Current and Future Challenges
Managing a Public Water Supply
System with Conjunctive Use:
The Tampa Bay Water Experience
Jeffrey S. Geurink, Ph.D., P.E.
Donald J. Polmann, Ph.D., P.E.
Tampa Bay Water
2nd UF Water Institute Symposium
“Managing Integrated Water Supplies”
February 24, 2010
1
Presentation Outline
Managing a Conjunctive Use System

Conjunctive Use Water Supply System
–  Defined
–  Tampa Bay Water, water utility



Management principles
Climatic and hydrologic variability
Objectively informed management
–  Assessment tools
–  Monte Carlo framework

Summary
Conjunctive Use Water Supply System
Tampa Bay Water Definition
Coordinated management and
combined use of multiple surface and
ground water resources, as available
and as needed, to maximize resource
yield and supply reliability, with
requisite treatment for compatible
blending, delivered through an
interconnected transmission system,
under a single regulatory scheme
Tampa Bay Water
Wholesale Regional Water Utility
Conjunctive Use Water
Supply System
2.4 Million
Residents Served
230 MGD Regional
Annual Average
Demand
130 to 260 MGD Tampa
Bay Water Daily Flow
Supply
Tampa Bay Water
Multiple Types of Raw Water Sources
Desal
Water
Ground Water
Surface Water
15 BG Reservoir
Tampa Bay Water
Conjunctive Use Water Supply System
Four water source types
combined into one
water supply system
Daily and seasonal
transitions in mix of
treated source types
Compatible finished
water quality regardless
of mix of treated source
types
Regional Blended Supply
Increasing Reliance on Surface Water

Uncertainty in climate variability affects
uncertainty in reliability of surface water
2009
2020
54%
39%
7%
40%
54%
6%
Tampa Bay Water
Management of a Conjunctive Use System

Water supply availability / reliability
–  Demand projections
–  Climate patterns and cycles
–  Regulatory limits
–  Infrastructure
–  Consistent finished water quality

Environmental stewardship

Cost effectiveness
Atlantic Multi-Decadal Oscillation
Correlated with Long-Term Rainfall Patterns
35
0.4
AMO Warm Cycle
25
0.3
Wetter periods
0.2
15
5
0
-5
-0.1
Drier periods
-15
-0.2
AMO Cool Cycle
-25
-0.3
-35
-0.4
Ten Year Wet periods
10 Year Dry period
AMO Cool Period
AMO Warm Period
Sea surface
temperature
differences
Inches
0.1
Local Rainfall Correlated with Sea Surface
Temperature Changes for Oct-Nov-Dec
Strong negative
correlation
Strong
positive
correlation
Tampa Bay Water Regional Rainfall
Annual Mean and Variability
Regional Rainfall (Water Years)
(Oct 1976 - Sept 2007)
31 Year Average Rainfall = 51 Inches
90
80
70
Inches
60
50
40
30
20
10
0
1978-1987 = 52.8 inches
Range
= 24.5 inches
1988-1997 = 50.1 inches
Range
= 11.8 inches
1998-2007 = 52.0 inches
Range
= 40.4 inches
Hillsborough River at Zephyrhills
Alafia River
2012
2010
2008
2006
2004
2002
2000
1998
1996
1994
1992
1990
1988
1986
1984
1982
1980
1978
1976
1974
1972
1970
1968
1966
1964
1962
1960
1958
1956
1954
1952
1950
1948
1946
1944
Annual Average Discharge in cfs
Climate Variability Affects
Annual Streamflow Variability
900
800
700
600
51.2
500
400
300
200
100
0
Climate Variability Affects
Seasonal Streamflow Variability
1000
900
Monthly Mean flow, cfs
800
700
600
500
400
300
200
100
0
Jan
Feb
Mar
Apr
May
June
Hillsborough River
July
Aug
Alafia River
Sep
Oct
Nov
Dec
Integrated Hydrologic Model (IHM)
Dynamically Links HSPF & MODFLOW
Water Shortage Mitigation Plan
• 4 Water Shortage Levels
• Triggers activate transitions
between water shortage
levels
• Hydrologic
• Early drought warning
• Surface water supply
• Severity of water shortage
Water Shortage
Mitigation Plan
Final Report
February, 2009
Water Shortage Mitigation Plan
Water Shortage Levels & Activation Triggers
Water Shortage Levels
Triggers
ON
OFF
I. Drought Alert
(Moderate)
RCD Rainfall < -5”
OR
RMD Flow < - 10 mgd
No RCD Rainfall
AND
RMD Flow > - 5 mgd
II. Drought Warning
(Severe)
RCD Rainfall < -5”
AND
RMD Flow < - 10 mgd
No RCD Rainfall
OR
RMD Flow > - 5 mgd
III. Regional Supply
Shortage
(Extreme)
RMD Flow < -10 mgd
AND
Reservoir Level drops below 100’
elevation (~60 days supply)
RMD Flow > - 5 mgd
OR
Reservoir Level moves above 110’
Elevation
IV. Water Supply Crisis
(Critical)
RMD Flow < - 10 mgd
AND
Reservoir Level drops below 85’
elevation (~20 days supply)
RMD Flow > - 5 mgd
OR
Reservoir Level moves above 100’
Elevation
Water Shortage Mitigation Plan
Trigger Activation Example (31 Years)
RCD-rainfall, RMD-flow, and ResELEV with simulated water-shortage-level declarations vs time (1977 -2007)
RCD-rainfall, in
20
15
WSMP Level 1
10
WSMP Level 2
5
WSMP Level 3
0
-5
WSMP Level 4
RCD-rainfall, in
-10
-5 in
-15
0 in
-20
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
RMD-flow, MGD
40
30
WSMP Level 1
20
WSMP Level 2
10
WSMP Level 3
0
-10
WSMP Level 4
-20
-10 MGD
-30
-5 MGD
RMD-flow, MGD
-40
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
ResELEV, ft
140
130
WSMP Level 1
120
WSMP Level 2
110
100
WSMP Level 3
WSMP Level 4
Reservoir level, ft
90
85 ft
80
100 ft
70
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
110 ft
Apply Simulation Tools Within a
Monte Carlo Framework

Management of extreme & intra-annual
–  Likelihood and duration of event
–  Existing and future system and climate

Monte Carlo framework
–  Statistical properties of historical data
–  Stochastically generate many time series of
uncertain variables (e.g., rainfall)
–  Simulate hydrology: likelihood-duration

Reliability, Stewardship, Cost
Managing a Conjunctive Use System
Summary

Management challenges
–  Compatible blending
–  Climate extremes and intra-annual
–  Changes in climate variability
–  Increasing reliance on surface water
–  Leading indicators for rainfall
–  Hydrologic/environmental assessments
–  Regulatory structure

Reliability, Stewardship, Cost