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DRAFT URBAN WATER MANAGEMENT PLAN ❑ 7.6% chance of a 10% Hetch Hetchy system -wide cutback. A 10% system -wide cutback equates to a 12% cutback for BAWUA in aggregate. A 12% cutback for BAWUA equates to a 17.5% cutback for Redwood City. A 17.5% cutback is a "major" event requiring water rationing. ❑ 2.5% chance of a 20% Hetch Hetchy system -wide cutback. A 20% system -wide cutback equates to a 23.6% cutback for BAWUA in aggregate. A 23.6% cutback for BAWUA equates to a 28.4% cutback for Redwood City. A 28.4% cutback would be a "dramatic" crisis involving significant disruptions and curtailments. (1) The Interim Water Shortrage Allocation Plan addresses system wide cutbacks up to 20 %. (2) Values provided by Nicole Sandkulla, Bay Area Water Users Association. (3) Based on worksheet from Nicole Sandkulla, updated with FY 1999/00 and 2000 /01 water use. (4) Based on FY 2000101 water use totals. (5) Probability of each scenario occurring in a given year based on hydrology from 1921 to 1999. Information taken from Figure 2 -5 in SFPUC Water Supply Master Plan, April 2000. The probability of a 5% and 15% cutbacks not addressed, hence reported as not available (NA). (6) Future probabilities based on interpolation of the 260 and 325 MGD demand scenarios in master plan. 3.2 Future Water Reliability 3.1.1 Base Case Situation Assuming the City does not implement new water conservation programs or develop new water supplies, the frequency and magnitude of the cutbacks will increase as members of BAWUA use more water in the future. In fact, BAWUA's water use has increased in the last few years and is projected to increase overtime to at least 2030 (BAWUA Annual Survey of Results FY 2000 -01, December 2001). The last column of Table 3.1 shows an estimate of the degradation in water supply reliability for the year 2010. The frequency of cutbacks equal to or exceeding 17.5% will grow from 10.1% to 16.4% over this period. Moreover, the increasing frequency of cutbacks will be of greater magnitude. 3.1.2 Future Alternative The City can, however, significantly improve its reliability and minimize the magnitude of water cutbacks by implementing water conservation and water recycling projects. ON Table 3.1 Current Water Reliability 11) ( ( (4) (5) Hatch Hetchy BAWUA RWC RWC Future System Remand Demand Demand Allocation Historical Probability Scenario 'Cutback Cutback Cutback AFY Probability 2010 1 0% 0.0% 0.0% Not limited NA 2 -5% -6.4% - 12.2% 11,584 NA NA 3 -10% - 12.0% - 17.5% 10,891 7.6% 6.3/0 4 -15% -18.2% - 23.3% 10,124 NA 5.1% F -20% -23.6% - 28.4% 9,456 2.5% 2.5^/0 (1) The Interim Water Shortrage Allocation Plan addresses system wide cutbacks up to 20 %. (2) Values provided by Nicole Sandkulla, Bay Area Water Users Association. (3) Based on worksheet from Nicole Sandkulla, updated with FY 1999/00 and 2000 /01 water use. (4) Based on FY 2000101 water use totals. (5) Probability of each scenario occurring in a given year based on hydrology from 1921 to 1999. Information taken from Figure 2 -5 in SFPUC Water Supply Master Plan, April 2000. The probability of a 5% and 15% cutbacks not addressed, hence reported as not available (NA). (6) Future probabilities based on interpolation of the 260 and 325 MGD demand scenarios in master plan. 3.2 Future Water Reliability 3.1.1 Base Case Situation Assuming the City does not implement new water conservation programs or develop new water supplies, the frequency and magnitude of the cutbacks will increase as members of BAWUA use more water in the future. In fact, BAWUA's water use has increased in the last few years and is projected to increase overtime to at least 2030 (BAWUA Annual Survey of Results FY 2000 -01, December 2001). The last column of Table 3.1 shows an estimate of the degradation in water supply reliability for the year 2010. The frequency of cutbacks equal to or exceeding 17.5% will grow from 10.1% to 16.4% over this period. Moreover, the increasing frequency of cutbacks will be of greater magnitude. 3.1.2 Future Alternative The City can, however, significantly improve its reliability and minimize the magnitude of water cutbacks by implementing water conservation and water recycling projects. ON