IRP Approach to Water Supply Alternatives for Duck River Watershed:

Presentation to XII TN Water Resources Symposium

William W. WadeEnergy and Water Economics

Columbia, TNApril 4, 2002

2

Overview

1 Duck River Reliability Planning

2 Demand Forecasts

3 Effects on Duck River Flows

4 Supply Planning

5 Hydrology Implications

6 Alternative Evaluation

7 Reliability Analysis8 Decision Issues

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Duck River Reliability Planning (1)

Two questions drive TVA Duck River Needs Analysis:

1.How much added water does the region need?

2.When will it be needed?

Don’t address the more fundamental questions . . .

4

Duck River Reliability Planning (2)

Five Better Questions for Duck River Needs Analysis:

1. What is existing reliability & what does region need?

2. What can the region afford?

3. When needed and what is the least cost way of meeting future needs?

4. How do alternatives relate to other needs in the watershed?

5. Do alternatives add benefits other than supply reliability?– Can these benefits absorb some costs?

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Integrated Resource Planning• Supply reliability measures a water system’s

expected success in avoiding detrimental economic, social, and environmental effects from water shortages.– Effects, not shortage per se, are the targets.

• Supply reliability planning entails a water management strategy that provides the watershed with a reliable and affordable water supply for the next 50 years. – Reliability is an economic outcome of the process.

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Reliability TargetsReliability planning begins with Objectives

• DRA reliability targets:

1. Maintain Normandy above 864 elevation. [or ?]2. Meet 120/155 cfs at Shelbyville + 10 cfs demand. 3. Avoid breaching 130 cfs flow benchmark at

Columbia more than 1 day every five years. [or ?]

4. Meet consumptive demands in the watershed.

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Reliability Targets (2)

• DRA must set its own reliability targets before evaluating resource options.

• Cost effects of less than 100% supply reliability of any target need to be compared to cost of achieving target.

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Water Demand ForecastDemand forecast initiates water needs

assessment.– Average daily demand - beginning point for

water needs analytics.

USGS demand forecast updated based on revised population. – Table 1 shows revised water demands

increased by population growth ratios.– Based on input from USGS (Susan Hutson)

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Revised Forecasts - avg mgd annually

Ratio 2020 2050 2050

2020 Low High Low High

DRUC na na 8.7 11.0 11.0

Total Bedford Cty 1.150 1.2 1.31 8.3 11.0 12.3Total Marshall Cty 1.370 1.5 1.85 6.4 9.1 11.1Total Maury/Williamson Cties 1.110 1.1 1.25 20.3 26.6 30.0

Sources: DRUC, Hutson, August 27 Memo to TVA; TVA, Water Supply Needs Analysis, 1998Others, EWE, Sept 26, 2001

Ratio-2050

Table 1: Public Water Demands from the Duck River Watershed

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Peak Water Demand ForecastWater supplies must meet peak needs.

Chart 1 shows that peaks occur July - Sept.

Withdrawal demands in the spring are about 65% of peak demands.

Planning to meet demands amounts to planning for growth to meet peak.– Key is peak month.

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Chart 1: Cumulative Monthly Supply Withdrawals: 1999 - 2001

7.000

9.000

11.000

13.000

15.000

17.000

19.000

21.000

23.000

25.000AugJulyJuneM

ayAprM

arFebJanDecNovOctSeptAugJulyJuneM

ayAprM

arFebJanDecNovOctSeptAug

mgd

CPWS mgd L'burg mgd S'ville mgd

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Peak Water Demand Forecast (2)

Table 2 shows requirements to meet peak monthly requirements.

– Except DRUC: USGS predicts peak day demand.

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Revised Forecasts - peak mgd monthly

Peak Month 2020 2050 2050

Factor Low High

DRUC 1.5 13.1* 16.5* 16 -19*

Total Bedford Cty 1.150 9.6 12.6 14.2Total Marshall Cty 1.150 7.3 10.4 12.8Total Maury/Williamson Cties 1.350 27.3 36.0 40.5*Each of these estimates is linked to a 1.5 peak day benchmark. The high DRUC number is supported by 1.8 peak day.

Sources: DRUC, Hutson, August 27 Memo to TVA; TVA, Water Supply Needs Analysis, 1998Others, EWE, Sept 26, 2001

Table 2: Public Water Maximum Demands from the Duck River Watershed

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Effects on Duck River Flows

Can the Duck supply future water demands?

Table 3 begins to answer the question.

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Revised Forecasts - peak cfs

1996 2020 2050 2050

Conversion Actuals Low Highcfs/mgd

DRUC 10.5 20.2 25.5 29.4

Total Bedford Cty Supply Intake 1.547 10.8 14.8 19.6 21.9Wastewater Discharge -4.2 -5.7 -7.5 -8.4Total Marshall Cty Supply Intake 1.547 5.3 11.3 16.1 19.7Wastewater Discharge -1.9 -4.0 -5.7 -7.0Total Maury/Williamson Cties Intake 1.547 22 42.3 55.6 62.7

Net Flow Reductions at Columbia Flow Gauge Mile 132.832.0 58.8 78.1 88.9Incremental withdrawal 26.8 46.1 56.9

Source: TVA, Water Supply Needs Analysis, 1998. EWE, Sept 17, 2001

Table 3: Duck River Maximum Water Withdrawals and Returns

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Effects on Duck River (2)Providing high quality drinking water under conditions of

drought and peak demand is difficult and expensive.

Chart 2 shows that DRUC’s target operating range between 865 - 875 elevation.

• Making drinkable water from Normandy is difficult . . .

Modeling shows that 20 mgd peak demand would bring the reservoir down to 858 feet in drought.

Treatment costs for DRUC to achieve drinking water quality for peak summer months and meet S’ ville flow targets are part of the needed data.

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Chart 2: DUCK RIVER UTILITY COMMISSION

860.0

865.0

870.0

875.0

880.0

J95F MAMJ J A SOND J

96F MAMJ J ASONDJ

97FMAM J J ASONDJ

98FMAMJ J A SOND J

99F MAMJ J A SONDJ

00FMAM J J ASONDJ

01FMAM J J

MONTH

EL

EV

AT

ION

(F

EE

T)

NORMAL LEVEL ACTUAL LEVEL

Normandy Reservoir Actual vs Normal Levels

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Planning Criteria

Assume that DRUC can meet Coffee County demands at reasonable costs while TVA meets Shelbyville flow target.

Can flows in the river meet future demands and TDEC requirement that flows exceed 130 cfs at river mile 133?

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Supply Planning Results

USGS flows at Columbia since 1904 can be used for statistical analysis.

But, flows before the river was regulated with opening of Normandy, January 1976, don’t directly apply.

Flows at Columbia since closure are used to compare supplies to requirements.

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Supply Planning Results (2)

Water supply shortfalls are measured in terms of:– Frequency– Duration– Magnitude

Hydrologic data post closure are “run” past future demands to determine frequency, duration and magnitude of breach to 130 cfs minimum flow.

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Supply Planning Results (3)Two scenarios are assumed:

– USGS demand forecast -- Revised by EWE.– Extraordinary industrial growth upstream of

Columbia withdrawing 12.5 cfs. (Four 2 MGD plants, one in each county.)

2050 demands are considered as Low or High.

Table 4 shows the equivalent benchmark minimum flows that will meet demands and minimum flow criteria.

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Table 4: Minimum Flow Conversions

Scenario 130 cfsEquivalent

2020 158 cfs2020 (HigherIndustrial Growth))

170 cfs

2050, low withdraws178 cfs

2050, high withdraws187 cfs

2050, high withdraws(Higher IndustrialGrowth)

199 cfs

These equivalent flows meet future demands and 130 cfs benchmark.

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Table 5: Critical Low-Flow Occurrences below 130 cfs and Probabilityat Columbia, based on 7,549 days, of data)

Variable 2020 2020

(HigherIndustrialGrowth)

2050, lowwithdraws

2050, highwithdraws

2050, highwithdraws

(HigherIndustrialGrowth)

1 Low Flow Occurrencesin 7,549 days 179 386 513 696 923

2 Low Flow Occurrencesper year (days) 8.7 18.7 24.8 33.6 44.7

3 Probability of anyshortfall in a year

.68 .68 .79 .84 .89

4 Average Duration LowFlow (days)

4.6 6.8 6.6 7.4 8.65 Average Daily

Shortfall (cfs) 15.0 16.0 19.1 22.0 27.46 Needed Expected

average annual addedsupply(2*5*3*.6464(million gallons) 1 mgd = 0.6464 cfs)

57 131 241 402 704

7 Acre Feet 175 402 740 1234 2,161

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Supply Planning Results (4)

Results show that a shortage could occur 68 % of the years, rising to 89 % of the by 2050.

Average shortfalls would rise from 15 - 22 cfs over time and scenario; 27 cfs with higher industrial growth.

Annual Shortfall days would rise from 9 to 34 within a year; 45 days with higher industrial growth.

Added supply of 1,234 AF would eliminate expected shortfall.

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Supply Planning Results (5)

A storage solution must target the maximum likely shortage event.– Table 6 shows this to range from 228 to

1,087 million gallons. [700 - 3,337 AF.]– Chart 5 interpolates the estimates to show

the growth in this requirement. – Chance of one year in 21 of 700 AF

shortfall rising to 2,450 AF by 2050.

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Table 6. Maximum Shortfalls - 130 cfs

Scenario Max Hydrologic Shortage Event1

(130 cfs Benchmark)

Days Mil Gal2020, low 25 2282020, high 27 4322050, low withdraws 36 5792050, high withdraws 37 7942050, high withdraws(Higher IndustrialGrowth)

38 1,087

1Each of the Shortage Events occurs only once in the 20.7 year hydrology data set.

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Chart 5: Duck River Maximum Water Supply Needs to meet 130 cfs target

500

1,000

1,500

2,000

2,500

3,000

Acre

Fe

et

Supply Shortfall

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Hydrology Implications

Protecting the Columbia benchmark, 130 cfs, will require new water supply.

• Protecting the 21-year drought of record requires 700 - 1,250 AF to meet 2020 low to high demands.

• Protecting the 21-year drought of record requires 2,450 AF to meet high demand for a 37-day 2050 drought.

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Hydrology Implications (2)• Final conclusions about new water supply

require hydrology study including historic droughts before Normandy closure; i. e., with synthetic data.

• Synthetic data would simulate the Duck River flows post closure to show how the managed river would operate with Normandy.

• Provide a longer statistical basis for conclusions.

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Alternatives Evaluation• Challenge is to find the most economic

mix of resources to achieve an acceptable supply reliability objective.

• An affordable alternative with acceptable risk is preferable to elimination of any chance of shortage at much higher costs.– Depends on cost of effects of shortage.

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Alternatives Evaluation (2)• Policy determinants of the best mix are

DRA’s four reliability targets:– Reliability of Normandy water levels.– Reliability of flow rate at Shelbyville.– Reliability of flow rates past Columbia.– Reliability of watershed demand coverage.

• What risk of shortfall is acceptable?• 50 years demand forecast is a long time with

considerable uncertainty.• Planning for the high forecast may be too risk

averse, or it may be prudent.

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Alternatives Evaluation (3)• Empirical determinants of the best mix are

hydrologic, economic and regulatory driven.– What added supply do you need to achieve

acceptable reliability?– What can you pay for?– What can you permit?

• TVA 1998 and 2000 reports were not intended to and did not answer these questions.

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Alternatives Evaluation (4)

TVA Alternatives: (All costs approximate)

• Raise Normandy Dam $ 8 million• Downstream Intake $11 million• Tims Ford Pipeline $13 million• Fountain Creek Reservoir $50 million

Added Alternatives:• Shift Tullahoma Demand to Tims Ford $?• Conservation $ 1 million

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Alternatives Evaluation (5)Water Supply Created by Alternatives:

2050 Conservation 2,160 AF in Normandy

Move Tullahoma Demand 4,000 AF in Normandy

Tims Ford Pipeline 22 cfs when needed

Raise Normandy 17,000 AF in Normandy

Raise Normandy+Shift Tullahoma 21,000 AF

Fountain Creek Reservoir 44,000 AF in Fountain Creek

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Reliability Analysis • Table 7 compares the needed supplies

and added water.

– Worst case requirements are shown in top of Table 7.

– New supplies in storage are shown on bottom.

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Worst Case Requirements*2050 Low2050 High2050 High, AddedSupply Additions ConservationShift Tullahoma DemandRaise NormandyShift and RaiseFountain Creek* One event in 21 years.

Table 7: Worst Case Requirements v. New Storage Supplies

4,000

Acre Feet

177524403337

17,00021,00044,000

2,160

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Reliability Analysis (2)

Hydrologic modeling reveals likelihood, duration of shortages, average and worst case amounts of needed new water. – About 15 cfs, 7 days duration, 2 year in 3: 2020.– About 22 cfs, 8 days duration, 4 years in 5: 2050.

– Max shortage event: – About 16 cfs, 27 days duration, 1 year in 21: 2020– About 22 cfs, 37 days duration, 1 year in 21: 2050

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Summary of Decision Issues

• Four reliability targets govern the selection of a resource mix.– Maintain Normandy above 864 elevation. [or ?]– Meet 120/155 cfs at Shelbyville. [treatment

determined]– Avoid breaching 130 cfs benchmark at Columbia

more than 1 day every five years. [or ?]– Meet all consumptive demands in the watershed

[except during droughts of some quantifiable measure.]

• DRA must select planning targets.

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Summary of Decision Issues (2)

All alternatives provide adequate to more than adequate supply reliability.

Challenge: find the most economic way of adding increments of supply to meet reliability targets.

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Summary of Decision Issues (3)Cost of new water supply created by alternative

only can be amortized over new water required to meet targets. – Other purposes than water supply could absorb

some costs not born by DRA. • Recreation or Water Quality.

Costs of effects of not meeting DRA reliability targets are needed to set quantitative targets.– How much to spend depends on cost of

missing target.