CC 2019-04-23_11c Monthly Water Supply and Demand March 2019_Two Year Projections_PP PresentationApril 23, 2019
City Council Meeting
Water Year 2019 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City Council rescinded Stage 1 Water Shortage Emergency and related water conservation measures and restrictions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 2, 2019, the United States Drought Monitor shows Arroyo Grande is not in a drought classification.
Rainfall to date (July 1, 2018 to April 4, 2019) is 17.7 inches at the Corporation Yard rain gauge.
Lopez Lake is at 59.2% capacity (29,243 acre-feet (AF) of storage) as of April 11, 2019
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Supply Summary
May 23, 2017, the County BOS rescinded the drought emergency proclamation. However, as recommended by the Zone 3 Advisory Board, the BOS kept the Low Reservoir Response Plan (LRRP) in
place until March 31, 2018.
A new Lopez water year (WY) began on April 1, 2019 with new allocations of 2,290 AF of entitlement plus 378 AF of surplus
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 (in.)
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Demand Summary WY 13/14-18/19
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 107 gpcd from the regression analysis formulas and assuming average rainfall (16 in.), projected demand for WY 19/20 & WY 20/21 is 2,200 AF
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Supporting Supply Reports
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Supply Summary
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