Homework comments • Office hours today and Wednesday • Equations: solve first using symbols. • Substitute numbers (with units) as the last step • Make sure you answer all parts of every question • Work in teams! • Each person should attempt the homework before meeting together • Final solution should be checked by a different team member than the person writing the solution • This will eliminate careless mistakes!
Overview • Quantity of water needed by NYC • Potential sources of water • ______________ • ______________ • ______________ • _____________ • History of NYC water supply • wells • Croton • Catskills/Delaware groundwater ocean streams rainfall
NYC Watersheds: Introduction • NYC needs 61 m3/s • How much land is needed to deliver that much water? • How do you choose which land to use for watersheds?
NYC Water Supply Strategy • 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 Quantity Quality Altitude Proximity
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
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
Annual Precipitation at Poughkeepsie NY Snow year (July to June)
Annual Precipitation at Poughkeepsie NY 40 year record Precipitation cm 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
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)
Stream Flow Vs. Precipitation Poughkeepsie Walton, NY Snow year (July to June)
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 andstream flow
Stream Flow vs. Precipitation Estimates for the Catskills • 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 _________________ 60% ground water flow
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
(Area - A) ^ Drought Year Watershed Sizing • Estimate the Watershed size required for NYC based on: • 61 m3/s demand • Drought-year stream flow of 27 cm/yr (flow rate - Q) (Velocity - V) Q=VA A=Q/V = 7130 km2
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
NYC Watersheds: Croton and Catskill • Croton system (1842) • 12 reservoirs and 3 controlled lakes • 960 km2 of watershed • _____ of the City’s drinking water • Catskill system (1927) • 2 source reservoirs • 1461 km2 of watershed • _____ of the City’s drinking water 10% 40%
NYC Watersheds: Delaware and Total system • Delaware system (1965) • 4 source reservoirs • 2585 km2 of watershed • _____ of the City’s drinking water • Total System • 5000 km2 of watershed • our estimate: 7130 km2 MAP 50%
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?
Catskill/Delaware Watersheds Schoharie Cannonsville Pepacton Ashokan Rondout Neversink