monroe l. weber-shirk s chool of civil and environmental engineering nyc watersheds
Post on 19-Dec-2015
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Monroe L. Weber-Shirk
School of Civil and Environmental Engineering
NYC WatershedsNYC Watersheds
Homework commentsHomework 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 supplywellsCrotonCatskills/Delaware
groundwateroceanstreamsrainfall
NYC Watersheds: Introduction
NYC needs 61 m3/sHow much land is needed to deliver that
much water?How do you choose which land to use for
watersheds?
NYC Water Supply Strategy
QuantityQualityAltitudeProximity
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
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
Hydrologic Cycle
Data Requirements for Predicting Stream Flows
PrecipitationWill need to use rain gage data from site close byUS climate data
Evaporation/TranspirationEvaporation data may be available for lakesEvaporation and Transpiration are strongly affected by
Type of vegetationGround coverTemperatureWind _____________Season
Annual Precipitation at Poughkeepsie NY
Snow year (July to June)
60
80
100
120
140
1950 1955 1960 1966 1971 1976 1981 1986 1995
year
prec
ipit
atio
n (c
m)
Annual Precipitation at Poughkeepsie NY
Precipitation cmLowest 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
60
80
100
120
140
0 0.2 0.4 0.6 0.8 1
rank
prec
ipita
tion
(cm)
40 year record
Land Area Required for NYC Watersheds: Detail Approach
Measure the stream flow over time in potential watershedsUnited States Geological SurveyUSGS home pageThe National Atlas of the
United States of America
Calculate the annual water yield per watershed area (cm/year)
Stream Flow Vs. Precipitation
Snow year (July to June)
0
50
100
150
year
cm/y
ear
streamflow precipitationWalton, NY Poughkeepsie
Why is Correlation Between Precipitation and Stream Flow so Poor?
Stations are too far apartEvapo-transpiration
changes with land useTime lag between
precipitation andstream flow
y = 0.4351x + 14.857
R2 = 0.29420
20
4060
80
100
50 70 90 110 130 150
precipitation (cm/yr)
stre
amflo
w (c
m/y
r)
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 _________________
Annual Stream Flow at Walton NY
0
20
40
60
80
100
0 0.2 0.4 0.6 0.8 1
rank
stre
amfl
ow (
cm/y
r)
Stream Flow
(cm/yr)
Lowest year:
27
First quartile:
53
Median:
58
Third quartile:
70
Highest year:
92
Mean:
60
Drought Year Watershed Sizing
Estimate the Watershed size required for NYC based on:61 m3/s demandDrought-year stream flow of 27 cm/yr
= 7130 km2
(flow rate - Q)
(Velocity - V)
(Area - A)
^
Q=VA A=Q/V
361m
s
86400s
day
365.25days
year
year
0.27m
2
2
km
1,000,000m
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 flowsreduce water
consumption
Where Can NYC Get Its Water?
NYC Watersheds: Croton and Catskill
Croton system (1842)12 reservoirs and 3 controlled lakes960 km2 of watershed _____ of the City’s drinking water
Catskill system (1927)2 source reservoirs1461 km2 of watershed _____ of the City’s drinking water
10%
40%
NYC Watersheds: Delaware and Total system
Delaware system (1965)4 source reservoirs2585 km2 of watershed _____ of the City’s drinking water
Total System5000 km2 of watershedour estimate: 7130 km2
50%
MAP
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?
NY Map
NYC Watersheds
Pepacton
Schoharie
Ashokan
Neversink
Rondout
Cannonsville
Catskill/Delaware Watersheds