Ashokan Reservoir Operations

Burea u of Water S uppl y December 17, 2010 Outline

!Water Supply Overview !Catskill System Operations !Catskill Turbidity !Catskill Turbidity Control Program !Overview of Current Situation !Operations Support Tool !Next Steps

2 Water Supply Overview

!Surf ace Water S upply !Source of water is a 2,000 square mile watersh e d !19 reservoirs & 3 controlled lakes !Syst em C apac ity: ! 580 billion gallons !System Serves: ! 9 million people ! (1/2 of population of New York State) !System Delivers: ! approx. 1.1 BGD !Operated and maintained by NYC DEP

3 Water Supply Overview !System Operations ! Maintain system balance !Reservoirs full by June 1st ! Meet consumption demand & divert highest quality water ! Adhere to Federal and State laws !1954 Supreme Court Decree !Part 670 & Shandaken Tunnel Portal SPDES !Part 671 & FFMP – Delaware System releases !Part 672 – Rondout and Croton System releases

4 Catskill System Operations

!Catskill System ! Designed to handle turbidity !Sch o hari e R eservoir i ! Schoharie Creek impoundment (1926) ! 19.6 BGCG Capacity ! Diverting System ! Shandaken Tunnel !Ashokan Reservoir ! Esopus Creek impoundment (1915) ! 127.9 BG Capacity ! West and East Basins

5 Catskill System Operations

!Ashokan Operations ! Dividing Weir ! GthGatehouse !East or West draw !Aqueduct or Waste Channe l Spillway ! Spillway !East Basin

Waste Channel

Esopus Creek

6 Catskill System Operations

!Ashokan Waste Channel !Designed to drain either basin and maintain in lowered state.

Ash oka n !Used to discharge water from the Gatehouse West Basin. ! To prevent turbid water from entering East Basin either through spill or Dividing Weir. ! To lower the West Basin to attenuate runoff events. WtWaste Channel Catskill ! Lessens need for alum Aqueduct treatments.

7 Catskill Turbidity

Turbidity What is it and why is it important?

8 Catskill Turbidity

!Turbidity !Suspended or stirred up particles or sediment that interfere w ith water clarity !Neppyhelometry !A laboratory measurement of the light scattered at 90° to an incident light path entering a sample of water. !Neppyhelometric Turbidity Units !A nephelometer assesses scattered light in units called Nephelometric Turbidity Units (NTU)

9 Catskill Turbidity

What is the Regu latory Importance of Tu rbidity ?

! EPA Surface Water Treatment Rule Limits ! 5 NTU – Unfiltered Supply ! Filtration Avoidance Criteria

Turbidity can shield pathogens from disinfection.

10 Catskill Turbidity

! Sources o f T urbidit y ! Watershed modeling indicates that 76-91% of turbidity inputs come from in-stream sources. ! Significant events are the major cause of turbidity issues in Ashokan Reservoir

In-stream Turbidity Source

11 Catskill Turbidity Shandaken Tunnel Portal !Not a significant source of turbidity to Ashokan during runoff events. !Since October storm Schoharie flow is 0.47% on inflow to Ashokan Reservoir.

December 15, 201012 Catskill Turbidity !Uncontrolled Ashokan Reservoir turbidity !Ashokan water spills or is diverted

13 Catskill Turbidity Control Program ! Catskill Turbidity Control Study ! Comprehensive analysis of engineering and structural alternatives to reduce turbidity levels in the Catskill System

14 Catskill Turbidity Control Program ! Phase I Screening -level Assessment ! First level assessment of potential alternatives for Schoharie and Ashokan (2004) ! Phase II Schoharie Alternatives ! DEP selected Modified Operations (Opera tions Suppor t Too l) as a lterna tive (2006)

15 Catskill Turbidity Control Program ! Phase III Ashokan Alternatives

16 Catskill Turbidity Control Program

! Phase III Implementation Plan ! Modified Operations !OST Development !West Basin Drawdown !Waste Channel Operation ! Catskill Aqueduct Improvements !Stop Shutter Improvements !Shaft 4 Interconnection ! Approved pursuant to the FAD by DOH/DEC/EPA

17 Overview of Current Situation

! Storm Event #1 – September 26 – October 1, 2010 ! 6.98” average rainfall Ashokan Watershed ! Inflow 9/30 – 10/3: Ashokan = 18 BG / Schoharie = 18 BG ! Turbidities above 2300 NTU entered Ashokan Reservoir ! Ashokan West Basin turbidity ranged from 10–360 NTU

Oct!1,!2010!rainfall!(inches) Selected!rain!gages

Greene!County

TANNERSVILLE 9.0

Ulster!County

PHOENICIA 8.3

WEST!SHOKAN 7.6

SLIDE!MOUNTAIN 7.4

18 Overview of Current Situation

! Operational Response to Storm Event #1 ! Delaware diversions shut down ! Shandaken Tunnel closed ! Ashokan Dividing Weir opened ! Ash o kan dra ft red uced ! Rondout draft maximized ! Waste Channel activated on October 7th ! Ashokan draft reductions required down-stream stop shutter placement and increased dependence on the Delaware System. ! Dividing Weir flow reduced once it was determined West Basin would not spill and East Basin could be isolated

19 Overview of Current Situation

! Storm Event #2 – November 30 – December 1 , 2010 ! 4.74” average rainfall Ashokan Watershed ! Runoff 12/1 – 12/6: Ashokan = 18 BG / Schoharie = 15 BG ! Turbidities above 1100 NTU entered Ashokan Reservoir ! West Basin Turbidity ranged from 30 – 500 NTU

Dec!1,!2010!rainfall!(inches) Selected!rain!gages

Greene!County

TANNERSVILLE 5.5

EAST!JEWETT 5.3

LEXINGTON 363.6

Ulster!County

PHOENICIA 6.7

WEST!SHOKAN 6.0

SLIDE!MOUNTAIN 3.9

20 Overview of Current Situation

! Operational Response to Storm Event #2 Waste Channel ! Ashokan Dividinggp Weir opened to minimize spilling from west basin to east basin ! Shandaken Tunnel closed ! Waste Channel remains activated ! Ashokan flow reduced to 50 MGD ! Rondout draft remained maximized ! Dividing Weir flow reduced once it was determined West Basin would not spill and East Basin could be isolated

21 Overview of Current Situation

Recent Events ! Esopus C r eek at Co ldb roo k !In 77 years prior to 2010, annual peak flow exceeded 40,000 cfs only 8 times !In 2010, the Oct 1 and Dec 1 events both exceeded 40,000 cfs !2 of the top 10 annual peaks have occurred 2 months apart in 2010 Annual Peaks 1932-2009 Annual Peaks over 40 ,000 cfs 3/21/1980 65,300 3/30/1951 59,600 4/3/2005 55,200 8/24/1933 55,000 10/15/1955 54,000 1/19/1996 53,600 4/4/1987 51,700 12/21/1957 46,900 10/1/2010 45,200 12/1/2010 41,400 22 Overview of Current Situation

De laware / C a tskill S yst em

Storage Draft / Diversion Turbidity Release Reservoir % MGD NTU MGD 93.9 830 0.75 10 Rondout Cannonsville 93.9 0 2.2 970

PtPepacton 91.5 450 191.9 120

Neversink 94.0 200 3.4 65

Ashokan 85.0 50 45 Waste Channel

580 Schoharie 90.5 0 54 ____

West Branch 1090 191.9 20

Kensico 1045 1.3 ____

Total Water Supply Storage – 89.9% Normal Water Supply Storage – 74% December 15, 2010 23 Overview of Current Situation Ashokan Reservoir Attenuates Lower Esopus Flow

24 Overview of Current Situation Reservoirs Attenuate Flow Even When Full

From “ A Review of the Role of Dams in Flood Mitigation”, a paper submitted to the World Commission on Dams (www.dams.org) in March 2000 by Peter Hawker

25 Operations Support Tool (OST)

What is OST?

! Software that allows managers to simultaneously consider all aspects of water supply for all reservoirs ! System-wide & individual reservoir quantity ! Water quality—current and projected ! Required releases ! Required diversions ! Inflows—current and projected ! Infrastructure status

26 Operations Support Tool (OST) OST Components

27 Operations Support Tool (OST) How does the OST work? ! Link water quality and quantity models ! Incorporate near-real-time data ! Meteorological & snowpack data ! Water quality data ! Streamflow data ! Reservoir status data ! Ingest river forecasts ! Apply operating rules ! OST Benefits and Provides Analysis for: ! Decision on Waste Channel ! Decisions on Releases ! Dec is ions on Sys tem B a lanci ng ! OST scheduled to be completed 2013 28 Operations Support Tool (OST)

OST Projections ! OST was used to determine waste channel could be used and Rondout could be maximized and Delaware and Catskill systems would still be refilled

29 Catskill System Modeling Dividing Weir Gate Turbidity (Flow from West Basin to East Basin) 56 Traces based on 1948-2004 Meteorology and Input Flow

100

80

60

Turbidty(NTU) 40

20

0

4 1 8 4 8 1 8 /1 /2 2 1/ 11 1 2/ 2/ /15 3/1 3/8 /22 12/7 2 2 2/ 1/ 1/ 1/25 2 2/22 3/15 3 3/29 1 1 1 Date Shaded Region Show 10th-90th percentiles of traces Heavy black solid line shows median of traces 30 Kensico Reservoir Modeling DEP has developed an extensive suite of water quality and water system models which are used to analyze turbidity transport in the Catskill System.

Catskill Aqueduct Inflow = 50 MGD ; Delaware Aqueduct Inflow = 1050 MGD

Catskill Effluent Turbidity Delaware Effluent Turbidity 6.0 6.0

5.0 5.0 Catskill 4.0 4.0 Turbidity = 3.0 3.0 bidity (NTU) bidity (NTU) r 2.0 r 2.0 40 NTU Tu Tu 1.0 1.0

0.0 0.0 4-Jan 8-Jan 4-Jan 8-Jan 12-Jan 12-Jan 15-Dec 19-Dec 23-Dec 27-Dec 31-Dec 15-Dec 19-Dec 23-Dec 27-Dec 31-Dec DtDate DtDate Catskill Aqueduct Inflow = 100 MGD ; Delaware Aqueduct Inflow = 1000 MGD Catskill Effluent Turbidity Delaware Effluent Turbidity 6.0 6.0

5.0 5.0 Catskill 4.0 4.0 Turbidity = 3.0 3.0 2.0 2.0 Turbidity (NTU) Turbidity (NTU)

40 NTU 1.0 1.0

0.0 0.0 4-Jan 8-Jan 4-Jan 8-Jan 12-Jan 12-Jan 15-Dec 19-Dec 23-Dec 27-Dec 31-Dec 15-Dec 19-Dec 23-Dec 27-Dec 31-Dec Date Date 31 Use of OST Moving Forward

! OST will help to: ! Design clean water flushing releases that would follow high turbidity releases at a point when storage is high and water available ! Consider base release if OST assessment d et ermi nes wa ter i s available

32 Next Steps

! Further Studies on Impacts on Lower Esopus Creek ! Upper Esopus Studies indicate excellent aquatic stream health ! Develop Waste Channel operation protocols ! Maximize system water quality for public health ! Reduce need for alum treatment ! Minimize ecologic impacts to Lower Esopus Creek ! Flood Attenuation ! Acquire stakeholder input for decision making

33 Thank you!

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