Mobile District

Water Supply Reallocation Workshop

Determining Yield and Storage RequirementJune 2, 2009

Tulsa, OKJames Hathorn, Jr

Mobile District

Redistribution of WaterThe function of a reservoir system is to redistribute the natural occurrence of water in time and place.

– Formerly, people settled near rivers and used water when it arrived.

– Then we built reservoirs to accumulate and release water to improve the distribution in time

flood control, water supply storage– And conveyance to improve the distribution in space

Mobile District

Distribution of Water in Time• Within-year Reservoir Storage

– Reservoir stores wet season water for use in dry season

• Over-year Reservoir Storage– Reservoir stores wet year water for use in dry years

or extended drought

• Evaluation of current and future demand and local hydrology will determine if within- or over-year is needed, and the required size of reservoir.

Mobile District

Within-year and Over-year Reservoir Storage and Yield

0

200000

400000

600000

800000

1000000

1200000

1400000

Inflo

w, R

elea

se (a

f/mon

th)

0

500000

1000000

1500000

2000000

2500000

Res

ervo

ir St

orag

e (a

f)

DemandInflow

Reservoir Storage

Mobile District

Corp Guidelines• EM 1110-2-1420

– “Hydrologic Engineering Requirements for Reservoirs” (Oct 1997)

• EM 1110-2-1417 – “Flood Runoff Analysis” (Aug 1994)

• EM 1110-2-1701 – “Engineering and Design Hydropower” (Dec 1985)

Mobile District

Terms

• Yield – also know as firm yield and critical yield is the maximum sustainable flow at some point in time during the most adverse sequence of streamflow (critical period).

• Storage – water impounded in surface or underground reservoirs for future use.

Mobile District

Storage / Yield of a Reservoir• YIELD = amount of water provided on a

regular basis (yield ≤

average flow)

• The most basic evaluation is the Storage / Yield relationship.

Reservoir Storage VolumeReservoir Storage Volume

YieldYieldAverage FlowAverage Flow

Mobile District

Storage / Yield Relationship

• In a study, there are 2 ways define the relationship:

– Planning: For a given demand, how large must the reservoir at that location be?

– Reassessment/Operations: For a given reservoir, what is the annual yield?

Fix one variable, vary the other

Mobile District

Storage / Yield Relationship• There are various methods for determining

the relationship between reservoir storage and yield– Simplified Methods (Planning)

• Rippl Mass Diagram• Sequent Peak Algorithm

– Sequential Reservoir Routing (Operations)– simulation of realistic reservoir operation over a

multiple year period– more complex demand patterns and sources can

be evaluated, as well as losses

Mobile District

Purpose

• Storage requirements for – Water supply– Water quality– Hydroelectric power– Navigation – Irrigation– Other conservation purpose

Navigation

Water QualityIrrigation

Water Supply

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Yield Objectives

• Determine yield given a storage allocation• Find storage required given a desired yield• Determination of complementary or

competitive aspects of multi project development

• Analysis of alternative operation rules for a project or group of projects

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Input Data Needed...• The supply data used can be either

– the historical record, or a critical dry period within the record

– a synthetic event or data series

• The demand requirements can be either– 100% of actual or forecasted demandconstant or varied, depending on the method

– or met with some frequency or reliability

Mobile District

Simplified

• Sequential Mass Curve – Constructed by accumulating inflows to a

reservoir site throughout the period of record & plotting the accumulated inflows versus the sequential time period

• Depth Duration– Relationship of storage yield vs shortage

frequency

Mobile District

Sequential Mass Curve• Manual graphical procedure used to identify the

critical period and firm yield• Firm yield is maximized by fully drafting available

storage to supplement natural streamflow• Mass curve is cumulative plotting of reservoir

inflow• The slope of the mass curve at any point in time

represents the inflow at that time.

Mobile District

Sequential Mass Curve

Mobile District

Mass Curve & Constant Yield Lines

Mobile District

Yield Given Storage

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Simplified Limitations

• Does not reflect seasonal variations in demand

• Inability to accurately evaluate evaporation losses

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Detailed Sequential Analysis

• Conservation of massI – O = Δ

S

I = inflow, O= outflow, ΔS=change in storage

• Computer Simulation (HEC-5, ResSim)– Multipurpose reservoir– Varying demand– Evaporation evaluation– Firm yield optimization

Mobile District

Maximize Firm Yield

Mobile District

Firm Yield Curve

Mobile District

Critical Period Analysis• These methods looked at historical critical

periods of low streamflow and determined demand that could be met without failure (worst case analysis)– only one particular duration and magnitude -- many other

options are possible– can be subject to sampling error with a short data set– also leads to false confidence about reliability

• Alternatives to critical period are probabilistic descriptions...

Mobile District

Case Study #1

• ACF Litigation– Buford Dam forms Lake Lanier– Currently no water storage contracts exist– What percent of yield / storage currently

provided to metro Atlanta area?

Mobile District

Mobile District

750 cfs Instream Flow Requirement

1,100- 1,500 cfs minimum release to meet Metro-Atlanta

Water Supply and WQ

Atlanta Returns

Metro Atlanta Avg Gross Withdrawals = 605 cfs

~ 56% Returned to River

Mobile District

750 cfs Flow Required

For Water Quality

Atlanta Intake

Water Quality Requirement

Mobile District

Rippl Mass Diagram Analysis

1940 1950 1960 1970 1980 1990 2000

Flow

(cfs

)

5,000,000

10,000,000

15,000,000

20,000,000

25,000,000

30,000,000

35,000,000

40,000,000

45,000,000

50,000,000

55,000,000

BUFORD UNIMP_CMA7_ACC FLOW_INC

critical periods

Mobile District

1954-1964 Critical Period

1954 1955 1956 1957 1958 1959 1960 1961 1962 1963 1964

Flow

(cfs

)

11,000,000

12,000,000

13,000,000

14,000,000

15,000,000

16,000,000

17,000,000

18,000,000

19,000,000

20,000,000

BUFORD UNIMP_CMA7_ACC FLOW_INC

Mobile District

1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994

Flow

(cfs

)

33,000,000

34,000,000

35,000,000

36,000,000

37,000,000

38,000,000

39,000,000

40,000,000

41,000,000

42,000,000

43,000,000

BUFORD UNIMP_CMA7_ACC FLOW_INC

1985-1993 Critical Period

Mobile District

1999-2005 Critical Period

1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007

Flow

(cfs

)

42,000,000

43,000,000

44,000,000

45,000,000

46,000,000

47,000,000

48,000,000

49,000,000

50,000,000

51,000,000

52,000,000

BUFORD UNIMP_CMA7_ACC FLOW_INC

Mobile District

Current Critical Period

1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007

Flow

(cfs

)

42,000,000

43,000,000

44,000,000

45,000,000

46,000,000

47,000,000

48,000,000

49,000,000

50,000,000

51,000,000

52,000,000

BUFORD UNIMP_CMA7_ACC FLOW_INC

?

Mobile District

Buford Storage-Yield (with revised unimpaired flow)

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500

1000

1500

2000

2500

- 100,000 200,000 300,000 400,000 500,000 600,000 700,000 800,000

Storage (dsf)1 acft = 0.5 dsf

Yiel

d (c

fs)

1955-581941198119861988Average QSeries7

Average Q = 2,064

Buford Conservation Storage1071 - 1035 = 548,368 dsf

Year Yield (cfs)1941 1,8901954 1,9501986 1,524

Yield is dependent on critical period selected. The analysis period should accompany the published value.

Mobile District

Lanier Critical Period Duration

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3500

0 200 400 600 800 1000 1200 1400 1600 1800 2000

Yield in CFS

Res

ervo

ir D

raw

dow

n Pe

riod

in D

ays Critical Period Duration data

Date Begin Date Refill Date of Ma Yield Duration1-Jul-86 1-Sep-86 13-Aug-86 300 62

11-Jun-86 24-Oct-86 28-Aug-86 500 13526-Mar-86 16-Jan-87 9-Oct-86 1000 296

6-Jul-87 1-Jul-89 28-Dec-88 1200 72614-May-85 25-Jan-90 28-Dec-88 1400 171719-Aug-84 14-Mar-90 28-Dec-88 1500 203319-Aug-84 19-Mar-90 17-Feb-89 1524 203817-Aug-84 6-Mar-91 17-Feb-89 1600 239215-Aug-84 28-Dec-92 17-Feb-89 1800 305715-Aug-84 17-Apr-93 17-Feb-89 1900 3100 4 yrs, 8 months

Mobile District

Buford Dam Critical Yield

• Graphical Method• Unimpaired Flow 1939-1993• Critical Period 1980’s• Buford Conservation Storage 549,000 dsf

(1071-1035)• Critical Yield = 1,524 cfs (w/o evap)

Mobile District

Buford Yield – Sequential Analysis

Yield = 1,465 cfswith evaporation

Buford TOC1070 - 1071

Mobile District

Buford Yield

• Graphical– 1,524 cfs (w/o evap)

• Sequential– 1,465 cfs

• Current critical period may be the worst, awaiting additional data

Buford Yield Analysis

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Graphical SequentialFl

ow in

cfs

Mobile District

Case Study #2

• Okatibbee Reservoir, Meridian MS– US Department of Energy, emergency water

supply agreement– Development and operations of the planned

Strategic Petroleum Reserve storage– Dependable water source during drought

conditions

Mobile District

Background• The U.S. Department of Energy (DOE) is interested in

establishing an emergency water supply agreement with the US Army Corps of Engineers (USACE) for water from the Okatibbee Reservoir to support the development and operations of the planned Strategic Petroleum Reserve storage site at Richton, MS. DOE is currently looking at the construction of a raw water intake facility on the Pascagoula River near the Merrill gage to support the development and operations of the Richton storage site. This water intake facility will be used to supply fresh water to the Richton site for the solution mining of storage caverns and oil drawdown operations.

Mobile District

I II

III IV

VVI

VII

VIII

IX

I - Yazoo River Basin

II - Tombigbee River Basin

III - North Independent Streams

IV - Tennessee River Basin

V - Big Black River Basin

VI - Pearl River Basin

VII - Pascagoula River Basin

VIII - Coastal Streams

IX - South Independent Streams

Pascagoula River Basin

Mobile District

Okatibbee Reservoir

Chickasawhay River

Merrill Gage

PascagoulaRiver

Leaf River

Pascagoula River Basinwith Major Tributaries

Mobile District

Okatibbee LakeElevation

(msl)Total Storage

(acre-feet)

Top of Flood Control 350 88,6500

Top of Conservation(May thru 15 Oct)

344 46,060

Top of Conservation(Dec thru Mar)

339 29,160

Maximum Drawdown for Water Quality and Water Supply

328 7,760

Mobile District

Okatibbee Operation Levels

Mobile District

Okatibbee Reservoir

Elevation 309

Elevation 344

Elevation 352

Elevation 328

Flood Storage = 42,590 Acre-feet

Conservation Storage = 38,300 Acre-feet

Spillway 359

Sluice 310

Inactive Storage =760 Acre-feet

Record Low, 20Oct84 – 329.04

Mobile District

Okatibbee Lake

Mobile District

Okatibbee Outlet

Mobile District

Stream Gauge Station At MerrillPascagoula River

George County

Record Low Flow Recorded2007

Mobile District

Remaining Conservation Storage 25,200 ac-ft (65.8 %)

Pat Harrison (PHWD) 13,100 ac-ft (34.2 %)

Okatibbee Conservation StorageOkatibbee Conservation Storage

USACE entered into aWater Storage contract withPat Harrison Waterway DistrictApril 23, 1965 for 13,100 acre-feet of storage (25 mgd)

Existing Storage Account

Mobile DistrictE

lev

(ft)

325

330

335

340

345

350

Jul Oct Jan Apr Jul Oct Jan Apr2006 2007 2008

Flow

(cfs

)

0

50

100

150

200

250

OKATIBBEE-POOL YIELD-----0 ELEV OKATIBBEE-INACTIVE YIELD-----0 ELEV-ZONE

OKATIBBEE-CONSERVATION YIELD-----0 ELEV-ZONE OKATIBBEE-YIELDRELEASE_41 YIELD-----0 FLOW-MIN

OKATIBBEE OUT YIELD-----0 FLOW

Okatibbee Yield Analysis Immediately Downstream

Yield = 40 cfs

Inactive Storage

Conservation Storage

Flow at Dam

Critical Period Apr 2007-Mar2008

Mobile DistrictE

lev

(ft)

325

330

335

340

345

350

Jan Jul Jan Jul Jan Jul Jan1999 2000 2001

Flow

(cfs

)

0

100

200

300400

500

600700

OKATIBBEE-POOL YIELD-----3 ELEV OKATIBBEE-INACTIVE YIELD-----3 ELEV-ZONE

OKATIBBEE-CONSERVATION YIELD-----3 ELEV-ZONE OKATIBBEE-YIELDRELEASE_41 YIELD-----3 FLOW-MIN

OKATIBBEE OUT YIELD-----3 FLOW

Okatibbee Yield Analysis Immediately Downstream

Yield = 47 cfs

Inactive Storage

Conservation Storage

Flow at Dam

Critical Period Apr 1999-Mar2001

Mobile DistrictE

lev

(ft)

325

330

335

340

345

350

355

360

Jan Apr Jul Oct Jan Apr Jul Oct Jan1999 2000 2001

Flow

(cfs

)

0

1,000

2,000

3,000

4,000

5,000

OKATIBBEE-POOL YIELD_DS--0 ELEV OKATIBBEE-INACTIVE YIELD_DS--0 ELEV-ZONE

OKATIBBEE-CONSERVATION YIELD_DS--0 ELEV-ZONE MERRILL_MIN_Q YIELD_DS--0 FLOW-MIN

MERRILL YIELD_DS--0 FLOW

Okatibbee Yield Analysis Operation for Merrill

Yield = 845 cfs

Inactive Storage

Conservation Storage

Flow at Merrill

Critical Period Apr 2000-Mar2001

Mobile District

Yield Analysis Summary

Storage Account Critical PeriodApr 1999- Mar2001

Critical PeriodApr 2007- Mar2008

Pat Harrison 16.07 cfs 13.68 cfs

Remaining Storage 30.93 cfs 26.32 cfs

Okatibbee Conservation Storage = 38,300 ac-ft

Storage Yield from the most severe critical periods

Critical Period YieldApr 1999- Mar2001 47 cfsApr 2007- Mar2008 40 cfs

Distribution of Yield

Mobile District

Pascagoula River at Merrill, MS

0

500

1,000

1,500

2,000

2,500

3,000

3,500

4,000

1930 1940 1950 1960 1970 1980 1990 2000Calendar Year

Min

imum

Dai

ly D

isch

arge

in c

fs

0

500

1,000

1,500

2,000

2,500

3,000

3,500

4,000

7Q10 = 917 cfs

Flow below MIF in 9 of 78 years (12%)

Mobile District

Model Results

• Number of days each year that releases from Okatibbee not available

• Percent of Time Okatibbee releases made to meet DOE requirement

Mobile District

ResSim Model

Mobile District

Days Okatibbee Release Not AvailableMIF = 917 cfs

15

53

0

10

20

30

40

50

60

1969

1970

1971

1972

1973

1974

1975

1976

1977

1978

1979

1980

1981

1982

1983

1984

1985

1986

1987

1988

1989

1990

1991

1992

1993

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1995

1996

1997

1998

1999

2000

2001

2002

2003

2004

2005

2006

2007

2008

Day

s

Sum of MIF_917 Shortage

Year

Mobile District

Okatibbee Operation forMIF = 917

0

200

400

600

800

1000

12001/

1/20

07

2/1/

2007

3/1/

2007

4/1/

2007

5/1/

2007

6/1/

2007

7/1/

2007

8/1/

2007

9/1/

2007

10/1

/200

7

11/1

/200

7

12/1

/200

7

Flow

in c

fs

DOE Required Release Okatibbee Release

DOE RequirementNot meet (15 days)

Mobile District

Modeling Results• The results indicate that the DOE release requirements

can be meet during the non-critical periods. As a reminder the critical periods are – Apr 1999- Mar2001– Apr 2007- Mar2008

• The 2007 drought period is the most severe recorded since the construction of Okatibbee Dam. In fact it’s so severe no DOE releases can be made for any of the 4 scenarios. During this period all available storage is allocated to existing project purposes.

• The following charts indicate the periods DOE releases requirement is not meet.

Mobile District