does not intend to prescribe how the City should develop, but inform current leaders and provide future leaders the ability to meet an uncertain, yet probable, In addition, this effort is not intended to describe the best alternatives for meeting future needs or best management practices to reduce this vulnerability Water Supply Shortage Risk Model and assumptions that went into the risk model were discussed during the July 11 work session and summarized in the Headwater’s memo dated July 9, 2017. A sensitivity analysis indicates that the percentage contribution of these key variables to the model outputs are three scenarios across a broad spectrum was developed to frame the These scenarios assume the same climate impacts, but vary the amount of demand that may be put on the water system. Attachment A details the impacts to the water supply ows for each of the three scenarios. Summaries of impacts are discussed below. (See Attachment A) The importance of estimating a worst-case scenario is largely in providing the ability to determine how Aspen’s Water System can be expected to perform during the most extreme, yet probable, The model was adapted to represent a set of conditions with a combined 0.01 probability of occurring, meaning there is approximately 1 chance in 100 that this combination of assumptions will coincide. Planning for the 1/100 event is common for infrastructure designs. statistical techniques to provide a ater system in 2065, magnitude for each key variable. Results of this analysis are meant to frame the level of risk that is appropriate for the City’s is analysis does not intend to prescribe how the City should develop, but provide future leaders the ability to meet an uncertain, yet probable, rnatives for meeting future needs or and assumptions that went into the risk model were discussed during the July 11th Council A sensitivity analysis are: was developed to frame the These scenarios assume the same climate impacts, but vary the amount of demand supply system and in- ows for each of the three scenarios. Summaries of impacts are discussed below. the ability to determine how Aspen’s Water System can be expected to perform during the most extreme, yet probable, was adapted to represent a set of conditions with a combined 0.01 0 that this combination of Planning for the 1/100 event is common for infrastructure designs. P3 I. Assumptions: · Climate change will fully impact the Maroon Creek and Castle Creek watersheds through earlier snowmelt, increased evapo-transpiraton and reduced streamflow. · Over the 50-year period, residential usage increases at a rate less than 1% to 8,400 full-time residents with non-residential sectors including tourism at a rate of 2% resulting in an overall weighted average rate of 1.2%. Results: · 19 out of 25 years municipal shortages will be experienced · Minimum instream flows will chronically be invaded resulting in drying-up Castle and Maroon Creeks multiple weeks during most years in the period of record. 2) No growth Scenario (See Attachment B) Planning for a future with water demand at existing levels provides guidance on how Aspen’s water system can be expected to perform with no new taps or increased outdoor watering. Assumptions: · Climate change will fully impact the Maroon Creek and Castle Creek watersheds through earlier snowmelt, increased evapo-transpiraton and reduced streamflow · Water demand remains at the existing level through 2065. Results: · 15 out of 25 years municipal shortages will be experienced, · Minimum instream flows will periodically be invaded drying-up Castle and Maroon Creeks at least one week during most years in the period of record. 3) Intervention Scenario (See Attachment C) At another end of the potential shortage continuum is a future in which, during times of shortage, all outdoor watering would be eliminated to conserve water. This scenario would require a shift in Aspen’s landscaping philosophy and would require infrastructure to allow for control of outdoor watering. Assumptions: · Climate change will fully impact the Maroon Creek and Castle Creek watersheds through earlier snowmelt, increased evapo-transpiraton and reduced streamflow · Demand will decrease as growth will be held constant · During times of shortage outdoor watering will be eliminated. Results: · 14 out of 25 years municipal shortages will be experienced, · Minimum instream flows will periodically be invaded drying-up Castle and Maroon Creeks at least one week during most years in the period of record. P4 I. COUNCIL DIRECTION REQUESTED: During the work session, Council is asked to provide direction regarding level of risk appropriate for Aspen’s Water System to be used for determining the future water supply demand. ENVIRONMENTAL IMPACTS: The City is committed to reducing its footprint (carbon and water) and fighting climate change, but even with this effort and action the City recognizes that it is best practice to plan for a future that looks very different than today. Incorporating risk into the City’s demand and supply projections is necessary to ensure the resiliency of its water system. BUDGET IMPACT: Funds to support the work associated with Aspen’s Water Future was included in the recently adopted spring supplemental budget. CITY MANAGER COMMENTS: ATTACHMENTS: Attachment A – Worst Case Shortage Scenario for Aspen’s Water System, Headwaters Corporation Attachment B – No Growth Shortage Scenario for Aspen’s Water System, Headwaters Corporation Attachment C – Intervention Shortage Scenario for Aspen’s Water System, Headwaters Corporation P5 I. ATTACHMENT A: Worst Case Scenario Summary This scenario is intended to represent assumptions with a combined 1 in 100 probability of occurring. · Climate change is at the worst end of consideration: -6 weeks peak, 50% combined flow and ET impacts; · Weighted average demand growth rate is 1.2%, resulting in a 2065 treated water demand of approximately 6,320 acre-feet; · Flow adjustment factors are at their expected values; Total Shortages Below are the shortages to Aspen and instream flows, relative to Aspen’s annual treated water demand - 2,000 4,000 6,000 8,000 10,000 12,000 1970197119721973197419751976197719781979198019811982198319841985198619871988198919901991199219931994Acre-feetHydrologic year Annual Shortages Annual shortage to Aspen Annual instream flow shortage Aspen's estimated demand P6 I. Municipal Shortages Municipal and Industrial (M&I) water refers to the portion of Aspen’s water system that is diverted to supply its residential, commercial and industrial customer needs. Assuming M&I is the higher priority and instream flows take the first “hit”, there are still M&I shortages in 19 of 25 years, with 4 of those years with shortages of 1,000 acre-feet or more Instream Flows The following graphic summarizes instream flow levels that either meet or fall below instream flow decrees, over the 1970 to 1994 hydrologic period of record. The combined flows of Castle and Maroon Creek should total 27.3 cfs to meet instream flow levels (13.3 cfs for Castle Creek; 14.0 cfs for Maroon Creek). Impacts to the creeks increase in severity with darkening colors. Number of years with M&I shortages 19 Number of years M&I shortage exceeds 100 acre-feet 15 Number of years M&I shortage exceeds 1000 acre-feet 4 Number of years M&I shortage exceeds 2000 acre-feet 1 Number of years M&I shortage exceeds 3000 acre-feet 0 Number of years M&I shortage exceeds 5000 acre-feet 0 KEY <=0 Combined 0.01-5 Castle/Maroon 5.01-10 Flow 10.01-15 in 15.01-20 CFS 20.01-27.3 P7 I. CY Wk 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 WY Wk 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 1 2 3 4 5 6 7 8 9 10 11 12 13 1969 3 1 14 13 21 20 19 18 17 16 15 15 14 1970 17 16 17 16 14 14 15 16 19 26 34 46 59 87 ## ## ## ## ## ## ## ## ## 67 98 94 60 38 21 14 14 13 8 16 10 35 46 29 16 15 13 25 24 31 30 27 25 24 22 21 21 19 1971 18 18 20 19 19 19 19 18 20 23 30 46 79 ## ## ## ## ## ## ## ## ## 60 80 ## 79 56 47 37 21 19 13 9 15 19 19 7 3 -1 4 1 16 15 23 22 20 19 19 17 16 15 15 1972 15 16 17 16 15 14 15 15 18 24 36 59 87 ## ## ## ## ## ## ## ## ## ## ## 48 17 7 -4 -9 ## -4 -6 -6 -7 -7 1 -3 -0 -3 -0 2 23 20 25 23 20 19 18 16 17 16 16 1973 15 18 15 14 13 12 12 11 14 19 25 40 59 87 ## ## ## ## ## ## ## ## 74 ## 54 ## 69 55 41 23 29 30 18 14 10 9 6 -0 -2 2 -1 12 11 19 19 17 17 16 15 15 14 15 1974 17 16 16 15 14 13 12 13 14 19 28 42 66 99 ## ## ## ## ## ## ## ## 94 ## 95 44 21 1 1 -3 -0 -0 -6 ## ## ## ## ## ## -8 -8 7 8 18 17 17 17 17 17 16 15 15 1975 16 14 14 14 14 14 14 13 16 22 26 42 55 86 ## ## ## ## ## ## ## 75 84 60 37 54 ## ## 97 47 42 29 22 14 7 7 6 2 -3 -1 -2 13 12 20 19 18 17 16 16 15 15 15 1976 15 14 15 14 13 13 15 15 18 23 32 48 70 ## ## ## ## ## ## ## ## ## ## 77 27 19 20 7 2 -3 4 -1 -4 -5 -6 -6 -8 -9 -5 1 -2 11 9 17 15 14 13 13 13 13 12 12 1977 12 12 11 11 10 9 9 10 11 15 21 34 52 82 ## ## ## ## ## ## 88 ## 75 14 ## ## ## ## ## ## ## ## ## ## ## ## ## ## ## ## ## 0 0 9 8 7 7 7 6 7 6 7 1978 8 8 8 8 7 7 8 9 10 14 19 31 48 75 ## ## ## ## ## ## ## ## ## ## ## 85 53 51 47 22 19 6 2 -6 -8 -4 -7 -9 ## -7 -9 5 6 14 14 14 13 13 11 12 12 11 1979 10 10 10 10 10 10 10 11 13 18 25 39 58 85 ## ## ## ## ## ## ## ## ## ## 77 ## 92 73 71 63 47 36 39 20 9 7 -1 -4 -5 -1 -3 12 12 20 20 17 15 14 14 12 12 13 1980 14 13 14 13 13 13 14 15 17 22 29 44 60 87 ## ## ## ## ## ## ## ## ## ## ## 94 68 48 27 19 21 14 14 8 7 9 14 2 -1 4 2 17 15 23 22 20 18 19 18 18 17 18 1981 19 18 16 14 13 12 11 12 14 18 24 37 54 82 ## ## ## ## ## ## ## ## ## 80 18 -1 -3 -8 ## ## ## ## ## ## ## -5 -5 -8 ## -5 -6 10 9 18 17 15 14 14 12 12 11 7 1982 6 7 9 14 14 14 14 16 19 22 30 40 58 86 ## ## ## ## ## ## ## ## ## ## 83 86 73 59 58 65 69 42 38 25 17 18 17 20 22 24 17 29 25 31 28 24 23 22 20 19 19 17 1983 18 17 18 18 17 16 16 17 19 25 34 51 73 ## ## ## ## ## ## ## ## ## ## 95 ## ## ## ## 79 60 93 88 59 44 38 29 12 6 3 9 7 21 19 28 27 25 23 22 21 20 19 20 1984 21 20 18 19 20 19 20 21 22 26 33 53 80 ## ## ## ## ## ## ## ## ## ## ## ## ## ## ## ## ## 94 69 69 64 54 43 30 26 23 26 23 33 32 37 35 34 32 31 30 30 29 30 1985 32 30 29 29 28 27 27 26 27 33 44 65 87 ## ## ## ## ## ## ## ## ## ## ## ## 92 90 73 59 44 49 42 25 18 16 24 19 19 13 16 18 28 26 34 32 29 29 29 26 24 24 23 1986 24 24 23 23 22 21 21 22 24 32 46 72 ## ## ## ## ## ## ## ## ## ## ## ## ## 99 ## 71 57 42 39 36 33 42 35 28 29 21 21 23 20 32 29 37 33 30 28 27 26 24 23 22 1987 24 23 21 19 18 18 19 18 20 31 36 56 73 ## ## ## ## ## ## ## ## ## ## ## 56 23 20 10 6 13 23 23 14 21 6 6 -1 -3 -5 0 -1 14 14 24 23 19 16 16 15 14 17 16 1988 18 18 17 15 16 17 17 19 24 29 35 58 91 ## ## ## ## ## ## ## ## ## ## 82 46 24 9 -7 ## ## -0 -5 -8 -7 -7 -6 -3 -3 -5 -1 -4 9 7 16 15 16 16 15 13 14 14 14 1989 14 14 15 16 16 15 16 18 18 20 31 47 76 ## ## ## ## ## ## ## ## ## ## 82 60 31 36 22 4 19 20 8 4 -5 -9 -6 -8 -7 -7 -3 -6 8 6 14 14 13 13 13 12 11 10 9 1990 9 10 9 9 10 11 11 13 18 21 28 44 71 ## ## ## ## ## ## ## ## ## ## ## 67 38 20 11 -5 -9 -7 ## -7 ## ## -9 ## -8 ## -1 -1 12 11 19 18 16 15 14 14 16 12 12 1991 13 13 12 10 11 11 12 11 13 18 23 36 53 ## ## ## ## ## ## ## ## ## ## ## 93 44 47 32 19 10 13 6 1 -4 -4 3 9 4 -2 7 2 14 12 21 20 19 19 19 18 16 17 16 1992 16 15 16 14 14 15 15 16 18 21 31 49 75 ## ## ## ## ## ## ## ## ## 71 65 51 34 29 26 11 15 10 14 7 9 10 8 -2 2 0 3 0 14 13 23 22 20 18 17 17 17 17 18 1993 18 19 20 19 19 19 20 22 25 30 40 60 98 ## ## ## ## ## ## ## ## ## ## ## ## ## ## ## 72 56 70 66 46 39 31 31 22 14 8 10 10 24 21 29 27 25 23 22 21 19 17 19 1994 20 18 19 17 14 16 16 17 19 22 28 40 58 83 ## ## ## ## ## ## ## ## ## ## 89 34 17 2 -5 -7 1 -0 -1 -7 -7 2 -5 -6 -8 Apr May Jun Jul Aug Sep Oct Nov DecJanFebMar P8 I. ATTACHMENT B: No Growth Scenario Summary · Climate change is at the worst end of consideration: -6 weeks peak, 50% combined flow and ET impacts; · Demand growth rate is zero; current treated water demand of approximately 3,500 acre-feet continues through 2065; · Flow adjustment factors are at their expected values; Total shortages Below are the shortages to Aspen and instream flows, relative to Aspen’s annual treated water demand - 2,000 4,000 6,000 8,000 10,000 12,000 1970197119721973197419751976197719781979198019811982198319841985198619871988198919901991199219931994Acre-feetHydrologic year Annual Shortages Annual shortage to Aspen Annual instream flow shortage Aspen's estimated demand P9 I. Municipal Shortages Municipal and Industrial (M&I) water refers to the portion of Aspen’s water system that is diverted to supply its residential, commercial and industrial customer needs. Assuming M&I is the higher priority and instream flows take the first “hit”, there are still M&I shortages in 15 of 25 years. Instream Flows The following graphic summarizes instream flow levels that either meet or fall below instream flow decrees, over the 1970 to 1994 hydrologic period of record. The combined flows of Castle and Maroon Creek should total 27.3 cfs to meet instream flow levels (13.3 cfs for Castle Creek; 14.0 cfs for Maroon Creek). Impacts to the creeks increase in severity with darkening colors. Number of years with M&I shortages 15 Number of years M&I shortage exceeds 100 acre-feet 10 Number of years M&I shortage exceeds 1000 acre-feet 1 Number of years M&I shortage exceeds 2000 acre-feet 0 Number of years M&I shortage exceeds 3000 acre-feet 0 Number of years M&I shortage exceeds 5000 acre-feet 0 KEY <=0 Combined 0.01-5 Castle/Maroon 5.01-10 Flow 10.01-15 in 15.01-20 CFS 20.01-27.3 P10 I. CY Wk 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 WY Wk 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 1 2 3 4 5 6 7 8 9 10 11 12 13 1969 5 3 16 15 23 22 22 21 20 18 18 18 17 1970 19 19 20 19 17 17 17 19 21 28 36 48 62 90 ## ## ## ## ## ## ## ## ## 75 ## ## 67 45 28 21 19 18 13 21 15 39 50 33 20 17 15 27 26 33 32 30 27 27 25 24 23 22 1971 21 21 22 21 22 21 22 21 23 26 33 49 81 ## ## ## ## ## ## ## ## ## 67 87 ## 87 63 53 43 28 25 18 15 21 25 23 11 7 3 6 3 18 17 25 24 23 21 21 20 19 18 17 1972 18 19 19 19 17 17 17 18 21 27 38 61 89 ## ## ## ## ## ## ## ## ## ## ## 55 25 14 3 -2 -6 1 -1 -0 -2 -2 5 1 4 1 2 4 25 22 28 25 23 21 20 19 20 19 18 1973 18 20 17 16 16 15 14 13 17 21 28 42 61 89 ## ## ## ## ## ## ## ## 81 ## 62 ## 76 62 47 30 35 36 23 20 16 13 10 4 2 4 1 14 13 22 21 20 19 18 18 18 17 18 1974 19 18 18 18 17 16 15 15 17 21 31 45 69 ## ## ## ## ## ## ## ## ## ## ## ## 51 27 8 8 4 5 5 -0 -5 -9 -7 -9 -9 ## -6 -6 9 10 21 20 20 20 19 20 18 18 17 1975 18 16 16 17 16 16 17 15 18 24 29 45 58 88 ## ## ## ## ## ## ## 80 92 68 45 62 ## ## ## 54 47 34 27 19 12 11 10 6 1 1 0 15 14 23 22 21 20 18 18 18 17 18 1976 17 16 17 17 16 16 18 17 20 25 34 50 72 ## ## ## ## ## ## ## ## ## ## 84 35 26 27 13 9 4 10 4 1 1 -1 -1 -4 -5 -1 3 -0 13 11 19 18 17 16 15 16 15 15 15 1977 15 14 14 13 12 12 12 12 14 18 24 37 54 84 ## ## ## ## ## ## 93 ## 83 22 ## ## ## ## ## ## ## ## ## ## ## ## ## ## ## ## ## 2 2 12 11 10 10 10 9 9 9 10 1978 10 11 10 10 10 10 11 11 13 17 22 34 50 77 ## ## ## ## ## ## ## ## ## ## ## 93 60 58 54 29 24 11 7 -0 -3 -0 -3 -5 -7 -5 -7 7 8 17 17 16 15 15 14 15 15 14 1979 13 12 13 12 13 13 13 13 16 20 27 42 60 88 ## ## ## ## ## ## ## ## ## ## 85 ## 98 79 78 69 53 42 44 25 15 11 3 0 -1 1 -1 14 14 22 22 20 18 17 17 15 15 15 1980 16 16 16 16 16 16 17 17 20 25 32 47 62 89 ## ## ## ## ## ## ## ## ## ## ## ## 75 54 34 26 27 20 19 14 12 13 18 6 4 6 4 19 17 26 25 22 21 21 21 21 20 21 1981 21 20 18 16 15 15 14 14 16 20 27 40 57 84 ## ## ## ## ## ## ## ## ## 88 26 7 3 -1 -5 -6 -5 -6 -5 -8 -6 -1 -0 -4 -6 -3 -4 12 11 21 19 18 17 16 15 15 13 10 1982 9 10 12 16 17 17 16 19 22 25 32 42 60 89 ## ## ## ## ## ## ## ## ## ## 91 94 80 66 65 72 74 47 44 30 22 22 21 25 26 26 19 31 27 33 30 27 25 25 23 22 22 19 1983 20 20 21 20 19 19 19 20 22 27 36 54 76 ## ## ## ## ## ## ## ## ## ## ## ## ## ## ## 86 67 98 93 64 49 44 33 16 11 7 11 9 23 21 31 30 27 26 25 24 23 21 23 1984 23 22 20 22 22 22 22 23 24 29 35 55 82 ## ## ## ## ## ## ## ## ## ## ## ## ## ## ## ## ## ## 74 74 70 59 47 34 30 27 28 25 35 34 40 38 36 34 34 33 33 32 33 1985 34 32 32 32 30 30 29 29 29 36 46 68 89 ## ## ## ## ## ## ## ## ## ## ## ## ## 96 80 66 51 55 47 31 23 22 28 24 23 18 18 20 30 28 36 35 32 31 31 29 26 26 26 1986 26 26 26 25 25 24 23 25 27 35 48 74 ## ## ## ## ## ## ## ## ## ## ## ## ## ## ## 77 63 49 44 41 38 48 40 32 34 25 26 25 22 34 31 39 36 32 30 29 28 27 25 24 1987 26 25 24 21 21 21 22 21 23 34 39 58 75 ## ## ## ## ## ## ## ## ## ## ## 64 31 27 17 13 20 28 29 20 26 12 11 3 1 -0 2 1 16 16 27 25 21 19 19 18 16 20 19 1988 20 20 19 18 19 20 20 22 26 31 37 60 94 ## ## ## ## ## ## ## ## ## ## 89 54 32 16 -1 -7 -7 5 -0 -3 -1 -2 -2 1 1 -1 1 -2 11 9 19 18 18 18 17 16 17 17 17 1989 17 16 18 19 19 17 19 21 20 22 33 50 78 ## ## ## ## ## ## ## ## ## ## 90 67 39 43 29 10 26 25 14 10 1 -4 -2 -4 -2 -3 -1 -4 10 8 17 16 16 16 15 15 14 13 12 1990 12 12 11 12 13 13 14 16 20 24 31 47 73 ## ## ## ## ## ## ## ## ## ## ## 75 46 27 18 2 -3 -2 -5 -2 -6 -8 -4 -9 -4 -5 1 1 14 13 22 21 18 18 17 16 19 15 15 1991 16 15 15 13 13 14 14 14 16 20 26 39 55 ## ## ## ## ## ## ## ## ## ## ## ## 52 54 39 26 17 19 12 6 1 2 8 13 8 2 9 4 16 14 24 23 22 21 21 21 19 20 19 1992 18 17 18 16 16 17 18 19 21 24 34 51 78 ## ## ## ## ## ## ## ## ## 79 73 59 42 36 33 18 21 15 20 12 14 15 12 2 6 5 5 2 16 15 26 25 22 21 20 20 19 20 21 1993 20 21 23 21 22 22 23 25 28 33 43 62 ## ## ## ## ## ## ## ## ## ## ## ## ## ## ## ## 79 63 76 71 51 44 37 35 27 19 12 12 12 26 23 32 30 28 26 25 23 22 20 22 1994 23 20 21 19 16 19 18 20 21 25 31 42 61 85 ## ## ## ## ## ## ## ## ## ## 97 42 24 8 2 0 7 5 4 -1 -1 6 -1 -2 -3 Apr May Jun Jul Aug Sep Oct Nov DecJanFebMar P11 I. ATTACHMENT C: Intervention Scenario Summary · Climate change is at the worst end of consideration: -6 weeks peak, 50% combined flow and ET impacts; · Demand growth rate is zero, no outdoor usage during shortages; effective treated water demand during shortages is 2,280 acre-feet; · Flow adjustment factors are at their expected values; Total Shortages Below are the shortages to Aspen and instream flows, relative to Aspen’s annual treated water demand - 2,000 4,000 6,000 8,000 10,000 12,000 1970197119721973197419751976197719781979198019811982198319841985198619871988198919901991199219931994Acre-feetHydrologic year Annual Shortages Annual shortage to Aspen Annual instream flow shortage Aspen's estimated demand P12 I. Municipal Shortages Municipal and Industrial (M&I) water refers to the portion of Aspen’s water system that is diverted to supply its residential, commercial and industrial customer needs. Assuming M&I is the higher priority and instream flows take the first “hit”, there are still M&I shortages in 14 of 25 years. Instream Flows The following graphic summarizes instream flow levels that either meet or fall below instream flow decrees, over the 1970 to 1994 hydrologic period of record. The combined flows of Castle and Maroon Creek should total 27.3 cfs to meet instream flow levels (13.3 cfs for Castle Creek; 14.0 cfs for Maroon Creek). Impacts to the creeks increase in severity with darkening colors. Number of years with M&I shortages 14 Number of years M&I shortage exceeds 100 acre-feet 5 Number of years M&I shortage exceeds 1000 acre-feet 0 Number of years M&I shortage exceeds 2000 acre-feet 0 Number of years M&I shortage exceeds 3000 acre-feet 0 Number of years M&I shortage exceeds 5000 acre-feet 0 KEY <=0 Combined 0.01-5 Castle/Maroon 5.01-10 Flow 10.01-15 in 15.01-20 CFS 20.01-27.3 P13 I. CY Wk 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 WY Wk 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 1 2 3 4 5 6 7 8 9 10 11 12 13 1969 5 3 16 15 23 22 22 21 20 18 18 18 17 1970 19 19 20 19 17 17 17 19 21 28 36 48 62 90 ## ## ## ## ## ## ## ## ## 81 ## ## 72 50 33 26 23 21 17 24 19 41 52 35 22 17 15 27 26 33 32 30 27 27 25 24 23 22 1971 21 21 22 21 22 21 22 21 23 26 33 49 81 ## ## ## ## ## ## ## ## ## 73 94 ## 93 68 59 49 33 28 21 18 24 28 25 13 9 5 6 3 18 17 25 24 23 21 21 20 19 18 17 1972 18 19 19 19 17 17 17 18 21 27 38 61 89 ## ## ## ## ## ## ## ## ## ## ## 62 31 19 8 3 -0 5 2 3 2 2 7 3 6 3 2 4 25 22 28 25 23 21 20 19 20 19 18 1973 18 20 17 16 16 15 14 13 17 21 28 42 61 89 ## ## ## ## ## ## ## ## 87 ## 68 ## 81 67 53 35 38 39 27 23 19 15 12 6 4 4 1 14 13 22 21 20 19 18 18 18 17 18 1974 19 18 18 18 17 16 15 15 17 21 31 45 69 ## ## ## ## ## ## ## ## ## ## ## ## 58 33 13 13 9 9 8 3 -2 -5 -5 -7 -7 -8 -6 -6 9 10 21 20 20 20 19 20 18 18 17 1975 18 16 16 17 16 16 17 15 18 24 29 45 58 88 ## ## ## ## ## ## ## 83 98 74 51 68 ## ## ## 59 51 38 31 22 16 13 12 8 3 1 0 15 14 23 22 21 20 18 18 18 17 18 1976 17 16 17 17 16 16 18 17 20 25 34 50 72 ## ## ## ## ## ## ## ## ## ## 90 41 33 32 19 14 9 13 8 4 4 3 1 -2 -3 1 3 -0 13 11 19 18 17 16 15 16 15 15 15 1977 15 14 14 13 12 12 12 12 14 18 24 37 54 84 ## ## ## ## ## ## 97 ## 89 28 -5 ## ## ## ## ## ## ## ## ## ## ## ## ## ## ## ## 2 2 12 11 10 10 10 9 9 9 10 1978 10 11 10 10 10 10 11 11 13 17 22 34 50 77 ## ## ## ## ## ## ## ## ## ## ## 99 65 63 59 34 28 15 11 3 1 2 -1 -3 -5 -5 -7 7 8 17 17 16 15 15 14 15 15 14 1979 13 12 13 12 13 13 13 13 16 20 27 42 60 88 ## ## ## ## ## ## ## ## ## ## 91 ## ## 85 83 75 56 45 48 29 18 13 5 2 1 1 -1 14 14 22 22 20 18 17 17 15 15 15 1980 16 16 16 16 16 16 17 17 20 25 32 47 62 89 ## ## ## ## ## ## ## ## ## ## ## ## 80 60 39 31 30 23 23 17 16 15 20 8 6 6 4 19 17 26 25 22 21 21 21 21 20 21 1981 21 20 18 16 15 15 14 14 16 20 27 40 57 84 ## ## ## ## ## ## ## ## ## 94 32 13 9 4 -0 -1 -2 -2 -2 -4 -3 1 2 -2 -4 -3 -4 12 11 21 19 18 17 16 15 15 13 10 1982 9 10 12 16 17 17 16 19 22 25 32 42 60 89 ## ## ## ## ## ## ## ## ## ## 97 ## 85 71 70 77 78 51 47 34 26 24 23 27 28 26 19 31 27 33 30 27 25 25 23 22 22 19 1983 20 20 21 20 19 19 19 20 22 27 36 54 76 ## ## ## ## ## ## ## ## ## ## ## ## ## ## ## 91 72 ## 96 68 52 47 35 18 13 9 11 9 23 21 31 30 27 26 25 24 23 21 23 1984 23 22 20 22 22 22 22 23 24 29 35 55 82 ## ## ## ## ## ## ## ## ## ## ## ## ## ## ## ## ## ## 78 77 73 62 49 36 32 29 28 25 35 34 40 38 36 34 34 33 33 32 33 1985 34 32 32 32 30 30 29 29 29 36 46 68 89 ## ## ## ## ## ## ## ## ## ## ## ## ## ## 85 71 56 58 51 34 26 25 30 26 25 20 18 20 30 28 36 35 32 31 31 29 26 26 26 1986 26 26 26 25 25 24 23 25 27 35 48 74 ## ## ## ## ## ## ## ## ## ## ## ## ## ## ## 83 69 54 48 45 42 51 44 34 36 27 28 25 22 34 31 39 36 32 30 29 28 27 25 24 1987 26 25 24 21 21 21 22 21 23 34 39 58 75 ## ## ## ## ## ## ## ## ## ## ## 70 37 32 22 18 25 31 32 23 29 15 13 5 3 2 2 1 16 16 27 25 21 19 19 18 16 20 19 1988 20 20 19 18 19 20 20 22 26 31 37 60 94 ## ## ## ## ## ## ## ## ## ## 96 60 38 21 5 -2 -2 9 3 1 2 2 -0 3 3 1 1 -2 11 9 19 18 18 18 17 16 17 17 17 1989 17 16 18 19 19 17 19 21 20 22 33 50 78 ## ## ## ## ## ## ## ## ## ## 96 73 45 48 34 16 31 29 17 13 4 -0 0 -2 -0 -1 -1 -4 10 8 17 16 16 16 15 15 14 13 12 1990 12 12 11 12 13 13 14 16 20 24 31 47 73 ## ## ## ## ## ## ## ## ## ## ## 81 52 32 23 7 3 2 -2 1 -2 -4 -2 -7 -2 -3 1 1 14 13 22 21 18 18 17 16 19 15 15 1991 16 15 15 13 13 14 14 14 16 20 26 39 55 ## ## ## ## ## ## ## ## ## ## ## ## 58 59 44 31 22 22 15 10 5 5 10 15 10 4 9 4 16 14 24 23 22 21 21 21 19 20 19 1992 18 17 18 16 16 17 18 19 21 24 34 51 78 ## ## ## ## ## ## ## ## ## 85 79 65 48 41 38 23 27 19 23 16 18 19 14 4 8 7 5 2 16 15 26 25 22 21 20 20 19 20 21 1993 20 21 23 21 22 22 23 25 28 33 43 62 ## ## ## ## ## ## ## ## ## ## ## ## ## ## ## ## 84 68 79 75 54 48 40 37 29 21 14 12 12 26 23 32 30 28 26 25 23 22 20 22 1994 23 20 21 19 16 19 18 20 21 25 31 42 61 85 ## ## ## ## ## ## ## ## ## ## ## 48 29 14 7 5 10 9 8 2 2 8 1 0 -1 Apr May Jun Jul Aug Sep Oct Nov DecJanFebMar P14 I.