211CAT

Advanced Modeling Tools for EvaluatingAdvanced Modeling Tools for EvaluatingCatskill Turbidity Control AlternativesCatskill Turbidity Control Alternatives

New York CityNew York CityDepartment of Environmental ProtectionDepartment of Environmental Protection

NYWEA Watershed Science and Technical ConferenceNYWEA Watershed Science and Technical Conference

September 17, 2008 ▪ West PointSeptember 17, 2008 ▪ West Point

Grantley Pyke, P.E. Hazen and SawyerSteve Effler, Ph.D., P.E. Upstate Freshwater InstituteDaniel Sheer, Ph.D., P.E. HydroLogicsDavid Warne NYCDEP

2

I. Study Overview

-Issue & Objectives

-Alternatives Evaluated

II. Reservoir Modeling Framework

-Reservoir Water Quality Models

-Reservoir System Operations Model

III. Evaluation of Alternatives

-Water Quality Performance

IV. Conclusions

OutlineOutline

3Catskill Turbidity Catskill Turbidity Control StudyControl Study

Issue:Issue:– Major storm events in the Major storm events in the

Schoharie & Ashokan Schoharie & Ashokan watersheds lead to periodic watersheds lead to periodic elevated turbidity levels in the elevated turbidity levels in the Catskill systemCatskill system

Overall Study Goal:Overall Study Goal:– Evaluate turbidity control Evaluate turbidity control

alternatives at Ashokan that alternatives at Ashokan that can:can:a) reduce the frequency of a) reduce the frequency of high turbidity levels entering high turbidity levels entering Kensico, and Kensico, and b) reduce the need for alum b) reduce the need for alum treatment at Kensicotreatment at Kensico

Why Interesting?Why Interesting?– Demonstrates how models Demonstrates how models

are critical for sound decision-are critical for sound decision-making in complex systemsmaking in complex systems

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Esopus Creek Flow and Alum Treatment EventsEsopus Creek Flow and Alum Treatment Events

Esopus Creek at Coldbrook (USGS Flow)

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Esopus Creek at Coldbrook (USGS Flow)

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46 BG in 12 days

44 BG in 13 days

46 BG in 11 days

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Photo Courtesy NYCDEP

Catskill Turbidity SourcesCatskill Turbidity SourcesStreambank and streambed erosionStreambank and streambed erosion

Watershed underlain by glacial lake silts and claysWatershed underlain by glacial lake silts and clays

Minimally armored streamsMinimally armored streams

Small particles scatter light efficientlySmall particles scatter light efficiently

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Ashokan Reservoir Turbidity Control AlternativesAshokan Reservoir Turbidity Control Alternatives

Alt. 1: West Basin Outlet Structure: To release water from the W Basin and reduce turbidity load into the E Basin

~$250M

Alt. 4: Upper Gate Chamber Modifications: To improve selective withdrawal capability

~$65M

Alt. 2: Dividing Weir Crest Gates: To increase W Basin detention storage

~$140M

Alt. 3: E Basin Diversion Wall: To reduce short-circuiting into Upper Gate Chamber

~$130M

Alt. 5: New East Basin Intake: To withdraw from a location less susceptible to high turbidity

~$330M

Alt. 6: Catskill Aqueduct Improvements and Modified Operations:

a) West Basin Drawdown

b) Waste Channel Operation

c) Catskill Aqueduct Improvements

~$90M

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Performance Evaluation ApproachPerformance Evaluation Approach

How will an alternative improve Catskill turbidity control under the How will an alternative improve Catskill turbidity control under the full range of conditions that the system will experience?full range of conditions that the system will experience?

Water QualityWater Quality

• Depends on forcing conditionsDepends on forcing conditions

• Depends how reservoirs and Depends how reservoirs and aqueducts are operated (feedback aqueducts are operated (feedback effects)effects)

– Extent of drawdownExtent of drawdown

– Timing of diversions & releasesTiming of diversions & releases

– Reservoir balancingReservoir balancing

OperationsOperations

• Depends on water qualityDepends on water quality

• Depends on Catskill conditionsDepends on Catskill conditions

– Ashokan storage, Esopus flowAshokan storage, Esopus flow

• Depends on system conditionsDepends on system conditions

– seasonal demands, storage seasonal demands, storage levels, drought statuslevels, drought status

Water Quality Water Quality from from

Schoharie & Ashokan 2-D ModelsSchoharie & Ashokan 2-D Models

Operations Operations from from

Reservoir System Model (OASIS)Reservoir System Model (OASIS)

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Schoharie, Ashokan, and Kensico Reservoir Schoharie, Ashokan, and Kensico Reservoir Water Quality Models (W2)Water Quality Models (W2)

Developed by UFI using CE-QUAL-W2 frameworkModel development & testing supported by:

Continuous Automated Monitoring

– Continuous automated in-stream and in-reservoir monitoring

– Detailed Daily Depth Profiles

– Temperature, Specific Conductance, Beam Attenuation Coefficient, Optical Backscatter

Process Studies

– Particle Settling Velocity

– Sediment Resuspension

– Downward Sediment Flux

– Internal Wave Characterization

– Wave Pressure Measurements

Storm Event Gridding/Profiling

– Detailed vertical profiles of reservoir water quality collected during and after storm events

– Lateral and longitudinal transects

Sensitivity Analysis

– Robust analysis of sensitivity of Ashokan model predictions to sensitivity of Ashokan model predictions to model drivers and model parameters model drivers and model parameters

Tri-hull buoy containing on-board computer, communications and

batteries (~8 feet in diameter)

Solar power unit

Profiler - depth controlled by on-board computer

Underwater sensors

Anchor lines

Meteorologicalinstruments

Tri-hull buoy containing on-board computer, communications and

batteries (~8 feet in diameter)

Solar power unit

Profiler - depth controlled by on-board computer

Underwater sensors

Anchor lines

Meteorologicalinstruments

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OASIS ModelOASIS Model

• Mass-balance reservoir system operations modelMass-balance reservoir system operations model

• Developed by HydroLogicsDeveloped by HydroLogics

• Simulates operation of the reservoir system using goals, Simulates operation of the reservoir system using goals, constraints, and linear programmingconstraints, and linear programming

• Makes decisions every day about how much water to Makes decisions every day about how much water to release from each reservoir in order to meet demands release from each reservoir in order to meet demands and environmental requirementsand environmental requirements

OASIS Model ofNew York City

Water Supply System and Delaware River Basin

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Operating Rules coded into Operations Control Language:

OASISOASISSystem ModelSystem Model

Physical DataPhysical Data

– Storage – Elevation Storage – Elevation curvescurves

– Spillway rating curvesSpillway rating curves

– Head-discharge functions Head-discharge functions for tunnels/aqueductsfor tunnels/aqueducts

– Reservoir storage zonesReservoir storage zones

Operating RulesOperating Rules

– Stream releasesStream releases

– Reservoir balancingReservoir balancing

– Operating preferencesOperating preferences

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OASIS Modeling Approach: Historical OASIS Modeling Approach: Historical Inflows combined with System ScenariosInflows combined with System Scenarios

System Scenario

• Demand

• Regulations

• Infrastructure

• Operating Rules

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Schoharie Reservoir Average Daily Inflow (1948 - 2004)

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• Daily, for each stream reach and reservoir

• Represents range of future inflows

Performance

• Water Supply

• Water Quality

Model includes net daily inflow to each Model includes net daily inflow to each reservoir and stream reach for the reservoir and stream reach for the period 1948 - 2004period 1948 - 2004

Objective is NOT to model history and Objective is NOT to model history and recreate what happenedrecreate what happened

Objective is to use historical inflows as Objective is to use historical inflows as an indicator of the range of inflows that an indicator of the range of inflows that could occur in the futurecould occur in the future

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• Daily Simulation:Daily Simulation:1948 – 2004 (57 yrs)1948 – 2004 (57 yrs)

• Daily Turbidity Predictions at Daily Turbidity Predictions at Schoharie-Ashokan-KensicoSchoharie-Ashokan-Kensico

• Daily Release and Diversion Daily Release and Diversion Decisions throughout the Decisions throughout the SystemSystem

OASIS-W2 Linked ModelOASIS-W2 Linked Model

Schoharie W2

OASIS Model of NYC Reservoir System & Delaware River Basin

Kensico W2Ashokan W2

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OASIS-W2 Linked ModelOASIS-W2 Linked ModelHow are the Models Linked?How are the Models Linked?

OASIS ModelNYC Reservoir System & Delaware River Basin

What is the most reliable way to movewater around the system?

Daily Diversion & Release DecisionsDaily Diversion & Release Decisions

• Diversions from Schoharie ReservoirDiversions from Schoharie Reservoir

• Diversions from Ashokan ReservoirDiversions from Ashokan Reservoir

• Releases from Ashokan West BasinReleases from Ashokan West Basin

• Operation of Ashokan Dividing Weir GatesOperation of Ashokan Dividing Weir Gates

• Alum application at KensicoAlum application at Kensico

Daily Water Quality InfoDaily Water Quality Info

• Turbidity (& Temp) at the Turbidity (& Temp) at the IntakeIntake

What water quality isavailable for withdrawal?

Daily SimulationDaily Simulation1948 – 2004 (57 yrs)1948 – 2004 (57 yrs)

n = 20,728 daysn = 20,728 days

CE-QUAL-W2Schoharie ReservoirAshokan Reservoir

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What constitutes a reasonable simulation of operations?What constitutes a reasonable simulation of operations?– Similar patterns of drawdown and refillSimilar patterns of drawdown and refill– Conservative operations re: water supply reliabilityConservative operations re: water supply reliability– Simulated operations are feasible and implementableSimulated operations are feasible and implementable

OASIS operating rules have been reviewed by DEP Ops Staff OASIS operating rules have been reviewed by DEP Ops Staff and found to provide a sound and realistic simulation of system operationsand found to provide a sound and realistic simulation of system operations

Linked OASIS-W2 Model PerformanceLinked OASIS-W2 Model PerformanceComparison with Historical OperationsComparison with Historical Operations

Goal: demonstrate that the model Goal: demonstrate that the model provides a provides a reasonablereasonable simulation simulation of how the NYC water supply of how the NYC water supply system is operatedsystem is operated

OASIS assumptions:OASIS assumptions:– 1/1/87 - 9/30/041/1/87 - 9/30/04– CurrentCurrent baseline operating baseline operating

rules rules – Historical demand levelsHistorical demand levels

Exact match is Exact match is notnot expected due to expected due to changes in model drivers over the changes in model drivers over the comparison period:comparison period:– Model reflects Model reflects currentcurrent regulations regulations– Model reflects Model reflects currentcurrent operating rules operating rules– Model reflects Model reflects currentcurrent infrastructure infrastructure

capacitiescapacities– Model has Model has allall system components in system components in

serviceservice

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Croton System Storage

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Comparison with Historical OperationsComparison with Historical OperationsSystem Storage LevelsSystem Storage Levels

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East Ashokan Reservoir Elevation

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Comparison with Historical OperationsComparison with Historical OperationsCatskill Reservoir ElevationsCatskill Reservoir Elevations

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Catskill Aqueduct Turbidity

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Kensico Turbidity and Alum Application

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Comparison with Historical OperationsComparison with Historical OperationsCatskill Turbidity LevelsCatskill Turbidity Levels

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Evaluation of AlternativesEvaluation of Alternatives

AlternativesAlternatives

Alt 1: West Basin Outlet StructureAlt 1: West Basin Outlet Structure (2000, 4000, 6000 mgd release (2000, 4000, 6000 mgd release capacity)capacity)

Alt 2: Dividing Weir Crest GatesAlt 2: Dividing Weir Crest Gates (4’ crest gate on Dividing Weir)(4’ crest gate on Dividing Weir)

Alt 3: East Basin Diversion Wall**Alt 3: East Basin Diversion Wall** (750’, 1700’, 2400’ wall; 3-D (750’, 1700’, 2400’ wall; 3-D simulations)simulations)

Alt 4: Upper Gate Chamber ModificationsAlt 4: Upper Gate Chamber Modifications (East only, East + West)(East only, East + West)

Alt 5: East Basin IntakeAlt 5: East Basin Intake (Single- and Multi-level intakes)(Single- and Multi-level intakes)

Alt 6: Catskill Aqueduct Improvements and Modified Operations Alt 6: Catskill Aqueduct Improvements and Modified Operations

– West Basin DrawdownWest Basin Drawdown

– Waste Channel OperationWaste Channel Operation (1200 mgd release capacity)(1200 mgd release capacity)

– Catskill Aqueduct ImprovementsCatskill Aqueduct Improvements

Alternatives 1- 5 in combination with Alternative 6Alternatives 1- 5 in combination with Alternative 6

Water Quality Performance MeasuresWater Quality Performance Measures

# Days with Ashokan Diversion Turbidity > 8 NTU# Days with Ashokan Diversion Turbidity > 8 NTU

# Days when Alum Treatment could be required# Days when Alum Treatment could be required

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Total Number of Days with Predicted Ashokan Diversion Turbidity > 8 NTU(Post-Croton Filtration Scenario, BFD Regression)

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BaseRun

Alt. 1Outlet

(6000) +ModOps2

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Wall(1700 ft)

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Mods (E)

Alt. 5 EBasin SLI

Alt. 5 EBasin MLI

Alt. 6ModOps1

AshWDrawdown

Alt. 6ModOps2

WasteChannel

Alt. 6CatAqMods

Alt. 6ModOps1 +ModOps2 +CatAqMods

Alt. 6 +Outlet(2000)

Alt. 6 +Outlet(4000)

Alt. 6 +Outlet(6000)

Alt. 6 +Outlet(4000)(MLO)

Alt. 6 +CrestGates

Alt. 6 +E. BasinDiversion

Wall(1700 ft)

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(W & E)

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MLI

Stand-alone Alternatives Combined Alternatives

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Total Number of Predicted Alum Application Days(Post-Croton Filtration Scenario, BFD Regression)

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Mods (E)

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AshWDrawdown

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WasteChannel

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Alt. 6ModOps1 +ModOps2 +CatAqMods

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Wall(1700 ft)

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(W & E)

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Stand-alone Alternatives Combined Alternatives

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Proposed Alternative 6:Proposed Alternative 6:West Basin DrawdownWest Basin Drawdown

Current practiceCurrent practice: typically divert water from the East Basin: typically divert water from the East Basin

Proposed practiceProposed practice: divert water from West Basin during periods of low : divert water from West Basin during periods of low turbidity to develop/maintain a voidturbidity to develop/maintain a void

Reduces chance of spilling turbid water from West to East Basin during Reduces chance of spilling turbid water from West to East Basin during storm eventsstorm events

– Provides slight reduction in alum treatment days; large events still Provides slight reduction in alum treatment days; large events still require alum treatmentrequire alum treatment

Operating rules can be further refined with planned Operations Support Tool Operating rules can be further refined with planned Operations Support Tool (OST)(OST)

– OST would link near-real time water quality data with OASIS-W2 OST would link near-real time water quality data with OASIS-W2 platform and allow look-ahead simulationsplatform and allow look-ahead simulations

– OST expected to provide system-wide benefit – help balance water OST expected to provide system-wide benefit – help balance water supply reliability, water quality, environmental objectivessupply reliability, water quality, environmental objectives

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Proposed Alternative 6:Proposed Alternative 6:Waste Channel OperationWaste Channel Operation

Existing Waste Channel can be used to release water from Ashokan to Existing Waste Channel can be used to release water from Ashokan to Esopus CreekEsopus Creek

Current practiceCurrent practice: not used under normal operations: not used under normal operations

Proposed practiceProposed practice: routine use of Waste Channel for turbidity control: routine use of Waste Channel for turbidity control

– Helps reduce turbid spill into East BasinHelps reduce turbid spill into East Basin

– Could be used during storm events, or in anticipation of peak flows Could be used during storm events, or in anticipation of peak flows based on Esopus forecast databased on Esopus forecast data

– Provisional operating rules could be further refined/improved with the Provisional operating rules could be further refined/improved with the OSTOST

Current NYCDEP actionsCurrent NYCDEP actions

– Acquisition/restoration of low-lying portions of the Ashokan Field Acquisition/restoration of low-lying portions of the Ashokan Field CampusCampus

– Valve improvements at Lower Gate Chamber to restore original 1200 Valve improvements at Lower Gate Chamber to restore original 1200 mgd release capacitymgd release capacity

– Operations Support ToolOperations Support Tool

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Proposed Alternative 6:Proposed Alternative 6:Catskill Aqueduct ModificationsCatskill Aqueduct Modifications

Current practiceCurrent practice: DEP must maintain minimum flow of 275 mgd in Cat. Aq. : DEP must maintain minimum flow of 275 mgd in Cat. Aq. to keep outside community (OC) taps submergedto keep outside community (OC) taps submerged

– Operation at lower flow rates requires installation of stop shutters at up Operation at lower flow rates requires installation of stop shutters at up to 5 locationsto 5 locations

– Cumbersome, time-consuming, emergency operationCumbersome, time-consuming, emergency operation

– Cannot be implemented as a routine turbidity control measureCannot be implemented as a routine turbidity control measure

Proposed practiceProposed practice: Improve DEP’s ability to operate the Catskill Aqueduct : Improve DEP’s ability to operate the Catskill Aqueduct at minimum flow rates during turbidity eventsat minimum flow rates during turbidity events

3 main options:3 main options:

1.1. Improvements to stop shutter facilitiesImprovements to stop shutter facilities

2.2. Improvements to OC tapsImprovements to OC taps

3.3. Connection with Delaware AqueductConnection with Delaware AqueductShaft 4Shaft 4

-Further study required to select among options-Further study required to select among options

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Shaft 4 ConnectionShaft 4 Connection

Catskill and Delaware Aqueducts Catskill and Delaware Aqueducts cross, but are not connectedcross, but are not connected

Shaft 4 of Delaware Aqueduct was Shaft 4 of Delaware Aqueduct was designed for a future connectiondesigned for a future connection

BenefitsBenefits

Divert Delaware water into Cat. Divert Delaware water into Cat. Aq. during turb events Aq. during turb events

– Reduce/eliminate Ashokan Reduce/eliminate Ashokan diversion, while maintaining diversion, while maintaining supply to outside communitiessupply to outside communities

– Improved WQ to OC’sImproved WQ to OC’s

Greater operational flexibilityGreater operational flexibility

Improve system reliabilityImprove system reliability

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Summary of Phase III Study FindingsSummary of Phase III Study Findings

Reducing Catskill diversions is the most effective way to reduce alum treatmentReducing Catskill diversions is the most effective way to reduce alum treatment

– Catskill Aqueduct Improvements & Croton WTP will dramatically increase DEP Catskill Aqueduct Improvements & Croton WTP will dramatically increase DEP operational flexibilityoperational flexibility

Releases from Ashokan West Basin prior to or during major events also provide Releases from Ashokan West Basin prior to or during major events also provide substantial benefitsubstantial benefit

Planned Operations Support Tool will bolster DEP ability to optimize operations for Planned Operations Support Tool will bolster DEP ability to optimize operations for water quality & water supply reliabilitywater quality & water supply reliability

Powerful modeling framework enabled a robust, performance-based evaluation of Powerful modeling framework enabled a robust, performance-based evaluation of alternativesalternatives

– Captures feedback between system operation and reservoir water qualityCaptures feedback between system operation and reservoir water quality

– Captures a wide range (57 years) of forcing conditions to represent long-term Captures a wide range (57 years) of forcing conditions to represent long-term performanceperformance

– Worthwhile evaluating alternatives using a robust modeling framework before Worthwhile evaluating alternatives using a robust modeling framework before making major capital decisionsmaking major capital decisions

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Question & AnswerQuestion & Answer

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Operations during Catskill Turbidity Events:Operations during Catskill Turbidity Events:System DiversionsSystem Diversions

Catskill Aqueduct diversion turbidity > 8 NTUCatskill Aqueduct diversion turbidity > 8 NTU

– Minimize diversions from the Catskill SystemMinimize diversions from the Catskill System

– Increase diversions from the Delaware and Croton SystemsIncrease diversions from the Delaware and Croton Systems

Minimum diversion from the Catskill SystemMinimum diversion from the Catskill System

– Baseline OperationsBaseline Operations: : Cut back to 275 mgd (minimum flow needed to satisfy outside Cut back to 275 mgd (minimum flow needed to satisfy outside community demands without installing stop shutters at 5 locations along community demands without installing stop shutters at 5 locations along the Catskill Aqueduct)the Catskill Aqueduct)

– Alt. 6 Catskill Aqueduct Improvements (and combined alts)Alt. 6 Catskill Aqueduct Improvements (and combined alts): : Cut back to the minimum flow possible while still satisfying NYC and Cut back to the minimum flow possible while still satisfying NYC and outside demandsoutside demands

Maximum flow from Delaware System:Maximum flow from Delaware System: 890 mgd890 mgd

Maximum flow from Croton System:Maximum flow from Croton System: 160 mgd (Current Conditions) 160 mgd (Current Conditions) 290 mgd (Post-Croton Filtration)290 mgd (Post-Croton Filtration)

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Operations during Catskill Turbidity Events:Operations during Catskill Turbidity Events:Alum ApplicationAlum Application

Alum application at Kensico is approximated using a simple rule based on Alum application at Kensico is approximated using a simple rule based on Catskill Aqueduct turbidity load:Catskill Aqueduct turbidity load:– Alum on when load > 5,000 mgd*NTUAlum on when load > 5,000 mgd*NTU– Alum off when load < 4,000 mgd*NTU (5-day running average basis)Alum off when load < 4,000 mgd*NTU (5-day running average basis)

Alum rule is a simple surrogate for the actual decision-making process, Alum rule is a simple surrogate for the actual decision-making process, which is more complex and depends on:which is more complex and depends on:– Delaware System turbidity levelsDelaware System turbidity levels– Overall system statusOverall system status– Time of yearTime of year– Extent of stratification in KensicoExtent of stratification in Kensico– ‘‘Look-ahead’ modeling of Kensico diversion turbidity levelsLook-ahead’ modeling of Kensico diversion turbidity levels

Alum rule is a simple surrogate and should be interpreted as days when Alum rule is a simple surrogate and should be interpreted as days when alum application alum application could becould be required required– Focus on relative performance of alternativesFocus on relative performance of alternatives

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Alt 1: West Basin Outlet StructureAlt 1: West Basin Outlet StructureOperating RulesOperating Rules

Physical alternatives:Physical alternatives:

– Outlet Structure with weir elevation 585’Outlet Structure with weir elevation 585’ 3 max capacities evaluated: 2000, 4000, 6000 mgd3 max capacities evaluated: 2000, 4000, 6000 mgd

(actual flow is head-dependent)(actual flow is head-dependent)

– Outlet Structure with multi-level withdrawal capability (4000 mgd)Outlet Structure with multi-level withdrawal capability (4000 mgd) Operated to withdraw from strata with highest turbidity waterOperated to withdraw from strata with highest turbidity water

RulesRules

– Short-termShort-term: release the amount expected to spill into the East Basin, : release the amount expected to spill into the East Basin, based on 2-day AHPS* inflow forecastbased on 2-day AHPS* inflow forecast

– Long-term (snowpack management)Long-term (snowpack management): release the amount needed to : release the amount needed to maintain void equal to half the snowpack volumemaintain void equal to half the snowpack volume

– Outlet Structure operated only when 1200 mgd release capacity via Outlet Structure operated only when 1200 mgd release capacity via Waste Channel is insufficient to meet the above objectivesWaste Channel is insufficient to meet the above objectives

*AHPS = Advanced Hydrologic Prediction Service; provides 24 and 48hr forecasts of *AHPS = Advanced Hydrologic Prediction Service; provides 24 and 48hr forecasts of Esopus Creek flow at ColdbrookEsopus Creek flow at Coldbrook

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Alt 6: Catskill Aqueduct Improvements and Alt 6: Catskill Aqueduct Improvements and Modified Operations: Operating RulesModified Operations: Operating Rules

Mod Ops 1: West Basin DrawdownMod Ops 1: West Basin Drawdown

– Make diversions from W. Basin whenever turb < 5 NTU and Make diversions from W. Basin whenever turb < 5 NTU and E. Basin has more than 1’ freeboardE. Basin has more than 1’ freeboard

Mod Ops 2: Optimize Operation of Existing Waste ChannelMod Ops 2: Optimize Operation of Existing Waste Channel

– 1200 mgd capacity (after planned valve repairs)1200 mgd capacity (after planned valve repairs)

– Short-termShort-term: release the amount expected to spill to the E. Basin: release the amount expected to spill to the E. Basin

– Long-termLong-term: maintain void equal to half the snowpack volume: maintain void equal to half the snowpack volume

Catskill Aqueduct ImprovementsCatskill Aqueduct Improvements

– Improve ability to readily operate at flows <275 mgd while still meeting Improve ability to readily operate at flows <275 mgd while still meeting outside community demandsoutside community demands

– Turbidity > 8 NTU: reduce Catskill diversion to the minimum flow Turbidity > 8 NTU: reduce Catskill diversion to the minimum flow possible while still satisfying NYC and outside demandspossible while still satisfying NYC and outside demands

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Catskill Aqueduct ProfileCatskill Aqueduct Profile

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Sensitivity and Uncertainty Analysis for 2D Sensitivity and Uncertainty Analysis for 2D Ashokan Reservoir ModelAshokan Reservoir Model

Examined sensitivity of predictions to model Examined sensitivity of predictions to model driversdrivers and model and model parametersparameters

Parameters/drivers examined included:Parameters/drivers examined included:– Hydrodynamic model coefficients (n = 7 parameters)Hydrodynamic model coefficients (n = 7 parameters)– Thermal model coefficients (n = 3)Thermal model coefficients (n = 3)– Turbidity sub model coefficients (n = 3)Turbidity sub model coefficients (n = 3)– Model boundary conditions / drivers (n = 10)Model boundary conditions / drivers (n = 10)– Bathymetry (n = 3)Bathymetry (n = 3)

Representation of variability in Representation of variability in driversdrivers more important than more important than uncertainty in model uncertainty in model parametersparameters

Dominant source of uncertainty for performance of alternatives is Dominant source of uncertainty for performance of alternatives is Esopus Creek Q-Tn relationshipEsopus Creek Q-Tn relationship– Evaluated multiple turbidity loading scenarios; developed Monte Evaluated multiple turbidity loading scenarios; developed Monte

Carlo approach to accommodate inter-event variabilityCarlo approach to accommodate inter-event variability