CC 2018-04-24_11a Water Supply Update and PP PresentationApril 24, 2018
City Council Meeting
Water Year 2018 Water Supply & Demand Update
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Presentation Topics
Background
Supply Summary
Demand Summary
Two Year Water Supply and Demand Look-Ahead
Supporting Supply Reports
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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City Council rescinded Stage 1 Water Shortage Emergency and related water conservation measures and restrictions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)
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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May 23, 2017, the County BOS rescinded the drought emergency proclamation.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
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Demand Summary
Change charts, and say WY 17/18
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Demand Summary
Historical per capita water use, measured in gallons per capita per day (gpcd), compared to rainfall
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Demand Summary WY 13/14-17/18
gpcd correlated to rainfall using regression analysis1
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.
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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
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Supporting Supply Reports
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Supply Summary
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Supply Summary
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Supply Summary
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