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Using Hydrologic Forecasts for Dynamic Management of
NYC's Reservoir Releases for the Delaware River Basin
W. Josh Weiss1; Luke Wang1; Paul Rush2; Thomas Murphy2
1Hazen and Sawyer, P.C.; [email protected]
2New York City Department of Environmental Protection
93rd American Meteorological Society Annual Meeting
Austin, TX | January 8, 2013
2
Outline
Background
New York City water supply system
Delaware River Basin
NYC’s Operations Support Tool (OST)
Use of forecasts to improve Delaware River
Basin release management
Forecasted Available Water (FAW) approach to NYC
releases
Enhanced spill mitigation program
Implementation and performance of forecast-based
approach
3
3 systems – Delaware,
Catskill, and Croton
19 reservoirs & 3
controlled lakes
2,000 mi2 watershed in
parts of 8 upstate
counties
Serves 9 million people
(1/2 of New York State)
Delivers ~1.1 BGD
Unfiltered supply
(Cat/Del)
NYC Water Supply System
4
Catskill / Delaware Systems
5
Headwaters in the Catskill
Mountains
Drains to New York State,
Pennsylvania, New Jersey,
and Delaware
Water source for NYC, New
Jersey (D&R Canal),
Philadelphia
Ecological and recreational
value
Delaware River Basin
6
1954 U.S. Supreme
Court Decree
1961 Delaware River
Basin Compact
1983 “Good Faith”
Agreements
2008 Flexible Flow
Management Plan
Key Dates in DRB Management
Images from DRBC website: www.state.nj.us/drbc/
7
Relied on release
schedules based on
annual estimation of
“available water”
Expired on May 31, 2011
Opportunity to implement
better approach to
estimating available
water, using ensemble
hydrologic forecasts
2008 Flexible Flow Management Plan (FFMP)
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NYC Operations Support Tool
9
0%
20%
40%
60%
80%
100%
10/1 11/1 12/1 1/1 2/1 3/1 4/1 5/1 6/1 7/1 8/1 9/1
Da
ily E
OP
Usa
ble
Sto
rag
e
Delaware System Usable Storage
OST to Support Real-Time Operations
Ensemble forecasted inflows drive model
predictions over the next ~1 year
Probabilistic output provides information on the
likelihood of system refill to guide operations
10
100
1000
10000
10/1 11/1 12/1 1/1 2/1 3/1 4/1 5/1 6/1 7/1 8/1 9/1
Da
ily A
vg In
flo
w (m
gd
)
Delaware System Inflow80 years of climatology
80 one-year simulations
0
0.2
0.4
0.6
0.8
1
10/1 11/1 12/1 1/1 2/1 3/1 4/1 5/1 6/1 7/1 8/1 9/1
Dai
ly E
OP
Usa
ble
Stor
age PR.01
PR.10
PR.20
PR.30
PR.40
PR.50
PR.60
PR.70
PR.80
PR.90
PR.99
Provides robust probabilistic basis for decision-making
10
OST-FFMP Framework
DELAWARE
RELEASE
DECISIONS
Probability of Excess Water At Specified Risk Level Low Water
Availability High Water
Availability
Schedule A
Schedule B
Schedule C
Schedule D
Schedule E
Schedule F
Schedule G
• Reservoir Levels • Infrastructure Status
• Water Quality
• Demand Projections
Today’s Conditions Ensemble Inflow Forecasts
• System Reliability • Reservoir Balancing
• Drinking Water Quality
• Releases
Operating Rules
OST
INPUT
OST
DECISION-
MAKING
Storage Levels Water Quality Refill Probability
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Forecasted Available Water Balance
Today’s Total PCN Storage Current System Status
Cumulative PCN Inflows
through June 1 Probabilistic Streamflow
Forecasts
+
Cumulative PCN Diversions
through June 1
Estimated Volume to
meet NYC Demand
–
June 1 Storage Target 100% Usable Storage –
Cumulative PCN Release
Target through June 1
Distribute over Number
of Days to June 1 and
Re-Evaluate Regularly
=
12
Risk represented by
forecast probability
Transition to more
conservative risk when
approaching June 1
Seasonal risk factor:
Risk-Based Approach
0
10
20
30
40
50
60
70
80
Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May
Fo
rec
as
t P
erc
en
tile
70% probability
of less inflow
50% probability
of less inflow 30% probability
of less inflow
13
Enhanced Flood Mitigation Program
Even full reservoirs help reduce downstream
flooding
Strong downstream pressure to maintain year-
round voids in NYC reservoirs
Not feasible for water supply reliability
When water is available (based on OST
predictions):
Maintain seasonal storage target to provide spill buffer
Monitor short-term (24/48-hr) forecasts for possible
proactive releases
14
Enhanced Flood Mitigation Releases
Conditional Storage Objective (CSO)
for enhanced flood mitigation rule
15
Enhanced Flood Mitigation Mass Balance
Today’s Total PCN Storage Current System Status
Cumulative PCN Inflows
over the Next 7 Days
Streamflow Forecasts
(50th Percentile)
+
Cumulative PCN Diversions
over the Next 7 Days
Estimated Volume to
Meet NYC Demand
–
Conditional Storage
Objective (CSO)
Boundary between L1-b
and L1-c Zones –
Predicted Storage
Surplus Relative to CSO
Release Estimated
Surplus; Re-Evaluate
Daily
=
Cumulative PCN Release
over the Next 7 Days
Based on OST-FFMP
Table Selection
–
16
Rule Testing and Implementation
Rule testing: long-term simulation mode
Implementation: real-time position analysis mode
17
Long-Term Performance Testing (1927-2008)
0 100 200 300 400 500 600 700 800 900
PCN Spill
Neversink Spill
Pepacton Spill
Cannonsville Spill
PCN Release
Neversink Release
Pepacton Release
Cannonsville Release
Average Flow (cfs)
Average Simulated PCN Release and Spill, OST-FFMP vs FFMP 35 mgdFFMP 35 mgd
OST-FFMP
-40% -30% -20% -10% 0% 10% 20% 30% 40%
PCN Spill
Neversink Spill
Pepacton Spill
Cannonsville Spill
PCN Release
Neversink Release
Pepacton Release
Cannonsville Release
Percent Change (OST-FFMP relative to FFMP-35)
Percent Change in Average Simulated PCN Release and Spill
18
Stakeholder Involvement
How to bring
stakeholders on board?
How to minimize “black
box” perceptions?
How to ensure
transparency while
protecting NYC system
information?
19
Unanimous agreement to
implement OST-FFMP
program
Implementation begun
on June 1, 2011
OST-FFMP Agreement
20
Future: DRB OST?
NOAA-ACOE-USGS Integrated Water
Resources Science and Services (IWRSS)
partnership
Opportunity for pilot-testing Basin-wide OST?
Use existing model/forecast framework
21
Conclusions
Forecast-based approach to DRB release
management
Allows for frequent increased releases
Supports quantification of risk to water supply reliability
Helps convert uncontrolled spill into managed releases
Framework for developing ‘win-win’ solutions