Reservoirs

1. Ashokan Reservoirs Kensico Balancing Supply and Demand Croton Reservoir Spillway Hillview

2. How Big must the Reservoirs be? • What is the objective that you are trying to meet? • What information do you need in order to solve this problem? • What algorithm could you use to solve the problem?

3. Water Supply and Demand Fluctuations • Supply • Seasonal supply fluctuations • Buffered using _________ reservoirs • Demand • Seasonal demand fluctuations • Daily demand fluctuations • Buffered using _________ reservoirs • Effect of flow fluctuations on system design • Size of balancing reservoirs • pipe sizes watershed distribution

4. Average Total Monthly Flow into Pepacton Reservoir (0.540 km3 storage) Reservoir full (hopefully) 140 120 100 80 Million m3/month average 60 40 20 0 Deficit provided by storage July May March January November September 35 175 ____ million m3/month * __ month = ___ million m3 5 Better design is based on drought conditions!

5. What is the safe yield from the Cannonsville Reservoir? • What is the maximum rate that we can withdraw water from the Cannonsville Reservoir without emptying the reservoir?_________________________________ • What are the critical events in history that determine how big the reservoir has to be?__________ The average stream flow into the reservoir. Droughts

6. Reservoir Mass Balance Equations + = + Storage Cumulative Inflow Initial storage Cumulative Outflow O = Cumulative (________ + _________ + ___________ ) Demand River flow Evaporation True at any time! or Ii= Di=

7. 1000 990 980 Density (kg/m3) 970 960 950 0 50 100 Temperature (C) 1000 999 Density (kg/m3) 998 997 0 10 20 Temperature (C) Density of Water • Density (mass/unit volume) r • density of water: 1000 kg/m3

8. Downstream River Flow? • Simplest operating rule • Waste from reservoir when reservoir is full • Don’t waste from reservoir if reservoir isn’t full • More complex rules could easily be incorporated into a spreadsheet model • Minimum discharge into stream as a function of reservoir storage volume or ______________ • Based on regulations drought status

9. Reservoir Rules in Equation Form When Si = Smax When is reservoir full? ___________________ Reservoir is overflowing Overflow goes into river No additional river flow Reservoir Capacity Smax=

10. Cannonsville Reservoir Storage (Demand of 1.04 x 106 m3/day) How could we increase safe yield? Increase reservoir volume

11. What is the asymptote? 1.5 1 0.5 0 0 250 500 750 1000 Storage vs. Safe Yield for Cannonsville Reservoir Average stream flow safe yield (million m3/day) 367 storage volume (million m3)

12. NYC Reservoirs • NYC supply reservoirs have a storage capacity of 550 billion gallons (2 km3) • How long could NYC go without any inflow into the reservoirs? • Current Reservoir levels (http://www.ci.nyc.ny.us/nyclink/html/dep/html/current.html) solution Reservoir Levels

13. Seasonal, Daily, and Hourly Fluctuations • Substantial increase in water demand during summer due to_______________________ • Peak flows___________________________________________________________ • Low flows______________________ watering lawns, swimming pools Early morning as people get ready to go to work/school Commercial Breaks (not any more) Between midnight and 5 am

14. Estimates of Daily and Hourly Fluctuations* • As the time interval of analysis decreases in length the maximum rate of water demand during that time interval __________ • If the average annual flow rate is 1.0 then • the maximum season rate is 1.25 (summer) • the maximum daily rate is 1.5 (range of 1.2-2.0) • the maximum hourly rate is 2.5 (range of 1.5-3.5) • for NYC the maximum instantaneous rate was _____ increases 100?) 100?) 1.75 *Henry and Heinke p 386

15. Methods to Even Out Fluctuations • Seasonal fluctuations • Source (watershed) reservoirs • Kensico and West Branch Reservoirs • Daily fluctuations • Hillview and Jerome Park Reservoirs (directly connected to distribution tunnels) • Hillview has 3.4 million m3 useable storage • Flows from Kensico to Hillview are adjusted every ________ two hours

16. Balancing Reservoirs OK Fred, I’ll go give it a turn. Did you say you have more water than you need? Hey Bob, I need some more water. Could you open the valve another turn? Where are the largest tunnels in the NYC water supply and distribution system?

17. How Can You Estimate Required Balancing-Reservoir Capacity? • Variable supply • Variable demand • Analyze historic record to search for worst case conditions • Use same Mass Balance analysis • Include variable ________ in analysis • Other unusual demands… demand Fire fighting needs Maintenance of supply tunnels Main breaks

18. Summary • An understanding of the variability in supply and demand are essential for the sizing of reservoirs and pipes in a water supply system • Supply Reservoirs must be sized to store water during drought periods • Balancing Reservoirs must be sized for daily or hourly fluctuations • Distribution pipes must be sized to handle peak flows

19. Catskill/Delaware Watersheds Schoharie Cannonsville Pepacton Ashokan Roundout Neversink

20. NYC Watersheds

21. Croton System

22. Ashokan Reservoir

23. Schoharie Reservoir

24. Neversink Reservoir

25. West Branch Reservoir

26. NY 301 crosses West Branch Reservoir

27. Kensico Reservoir

28. City Tunnels

29. Jerome Park Reservoir

30. Gaging Stations

31. Empty NYC Reservoirs • NYC supply reservoirs have a storage capacity of 550 billion gallons (2 km3) • Average demand is 61 m3/s • How long could NYC go without any inflow into the reservoirs?

32. Cannonsville Reservoir Storage (Demand of 0.5 x 106 m3/day) Stream flow gage station map

33. Cannonsville Reservoir Storage (Demand of 0.75 x 106 m3/day)

34. Cannonsville Reservoir Storage (Demand of 1 x 106 m3/day)