1. 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. 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. 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. 4 Land use in the Neversink Basin

5. 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. 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. 7 Turbidity and Stream flow Complex relationship o Available sediment supply o Location of sediment supply High turbidity at onset => available material in channel High turbidity later on hydrograph o Sediment sources faraway o New sediment sources become available

8. 8 Mean Daily Flow (cfs ) Neversink River @ NCG Mean Turbidity (NTU) Long-term turbidity at Neversink Reservoir and Streams Reservoir Elevation taps (1-4) 1. 2. 3. Turbidity (NTU) PREPOST Mean Max 1.8 30 8.5 200 October 1, 2010 Pre conditions Post Neversink River (NCG) Aden Brook (NK4) Turbidity (NTU) Kramer Brook (NK6) Year Mean Max 0.8 60 1.9 26 Mean Max 1.1 22 1.9 18 Mean Max 3.7 150 3.4 12

9. 9 Mean Daily Flow (cfs ) Neversink River @ NCG Mean Turbidity (NTU) Reservoir Elevation taps (1-4) Neversink River (NCG) Kramer Brook (NK6) Aden Brook (NK4) Long-term turbidity at Neversink Reservoir and Streams 1. 2. 3. Turbidity (NTU) ? Year Monthly stream samples not adequate for flashy mountain streams ? ? ?

10. 10 Details of recent flow events Mean Daily Flow (cfs ) Neversink River @ NCG Event 2 Aug 28, 2011 (Irene) Daily mean flow was 7,220 cfs (largest on record) Peak flow was 20,900 cfs (60 yr event, 2 nd largest) 4.8 inches Aug 27-28, 3.6 inches on Aug 15 Event 3 Sept 18, 2012 Daily mean flow was 3410 cfs Peak flow was 17,800 cfs ( 45 yr. flood, 4 th largest) 5.3 inches Sept 17-18 (localized). Event 1 Oct 1, 2010 Daily mean flow was 6030 cfs Peak flow was 16,400 cfs (about 20 yr flood, 6 th largest) 7.8 inches 5 days prior w/ 5.7 on Sep. 30 162.5 NTU 59.5 ntu 29.6 NTU Mean Turbidity (NTU) Reservoir Elevation taps (1-4)

11. 11 Turbidity Recovery Rates  Why the slow recovery after Event 3 ??? Reservoir Elevation taps (1-4) Mean Turbidity (NTU) 124 days 130 days 162.5 NTU 59.5 ntu 2.7 ntu 3.8 ntu 40% higher (3.2 vs. 1.9 NTU) Mean Turbidity (NTU) Low Range 29.6 NTU 1.6 ntu 28 days 1. 2. 3. 1430 cfs 1180 cfs 1270 cfs Event 1 Event 2 Event 3 Mean Daily Flow (cfs ) HHigher resolution stream data needed! Neversink River (NCG) Turbidity (NTU) Historic 95 th percentile (1.9 ntu)

12. 12 Additional factors - particle size  Post Irene, Upstate Freshwater Institute (UFI) contracted to evaluate turbidity causing particles in the Delaware Reservoirs Size distribution and composition Scanning electron microscopy interfaced with Automated image and X-ray analyses From “Hurricane Irene Turbidity Studies” prepared by Upstate Freshwater Institute December 14, 2012 Neversink Results  80% of turbidity caused by particles < 4 µm  Composition: 69% clay, 18% quartz Particle size Settling rate

13. 13 Neversink Basin Surficial Geology  Most deposits contain very little fine sediment  Glacial till most likely source of small particles Very abundant  Streams are often in close proximity to the glacial tills  Tills generally tightly packed; impermeable

14. 14 Eroding glacial till hillslopes  Hypothesis High flows caused new hillslope failures (or exploited old ones) freeing fine sediment to become entrained  Currently 15 large failures in till (>1000 sq. ft. eroding bank) Some old but enlarged, some initiated by Irene  How much fine material? How transportable?

15. 15 What about glacial lake clays?  Exposed glacial lake clays are rare in the main branches of Neversink River  Smaller tributaries still to be assessed Figure 5. Channel incision into lacustrine deposits post Irene. W. Branch Neversink upstream of Frost Valley (December 2011)

16. 16 Real time turbidity data is here!  Digital Turbidity, Temperature Sensors and Data logger Forest Technology Systems and Campbell Scientific  Real-time data access via phone-line  Benefits Early warning Evaluate flow-turbidity relationship Basin changes

17. 17 Vertical Profiling Systems  YSI vertical profiling system to be installed next year Turbidity, temperature, conductivity, dissolved oxygen etc. Real-time data access via radio modem to land line connection  Benefits Early-warning Track turbidity interflows Monitor resuspension Select appropriate intake

18. 18 Conclusions  Recent elevated turbidities in Neversink Reservoir related to large storm events starting on October 1, 2010 Turbidity (NTU) Elevation taps (1-4) Mean Daily Flow (cfs ) Neversink River @ NCG  And possibly to greater availability of fine sediment courtesy of Irene

19. 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 ) Reservoir Elevation taps (1-4) Mean Turbidity (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

20. 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. 21 Questions ?

22. 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. 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. 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. 25 Extreme flow event trends in Neversink basin Mean Daily Flows>95 th 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. 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 Recovery period (days) DOC (mgL -1 )Temp (C) Event 1282.5 (2.2)8.2 (7.6) Event 21242.9 (2.1)10.2 (8.2) Event 31302.5 (2.2)7.8 (6.7)  Slow recovery not related to DOC and temperature  Particle size?

27. 27 1 2 3 4 Turbidity interflow post Irene