nywea wstc at west point, ny september 15, 2009 the impacts of reservoir drawdown on water quality...

NYWEA WSTC at West Point, NYNYWEA WSTC at West Point, NYSeptember 15, 2009September 15, 2009

The Impacts of Reservoir Drawdown on Water The Impacts of Reservoir Drawdown on Water Quality in NYC’s Catskill and Delaware ReservoirsQuality in NYC’s Catskill and Delaware Reservoirs

by L. Janus, R. VanDreason, G. Marzec, J. Mayfield, D. Pierson, R. Gelda

Impacts of Drawdown on Water Quality Impacts of Drawdown on Water Quality

Outline:Outline: 1.0 Introduction1.0 Introduction

Why is drawdown important?Why is drawdown important? How was the analysis conducted?How was the analysis conducted?

2.0 Hydrology and water quality 2.0 Hydrology and water quality Elevation historiesElevation histories Water residence times – headwaters vs terminal Water residence times – headwaters vs terminal Relation of hydrodynamics to WQRelation of hydrodynamics to WQ

3.0 Reservoir WQ observations:3.0 Reservoir WQ observations: Time series plots: 20-years of water quality Time series plots: 20-years of water quality WQ vs elevation relationshipsWQ vs elevation relationships ‘‘Breakpoints’ and correlationsBreakpoints’ and correlations

4.0 Diagnostic Modeling 4.0 Diagnostic Modeling Ashokan – 2008 drawdown Ashokan – 2008 drawdown West Branch during 2008 drawdown West Branch during 2008 drawdown

5.0 Conclusions5.0 Conclusions

Approach:Approach: literature review - nation-wideliterature review - nation-wide Review hydrodynamicsReview hydrodynamics Relate elevations to reservoir WQ Relate elevations to reservoir WQ

Time series behaviorTime series behavior Correlations of WQ with elevationsCorrelations of WQ with elevations

Analyze case studies of specific events Analyze case studies of specific events diagnostic modelingdiagnostic modeling

1. Introduction1. IntroductionObjectives:Objectives: Define how and when DEP reservoirs respond to drawdown.Define how and when DEP reservoirs respond to drawdown. Determine elevation ‘targets’ that are protective of WQ. Determine elevation ‘targets’ that are protective of WQ. Understand how drawdown or prolonged drought might affect WQ.Understand how drawdown or prolonged drought might affect WQ. Gain insight into impacts of climate change.Gain insight into impacts of climate change.

Literature ReviewLiterature Review

Nationwide review; studies have demonstrated:Nationwide review; studies have demonstrated:• Increased sediment resuspension occurs at a threshold Increased sediment resuspension occurs at a threshold

level.level.• Impacts on algal dynamics with increases in chlorophyllImpacts on algal dynamics with increases in chlorophyll• Impacts on the thermal structure, with decreases in the Impacts on the thermal structure, with decreases in the

duration of stratification.duration of stratification.• changes to benthic invertebrate communitieschanges to benthic invertebrate communities• impacts on fish populationsimpacts on fish populations

3 NYC Watershed Studies: 3 NYC Watershed Studies: • Effler & Matthews, 2004; Effler & Bader, 1998; Effler, et al., Effler & Matthews, 2004; Effler & Bader, 1998; Effler, et al.,

1998 1998 • Major drawdown at Cannonsville in 1995 demonstrated:Major drawdown at Cannonsville in 1995 demonstrated:

Increased tripton (suspended particles other than algae)Increased tripton (suspended particles other than algae) Increased turbidityIncreased turbidity Increased phosphorus Increased phosphorus Enhanced phytoplankton growthEnhanced phytoplankton growth Decreased Secchi depthDecreased Secchi depth

2.0 Hydrology and water quality 2.0 Hydrology and water quality

Configuration of NYC’s Catskill and Delaware Reservoirs:Configuration of NYC’s Catskill and Delaware Reservoirs:

Map by D. Lounsbury

- terminal reservoirs receive flow from - terminal reservoirs receive flow from upstream headwater reservoirsupstream headwater reservoirs

Schoharie Water Elevation

320

325

330

335

340

345

1966 1969 1972 1975 1978 1981 1984 1987 1990 1993 1996 1999

me

ters

ab

ove

se

a le

ve

l

Schoharie

West Basin Ashokan

East Basin Ashokan

West Basin Ashokan Water Elevation

155

160

165

170

175

180

1966 1969 1972 1975 1978 1981 1984 1987 1990 1993 1996 1999

me

ters a

bo

ve

se

a le

ve

l

East Basin Ashokan Water Elevation

159

164

169

174

179

1966 1969 1972 1975 1978 1981 1984 1987 1990 1993 1996 1999

me

ters a

bo

ve

se

a le

ve

l

Pro

po

rtio

n o

f A

vail

able

Sto

rag

e

Wat

er S

urf

ace

Ele

vat

ion

(m

eter

s ab

ove

sea

lev

el)

Catskill Reservoirs - elevation and storage histories:

Cannonsville Water Elevation

315

320

325

330

335

340

345

350

355

1966 1969 1972 1975 1978 1981 1984 1987 1990 1993 1996 1999

me

ters

ab

ove

se

a le

ve

l

Pepacton Water Elevation

348353358

363368373378

383388393

1966 1969 1972 1975 1978 1981 1984 1987 1990 1993 1996 1999

me

ters

ab

ove

se

a le

ve

l

Neversink Water Elevation

401

406

411

416

421

426

431

436

1966 1969 1972 1975 1978 1981 1984 1987 1990 1993 1996 1999

me

ters

ab

ove

se

a le

ve

l

Rondout Water Elevation

219

224

229

234

239

244

249

254

259

1966 1969 1972 1975 1978 1981 1984 1987 1990 1993 1996 1999

me

ters

ab

ove

se

a le

ve

l

Cannonsville

Pepacton

Neversink

RondoutWat

er S

urf

ace

Ele

vat

ion

(m

eter

s ab

ove

sea

lev

el)

Pro

po

rtio

n o

f A

va

ila

ble

Sto

rag

e

Catskill System Reservoir Residence Time

0

50

100

150

200

250

1967 1970 1973 1976 1979 1982 1985 1988 1991 1994 1997

Da

ys

Schoharie

West Basin Ashokan

East Basin Ashokan

Delaware System Reservoir Residence Time

0

100

200

300

400

500

1967 1970 1973 1976 1979 1982 1985 1988 1991 1994 1997

Da

ys

Rondout

Pepacton

Cannonsville

Neversink

Water Residence Times - 30 years (Volume/Hydraulic load = replacement rate)

How does hydrology affect water quality?How does hydrology affect water quality?

History: History: equations developed in 1960s by Vollenweiderequations developed in 1960s by Vollenweider

basis of OECD solution to eutrophication problems in Europebasis of OECD solution to eutrophication problems in Europe basis of TMDLs in the USbasis of TMDLs in the US

Late 1960s National Eutrophication Survey by USEPALate 1960s National Eutrophication Survey by USEPA 1981 EPA issued Restoration of Lakes and Inland Waters resulting 1981 EPA issued Restoration of Lakes and Inland Waters resulting

from conference in Portland, Maine from conference in Portland, Maine 1983 Chapra & Reckhow explored refinements – sedimentation1983 Chapra & Reckhow explored refinements – sedimentation

Hydrology is a determinant of Water Quality:Hydrology is a determinant of Water Quality: Hydraulic loadsHydraulic loads determine water residence times, nutrient loads, determine water residence times, nutrient loads,

and reservoir nutrient concentrationsand reservoir nutrient concentrations Water residence timesWater residence times are a primary determinant of nutrient are a primary determinant of nutrient

concentrations and influence primary production, turbidity, and concentrations and influence primary production, turbidity, and Secchi depthsSecchi depths

Critical phosphorus loadCritical phosphorus load - is a function of depth and hydraulic load. - is a function of depth and hydraulic load.

- shallower lakes tolerate lower nutrient loads- shallower lakes tolerate lower nutrient loads

(from (from Vollenweider, Vollenweider, 1976)1976)

Observations on hydrology of NYC reservoirs:Observations on hydrology of NYC reservoirs:

Reservoirs typically have shorter water residence times than lakes Reservoirs typically have shorter water residence times than lakes (average of 1.3 years for North American lakes).(average of 1.3 years for North American lakes).

Terminal reservoirs show very stable elevations and water Terminal reservoirs show very stable elevations and water residence times (with the exception of drought periods).residence times (with the exception of drought periods).

Terminal reservoirs have greater hydraulic loads than upstream Terminal reservoirs have greater hydraulic loads than upstream reservoirs, and therefore shorter water residence times. More rapid reservoirs, and therefore shorter water residence times. More rapid flushing benefits WQ.flushing benefits WQ.

Headwater (upstream) reservoirs are more frequently drawn down Headwater (upstream) reservoirs are more frequently drawn down than terminal (downstream) reservoirs, therefore provide insight into than terminal (downstream) reservoirs, therefore provide insight into WQ changes due to drought.WQ changes due to drought.

3.0 Water Quality: 3.0 Water Quality: potential impacts of drawdown cited in the literature were potential impacts of drawdown cited in the literature were

explored with reservoir data:explored with reservoir data:

Turbidity Turbidity

Conductivity Conductivity

Eutrophication indicators:Eutrophication indicators: (Secchi depth, nutrients, (Secchi depth, nutrients,

algae)algae)

Bacteria – fecal coliformsBacteria – fecal coliforms

Cannonsville

Mo

nth

ly m

edia

n t

urb

idit

y (N

TU

)

0

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

Distance below spillway elevation (feet)

10 0 -10 -20 -30 -40 -50 -60 -70 -80 -90

Scatter Plot Analysis Methodology:Scatter Plot Analysis Methodology:

Monthly (April-December) Monthly (April-December) reservoir medians using all reservoir medians using all sample depths and sites sample depths and sites from1988-2007from1988-2007

Only elevations 0.5 ft below Only elevations 0.5 ft below spill consideredspill considered

LOWESS curves shownLOWESS curves shown Spearman correlationsSpearman correlations

• Non-parametric rankingNon-parametric ranking• P<0.05P<0.05

R= -0.71

Cannonsville

Mo

nth

ly m

edia

n t

ota

l p

ho

sph

oru

s (u

g/L

)

0

10

20

30

40


0 -10 -20 -30 -40 -50 -60 -70 -80 -90

Cannonsville

Mo

nth

ly m

edia

n t

urb

idit

y (N

TU

)

1

2

3

4

5

6

7

8

9

10


0 -10 -20 -30 -40 -50 -60 -70 -80 -90

Cannonsville

Mo

nth

ly m

edia

n S

ecch

i d

epth

(m

eter

s)0

1

2

3

4

5

6

7

8


0 -10 -20 -30 -40 -50 -60 -70 -80 -90

Cannonsville

Mo

nth

ly m

edia

n c

hlo

rop

hyl

l a

(ug

/L)

0

10

20

30

40


0 -10 -20 -30 -40 -50 -60 -70 -80 -90

Cannonsville

Mo

nth

ly m

edia

n f

ecal

co

lifo

rm (

cfu

100

mL

)

0.1

1.0

10.0

100.0


0 -10 -20 -30 -40 -50 -60 -70 -80 -90

Cannonsville

Mo

nth

ly m

edia

n c

on

du

ctiv

ity

(uS

/cm

)60

70

80

90

100


0 -10 -20 -30 -40 -50 -60 -70

Cannonsville Scatter PlotsCannonsville Scatter Plots

R= -0.71

R= -0.55R= -0.30

R= -0.66

R= -0.11 (ns)R= 0.50

Pepacton

Mo

nth

ly m

edia

n S

ecch

i d

epth

(m

eter

s)0

1

2

3

4

5

6


0 -10 -20 -30 -40 -50 -60 -70

Pepacton

Mo

nth

ly m

edia

n t

urb

idit

y (N

TU

)

0

1

2

3

4

5

6

7

8

9

10

11

12


0 -10 -20 -30 -40 -50 -60 -70

Pepacton

Mo

nth

ly m

edia

n t

ota

l p

ho

sph

oru

s (u

g/L

)

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24


0 -10 -20 -30 -40 -50 -60 -70

Pepacton

Mo

nth

ly m

edia

n c

hlo

rop

hyl

l a

(ug

/L)

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15


0 -10 -20 -30 -40 -50 -60 -70

Pepacton

Mo

nth

ly m

edia

n f

ecal

co

lifo

rm (

cfu

100

mL

)

0.1

1.0

10.0

100.0


0 -10 -20 -30 -40 -50 -60 -70

Pepacton

Mo

nth

ly m

edia

n c

on

du

ctiv

ity

(uS

/cm

)49

50

51

52

53

54

55

56

57

58

59

60

61

62

63

64

65


0 -10 -20 -30 -40 -50 -60 -70

Pepacton Scatter PlotsPepacton Scatter Plots

R= -0.46 R= 0.33 R= -0.10 (ns)

R= -0.33 R= -0.32R= -0.20

R= -0.51

R= -0.47R= 0.59

Neversink

Mo

nth

ly m

edia

n S

ecch

i d

epth

(m

eter

s)0

1

2

3

4

5

6

7

8


0 -10 -20 -30 -40 -50 -60 -70 -80 -90

Neversink

Mo

nth

ly m

edia

n t

urb

idit

y (N

TU

)

0

1

2

3

4

5

6

7

8

9

10

11

12

13

14


0 -10 -20 -30 -40 -50 -60 -70 -80 -90

Neversink

Mo

nth

ly m

edia

n t

ota

l p

ho

sph

oru

s (u

g/L

)

0

10

20

30


0 -10 -20 -30 -40 -50 -60 -70 -80 -90

Neversink

Mo

nth

ly m

edia

n c

hlo

rop

hyl

l a

(ug

/L)

0

1

2

3

4

5

6

7

8

9

10

11

12


0 -10 -20 -30 -40 -50 -60 -70 -80 -90

Neversink

Mo

nth

ly m

edia

n c

on

du

ctiv

ity

(uS

/cm

)23

24

25

26

27

28

29

30

31

32

33

34

35

36


0 -10 -20 -30 -40 -50 -60 -70 -80 -90

Neversink

Mo

nth

ly m

edia

n f

ecal

co

lifo

rm (

cfu

100

mL

)

0.1

1.0

10.0

100.0


0 -10 -20 -30 -40 -50 -60 -70 -80 -90

Neversink Scatter PlotsNeversink Scatter Plots

R= -0.28

R= -0.12R= -0.44

R= -0.37R= 0.51R= -0.36

R= -0.68

R= -0.47

R= 0.63

R= -0.37

Water quality variables vs. elevationWater quality variables vs. elevationcorrelations with r > 0.50correlations with r > 0.50

(r values shown were highest at the designated elevation range)(r values shown were highest at the designated elevation range)

Note: There were no examples where chlorophyll a had an r of > 0.5

Turbidity Phosphorus Conductivity Secchi Depth Fecal Coliform Cannonsville -0.71 -0.66 -0.55 0.5

Pepacton -0.51 0.59

Neversink-0.68 0.63

Schoharie -0.57-0.58 0.77

RondoutAshokan-West

0.61Ashokan-East

0.56 -0.53West Branch

Kensico

0 to -15-3.5 to -15

-1.8 to 7

-20 to -62

-20 to -900 to -58

0 to -90

-6 to -45

0 to 7

-11 to -580 to -60

-12 to -280 to -28

0 to -45

Elevation Range (ft.)0 to -85

-10 to -850 to -62

Bathymetry - Ashokan Reservoir(5-meter contour interval)

0 5

Kilometers

±

Esopus Creek

Source: Bathymetry, GZA, 1998.

Depth (m)

0 - 5

5 - 10

10 - 15

15 - 20

20 - 25

25 - 30

30 - 35

35 - 40

40 - 45

45 - 55.4

Ashokan Reservoir BathymetryAshokan Reservoir Bathymetry

Waterfowl in the East Basin of Ashokan Waterfowl in the East Basin of Ashokan – coincident with high fecal coliform bacteria– coincident with high fecal coliform bacteria

4.0 Two Examples of diagnostic modeling:4.0 Two Examples of diagnostic modeling:

Example 1. AshokanExample 1. Ashokan

Example 2. West BranchExample 2. West Branch

• Both occurred during a Rondout–West Branch Both occurred during a Rondout–West Branch Tunnel valve repair in 2008.Tunnel valve repair in 2008.

• Both analyses depended on high frequency Both analyses depended on high frequency monitoring.monitoring.

(c) site 1.4, 10 m-bottom avg

10/6/08 10/13/08 10/20/08 10/27/08

Tn

(NT

U)

1

10

(a) site 1.4, 0-5 m avg

Tn

(NT

U)

1

10

100

observedpredicted without resuspensionpredicted with resuspensionpredicted with current driven resuspension only

(b) site 1.4, 5-10 m avg

Tn

(NT

U)

1

10

(c) site 3.1, 10 m-bottom avg

10/6/08 10/13/08 10/20/08 10/27/08

Tn

(NT

U)

0

10

(a) site 3.1, 0-5 m avg

Tn

(NT

U)

0

10

20

observed

predicted without resuspension

predicted with resuspension

(b) site 3.1, 5-10 m avg

Tn

(NT

U)

0

10

Example 1. Ashokan: Simulated Turbidity Compared to Turbidity Measured in the Reservoir by Robotic Monitoring

• Model simulations that include resuspension more closely match measured data.

• Wind driven shoreline resuspension is important.

What does wind resuspension look like?What does wind resuspension look like?

This photo shows resuspended clays in Schoharie Reservoir.This photo shows resuspended clays in Schoharie Reservoir.

Note photos on right: Note photos on right: very sensitive even when nearly flat calm very sensitive even when nearly flat calm

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

8-Nov 13-Nov 18-Nov 23-Nov 28-Nov 3-Dec 8-Dec 13-Dec

Tu

rbid

ity (

NT

U)

145

146

147

148

149

150

151

152

Wa

ter

Su

rfa

ce E

leva

tion

(m

)

Turbidity

Water Elevation

R2 = 0.2404

1

1.5

2

2.5

3

3.5

144 146 148 150

Water Elevation Above Sea Level

Tu

rbid

ity (

NT

U)

Example 2. West Branch - High Frequency Monitoring of Turbidity (black) and elevation (red) during 2008 Delaware Aqueduct Shutdown

Mean Daily Turbidity vs. Water Surface Elevation

Conclusion:

•These data clearly link drawdown to increased turbidity

•Turbidity nearly doubles, but levels only reach 4 NTU

5. Conclusions5. Conclusions

Water quality is affected negatively by reservoir drawdown.Water quality is affected negatively by reservoir drawdown. Draw-down affects flushing rates, which in turn affect water quality.Draw-down affects flushing rates, which in turn affect water quality.

Headwater reservoirs are more frequently drawn down than terminal Headwater reservoirs are more frequently drawn down than terminal reservoirs due to operations; this benefits WQ as it approaches intakes.reservoirs due to operations; this benefits WQ as it approaches intakes.

Time series and correlations of WQ data showed correspondence to Time series and correlations of WQ data showed correspondence to elevation, but with high variability.elevation, but with high variability.

Secchi depth and turbidity showed the highest correlations to elevation.Secchi depth and turbidity showed the highest correlations to elevation.

Diagnostic modeling provided insight into the role of wind-driven Diagnostic modeling provided insight into the role of wind-driven resuspension.resuspension.

Models are essential in deciphering functional relationships between Models are essential in deciphering functional relationships between dynamically changing parameters.dynamically changing parameters.

Thank YouThank You www.nyc.dep.govwww.nyc.dep.gov

Acknowledgements: Acknowledgements: D. Kent, and Y. Tokuz for literature search, D. Kent, and Y. Tokuz for literature search, D. Lounsbury for map, D. Lounsbury for map, C. Nadareski and M. Reid for waterfowl info, C. Nadareski and M. Reid for waterfowl info, WQD field and lab staff for historic data, and WQD field and lab staff for historic data, and UFI for modeling workUFI for modeling work

nywea wstc at west point, ny september 15, 2009 the impacts of reservoir drawdown on water quality...

Documents