Analysis of Raleigh’s Drought Triggers

Analysis of Raleigh’s Drought Triggers

May 8, 2013 and

BackgroundBackground

2

Previous assessments of current drought plan showed high frequency (as much as 1 out of every 3 years) of plan activation at current demands. Drought plan often triggered at times when it’s implementation is unnecessary and ineffective.

• Modeling parameters of previous assessments were more conservative; lower Swift WD, steeper demand pattern, higher triggers

Previous assessments of current drought plan showed high frequency (as much as 1 out of every 3 years) of plan activation at current demands. Drought plan often triggered at times when it’s implementation is unnecessary and ineffective.

• Modeling parameters of previous assessments were more conservative; lower Swift WD, steeper demand pattern, higher triggers

Previous Drought PlanPrevious Drought Plan Stage 1

• Activation : Falls Water Supply Storage Account <= 50%• Lift restrictions at 90% WS Storage• Primary restriction is limiting spray irrigation to 1 day/week

Stage 2• Activation : Falls Water Supply Storage Account <= 30%• Lift restrictions at 70% WS Storage• Residential spray irrigation prohibited. Golf course 50%

reduction, carwashes only on weekends, some indoor reduction expected.

Stage 3• Activation : Falls Water Supply Storage Account <= 10%• Lift restrictions at 50% WS Storage• Many non-essential uses banned and almost all outdoor use is

banned. Numerous indoor/commercial reductions mandated.

Stage 1• Activation : Falls Water Supply Storage Account <= 50%• Lift restrictions at 90% WS Storage• Primary restriction is limiting spray irrigation to 1 day/week

Stage 2• Activation : Falls Water Supply Storage Account <= 30%• Lift restrictions at 70% WS Storage• Residential spray irrigation prohibited. Golf course 50%

reduction, carwashes only on weekends, some indoor reduction expected.

Stage 3• Activation : Falls Water Supply Storage Account <= 10%• Lift restrictions at 50% WS Storage• Many non-essential uses banned and almost all outdoor use is

banned. Numerous indoor/commercial reductions mandated.3

Frequency of Trigger Activation with Current Drought Plan, Last 30 Years of RecordFrequency of Trigger Activation with Current Drought Plan, Last 30 Years of Record

4

0%

5%

10%

15%

20%

25%

30%

35%

40%

45%

50%

50 mgd, Current Plan, 8mgd Swift WD 55 mgd, Current Plan, 8mgd Swift WD 60 mgd, Current Plan, 8mgd Swift WD

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Stage 1 Stage 2 Stage 3

0%

5%

10%

15%

20%

25%

30%

35%

40%

45%

50%

50 mgd, Current Plan, 8mgd Swift WD 55 mgd, Current Plan, 8mgd Swift WD 60 mgd, Current Plan, 8mgd Swift WD

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Stage 1 Stage 2 Stage 3

1 in8 yrs

1 in4 yrs

1 in3 yrs

Questions to ConsiderQuestions to Consider

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Are you comfortable with the frequency of drought plan activation?

What is the appropriate waiting period between stages?

Is a more rigorous climate change analysis warranted?

Are you comfortable with the frequency of drought plan activation?

What is the appropriate waiting period between stages?

Is a more rigorous climate change analysis warranted?

Drawdown-Refill CyclesDrawdown-Refill Cycles

240

242

244

246

248

250

252

254

Lake

Ele

vatio

n in

Fee

t abo

ve m

sl

Falls Lake Elevation2007-08 Drought

Lake Elevation USACE Guide Curve

Drawdown PhaseRefill Phase

Falls Lake Water Supply has regular refill / drawdown cycle

Falls Lake Water Supply has regular refill / drawdown cycle

Water Shortage Response PlanWater Shortage Response Plan

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Water Shortage Response Plan

Stage 1 15%

Stage 2 25%

Stage 3 35%

Estimate contained in WSRP is a flat reduction, but in reality reductions will be greater during the irrigation season and lesser during winter months.

Response by Stage

Seasonal Reductions in Drought StagesSeasonal Reductions in Drought Stages Based on Hazen & Sawyer’s analysis of 2010 demand trends

(indoor, outdoor, etc.) Based on Hazen & Sawyer’s analysis of 2010 demand trends

(indoor, outdoor, etc.)

MonthTotal Demand Reductions in Each Stage

Stage 1 Stage 2 Stage 3

Jan 0.0% 5.0% 15.0%

Feb 0.0% 5.7% 16.4%

Mar 0.0% 5.4% 15.7%

Apr 3.3% 13.1% 26.1%

May 5.4% 17.3% 31.3%

Jun 3.7% 17.2% 33.1%

Jul 5.9% 20.4% 36.5%

Aug 8.4% 20.8% 34.1%

Sep 13.2% 26.4% 38.7%

Oct 8.8% 20.0% 32.2%

Nov 2.7% 10.6% 22.0%

Dec 0.0% 5.9% 16.7%

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Water Shortage Response PlanWater Shortage Response Plan

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Water Shortage Response Plan Hazen and Sawyer Rough Estimate*

Stage 1 15% 5%

Stage 2 25% 15%

Stage 3 35% 28%

* - Response dependent on season. Estimate presented here is simply an average of the estimates made for each of the 12 months.

Annual Average Response by Stage

Modeling Assumptions – All ScenariosModeling Assumptions – All Scenarios Use 2010 monthly demand pattern

Total Average Annual Daily Demand = 60 mgd

Benton plant operations• 8 mgd constant withdrawal

• Increase to 9.5 mgd when entering Stage 1 of drought plan• Never drop EMJ/Falls WD below 36 mgd

Assume 30 day waiting period between triggers

Use 2010 monthly demand pattern

Total Average Annual Daily Demand = 60 mgd

Benton plant operations• 8 mgd constant withdrawal

• Increase to 9.5 mgd when entering Stage 1 of drought plan• Never drop EMJ/Falls WD below 36 mgd

Assume 30 day waiting period between triggers

10

0

5

10

15

20

25

30

35

40

45

50

55

60

65

70

75

80

85

90

95

100

1-Jan 1-Feb 1-Mar 1-Apr 1-May 1-Jun 1-Jul 1-Aug 1-Sep 1-Oct 1-Nov 1-Dec

Falls

WS

Stor

age

%

Stage 1

Stage 2

Stage 3

Seasonal Drought PlanSeasonal Drought Plan Each stage’s storage trigger varies by month Rescission triggers at same levels as current drought plan Assume same demand reductions as current drought plan

Each stage’s storage trigger varies by month Rescission triggers at same levels as current drought plan Assume same demand reductions as current drought plan

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Seasonal Drought Plan, Option 2Seasonal Drought Plan, Option 2 Higher Stage 1 & 2 spring triggers Rescission triggers at same levels as current drought plan Assume same demand reductions as current drought plan

Higher Stage 1 & 2 spring triggers Rescission triggers at same levels as current drought plan Assume same demand reductions as current drought plan

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0

5

10

15

20

25

30

35

40

45

50

55

60

65

70

75

80

85

90

95

100

1-Jan 1-Feb 1-Mar 1-Apr 1-May 1-Jun 1-Jul 1-Aug 1-Sep 1-Oct 1-Nov 1-Dec

Falls

WS

Stor

age

%

Stage 1

Stage 2

Stage 3

0%

5%

10%

15%

20%

25%

30%

35%

40%

45%

50%

60 mgd, Current Plan, 8mgd Swift WD 60 mgd, Seasonal Plan 1, 8mgd Swift WD 60 mgd, Seasonal Plan 2, 8mgd Swift WD

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Stage 1 Stage 2 Stage 3

0%

5%

10%

15%

20%

25%

30%

35%

40%

45%

50%

60 mgd, Current Plan, 8mgd Swift WD 60 mgd, Seasonal Plan 1, 8mgd Swift WD 60 mgd, Seasonal Plan 2, 8mgd Swift WD

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Stage 1 Stage 2 Stage 3

Frequency of Alert Trigger Activation, Last 30 Years of RecordFrequency of Alert Trigger Activation, Last 30 Years of Record

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1 in6 yrs

1 in3 yrs

1 in5 yrs

Effect of Maximizing Swift Creek WithdrawalsEffect of Maximizing Swift Creek Withdrawals Maximum Swift withdrawal

• 14 mgd when Benson/Wheeler storage >= 60%• 12.6 mgd when Benson/Wheeler storage >= 30%• 11.2 mgd when Benson/Wheeler storage < 30%

Never drop EMJ/Falls WD below 36 mgd

Maximum Swift withdrawal• 14 mgd when Benson/Wheeler storage >= 60%• 12.6 mgd when Benson/Wheeler storage >= 30%• 11.2 mgd when Benson/Wheeler storage < 30%

Never drop EMJ/Falls WD below 36 mgd

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0%

5%

10%

15%

20%

25%

30%

35%

40%

45%

50%

60 mgd, Current Plan, Max Swift WD 60 mgd, Seasonal Plan 1, Max Swift WD 60 mgd, Seasonal Plan 2, Max Swift WD

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Stage 1 Stage 2 Stage 3

0%

5%

10%

15%

20%

25%

30%

35%

40%

45%

50%

60 mgd, Current Plan, Max Swift WD 60 mgd, Seasonal Plan 1, Max Swift WD 60 mgd, Seasonal Plan 2, Max Swift WD

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Stage 1 Stage 2 Stage 3

Max Swift Creek Scenarios, Last 30 Years of RecordMax Swift Creek Scenarios, Last 30 Years of Record

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1 in10 yrs

1 in4 yrs

1 in8 yrs

0%

5%

10%

15%

20%

25%

30%

35%

40%

45%

50%

60 mgd, Current Plan, Max Swift WD 60 mgd, Seasonal Plan 1, Max Swift WD 60 mgd, Seasonal Plan 2, Max Swift WD

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Stage 1 Stage 2 Stage 3

0%

5%

10%

15%

20%

25%

30%

35%

40%

45%

50%

60 mgd, Current Plan, Max Swift WD 60 mgd, Seasonal Plan 1, Max Swift WD 60 mgd, Seasonal Plan 2, Max Swift WD

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Stage 1 Stage 2 Stage 3

Max vs. 8 mgd Swift Creek Scenarios, Last 30 Years of RecordMax vs. 8 mgd Swift Creek Scenarios, Last 30 Years of Record

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1 in10 yrs

1 in4 yrs

1 in8 yrs

1 in6 yrs

1 in3 yrs

1 in5 yrs

1930

1935

1940

1945

1950

1955

1960

1965

1970

1975

1980

1985

1990

1995

2000

2005

2010

May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr

Year

Julian Day

1930

1935

1940

1945

1950

1955

1960

1965

1970

1975

1980

1985

1990

1995

2000

2005

2010

May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr

Year

Julian Day

Days in Drought Restrictions, Current Plan,60 mgd total demand, 8 mgd Swift WDDays in Drought Restrictions, Current Plan,60 mgd total demand, 8 mgd Swift WD

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Statistics for last 30 yearsMedian Start Date = Oct. 2Median End Date = Feb. 10Median Duration = 130 daysMax Duration = 210 days

1930

1935

1940

1945

1950

1955

1960

1965

1970

1975

1980

1985

1990

1995

2000

2005

2010

May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr

Year

Julian Day

1930

1935

1940

1945

1950

1955

1960

1965

1970

1975

1980

1985

1990

1995

2000

2005

2010

May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr

Year

Julian Day

Days in Drought Restrictions, Seasonal Plan,60 mgd total demand, 8 mgd Swift WDDays in Drought Restrictions, Seasonal Plan,60 mgd total demand, 8 mgd Swift WD

18

Statistics for last 30 yearsMedian Start Date = Oct. 10Median End Date = Feb. 25Median Duration = 119 daysMax Duration = 196 days

1930

1935

1940

1945

1950

1955

1960

1965

1970

1975

1980

1985

1990

1995

2000

2005

2010

May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr

Year

Julian Day

1930

1935

1940

1945

1950

1955

1960

1965

1970

1975

1980

1985

1990

1995

2000

2005

2010

May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr

Year

Julian Day

Days in Drought Restrictions, Seasonal Plan 2,60 mgd total demand, 8 mgd Swift WDDays in Drought Restrictions, Seasonal Plan 2,60 mgd total demand, 8 mgd Swift WD

19

Statistics for last 30 yearsMedian Start Date = Oct. 20Median End Date = Mar. 17Median Duration = 122 daysMax Duration = 196 days

1930

1935

1940

1945

1950

1955

1960

1965

1970

1975

1980

1985

1990

1995

2000

2005

2010

May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr

Year

Julian Day

1930

1935

1940

1945

1950

1955

1960

1965

1970

1975

1980

1985

1990

1995

2000

2005

2010

May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr

Year

Julian Day

Days in Drought Restrictions, Current Plan,60 mgd total demand, Max Swift WDDays in Drought Restrictions, Current Plan,60 mgd total demand, Max Swift WD

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Statistics for last 30 yearsMedian Start Date = Oct. 23Median End Date = Jan. 30Median Duration = 82 daysMax Duration = 195 days

1930

1935

1940

1945

1950

1955

1960

1965

1970

1975

1980

1985

1990

1995

2000

2005

2010

May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr

Year

Julian Day

1930

1935

1940

1945

1950

1955

1960

1965

1970

1975

1980

1985

1990

1995

2000

2005

2010

May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr

Year

Julian Day

Days in Drought Restrictions, Seasonal Plan,60 mgd total demand, Max Swift WDDays in Drought Restrictions, Seasonal Plan,60 mgd total demand, Max Swift WD

21

Statistics for last 30 yearsMedian Start Date = Oct. 14Median End Date = Feb. 1Median Duration = 101 daysMax Duration = 175 days

1930

1935

1940

1945

1950

1955

1960

1965

1970

1975

1980

1985

1990

1995

2000

2005

2010

May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr

Year

Julian Day

1930

1935

1940

1945

1950

1955

1960

1965

1970

1975

1980

1985

1990

1995

2000

2005

2010

May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr

Year

Julian Day

Days in Drought Restrictions, Seasonal Plan 2,60 mgd total demand, Max Swift WDDays in Drought Restrictions, Seasonal Plan 2,60 mgd total demand, Max Swift WD

22

Statistics for last 30 yearsMedian Start Date = Oct. 18Median End Date = Mar. 4Median Duration = 82 daysMax Duration = 175 days

‘Worst Case’ Drought Scenario‘Worst Case’ Drought Scenario

Start in April at 80% WS Storage• 249.7 ft starting elevation for Falls/Beaverdam

Use 2002 hydrology for April & May

Use 2007-2008 hydrology for rest of the trace

60 mgd total demand

8 mg withdrawal from Swift• 9.5 mgd when in drought plan• No less than 36 mgd from Falls/EMJ

Start in April at 80% WS Storage• 249.7 ft starting elevation for Falls/Beaverdam

Use 2002 hydrology for April & May

Use 2007-2008 hydrology for rest of the trace

60 mgd total demand

8 mg withdrawal from Swift• 9.5 mgd when in drought plan• No less than 36 mgd from Falls/EMJ

23

No Drought PlanNo Drought Plan

24

No Drought Plan – Falls Lake ElevationNo Drought Plan – Falls Lake Elevation

25 Note: For this run demand / min. releases are allowed to be met even when WS/WQ accounts are depleted.

Bottom ofConservation Pool

Sedimentation Pool

Current Drought PlanCurrent Drought Plan

26

Seasonal Drought PlanSeasonal Drought Plan

27

Seasonal Drought Plan Option 2Seasonal Drought Plan Option 2

28

Water Not Sold During Mandatory Conservation60 MGD demand scenario, 8 mgd Swift WD

Water Not Sold During Mandatory Conservation60 MGD demand scenario, 8 mgd Swift WD

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Drought EventVolume of Water Conserved (i.e. unsold) – in MG

Current Triggers Seasonal #1 Seasonal #2

2007-08 767 996 996

2002 503 537 537

1993 330 168 168

1980-81 270 270

2005 213 56 56

1988 213

1991 73

1987 45

1998 45

2010-2011 25 30 30

1994-95 6

1933-34 0* 0* 0*

Total 2490 1787 2057* - Mandatory conservation triggered, but no reduction in consumption expected

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