Analysis of Raleigh’s Drought Triggers May 8, 2013 and

Background 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 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 Record 4 1 in 8 yrs 1 in 4 yrs 1 in 3 yrs

Questions to Consider 5  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 Cycles Drawdown Phase Refill Phase  Falls Lake Water Supply has regular refill / drawdown cycle

Water Shortage Response Plan 7 Stage 115% Stage 225% Stage 335% 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 Stages  Based on Hazen & Sawyer’s analysis of 2010 demand trends (indoor, outdoor, etc.) Month Total Demand Reductions in Each Stage Stage 1Stage 2Stage 3 Jan0.0%5.0%15.0% Feb0.0%5.7%16.4% Mar0.0%5.4%15.7% Apr3.3%13.1%26.1% May5.4%17.3%31.3% Jun3.7%17.2%33.1% Jul5.9%20.4%36.5% Aug8.4%20.8%34.1% Sep13.2%26.4%38.7% Oct8.8%20.0%32.2% Nov2.7%10.6%22.0% Dec0.0%5.9%16.7% 8

Water Shortage Response Plan 9 Hazen and Sawyer Rough Estimate* Stage 115%5% Stage 225%15% Stage 335%28% * - Response dependent on season. Estimate presented here is simply an average of the estimates made for each of the 12 months. Draft Annual Average Response by Stage

Modeling 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

Seasonal 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 11

Seasonal 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 12

Frequency of Alert Trigger Activation, Last 30 Years of Record 13 1 in 6 yrs 1 in 3 yrs 1 in 5 yrs

Effect 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 14

Max Swift Creek Scenarios, Last 30 Years of Record 15 1 in 10 yrs 1 in 4 yrs 1 in 8 yrs

Max vs. 8 mgd Swift Creek Scenarios, Last 30 Years of Record 16 1 in 10 yrs 1 in 4 yrs 1 in 8 yrs 1 in 6 yrs 1 in 3 yrs 1 in 5 yrs

Days in Drought Restrictions, Current Plan, 60 mgd total demand, 8 mgd Swift WD 17 Statistics for last 30 years Median Start Date = Oct. 2 Median End Date = Feb. 10 Median Duration = 130 days Max Duration = 210 days

Days in Drought Restrictions, Seasonal Plan, 60 mgd total demand, 8 mgd Swift WD 18 Statistics for last 30 years Median Start Date = Oct. 10 Median End Date = Feb. 25 Median Duration = 119 days Max Duration = 196 days

Days in Drought Restrictions, Seasonal Plan 2, 60 mgd total demand, 8 mgd Swift WD 19 Statistics for last 30 years Median Start Date = Oct. 20 Median End Date = Mar. 17 Median Duration = 122 days Max Duration = 196 days

Days in Drought Restrictions, Current Plan, 60 mgd total demand, Max Swift WD 20 Statistics for last 30 years Median Start Date = Oct. 23 Median End Date = Jan. 30 Median Duration = 82 days Max Duration = 195 days

Days in Drought Restrictions, Seasonal Plan, 60 mgd total demand, Max Swift WD 21 Statistics for last 30 years Median Start Date = Oct. 14 Median End Date = Feb. 1 Median Duration = 101 days Max Duration = 175 days

Days in Drought Restrictions, Seasonal Plan 2, 60 mgd total demand, Max Swift WD 22 Statistics for last 30 years Median Start Date = Oct. 18 Median End Date = Mar. 4 Median Duration = 82 days Max Duration = 175 days

‘Worst Case’ Drought Scenario  Start in April at 80% WS Storage ft starting elevation for Falls/Beaverdam  Use 2002 hydrology for April & May  Use 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 ft starting elevation for Falls/Beaverdam  Use 2002 hydrology for April & May  Use 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 Plan 24

No 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 of Conservation Pool Sedimentation Pool

Current Drought Plan 26

Seasonal Drought Plan 27

Seasonal Drought Plan Option 2 28

Water Not Sold During Mandatory Conservation 60 MGD demand scenario, 8 mgd Swift WD 29 Drought Event Volume of Water Conserved (i.e. unsold) – in MG Current Triggers Seasonal #1Seasonal # * Total * - Mandatory conservation triggered, but no reduction in consumption expected

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