ReservoirsReservoirs

Balancing Supply and DemandBalancing Supply and Demand

AshokanKensico

Hillview Croton Reservoir Spillway

Water Supply and Demand Fluctuations

Water Supply and Demand Fluctuations

Supply Seasonal supply fluctuations Buffered using _________ reservoirs

Demand Seasonal demand fluctuations Daily demand fluctuations Buffered using _________ reservoirs

Effect of flow fluctuations on system design Size of balancing reservoirs pipe sizes

Supply Seasonal supply fluctuations Buffered using _________ reservoirs

Demand Seasonal demand fluctuations Daily demand fluctuations Buffered using _________ reservoirs

Effect of flow fluctuations on system design Size of balancing reservoirs pipe sizes

watershed

distribution

Average Total Monthly Flow into Pepacton Reservoir (0.540 km3 storage)Average Total Monthly Flow into Pepacton Reservoir (0.540 km3 storage)

020406080

100120140

Janu

ary

Marc

hM

ay July

Septem

ber

Novem

ber

Mil

lion

m3 /

mon

th

Reservoir full (hopefully)

average

Deficit provided by storage

Better design is based on drought conditions!____ million m3/month * __ month = ___ million m338 5 190

What is the safe yield from the Cannonsville Reservoir?

What is the safe yield from the Cannonsville Reservoir?

What is the maximum rate that we can withdraw water from the Cannonsville Reservoir without emptying the reservoir?_________________________________

What are the critical events in history that determine how big the reservoir has to be?__________

What is the maximum rate that we can withdraw water from the Cannonsville Reservoir without emptying the reservoir?_________________________________

What are the critical events in history that determine how big the reservoir has to be?__________

The average stream flow into the reservoir.

Droughts

Reservoir Mass Balance Equations

Reservoir Mass Balance Equations

Di=Di=Ii=Ii=

+ +=

0 i i iS I O S+ = +0 i i iS I O S+ = +

iiii0 SRDIS iiii0 SRDIS

O = Cumulative (________ + _________ + ___________ )O = Cumulative (________ + _________ + ___________ )

Initial st

orage

Cumulative I

nflow

Cumulative O

utflow

Storage

Demand River flow Evaporation

True at any time!

Q tjj

j i

1

I Q ti i 1 or Q t tNYC 0a f

Density of WaterDensity of Water

950960970980990

1000

0 50 100Temperature (C)

Den

sity

(kg

/m3 )

997

998

999

1000

0 10 20

Temperature (C)

Den

sity

(kg

/m3 )

Density (mass/unit volume) density of water:

1000 kg/m3

drought status

Downstream River Flow?Downstream River Flow?

Simplest operating rule Waste from reservoir when reservoir is full Don’t waste from reservoir if reservoir isn’t full

More complex rules could easily be incorporated into a spreadsheet model Minimum discharge into stream as a function of

reservoir storage volume or ______________ Based on regulations

Simplest operating rule Waste from reservoir when reservoir is full Don’t waste from reservoir if reservoir isn’t full

More complex rules could easily be incorporated into a spreadsheet model Minimum discharge into stream as a function of

reservoir storage volume or ______________ Based on regulations

Reservoir Rules in Equation Form

Reservoir Rules in Equation Form

Smax=Smax=

When is reservoir full? ___________________

iiii0 SRDIS iiii0 SRDIS

1-ii

maxii0i

max1-iii0

RR ELSE

S-D-ISR THEN

SR-D-IS IF

1-ii

maxii0i

max1-iii0

RR ELSE

S-D-ISR THEN

SR-D-IS IF

iii0i RDISS iii0i RDISS

Reservoir Capacity

When Si = SmaxWhen Si = Smax

Reservoir is overflowingOverflow goes into riverNo additional river flow

0.010.020.030.040.050.060.070.080.090.0

100.0

6/1/

50

6/1/

54

6/1/

58

6/1/

62

6/1/

66

6/1/

70

6/1/

74

6/1/

78

6/1/

82

6/1/

86

6/1/

90

perc

ent o

f fu

ll

0.010.020.030.040.050.060.070.080.090.0

100.0

6/1/

50

6/1/

54

6/1/

58

6/1/

62

6/1/

66

6/1/

70

6/1/

74

6/1/

78

6/1/

82

6/1/

86

6/1/

90

perc

ent o

f fu

llCannonsville Reservoir Storage (Demand of 1.04 x 106 m3/day)Cannonsville Reservoir Storage (Demand of 1.04 x 106 m3/day)

How could we increase safe yield?Increase reservoir volume

Storage vs. Safe Yield for Cannonsville Reservoir

Storage vs. Safe Yield for Cannonsville Reservoir

00

0.50.5

11

1.51.5

00 250250 500500 750750 10001000

storage volume (million m3)storage volume (million m3)

safe

yie

ldsa

fe y

ield

(mil

lion

m3 /

day)

(mil

lion

m3 /

day)

367367

Average stream flowWhat is the asymptote?

NYC ReservoirsNYC Reservoirs

NYC supply reservoirs have a storage capacity of 550 billion gallons (2 km3)

How long could NYC go without any inflow into the reservoirs?

Current Reservoir levels (http://www.ci.nyc.ny.us/nyclink/html/dep/html/current.html)

NYC supply reservoirs have a storage capacity of 550 billion gallons (2 km3)

How long could NYC go without any inflow into the reservoirs?

Current Reservoir levels (http://www.ci.nyc.ny.us/nyclink/html/dep/html/current.html)

Reservoir Levels

                                

 

solution

What happens as Reservoir Levels drop? __________________________________ __________________________________ __________________________________ __________________________________ __________________________________

What happens as Reservoir Levels drop? __________________________________ __________________________________ __________________________________ __________________________________ __________________________________

Empty NYC Reservoirs?Empty NYC Reservoirs?

Nutrient levels increase (less dilution)

Water quality deteriorates

Algae grows (taste and odors)

Shorter residence time (less time for pathogens to die)Drought watch

Seasonal, Daily, and Hourly Fluctuations

Seasonal, Daily, and Hourly Fluctuations

Early morning as people get ready to go to work/schoolEarly morning as people get ready to go to work/school

Commercial Breaks (not any more)Commercial Breaks (not any more)

Between midnight and 5 amBetween midnight and 5 am

Substantial increase in water demand during summer due to_______________________

Peak flows___________________________________________________________

Low flows______________________

Substantial increase in water demand during summer due to_______________________

Peak flows___________________________________________________________

Low flows______________________

watering lawns, swimming pools

Estimates of Daily and Hourly Fluctuations*

Estimates of Daily and Hourly Fluctuations*

As the time period of analysis decreases in length the maximum rate of water demand during that time period __________

If the average annual flow rate is 1.0 then the maximum season rate is 1.25 (summer) the maximum daily rate is 1.5 (range of 1.2-2.0) the maximum hourly rate is 2.5 (range of 1.5-3.5)

for NYC the maximum instantaneous rate was _____

As the time period of analysis decreases in length the maximum rate of water demand during that time period __________

If the average annual flow rate is 1.0 then the maximum season rate is 1.25 (summer) the maximum daily rate is 1.5 (range of 1.2-2.0) the maximum hourly rate is 2.5 (range of 1.5-3.5)

for NYC the maximum instantaneous rate was _____*Henry and Heinke p 386

increases

1.75

Methods to Even Out Fluctuations

Methods to Even Out Fluctuations

Seasonal fluctuations Source (watershed) reservoirs Kensico and West Branch Reservoirs

Daily fluctuations Hillview and Jerome Park Reservoirs (directly

connected to distribution tunnels) Hillview has 3.4 million m3 useable storage

Flows from Kensico to Hillview are adjusted every ________

Seasonal fluctuations Source (watershed) reservoirs Kensico and West Branch Reservoirs

Daily fluctuations Hillview and Jerome Park Reservoirs (directly

connected to distribution tunnels) Hillview has 3.4 million m3 useable storage

Flows from Kensico to Hillview are adjusted every ________two hours

Balancing ReservoirsBalancing Reservoirs

Hey Bob, I need some more water. Could you open the

valve another turn?

OK Fred, I’ll go give it another turn. Did you say you have more water than you need?

Where are the largest tunnels in the NYC water supply and distribution system?

How Can You Estimate Required Balancing-Reservoir Capacity?

How Can You Estimate Required Balancing-Reservoir Capacity?

Variable supply Variable demand Analyze historic record to search for worst

case conditions Use same Mass Balance analysis Include variable ________ in analysis Other unusual demands…

Variable supply Variable demand Analyze historic record to search for worst

case conditions Use same Mass Balance analysis Include variable ________ in analysis Other unusual demands…

demandFire fighting needs

Main breaks Maintenance of supply tunnels

SummarySummary

An understanding of the variability in supply and demand are essential for the sizing of reservoirs and pipes in a water supply system

Supply Reservoirs must be sized to store water during drought periods

Balancing Reservoirs must be sized for daily or hourly fluctuations

Distribution pipes must be sized to handle peak flows

An understanding of the variability in supply and demand are essential for the sizing of reservoirs and pipes in a water supply system

Supply Reservoirs must be sized to store water during drought periods

Balancing Reservoirs must be sized for daily or hourly fluctuations

Distribution pipes must be sized to handle peak flows

PepactonPepacton

SchoharieSchoharie

AshokanAshokan

NeversinkNeversink

Roundout

Roundout

CannonsvilleCannonsville

Catskill/Delaware WatershedsCatskill/Delaware Watersheds

NYC Watersheds

NYC Watersheds

Ashokan ReservoirAshokan Reservoir

Schoharie ReservoirSchoharie Reservoir

Neversink ReservoirNeversink Reservoir

Croton SystemCroton System

West Branch ReservoirWest Branch Reservoir

City TunnelsCity Tunnels

Ashokan ReservoirAshokan Reservoir

Schoharie Reservoir Schoharie Reservoir

Neversink Reservoir Neversink Reservoir

West Branch Reservoir West Branch Reservoir

City TunnelsCity Tunnels

Jerome Park ReservoirJerome Park Reservoir

Jerome Park ReservoirJerome Park Reservoir

Gaging StationsGaging Stations

Empty NYC ReservoirsEmpty NYC Reservoirs

NYC supply reservoirs have a storage capacity of 550 billion gallons (2 km3)

Average demand is 61 m3/s How long could NYC go without any

inflow into the reservoirs?

NYC supply reservoirs have a storage capacity of 550 billion gallons (2 km3)

Average demand is 61 m3/s How long could NYC go without any

inflow into the reservoirs?

21000

61 864003803

3

3kmm

kmsm

days

daysa fLNM

OQP 2

1000

61 864003803

3

3kmm

kmsm

days

daysa fLNM

OQP

Cannonsville Reservoir Storage (Demand of 0.5 x 106 m3/day)

Cannonsville Reservoir Storage (Demand of 0.5 x 106 m3/day)

0.010.020.030.040.050.060.070.080.090.0

100.0

6/1/

50

6/1/

54

6/1/

58

6/1/

62

6/1/

66

6/1/

70

6/1/

74

6/1/

78

6/1/

82

6/1/

86

6/1/

90

perc

ent o

f fu

ll

Stream flow gage station map

0.010.020.030.040.050.060.070.080.090.0

100.0

6/1/

50

6/1/

54

6/1/

58

6/1/

62

6/1/

66

6/1/

70

6/1/

74

6/1/

78

6/1/

82

6/1/

86

6/1/

90

perc

ent o

f fu

llCannonsville Reservoir Storage (Demand of 0.75 x 106 m3/day)Cannonsville Reservoir Storage (Demand of 0.75 x 106 m3/day)

0.010.020.030.040.050.060.070.080.090.0

100.06/

1/50

6/1/

54

6/1/

58

6/1/

62

6/1/

66

6/1/

70

6/1/

74

6/1/

78

6/1/

82

6/1/

86

6/1/

90

perc

ent o

f fu

ll

Cannonsville Reservoir Storage (Demand of 1 x 106 m3/day)

Cannonsville Reservoir Storage (Demand of 1 x 106 m3/day)

0.010.020.030.040.050.060.070.080.090.0

100.0

6/1/

50

6/1/

54

6/1/

58

6/1/

62

6/1/

66

6/1/

70

6/1/

74

6/1/

78

6/1/

82

6/1/

86

6/1/

90

perc

ent o

f fu

ll