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.; jweiss@hazenandsawyer.com

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/

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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)

8

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

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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

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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

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Enhanced Flood Mitigation Releases

Conditional Storage Objective (CSO)

for enhanced flood mitigation rule

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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

–

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Rule Testing and Implementation

Rule testing: long-term simulation mode

Implementation: real-time position analysis mode

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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

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Stakeholder Involvement

How to bring

stakeholders on board?

How to minimize “black

box” perceptions?

How to ensure

transparency while

protecting NYC system

information?

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Unanimous agreement to

implement OST-FFMP

program

Implementation begun

on June 1, 2011

OST-FFMP Agreement

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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

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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