Water Committee Agenda and Packet 2013 01 31

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Jan 2013 Draft Revisions Numerical indicators alone, such as the amount of water currently in storage, are not always accurate indicators of a drought event. When used in conjunction with more predictive indicators, such as projections for the amount of water becoming available from runoff, numeric indicators are more realistic. Confidence in the projections of the water supply will vary throughout the year, with the projections being most reliable during the late spring when quotas are setand the runoff is more predictable, to the least reliable in November when only the amount of water in storage is known.A quota is an amount of water the City is able to obtain from a share of a water right. These amounts are set depending on needs of share holders and availability of water. Therefore, the City establisheda predictive tool incorporating both Deleted: it is recommended that numerical and predictive indicators to determine when the City’s water supply may not meet the Deleted: indicate demand. A Water Supply Index (WSI) will be utilizedto compare water storageamounts,projected Deleted: is proposed based on the existing supplies,and demands for the City. The basic form of the WSI would be as follows: Deleted: and CarryoverSBCdirectsNCWCDMarshall Supply last WSI () DemandDemand(TargetedarryoverCarryover) next C () Supply incorporates the amount of water carried over from the previous year (carryover last), plus the projected amounts of water to be obtained from the City’s direct flow rights on South Deleted: (1) Boulder Creek(SBCdirects),Northern Colorado Water ConservancyDistrict’sallocations from Deleted: , C-BT and Windy Gap (NCWCD), and share yield of Farmers Irrigation and Reservoir Company Deleted: D interest held in Marshall Lake(Marshall). Demand is the projected water use by the City under Deleted: (2) ‘normal’ conditions plus the amount of carryover water determined necessary to reasonably Deleted: tion buffer the City from future events less carryover water in storage. Deleted: (3) The WSI equation results in anindexthat will indicate the expected amount of water available to Deleted: a meet current demands. A WSI of one (1.0) would mean that the supply would meet the demand, including designated reserves. A value greater than or less than one would mean that there is either an excess or a shortage of water, respectively. The WSI can be used to indicate the potential severity of a water shortage and how the City should respond. A WSI in the range of 0.95 to 0.85 would trigger a Stage 1 response. The trigger for a Stage 2 response would be a WSI between 0.85 and 0.75. A WSI between 0.75 and 0.65 would indicate a Stage 3 drought and a WSI less than 0.65 would trigger a Stage 4 response. Other factors may influence the level of response and vary from the response dictated bythe WSI. Projected inflows are based on historic relationships between snow pack and stream runoff. If this calculation indicates water supply for a drought stage is less than required, the City would enter the next level of drought response. The following guidelines will be utilized to indicate the drought event under existing conditions. The guidelines will be adjusted as demand increases and additional water resources are acquired. Stage 1 - Projected stream flow and reservoir yields are less than 95 percent of normal demand. South Boulder Creek direct flow diversions projected between 2300-2700 AF, CBT yield of 3