Recent Storm Activity and its Effect on Turbidity Levels in Neversink Reservoir Rich Van Dreason Watershed Water Quality Science and Research New York City Department of Environmental Protection NYC Watershed/Tifft Science & Technical Symposium September 19 , 2013 Thayer Hotel, West Point
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Recent Storm Activity and its Effect on Turbidity Levels in Neversink Reservoir
Recent Storm Activity and its Effect on Turbidity Levels in Neversink Reservoir. Rich Van Dreason Watershed Water Quality Science and Research New York City Department of Environmental Protection. NYC Watershed/Tifft Science & Technical Symposium - PowerPoint PPT Presentation
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Recent Storm Activity and its Effect on Turbidity Levels in Neversink Reservoir
Rich Van Dreason
Watershed Water Quality Science and Research
New York City Department of Environmental Protection
NYC Watershed/Tifft Science & Technical Symposium
September 19 , 2013 Thayer Hotel, West Point
2
Introduction
August 29, 2011
Neversink River just below dam
September 19, 2012
Neversink Reservoir
Neversink Reservoir not too long ago
September 19, 2012
Neversink River above reservoir
3
Objectives
Discuss factors associated with recent elevated turbidity in the Neversink Reservoir
• Occurrence of recent large storm events
• Increase in sources of turbidity resulting from Irene
Discuss factors that may be contributing to the slow recovery since Irene
o Occurrence of small storm events
o Particle size
Recent monitoring upgrades
4
Land use in the Neversink Basin
5
Hydrology and site locations in Neversink basin
West Branch
East Branch
Aden Brook
Kramer Brook
NR4
NR3
NR2
NR1
10
20
30
40
Neversink Reservoir (cross-section)
6
Turbidity Characteristics
Definition:
•Measure of the light-scattering effects of suspended particulate material.
o Nephelometer; results in NTU
Turbidity=-0.01435 + 0.7135 (TSS)
R-sq=85.7%
• Suspended particles that contribute to turbidity are generally in the 1-10 micron range
o Examples: clay, fine silt and algae
• SWTR Source Water turbidity limit = 5 NTU
• Turbidity is related to suspended sediment concentrations
o Also depends on the particle size distribution and refractive index which may change with turbidity source
7
Turbidity and Stream flow
• Complex relationshipo Available sediment supply
o Location of sediment supply
• High turbidity at onset => available material in channel
And possibly to greater availability of fine sediment courtesy of Irene
19
Conclusions (continued)
Longer recovery periods post Events 2 and 3 associated with:
• Occurrence of multiple storm events following initial major event
Mean Daily Flow(cfs)
the
mea
n, t
urb
0.1
1.0
10.0
50.0
100.0
200.0
Date Collected
JAN10
FEB10
MAR10
APR10
MAY10
JUN10
JUL10
AUG10
SEP10
OCT10
NOV10
DEC10
JAN11
FEB11
MAR11
APR11
MAY11
JUN11
JUL11
AUG11
SEP11
OCT11
NOV11
DEC11
JAN12
FEB12
MAR12
APR12
MAY12
JUN12
JUL12
AUG12
SEP12
OCT12
NOV12
DEC12
JAN13
FEB13
MAR13
APR13
MAY13
JUN13
JUL13
AUG13
Mean_taps
FL
OW
_CF
S
010002000300040005000600070008000
Date Collected
JAN10
FEB10
MAR10
APR10
MAY10
JUN10
JUL10
AUG10
SEP10
OCT10
NOV10
DEC10
JAN11
FEB11
MAR11
APR11
MAY11
JUN11
JUL11
AUG11
SEP11
OCT11
NOV11
DEC11
JAN12
FEB12
MAR12
APR12
MAY12
JUN12
JUL12
AUG12
SEP12
OCT12
NOV12
DEC12
JAN13
FEB13
MAR13
APR13
MAY13
JUN13
JUL13
AUG13
Neversink River
Reservoir Elevation taps (1-4)
MeanTurbidity
(NTU)
124 days
130 days
162.5 NTU
59.5 ntu
2.7 ntu 3.8 ntu
29.6 NTU
1.6 ntu
28 days
Multiple events Multiple events
20
Conclusions (continued)
• And possibly from an increase of clay-sized particles derived from eroding banks of glacial till
Glacial till bank
Exposed lake clay deposit
21
Questions ?
22
Conclusions
Recent elevated turbidities in Neversink Reservoir related to :
Large storm events starting on October 1, 2010
And possibly to greater availability of fine sediment
Longer recovery periods post Events 2 and 3 associated with:
Occurrence of multiple storm events following initial major event
And possibly from an increase of clay-sized particles derived from eroding banks of glacial till and recent exposures of lacustrine clays
23
Additional factors - particle size
Neversink Particle Size Distribution Post Irene, Upstate Freshwater Institute determined the size distribution of turbidity causing particles in all Delaware Reservoirs
Scanning electron microscopy interfaced with Automated image and X-ray analyses
Particle cross-sectional Area per unit Volume of water (PAV) strongly correlates to turbidity.
Modified from “Hurricane Irene Turbidity Studies” prepared by Upstate Freshwater Institute December 14, 2012
Key Findings
80% of turbidity caused by particles < 4 µm, substantially smaller than other Delaware Reservoirs
4 µm upper limit of clay-sized particles
4
Other Delaware reservoirs
24
Conclusions (continued)
• And possibly from an increase of clay-sized particles derived from eroding banks of glacial till
Neversink Particle Size Distribution
Glacial till bank
Exposed lake clay deposit
4
25
0
5
10
15
20
1930 1940 1950 1960 1970 1980 1990 2000 2010 2020
0
10
20
30
40
1930 1940 1950 1960 1970 1980 1990 2000 2010 2020
Extreme flow event trends in Neversink basin
0
10
20
30
40
1930 1940 1950 1960 1970 1980 1990 2000 2010 2020
Mean Daily Flows>95th percentile (579 cfs)
All months
Cold season(November-May)
Warm season(June-October)
Inspired by Matonse A. H. and A. Frei (In press)
All major Catskill streams show similar trends
o Schoharie Creek, Esopus Creek, E. and W. Branch of Delaware River
26
Additional Factors? More resuspension after Events 2 and 3?
o Unknown; no data
Did particles settle more slowly after Events 2 and 3?
o DOC tends to prevent aggradation of particles
o Settling rates decrease with decreasing water temperature, particle size