Ashokan Reservoir Operations - Lower Esopus Watershed Partnership

Ashokan Reservoir Operations
B rea of Water Supply
Bureau
S ppl
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
! Surface
S f
Water Supply
S
! Source of water is a
2,000 square mile
watershed
t h d
! 19 reservoirs & 3
controlled lakes
! System
S t
Capacity:
C
it
! 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
! Schoharie
S h h i Reservoir
R
i
! Schoharie Creek
impoundment (1926)
! 19.6 BG
G Capacity
C
! Diverting System
! Shandaken Tunnel
! Ashokan Reservoir
! Esopus Creek impoundment
(1915)
! 127.9 BG Capacity
! West and East Basins
5
Catskill System Operations
Spillway
! Ashokan Operations
! Dividing Weir
! Gatehouse
G t h
!East or West draw
!Aqueduct or Waste
Ch
Channel
l
! Spillway
!East Basin
Waste
Channel
Esopus
Creek
6
Catskill System Operations
!Ashokan Waste Channel
! Designed to drain either basin and
maintain in lowered state.
! Used to discharge water from the
West Basin.
Ashokan
s o a
Gatehouse
! To prevent turbid water from
entering East Basin either
through spill or Dividing Weir.
Catskill
Aqueduct
W t
Waste
Channel
! To lower the West Basin to
attenuate runoff events.
! Lessens need for alum
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 with
ith
water clarity
!Nephelometry
p
y
!A laboratory measurement of the
light scattered at 90° to an
incident light path entering a
sample of water.
!Nephelometric
p
Turbidityy Units
!A nephelometer assesses
scattered light in units called
Nephelometric Turbidity Units
(NTU)
9
Catskill Turbidity
What is the Reg
Regulatory
lator Importance of T
Turbidity?
rbidit ?
! EPA Surface Water Treatment Rule Limits
! 5 NTU – Unfiltered Supply
! Filtration Avoidance Criteria
Turbidity can shield pathogens from disinfection.
10
Catskill Turbidity
! Sources
S
off Turbidity
T bidit
! Watershed modeling indicates that 76-91% of turbidity
inputs
p
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, 2010
12
Catskill Turbidity
!Uncontrolled Ashokan Reservoir turbidityy
!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
Screening-level
level Assessment
! First level assessment of potential alternatives for Schoharie and
Ashokan (2004)
! Phase II Schoharie Alternatives
! DEP selected Modified Operations
(O
(Operations
ti
S
Supportt T
Tool)
l) as alternative
lt
ti (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
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
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
! Ashokan
A h k d
draft
ft reduced
d
d
! 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,
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
36
3.6
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 Dividing
g Weir opened
p
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
sopus Creek
C ee at Coldbrook
Co db oo
! In 77 years prior to 2010, annual
peak flow exceeded 40,000 cfs
onlyy 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
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
D l
Delaware
/ Catskill
C t kill System
S t
Storage
%
Draft / Diversion
MGD
Turbidity
NTU
Release
MGD
93.9
830
0.75
10
Cannonsville
93.9
0
2.2
970
P
Pepacton
t
91 5
91.5
450
19
1.9
120
Neversink
94.0
200
3.4
65
Ashokan
85.0
50
45
Waste Channel
Reservoir
Rondout
580
0
54
____
West Branch
1090
19
1.9
20
Kensico
1045
1.3
____
Schoharie
90.5
Total Water Supply Storage – 89.9%
Normal Water Supply Storage – 74%
December 15, 2010
23
Overview of Current Situation
Ashokan Reservoir Attenuates Lower Esopus
p 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
System-wide
wide & individual reservoir quantity
! Water quality—current and projected
! Required releases
! Required diversions
! Inflows—current and projected
! Infrastructure
f
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
g
river forecasts
! Ingest
! Apply operating rules
! OST Benefits and Provides Analysis for:
! Decision on Waste Channel
! Decisions on Releases
! Decisions
D i i
on S
System
t
Balancing
B l
i
! 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
60
40
20
3/
29
3/
22
3/
15
3/
8
3/
1
2/
22
2/
15
2/
8
2/
1
1/
25
1/
18
1/
11
1/
4
12
/2
8
12
/2
1
12
/1
4
0
12
/7
Turbidty(NTU)
80
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
System.
Catskill Aqueduct Inflow = 50 MGD ; Delaware Aqueduct Inflow = 1050 MGD
Delaware Effluent Turbidity
5.0
5.0
D t
Date
12-Jan
8-Jan
15-Dec
12-Jan
8-Jan
4-Jan
31-Dec
0.0
27-Dec
0.0
23-Dec
1.0
19-Dec
1.0
4-Jan
2.0
31-Dec
2.0
3.0
27-Dec
3.0
4.0
23-Dec
4.0
19-Dec
Turrbidity (NTU)
6.0
15-Dec
Catskill
Turbidity =
40 NTU
Turrbidity (NTU)
Catskill Effluent Turbidity
6.0
D t
Date
Catskill Aqueduct Inflow = 100 MGD ; Delaware Aqueduct Inflow = 1000 MGD
Delaware Effluent Turbidity
6.0
5.0
5.0
Date
Date
12-Jan
8-Jan
4-Jan
12-Jan
8-Jan
4-Jan
31-Dec
0.0
27-Dec
0.0
23-Dec
1.0
19-Dec
1.0
31-Dec
2.0
27-Dec
2.0
3.0
23-Dec
3.0
4.0
19-Dec
4.0
15-Dec
Turbidity (NTU)
6.0
15-Dec
Catskill
Turbidity =
40 NTU
Turbidity (NTU)
Catskill Effluent Turbidity
31
Use of OST Moving Forward
! OST will help
p 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
assessmentt determines
d t
i
water
t is
i
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!
34