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

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

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

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

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

Hydrologic Cycle

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

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

Annual Precipitation at Poughkeepsie NY Precipitationcm Lowest year: 66 First quartile: 92 Median: 106 Third quartile: 115 Highest year: 137 Mean: 103 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

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

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

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

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

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

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

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

Where Can NYC Get Its Water?

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

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

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

NY Map

NYC Watersheds

Pepacton Schoharie Ashokan Neversink Roundout Cannonsville Catskill/Delaware Watersheds