Analysis of Raleigh’s Drought Triggers

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

2. Background • 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

3. 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.

4. Frequency of Trigger Activation with Current Drought Plan, Last 30 Years of Record 1 in 3 yrs 1 in 4 yrs 1 in 8 yrs

5. Questions to Consider • 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?

6. Drawdown-Refill Cycles • Falls Lake Water Supply has regular refill / drawdown cycle Drawdown Phase Refill Phase

7. Water Shortage Response Plan Response by Stage Estimate contained in WSRP is a flat reduction, but in reality reductions will be greater during the irrigation season and lesser during winter months. 7

8. Seasonal Reductions in Drought Stages • Based on Hazen & Sawyer’s analysis of 2010 demand trends (indoor, outdoor, etc.)

9. Water Shortage Response Plan Annual Average Response by Stage Draft * - Response dependent on season. Estimate presented here is simply an average of the estimates made for each of the 12 months. 9

10. 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

11. 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

12. 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

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

14. 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

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

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

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

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

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

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

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

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

23. ‘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

24. No Drought Plan

25. No Drought Plan – Falls Lake Elevation Bottom of Conservation Pool Sedimentation Pool Note: For this run demand / min. releases are allowed to be met even when WS/WQ accounts are depleted.

26. Current Drought Plan

27. Seasonal Drought Plan

28. Seasonal Drought Plan Option 2

29. Water Not Sold During Mandatory Conservation60 MGD demand scenario, 8 mgd Swift WD * - Mandatory conservation triggered, but no reduction in consumption expected