1. Monroe L. Weber-Shirk S chool of Civil and Environmental Engineering NYC Watersheds

2. Overview  Quantity of water needed by NYC  Potential sources of water  ______________  _____________  History of NYC water supply  wells  Croton  Catskills/Delaware groundwater ocean streams rainfall

3. NYC Watersheds: Introduction  NYC needs 61 m 3 /s  How much land is needed to deliver that much water?  How do you choose which land to use for watersheds?

4. NYC Water Supply Strategy Quantity Quality Altitude Proximity  Choose streams to meet 4 criteria  _________  Build dams on streams to provide storage (reservoirs)  Build aqueducts to carry the water from the reservoirs to NYC

5. Land Area Required for NYC Watersheds (The Big Picture)  Where does the water in the streams come from?___________  How could we estimate the average stream flow?  ______________________ Precipitation Rain gage Direct stream measurements Rooftop rain catchment system analogy

6. Hydrologic Cycle

7. Data Requirements for Predicting Stream Flows  Precipitation  Will need to use rain gage data from site close by  US climate data  Evaporation/Transpiration  Evaporation data may be available for lakes  Evaporation and Transpiration are strongly affected by  Type of vegetation  Ground cover  Temperature  Wind  Season

8. Annual Precipitation at Poughkeepsie NY Snow year (July to June)

9. Annual Precipitation at Poughkeepsie NY Precipitationcm Lowest year: 66 First quartile: 92 Median: 106 Third quartile: 115 Highest year: 137 Mean: 103 For comparison, Binghamton’s mean precipitation is 94 cm/year 40 year record

10. Land Area Required for NYC Watersheds: Detail Approach  Measure the stream flow over time in potential watersheds  United States Geological Survey  USGS home page  The National Atlas of the United States of America  Calculate the annual water yield per watershed area (cm/year)

11. Stream Flow Vs. Precipitation Snow year (July to June) Walton, NY Poughkeepsie

12. Why is Correlation Between Precipitation and Stream Flow so Poor?  Stations are too far apart  Evapo-transpiration changes with land use  Time lag between precipitation and stream flow

13. Stream Flow vs. Precipitation Estimates for the Catskills 60% ground water flow  Approximately _____ of the rainfall leaves the watershed as stream flow  The majority of the remaining rainfall leaves the watershed as transpiration/evaporation  A small amount of water leaves the watershed as _________________

14. Annual Stream Flow at Walton NY Stream Flow(cm/yr) Lowest year:27 First quartile:53 Median:58 Third quartile:70 Highest year:92 Mean:60 Stream Flow(cm/yr) Lowest year:27 First quartile:53 Median:58 Third quartile:70 Highest year:92 Mean:60

15. Drought Year Watershed Sizing  Estimate the Watershed size required for NYC based on:  61 m 3 /s demand  Drought-year stream flow of 27 cm/yr = 7130 km 2 (flow rate - Q) (Velocity - V) (Area - A) ^ Q=VA A=Q/V

16. Analysis Assumptions  Reservoirs can store water to even out flow throughout a year  We assumed drought intensity is same in all NYC watersheds  We assumed all watersheds have same drought ___________  What about NYC’s ability to ____________ __________ during a drought? stream flows reduce water consumption

17. Where Can NYC Get Its Water?

18. NYC Watersheds: Croton and Catskill  Croton system (1842)  12 reservoirs and 3 controlled lakes  960 km 2 of watershed  _____ of the City’s drinking water  Catskill system (1927)  2 source reservoirs  1461 km 2 of watershed  _____ of the City’s drinking water 10% 40%

19. NYC Watersheds: Delaware and Total system  Delaware system (1965)  4 source reservoirs  2585 km 2 of watershed  _____ of the City’s drinking water  Total System  5000 km 2 of watershed  our estimate: 7130 km 2 50% MAP

20. Summary  We found how much land NYC needs to supply their water based on stream flow data  We found where the land is located and saw where the reservoirs are located  Coming up…  How big do the reservoirs have to be to provide adequate storage?  How does the water get from the reservoirs to NYC?

21. NY Map

22. NYC Watersheds

23. Pepacton Schoharie Ashokan Neversink Rondout Cannonsville Catskill/Delaware Watersheds