Monroe L. Weber-Shirk S chool of Civil and Environmental Engineering Reservoirs Balancing Supply and Demand Ashokan Kensico Hillview Croton Reservoir Spillway

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?

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

Average Total Monthly Flow into Pepacton Reservoir ( km 3 storage ) January March May July September November Million m 3 /month Reservoir full (hopefully) average Deficit provided by storage Better design is based on drought conditions! ____ million m 3 /month * __ month = ___ million m

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

Reservoir Mass Balance Equations Di=Di= Ii=Ii= ++= O = Cumulative (________ + _________ + ___________ ) Initial storage Cumulative Inflow Cumulative Outflow Storage DemandRiver flowEvaporation True at any time! or

Density of Water Temperature (C) Density (kg/m 3 ) Temperature (C) Density (kg/m 3 ) Density (mass/unit volume)  density of water: 1000 kg/m 3

drought status 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

Reservoir Rules in Equation Form S max = When is reservoir full? ___________________ Reservoir Capacity When S i = S max Reservoir is overflowing Overflow goes into river No additional river flow

Cannonsville Reservoir Storage (Demand of 1.04 x 10 6 m 3 /day) How could we increase safe yield? Increase reservoir volume

Storage vs. Safe Yield for Cannonsville Reservoir storage volume (million m 3 ) safe yield (million m 3 /day) 367 Average stream flow What is the asymptote?

NYC Reservoirs  NYC supply reservoirs have a storage capacity of 550 billion gallons (2 km 3 )  How long could NYC go without any inflow into the reservoirs?  Current Reservoir levels ( Reservoir Levels solution

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

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 )  the maximum hourly rate is 2.5 (range of )  for NYC the maximum instantaneous rate was _____ *Henry and Heinke p 386 increases ?)

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 m 3 useable storage  Flows from Kensico to Hillview are adjusted every ________ two hours

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

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 Main breaks Maintenance of supply tunnels

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

Pepacton Schoharie Ashokan Neversink Roundout Cannonsville Catskill/Delaware Watersheds

NYC Watersheds

Croton System

Ashokan Reservoir

Schoharie Reservoir

Neversink Reservoir

West Branch Reservoir

NY 301 crosses West Branch Reservoir

Kensico Reservoir

City Tunnels

Jerome Park Reservoir

Gaging Stations

Empty NYC Reservoirs  NYC supply reservoirs have a storage capacity of 550 billion gallons (2 km 3 )  Average demand is 61 m 3 /s  How long could NYC go without any inflow into the reservoirs?

Cannonsville Reservoir Storage (Demand of 0.5 x 10 6 m 3 /day) Stream flow gage station map

Cannonsville Reservoir Storage (Demand of 0.75 x 10 6 m 3 /day)

Cannonsville Reservoir Storage (Demand of 1 x 10 6 m 3 /day)