NYWEA WSTC at West Point, NY NYWEA WSTC at West Point, NY September 15, 2009 September 15, 2009 The Impacts of Reservoir Drawdown on Water The Impacts of Reservoir Drawdown on Water Quality in NYC’s Catskill and Delaware Quality in NYC’s Catskill and Delaware Reservoirs Reservoirs by L. Janus, R. VanDreason, G. Marzec, J. Mayfield, D. Pierson, R. Gelda
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NYWEA WSTC at West Point, NY September 15, 2009 The Impacts of Reservoir Drawdown on Water Quality in NYC’s Catskill and Delaware Reservoirs by L. Janus,
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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
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.
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:
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
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
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