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
Mobile District
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
Mobile District
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
Mobile District
Simplified Limitations
• Does not reflect seasonal variations in demand
• Inability to accurately evaluate evaporation losses
Mobile District
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)
0
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
0
500
1000
1500
2000
2500
3000
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
0
200
400
600
800
1000
1200
1400
1600
1800
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
1994
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