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On April 25, 2017, the City Council, by resolution, rescinded the Stage 1 Water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