Loading...
CC 2018-04-24_11a Water Supply Update and Presentation MEMORANDUM TO: CITY COUNCIL FROM: BILL ROBESON, PUBLIC WORKS DIRECTOR BY: SHANE TAYLOR, UTILITIES MANAGER SUBJECT: MONTHLY WATER SUPPLY AND DEMAND UPDATE AND TWO-YEAR WATER SUPPLY AND DEMAND PROJECTIONS DATE: APRIL 24, 2018 SUMMARY OF ACTION: This update reports the water supply and demand for March 2018. Current Lopez Reservoir levels and projected levels are provided in the attachments. IMPACT ON FINANCIAL AND PERSONNEL RESOURCES: Approximately two (2) hours of staff time was required to prepare the report. RECOMMENDATION: It is recommended the City Council receive and file the monthly Water Supply and Demand Report and two-year Water Supply and Demand projections. BACKGROUND: On April 25, 2017, the City Council, by resolution, rescinded the Stage 1 Water Shortage Emergency along with related emergency water conservation measures and restrictions. During the public hearing the City Council requested staff to continue preparing the monthly water supply and demand updates. The Council urged citizens to continue to practice every day water saving measures, and reiterated that the previously adopted water conservation measures were to remain in effect. In March 2018, the City’s water use was 144.2 acre-feet with a per capita use of 86 gallons per day/per person. There was a total of 5.43” of rainfall in March. The water use for the current “rolling” water year from March 2017 to March 2018 was 2,424 acre- feet, which equates to a per capita use of 123 gallons per day/per person. There was a total of 10.75” of rain fall for this period. ANALYSIS OF ISSUES: The United States Drought Monitor, as of April 12, 2018 shows San Luis Obispo County in a severe drought. Rain fall to date (July 1, 2017 to April 12, 2018):  9 inches at the Corporation Yard rain gauge. Item 11.a. - Page 1 CITY COUNCIL MONTHLY WATER SUPPLY AND DEMAND UPDATE AND TWO-YEAR WATER SUPPLY AND DEMAND PROJECTIONS APRIL 24, 2018 PAGE 2  Lopez Lake, as of April 12, 2018 is at 52.3% capacity (25,834 acre-feet of storage). The projected water use in water year 2017/18 was 2,500 acre-feet. The actual use was 2,294 acre-feet The new water year began on April 1, 2018 and the current total available supply from Lopez is 2,290 acre-feet, our normal entitlement. In addition we have 1,323 acre-feet of ground water entitlement from the Santa Maria Basin and 200 acre-feet from the Pismo Formation. The projected water use for 2018/19 is 2,000 acre-feet. In conclusion, based on average rainfall for the next two years, the current supply will meet the projected demand. ADVANTAGES: No advantages noted at this time. DISADVANTAGES: No disadvantages noted at this time. ALTERNATIVES: Not applicable at this time. ENVIRONMENTAL REVIEW: No environmental review is required for this item. PUBLIC NOTIFICATION AND COMMENTS: The Agenda was posted at City Hall and on the City’s website in accordance with Government Code Section 54954.2. Attachment: 1. Water Year 2018 Water Supply and Demand Update Presentation Item 11.a. - Page 2 1 April 24, 2018 City Council Meeting SOQUEL CREEK WATER DISTRICT Water Year 2018 Water Supply & Demand Update ATTACHMENT 1 Item 11.a. - Page 3 2 Presentation Topics •Background •Supply Summary •Demand Summary •Two Year Water Supply and Demand Look-Ahead •Supporting Supply Reports Item 11.a. - Page 4 3 Background •April 25, 2017 –City Council rescinded Stage 1 Water Shortage Emergency and related water conservation measures and restrictions –Directed staff to prepare ongoing monthly water supply and demand updates since direction •As of April 12, 2018, the United States Drought Monitor shows Arroyo Grande in a severe drought. •Rainfall to date (July 1, 2017 to April 12, 2018) is 9 inches at the Corporation Yard rain gauge. •Lopez Lake, as of April 12, 2018 is at 52.3% capacity (25,834 acre-feet (AF) of storage) Item 11.a. - Page 5 4 Supply Summary •May 23, 2017, the County BOS rescinded the drought emergency proclamation. However, as recommended by Zone 3 Advisory Board, the BOS kept the Low Reservoir Response Plan (LRRP) in place. •New water year (WY) began on April 1, 2018 with new allocations available, or 2,290 AF of entitlement •1,323 AF of Santa Maria Groundwater Basin (SMGB) •200 AF from the Pismo Formation Item 11.a. - Page 6 5 Demand Summary SMGB (AF) Pismo Formation (AF) Lopez (AF) Monthly Total (AF) Monthly Rainfall (in.) Water Year Cumulative Rainfall (in) Population Monthly Per Capita Water Use (gpcd) April-17 2.6 0.0 156.0 158.6 0.7 0.7 17,636 97.7 May-17 2.3 1.9 192.5 196.7 0.4 1.0 17,636 117.2 June-17 6.5 11.6 190.0 208.1 0.0 1.0 17,636 128.2 July-17 7.5 10.3 219.9 237.7 0.0 1.0 17,636 141.7 August-17 44.4 7.8 144.5 196.7 0.0 1.0 17,636 117.2 September-17 3.0 10.4 204.3 217.7 0.2 1.2 17,636 134.1 October-17 5.8 12.9 215.8 234.4 0.1 1.3 17,636 139.7 November-17 0.0 4.3 182.0 186.3 0.2 1.4 17,636 114.7 December-17 0.0 0.0 199.8 199.8 0.0 1.4 17,636 119.1 January-18 0.9 0.0 151.5 152.4 2.7 4.1 17,636 90.8 February-18 17.8 0.0 146.1 163.9 0.2 4.3 17,636 108.2 March-18 0.1 0.0 144.1 144.2 5.4 9.7 17,636 85.9 Water Year 2017/18 90.8 59.3 2,146.3 2,296.4 9.7 9.7 17,636 116.2 050100150200250300350 January-13March-13May-13July-13September-13November-13January-14March-14May-14July-14September-14November-14January-15March-15May-15July-15September-15November-15January-16March-16May-16July-16September-16November-16January-17March-17May-17July-17September-17November-17January-18March-18SMGB (AF)Pismo Formation (AF)Lopez (AF) Item 11.a. - Page 7 6 Demand Summary •Historical per capita water use, measured in gallons per capita per day (gpcd), compared to rainfall 160 138 103 94 116 0.0 20.0 40.0 60.0 80.0 100.0 120.0 140.0 160.0 180.0 200.0 0 5 10 15 20 25 30 gpcd in. Water Year gpcd & Rainfall Water Year Cumulative Rainfall (in) Monthly Rainfall (in.) Monthly Per Capita Water Use (gpcd) Water Year Per Capita Water Use (gpcd) Item 11.a. - Page 8 7 Demand Summary WY 13/14-17/18 •gpcd correlated to rainfall using regression analysis1 WY 15/16 WY 16/17 WY 17/18 WY 13/14 WY 14/15 Linear Regression Trendline y = -2.91349113024438x + 160.5482078108 R² = 0.794731360078806 Polynomial Regression Trendline y = 0.251272647960824x2 - 10.6733937149632x + 201.632013224255 R² = 0.992048530592929 0 20 40 60 80 100 120 140 160 180 0 5 10 15 20 25 30Water Year GPCD "y" Water Year Total Rainfall (in) "x" Regression Trendline Type Water Year Total Rainfall (in.) "x" Projected GPCD Using Regression Trendline to Solve "y" Actual GPCD Comparison WY 17/18 Linear = -2.91349113024438 * 9.7 + 160.548207810 8 132.2 116 Polynomial = 0.25127264796082 * 9.7 ^2- 10.6733937150 * 9.7 + 201.6320132 121.6 116 1Regression analysis: statistical processes for estimating the relationships among variables (rainfall & gpcd). Focus is on the relationship between a dependent variable (gpcd) and one or more independent variables (or 'predictors’, such as rainfall). Helps one understand how the typical value of the dependent variable (or 'criterion variable') changes when any one of the independent variables is varied. The observed water demand trend is assumed to be correlated to multiple factors in addition to rainfall, such as water conservation efforts. However, it is difficult to directly and discretely calculate all factors’ impact on water use. Therefore, rainfall is a reasonably attainable and discrete data source that can be used to project water demand due to their strong correlation with each other. Item 11.a. - Page 9 8 Two Year Water Supply and Demand Look-Ahead •Using the average of 105 gpcd from the regression analysis formulas and assuming average rainfall (16 in.), projected demand for WY 18/19 & WY 19/20 is 2,000 AF Water Supply Source Entitlement (AFY) WY 2017/18 Actual Use (AFY) WY 2018/19 Projected Use (AFY) WY 2019/20 Projected Use (AFY) Groundwater- SMGB 1,323 91 79 79 Groundwater- Pismo Formation 200 59 52 52 Lopez 2,290 2,146 1,869 1,869 Total 3,813 2,296 2,000 2,000 0 1,000 2,000 3,000 4,000 5,000 Entitlement WY 2017/18 Actual Use (AFY)WY 2018/19 Projected Use (AFY) WY 2019/20 Projected Use (AFY) Groundwater- SMGB Groundwater- Pismo Formation Lopez Item 11.a. - Page 10 9 Supporting Supply Reports Item 11.a. - Page 11 10 Supply Summary Item 11.a. - Page 12 11 Supply Summary Item 11.a. - Page 13 12 Supply Summary Item 11.a. - Page 14