Prepared in cooperation with the New York City Department of Environmental Protection

Bathymetry of Ashokan, Cannonsville,

Neversink, Pepacton, Rondout, and

Schoharie Reservoirs, New York, 2013–15

Scientific Investigations Report 2017–5064

U.S. Department of the Interior

U.S. Geological Survey
1

2

3

Cover. Background photograph: Schoharie Reservoir, September 2014; (1) U.S. Geological Survey boat on the Schoharie Reservoir; 

(2) data collection computer at Cannonsville Reservoir; (3) base station and radio antenna.
Bathymetry of Ashokan, Cannonsville, 

Neversink, Pepacton, Rondout, and 

Schoharie Reservoirs, New York, 2013–15

By Elizabeth A. Nystrom

Prepared in cooperation with the

New York City Department of Environmental Protection

Scientific Investigations Report 2017–5064

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

RYAN K. ZINKE, Secretary

U.S. Geological Survey

William H. Werkheiser, Deputy Director

 exercising the authority of the Director

U.S. Geological Survey, Reston, Virginia: 2018

For more information on the USGS—the Federal source for science about the Earth, its natural and living 

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U.S. Government.

Although this information product, for the most part, is in the public domain, it also may contain copyrighted materials 

as noted in the text. Permission to reproduce copyrighted items must be secured from the copyright owner.

Suggested citation:

Nystrom, E.A., 2018, Bathymetry of Ashokan, Cannonsville, Neversink, Pepacton, Rondout, and Schoharie 

Reservoirs, New York, 2013–15: U.S. Geological Survey Scientific Investigations Report 2017–5064, 29 p., 

https://doi.org/10.3133/sir20175064.

ISSN 2328-0328 (online)
iii

Acknowledgments

The author would like to thank the New York City Department of Environmental Protection for 

providing control point locations, coordinated spillway elevations, and water surface elevations, 

with special thanks to David Lounsbury, Terry Ringler, Terry Spies, and Jordan Gass. Additional 

sincere thanks to the following U.S. Geological Survey field hands for their hard work in the 

field: Daniel Edwards, John Byrnes, Patrick Phillips, Paul Heisig, and David Munsey.

v

Contents

Acknowledgments........................................................................................................................................iii

Abstract...........................................................................................................................................................1

Introduction.....................................................................................................................................................1

Purpose and Scope ..............................................................................................................................1

Description of Study Area ...................................................................................................................2

Methods...........................................................................................................................................................3

Survey Planning ....................................................................................................................................4

Data Collection......................................................................................................................................4

Horizontal and Vertical Control..................................................................................................4

Horizontal Position Data .............................................................................................................7

Water Surface Elevations and Vertical-Position Data ..........................................................7

Echo Sounder Data Collection...................................................................................................8

Sound Speed ................................................................................................................................9

Depth-Measurement Checks.....................................................................................................9

Data Integration (HYPACK).......................................................................................................10

Additional Sources of Depth and Elevation Data .................................................................10

Data Processing..................................................................................................................................11

Echo Sounder Data Processing ..............................................................................................11

Geographic Information System Database Creation and Linear Enforcement Editing .11

Contour Creation and Elevation-Area-Capacity Table Computations...............................13

Accuracy Assessment................................................................................................................................13

Survey Data Accuracy—Echo Sounder Points.............................................................................16

Survey Product Accuracy—Bathymetric Surfaces, Contours, and Capacity Tables.............17

Results of Surveys .......................................................................................................................................21

Effect of Linear Enforcement on Capacity Estimation ..................................................................21

Change in Reservoir Capacity Over Time .......................................................................................21

Summary........................................................................................................................................................27

References Cited..........................................................................................................................................27

Figures

1. Shaded-relief map showing locations of the West of Hudson reservoirs and

connecting aqueducts and tunnels in New York State ..........................................................2

2. Map showing example of the planned main transects and quality assurance

transects, Schoharie Reservoir in New York State.................................................................7

3. Photograph of base station and radio antenna at control point near Schoharie

Reservoir, New York State. .........................................................................................................8

4. Photograph of survey boat and global navigation satellite system (GNSS) rover

receiver used for the study of the West of Hudson reservoirs in New York State............9

5. Graph showing example of observed 5-minute interval and 2-hour moving-average

water surface elevation, Pepacton Reservoir, New York State, July 2015 .........................9

6. Photograph of bar check plate used during surveys of the West of Hudson

reservoirs in New York State. ..................................................................................................10
vi

7. Graphs showing sound-speed profiles, measured points, and processing averages

(lines) for each West of Hudson reservoir surveyed in New York State. .........................12

8. Cross section showing the profile of an echo sounder point screening and editing

example from Rondout Reservoir, New York State ...............................................................13

9. Map showing an example of a raw triangulated irregular network in the West

Basin of Ashokan Reservoir in New York State.....................................................................14

10. Map showing an example of breakline additions and edited triangulated irregular

network in the West Basin of Ashokan Reservoir in New York State................................14

11. Map showing example low-pass filtered raster and contours in the West Basin of

Ashokan Reservoir in New York State. ..................................................................................15

12. Boxplots showing accuracy assessment of survey data—elevation error

calculated by comparing quality assurance points to main echo sounder points,

triangulated irregular network (TIN) surfaces, and contours by reservoir in New

York State .....................................................................................................................................15

13. Boxplots showing accuracy assessment of survey data—elevation error

calculated by comparing quality assurance points to main echo sounder points,

triangulated irregular network (TIN) surfaces, and contours, by distance from main

echo sounder point in the West of Hudson reservoirs in New York State........................16

14. Map showing quality assurance echo sounder points compared to main echo

sounder points, Schoharie Reservoir, New York State ........................................................17

15. Map showing quality assurance echo sounder points compared to A, raw and B,

edited triangular irregular networks (TINs), Schoharie Reservoir in New York State....19

16. Map showing quality assurance echo sounder points compared to contours for

Schoharie Reservoir in New York State..................................................................................20

Tables

1. Information on West of Hudson reservoirs: U.S. Geological Survey station identifier,

year storage began, year in service, and water supply system in New York State ..........3

2. West of Hudson reservoirs as-built capacity values and corresponding elevations

of reservoir structures in New York State ................................................................................3

3. Transect spacing information used in surveying the West of Hudson reservoirs in

New York State..............................................................................................................................4

4. Data collection dates by type and water surface elevations during surveys of West

of Hudson reservoirs in New York State...................................................................................5

5. Spillway elevations and conversion factors for the surveyed West of Hudson

reservoirs in New York State. ....................................................................................................7

6. Control points used in the surveys of the West of Hudson reservoirs in New York

State. ..............................................................................................................................................8

7. Sound-speed corrections by depth applied to the West of Hudson reservoirs

surveyed in New York State. ....................................................................................................11

8. Number of data points used per West of Hudson reservoir in New York State after

data editing, classified by data source ...................................................................................13

9. Accuracy of point elevations for quality assurance echo sounder points compared

to main echo sounder points for the West of Hudson reservoirs, New York State.........17

10. Accuracy of triangulated irregular network (TIN) elevations for quality assurance echo

sounder points compared to edited and raw TIN surfaces for the West of Hudson

reservoirs, New York State. .....................................................................................................18
vii

11. Accuracy of raster elevations for quality assurance echo sounder points compared

to raster surfaces for West of Hudson reservoirs, New York State. .................................20

12. Accuracy of contour elevations for quality assurance echo sounder points

compared to contours for West of Hudson reservoirs, New York State. ........................20

13. Accuracy of reservoir capacity at spillway elevations for the West of Hudson

reservoirs, New York State. .....................................................................................................21

14. Reservoir area and capacity at specified elevations for Ashokan Reservoir, East

Basin, New York State ...............................................................................................................22

15. Reservoir area and capacity at specified elevations for Ashokan Reservoir, West

Basin, New York State ...............................................................................................................22

16. Reservoir area and capacity at specified elevations for Cannonsville Reservoir,

New York State............................................................................................................................23

17. Reservoir area and capacity at specified elevations for Neversink Reservoir, New

York State .....................................................................................................................................23

18. Reservoir area and capacity at specified elevations for Pepacton Reservoir, New

York State .....................................................................................................................................24

19. Reservoir area and capacity at specified elevations for Rondout Reservoir, New

York State .....................................................................................................................................24

20. Reservoir area and capacity at specified elevations for Schoharie Reservoir, New

York State .....................................................................................................................................25

21. Effect of linear enforcement on calculated capacity at spillway elevations in the

West of Hudson reservoirs in New York State.......................................................................25

22. Summary of change in reservoir capacity since construction in the West of Hudson

reservoirs in New York State ....................................................................................................26
viii

Conversion Factors

U.S. customary units to International System of Units

Multiply By To obtain

Length

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Area

square foot (ft2

) 0.09290 square meter (m2)

square mile (mi2

) 259.0 hectare (ha)

square mile (mi2

) 2.590 square kilometer (km2) 

Volume

gallon (gal) 0.003785 cubic meter (m3

) 

million gallons (Mgal) 3,785 cubic meter (m3

)

billion gallons (Ggal) 3,785,000 cubic meter (m3

)

Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as °F = (1.8 × 

°C) + 32.

Temperature in degrees Fahrenheit (°F) may be converted to degrees Celsius (°C) as °C = (°F – 

32) / 1.8.

Datum

Vertical coordinate information is referenced to the North American Vertical Datum of 1988 

(NAVD 88).

Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD 83).

Elevation, as used in this report, refers to distance above the vertical datum.
ix

Abbreviations

ADCP acoustic Doppler current profiler

BWS Bureau of Water Supply

CORS continuous operating reference station

DEP Department of Environmental Protection (New York City)

FGDC Federal Geographic Data Committee

GIS geographic information system

GNSS global navigation satellite system

GPS global positioning system

lidar light detection and ranging

NAIP National Agriculture Imagery Program

NOAA National Oceanic and Atmospheric Administration

NSSDA National Standard for Spatial Data Accuracy

NYSDOP New York State Digital Orthoimagery Program

QA quality assurance

RMSE root mean square error

RTK–GPS real-time kinematic global positioning system 

TIN triangulated irregular network

USGS U.S. Geological Survey

WOH West of Hudson

Bathymetry of Ashokan, Cannonsville, Neversink, 

Pepacton, Rondout, and Schoharie Reservoirs, 

New York, 2013–15

By Elizabeth A. Nystrom

Abstract

Drinking water for New York City is supplied from 

several large reservoirs, including a system of reservoirs west 

of the Hudson River. To provide updated reservoir capacity tables and bathymetry maps of the City’s six West of 

Hudson reservoirs, bathymetric surveys were conducted by 

the U.S. Geological Survey from 2013 to 2015. Depths were 

surveyed with a single-beam echo sounder and real-time 

kinematic global positioning system along planned transects at 

predetermined intervals for each reservoir. A separate quality assurance dataset of echo sounder points was collected 

along transects at oblique angles to the main transects for 

accuracy assessment. Field-survey data were combined with 

water surface elevations in a geographic information system 

to create three-dimensional surfaces in the form of triangulated irregular networks (TINs) representing the elevations 

of the reservoir geomorphology. The TINs were linearly 

enforced to better represent geomorphic features within the 

reservoirs. The linearly enforced TINs were then used to 

create raster surfaces and 2-foot-interval contour maps of the 

reservoirs. Elevation-area-capacity tables were calculated at 

0.01-foot intervals. The results of the surveys show that the 

total capacity of the West of Hudson reservoirs has decreased 

by 11.5 billion gallons (Ggal), or 2.3 percent, since construction, and the useable capacity (the volume above the minimum 

operating level required to deliver full flow for drinking water 

supply) has decreased by 7.9 Ggal (1.7 percent). The available 

capacity (the volume between the spillway elevation and the 

lowest intake or sill elevation used for drinking water supply) 

decreased by 10.0 Ggal (2.1 percent), and dead storage (the 

volume below the lowest intake or sill elevation) decreased by 

1.5 Ggal (9.0 percent).

Introduction

The New York City Department of Environmental 

Protection (DEP) maintains extensive systems of reservoirs 

and aqueducts for water collection, storage, and transport; it 

supplies about 1 billion gallons (Ggal) of drinking water daily 

to more than 9 million people (New York City Department 

of Environmental Protection, 2016a). The West of Hudson 

(WOH) reservoirs, in the Delaware and Hudson River drainage basins in New York State, includes six reservoirs (fig. 1): 

Ashokan, Cannonsville, Neversink, Pepacton, Rondout, and 

Schoharie, which were constructed from the early 1900s to the 

1960s (table 1) with a combined estimated as-built (original) 

useable storage capacity of more than 460 Ggal (table 2). 

The daily and seasonal management of the WOH reservoirs by DEP depends on accurate bathymetry information 

in several forms, including the mapped bathymetric surfaces, 

elevation-area-capacity tables, and bathymetric contours. The 

surfaces are used in several water-quality models, the elevation-area-capacity tables are used to determine current and 

available reservoir storage, and contours are used in mapping 

applications. The bathymetry of the reservoirs was initially 

determined from topographic maps made before a reservoir 

was completed, the newest of the WOH reservoirs is now 

more than 50 years old, and the oldest is more than 100 years 

old. The most recent systematic bathymetric survey of the 

WOH reservoirs was completed in 1998 with contour intervals 

of 16.4 feet (ft). Since the initial filling of the reservoirs, bed 

morphology has likely changed as a result of sedimentation. 

To provide updated surface, capacity, and contour data, the 

U.S. Geological Survey (USGS), in cooperation with New 

York City DEP, conducted bathymetric surveys of the six 

WOH reservoirs beginning in 2013. These data are available 

as separate data releases (Nystrom, 2018a–f).

Purpose and Scope

The purpose of this report is to document the methods of 

data collection, data-processing techniques, assessment of data 

accuracy, and results of bathymetric surveys of the six WOH 

reservoirs conducted by the USGS and New York City DEP 

between 2013 and 2015. The resulting bathymetric maps are 

not to be used for navigational purposes.
2 Bathymetry of Ashokan, Cannonsville, Neversink, Pepacton, Rondout, and Schoharie Reservoirs, New York, 2013–15

West Delaware Aqueduct

75°30' 75° 74°30' 74°

42°30'

42°

Elevation, in feet above NAVD 88

4,200

0 

EXPLANATION

0 10 20 MILES

0 10 20 KILOMETERS

Base from U.S. Geological Survey digital data

DELAWARE

ULSTER

GREENE

SULLIVAN

OTSEGO SCHOHARIE

ALBANY

BROOME

Pepacton

Ashokan

Cannonsville

Rondout Neversink

Schoharie

West

Basin

East

Basin

Pepacton

Ashokan

Cannonsville

Rondout Neversink

Schoharie

East

Basin West

Basin

NEW YORK

PENNSYLVANIA

Shandaken Tunnel

Esopus Creek

Neversink River

Rondout Creek

East Branch Delaware River

West Branch Delaware River

West Delaware Aqueduct

Catskill Aqueduct

Delaware Aqueduct

Neversink Tunnel

East Delaware Aqueduct

New York City

NEW YORK

CHENANGO

Figure 1. Locations of the West of Hudson reservoirs and connecting aqueducts and tunnels in New York State.

Description of Study Area

The six WOH reservoirs are in Delaware, Greene, 

Schoharie, Sullivan, and Ulster Counties in upstate New 

York (fig. 1). Ashokan Reservoir was the first of the WOH 

reservoirs to be constructed, with storage beginning in 1913 

(U.S. Geological Survey, 2016a), and Cannonsville was the 

last (U.S. Geological Survey 2016b), with storage beginning 

in 1963 (table 1). Pepacton Reservoir has the largest total 

capacity of the six WOH reservoirs at approximately 150 Ggal 

(table 2; U.S. Geological Survey, 2016d) and Schoharie 

has the smallest at approximately 21 Ggal (U.S. Geological 

Survey, 2016f). Cannonsville and Pepacton Reservoirs are the 

longest of the WOH reservoirs, both more than 20 miles long, 

and Schoharie is the shortest, at slightly more than 5 miles 

long (table 3).

The WOH reservoirs are grouped into two systems based 

on the aqueducts that supply New York City. Schoharie and 

Ashokan Reservoirs are part of the Catskill System, and Cannonsville, Neversink, Pepacton, and Rondout Reservoirs are 

part of the Delaware System. In the Catskill System, Schoharie Reservoir was formed by damming Schoharie Creek; water 

from Schoharie Reservoir travels through the Shandaken Tunnel into the Esopus Creek and then into Ashokan Reservoir. 

Ashokan Reservoir was formed by damming Esopus Creek; 

the reservoir has two drainage basins (the West Basin and East 

Basin). Esopus Creek enters the West Basin; water then flows 

from the West Basin over a dividing weir into the East Basin, 

where it travels through the Catskill Aqueduct to Kensico 
Methods 3

Table 1. Information on West of Hudson reservoirs: 

U.S. Geological Survey station identifier, year storage began, 

year in service, and water supply system in New York State.

[Locations of reservoirs shown in figure 1. USGS, U.S. Geological Survey]

Reservoir USGS

station ID

Year 

storage 

began1

Year in 

service2

Water-supply 

system

Ashokan 01363400 1913 1915 Catskill

Cannonsville 01424997 1963 1964 Delaware

Neversink 01435900 1953 1954 Delaware

Pepacton 01416900 1954 1955 Delaware

Rondout 01366400 1951 1954 Delaware

Schoharie 01350100 1926 1926 Catskill

1

Published value from USGS annual summaries

(U.S. Geological Survey, 2016a–f).

2

Published values from New York City Department of Environmental 

Protection (DEP) watershed protection pages (DEP, 2016b–g).

Reservoir just north of New York City. In the Delaware 

System, Cannonsville Reservoir was formed by damming the 

West Branch Delaware River, Pepacton Reservoir was formed 

by damming the East Branch Delaware River, and Neversink 

Reservoir was formed by damming the Neversink River. Water 

from these three reservoirs travels through aqueducts and 

tunnels to Rondout Reservoir, which was formed by damming 

the Rondout Creek. From Rondout, water travels through the 

Delaware Aqueduct to Kensico Reservoir.

Methods

Bathymetric data were collected using a single-beam 

echo sounder from a moving boat, following methods documented in Wilson and Richards (2006). Echo sounder points 

were collected along transects that were spaced at intervals 

determined by the length of the reservoir (table 3). Horizontal 

positions of the surveyed points were determined by using a 

real-time kinematic global positioning system (RTK–GPS), 

and water surface elevations measured by the DEP were used 

as a vertical reference, from which reservoir-bottom elevations 

Table 2. West of Hudson reservoirs as-built capacity values and corresponding elevations of reservoir structures in New York State.

[Locations of reservoirs shown in figure 1. Rows in italics present duplicative information and are not included in calculation of West of Hudson reservoirs 

total. BWS, New York City Department of Environmental Protection Bureau of Water Supply; NAVD 88, North American Vertical Datum of 1988; total capacity is total volume at spillway elevation including dead storage; useable capacity is the volume between the spillway elevation and the minimum operating level 

required to deliver full flow for drinking water supply; available capacity is the volume between the spillway elevation and the lowest intake or sill elevation 

used for drinking water supply; dead storage is the volume below lowest intake height or sill elevation for drinking water supply]

Reservoir

Spillway 

elevation

Minimum 

operating 

level

Intake/sill 

elevation

Spillway 

elevation

Minimum 

operating 

level

Intake/sill 

elevation

As-built

Total 

capacity

Useable 

capacity

Available 

capacity

Dead 

storage1

(feet above BWS datum) (feet above NAVD 88) (billions of gallons)

Ashokan (East Basin) 587.00 520.00 500.00 585.68 518.68 498.68 80.678 75.683 80.678 0.000

Ashokan (West Basin) 590.00 520.00 495.50 588.68 518.68 494.18 49.417 43.199 47.180 2.237

Ashokan (Total) 130.095 118.882 127.858 2.237

Cannonsville 1,150.00 1,040.00 1,035.00 1,149.58 1,039.58 1,034.58 98.618 95.706 96.726 1.892

Neversink 1,440.00 1,319.00 1,314.00 1,439.21 1,318.21 1,313.21 37.146 34.941 35.466 1.680

Pepacton 1,280.00 1,152.00 1,143.00 1,278.81 1,150.81 1,141.81 149.799 140.190 143.701 6.098

Rondout 840.00 723.00 720.00 838.88 721.88 718.88 52.435 49.617 50.048 2.387

Schoharie 

(before spillway reconstruction in 2015)

1,130.00 1,065.15 1,050.00 1,128.90 1,064.05 1,048.90 21.551 17.582 19.583 1.968

Schoharie

(after spillway reconstruction in 2015)

1,129.73 1,065.15 1,050.00 1,128.63 1,064.05 1,048.90 21.454 17.485 19.486 1.968

Total West of Hudson 

reservoirs

489.644 456.918 473.382 16.262

1

Published value from U.S. Geological Survey annual summaries (U.S. Geological Survey, 2016a–f, original source from City of New York Department of 

Water Supply, Gas & Electric values).
4 Bathymetry of Ashokan, Cannonsville, Neversink, Pepacton, Rondout, and Schoharie Reservoirs, New York, 2013–15

Table 3. Transect spacing information used in surveying the 

West of Hudson reservoirs in New York State.

[Locations of reservoirs shown in figure 1]

Reservoir

Approximate 

reservoir 

length 

(miles)

Transect 

spacing 

(feet)

Ratio of transect 

spacing to reservoir length

(percent)

Planned 

total length 

of transects 

(miles)

Ashokan 11.4 410 0.68 188

Cannonsville 21.7 361 0.31 161

Neversink 6.3 262 0.78 60

Pepacton 20.7 459 0.42 134

Rondout 6.3 328 0.98 60

Schoharie 5.2 213 0.78 55

were calculated. Echo sounder data points were supplemented with data from several additional sources including 

RTK–GPS, acoustic Doppler current profiler (ADCP), aerial 

orthophotographs, and light detection and ranging (lidar) in 

select areas to provide improved spatial coverage (table 4). 

Echo sounder data were processed and edited using the hydrographic software HYPACK (HYPACK Inc., 2016). Bathymetric surfaces were mapped and edited in ArcMap (Esri Inc., 

2016) before contours were created and elevation-area capacity was calculated. A second dataset of echo sounder points 

was collected along transects at oblique angles to the main 

transects for assessing the accuracy of the elevations. 

Survey Planning

Echo sounder transects were laid out using HYPACK 

(HYPACK Inc., 2016) to achieve a transect spacing to reservoir length ratio of 1 percent or less, as recommended by 

Wilson and Richards (2006). This ratio was chosen to produce 

data of sufficient density to accurately calculate bathymetric 

surfaces, elevation-area-capacity tables, and contours; resulting transect spacings were 213 to 459 ft (table 3). Planned 

transects were aligned perpendicular to the long axis of the 

reservoir; as most of WOH reservoirs follow the sinuous 

course of old river beds, the direction of the planned transects was altered to follow these bends. Schoharie Reservoir 

transects are shown as an example in figure 2 (main echo 

sounder transects shown as blue lines). Additional transects 

were added across bays to ensure that deep spots resulting 

from the presence of old stream channels were recorded. The 

total length of planned transects at each reservoir (table 3) 

ranged from 55 miles (Schoharie) to 188 miles (Ashokan). For 

quality assurance (QA), a second set of echo sounder transects 

was planned, with a spacing 10 times that of the main transect 

spacing, oriented at a 45-degree angle to the main transects 

(green lines in fig. 2). Collecting data along oblique transects 

allowed comparison of coincident depth measurements where 

the main transects and the QA transects intersected. 

Data Collection

Data collection began in September 2013, at the West 

Basin of Ashokan Reservoir, and continued through July 2015, 

at Pepacton Reservoir (table 4). Most reservoirs were nearly 

full (the water surface elevation was within a few feet of the 

spillway elevation) when surveyed (table 4); the water surface 

elevation during data collection was lowest in relation to the 

spillway elevation at Schoharie Reservoir (the water surface 

elevation was about 15–18 ft below the spillway elevation 

when surveyed.) 

Horizontal and Vertical Control

 The DEP Western Operations Surveying staff established 

horizontal and vertical control networks throughout the WOH 

system. Equipment utilized included Leica Viva GS 15 Smart 

Antennas paired with Leica Viva CS 15 Field Controllers; data 

were post-processed with Leica Geo Office version 7.01. Control points were established based upon the North American 

Datum of 1983 (NAD 83) Geoid 09 (horizontal) and North 

American Vertical Datum of 1988 (NAVD 88) (vertical).

Horizontal control was established by redundant (two) 

static observations with observation times of 2 hours. Continuous Operating Reference Stations (CORS) were utilized 

as primary control points; stations used were Binghamton, 

Hancock, Oneonta, Kingston, Hudson, Middletown, and Newburgh. Observations were collected between July 2012 and 

September 2014. 

Vertical control was established at or near each spillway, 

except at Schoharie Reservoir, by static global positioning system (GPS) observations. Additional observations of 

first-floor elevations of intake and effluent chambers were 

conducted at the Rondout and Schoharie Reservoirs. Occupation times varied by location based upon distance to the 1st 

or 2nd order USGS benchmarks that were used for elevation 

of the control points. Established elevations were compared 

to elevations determined by the horizontal control networks 

based upon the CORS stations. Results indicated a 2-centimeter confidence level.

Measurements of water surface elevations at each reservoir were referenced to the DEP Bureau of Water Supply 

(BWS) datum for each reservoir. Each datum was established 

during reservoir construction and, due to practical survey 

limitations at the time of establishment, does not correspond 

directly to any national vertical datum (for example NAVD 

88), and the offset to national datum varies slightly at each 

reservoir (Terry Ringler, New York City Department of Environmental Protection, oral commun., 2013). Vertical conversion factors between BWS datum and NAVD 88 were calculated for each reservoir based on the vertical control spillway 

observations (table 5).
Methods 

5

Table 4. Data collection dates by type and water surface elevations during surveys of West of Hudson reservoirs in New York State.[Locations of reservoirs shown in figure 1. GPS, global positioning system; RTK, real-time kinematic; NAVD 88, North American Vertical Datum of 1988, NAIP, National Agriculture Imagery Program; NYSDOP, New York Statewide Digital Orthoimagery Program; --, not used]

Reservoir

Echo sounder and latency correction method Manual 

RTK-GPS 

survey 

points

Acoustic Doppler current 

profiler points Aerial orthophotograph shoreline points Wide beam transducer and fixed offset latency Narrow beam transducer and GPS synchronization

Date

Average water

surface elevation

(feet above NAVD 88)

Date

Average water

surface elevation

(feet above NAVD 88)

Date Date

Average water

surface elevation

(feet above NAVD 88)

Date Source

Average water 

surface elevation

(feet above NAVD 88)

Ashokan

(East Basin)

-- -- 5/14/2014 585.94 -- -- -- 10/12/2008 NAIP1 572.8

5/15/2014 585.85 8/20/2013 NAIP1 581.45/20/2014 586.40 9/24/2013 NAIP1 581.45/27/2014 585.915/28/2014 585.88

Ashokan

(West Basin)

9/9/2013 584.47 5/28/2014 588.80 9/26/2013 -- -- 10/12/2008 NAIP1 569.89/10/2013 584.19 4/1/2009 NYSDOP2 582.59/11/2013 584.079/12/2013 583.989/23/2013 582.559/24/2013 582.379/25/2013 582.199/26/2013 582.04

Cannonsville -- -- 5/4/2015 1,149.34 -- 6/2/2015 1,145.78 5/28/2008 NAIP1 1,129.80

5/5/2015 1,149.17 9/1/2008 NAIP1 1,128.805/6/2015 1,148.995/12/2015 1,148.205/13/2015 1,148.055/14/2015 1,147.905/15/2015 1,147.725/18/2015 1,147.305/19/2015 1,147.20

Neversink -- -- 7/1/2014 1,438.42 -- -- -- 8/12/2006 NAIP1 1,424.60

7/9/2014 1,437.427/10/2014 1,437.447/11/2014 1,437.50
6 Bathymetry of Ashokan, Cannonsville, Neversink, Pepacton, Rondout, and Schoharie Reservoirs, New York, 2013–15 Table 4. Data collection dates by type and water surface elevations during surveys of West of Hudson reservoirs in New York State.—Continued [Locations of reservoirs shown in figure 1. GPS, global positioning system; RTK, real-time kinematic; NAVD 88, North American Vertical Datum of 1988, NAIP, National Agriculture Imagery Program; NYSDOP, New York Statewide Digital Orthoimagery Program; --, not used] Reservoir Echo sounder and latency correction method Manual RTK-GPS survey points Acoustic Doppler current profiler points Aerial orthophotograph shoreline points Wide beam transducer and fixed offset latency Narrow beam transducer and GPS synchronization Date Average water surface elevation (feet above NAVD 88) Date Average water surface elevation (feet above NAVD 88) Date Date Average water surface elevation (feet above NAVD 88) Date Source Average water surface elevation (feet above NAVD 88) Pepacton -- -- 7/6/2015 1,278.59 -- -- -- -- -- -- 7/7/2015 1,278.44 7/8/2015 1,278.28 7/9/2015 1,278.09 7/10/2015 1,278.05 7/13/2015 1,277.33 7/14/2015 1,277.05 7/15/2015 1,276.93 7/16/2015 1,276.83 Rondout 11/6/2013 835.32 4/28/2014 835.15 -- -- -- 4/1/2009 NYSDOP2 836.3 11/7/2013 835.25 4/29/2014 835.30 11/14/2013 835.03 5/12/2014 835.20 11/15/2013 834.95 5/13/2014 835.38 Schoharie -- -- 9/2/2014 1,113.24 9/30/2014 10/2/2014 -- 8/5/2013 NAIP1 1,115.90 9/3/2014 1,112.99 10/2/2014 9/4/2014 1,112.81 9/5/2014 1,112.59 9/12/2014 1,110.84

1U.S. Department of Agriculture (2016).2New York State (2016a).
Methods 7

74°27' 74°26'

42°23'

42°22'

42°21'

EXPLANATION

Main transects

Quality assurance transects

0 0.5 1 MILES

0 0.5 1 KILOMETERS

Figure 2. Example of the planned main transects and 

quality assurance transects, Schoharie Reservoir in New 

York State. Location of reservoir shown in figure 1.

Table 5. Spillway elevations and conversion factors for the 

surveyed West of Hudson reservoirs in New York State. 

[Locations of reservoirs shown in figure 1. NAVD 88, North American 

Vertical Datum of 1988; BWS, New York City Department of Environmental 

Protection Bureau of Water Supply]

Reservoir

Spillway 

elevation

(feet above 

NAVD 88)

Spillway 

elevation 

(feet above 

BWS datum)

Datum 

conversion 

factor

(feet)

Ashokan 

(East Basin)

585.68 587.00 1.32

Ashokan 

(West Basin)

588.68 590.00 1.32

Cannonsville 1,149.58 1,150.00 0.42

Neversink 1,439.21 1,440.00 0.79

Pepacton 1,278.81 1,280.00 1.19

Rondout 838.88 840.00 1.12

Schoharie

(before spillway reconstruction in 2015)

1,128.90 1,130.00 1.10

Schoharie

(after spillway reconstruction in 2015)

1,128.63 1,129.73 1.10

Horizontal Position Data

Horizontal position data were collected using RTK–GPS 

with two Trimble R8 global navigation satellite system 

(GNSS) receivers and a radio communication link (Trimble, 

2016). The base GNSS receiver occupied horizontal control 

points established and surveyed by DEP using static GPS 

observations (fig. 3 and table 6). Due to local topography, control point location, reservoir characteristics, and radio range, 

as few as one control point was required for some reservoirs 

(Ashokan and Schoharie) and as many as four control points 

were required for other reservoirs (Cannonsville). The rover 

GNSS receiver was mounted on the boat directly above the 

echo sounder transducer (fig. 4).

Water Surface Elevations and Vertical-Position 

Data

Vertical-position data were determined from water surface elevations supplied by DEP, measured at 5- to 15-minute 

intervals, typically at reservoir intake structures, using floattape gages with shaft encoders, recorded digitally to the nearest hundredth of a foot. A 2-hour moving-average window was 

applied to the instantaneous observed values to smooth the 

effects of noise and waves in the final processing of the hydrographic data (example observations at Pepacton Reservoir 

shown in fig. 5). Water surface elevations typically decreased 
8 Bathymetry of Ashokan, Cannonsville, Neversink, Pepacton, Rondout, and Schoharie Reservoirs, New York, 2013–15

Figure 3. Base station and radio antenna at control point near 

Schoharie Reservoir, New York State. 

slightly over the course of data collection, usually at a rate not 

greater than 1 ft over the course of a week of data collection. 

Water surface elevations as supplied were referenced to DEP 

BWS datum. To standardize the dataset and because additional 

spatial data referenced to NAVD 88 were used, all observed 

water surface elevations were converted to NAVD 88 using 

the constant conversion factor for each reservoir.

Echo Sounder Data Collection

Depth data were collected with a Syqwest Bathy-500 MF, 

a survey-grade echo sounder with a resolution of 0.1 ft and 

a manufacturer-specified accuracy of 0.1 ft plus 0.1 percent 

of the depth (Syqwest, Inc., 2008). Data collected in 2013 

used a 200-kilohertz (kHz) wide-beam transducer (8 degrees 

wide, measured at 3 decibels [dB]); in 2014 and 2015, data 

were collected with a 200-kHz narrow-beam transducer 

(3 degrees at 3 dB). The narrow-beam transducer was acquired 

to improve measurements made in the extremely steep areas 

within the WOH reservoirs. The minimum measurable depth 

varied depending on echo sounder settings but was typically 

approximately 3 ft. The echo sounder transducer was installed 

on the boat in a manner that allowed it to be adjusted using 

bubble levels to account for the trim of the boat; this correction was not dynamic, but rather the transducer was adjusted 

to be vertical at typical boat operation speeds (around 5 knots). 

Transducer draft was typically 0.7 ft and was measured using 

marked tape applied to the echo sounder transducer mount.

Table 6. Control points used in the surveys of the West of Hudson reservoirs in New York State. 

[Locations of reservoirs shown in figure 1. NAVD 88, North American Vertical Datum of 1988; UTM18N, Universal Transverse Mercator Zone 18 north]

Point Reservoir

Elevation

(feet above 

NAVD 88)

Latitude Longitude

Northing, 

UTM18N

(meters)

Easting, 

UTM18N

(meters)

Ashokan A1 Ashokan 608.442 41.948879 -74.207635 4644403.906 565674.511

BEERS Cannonsville 1160.608 42.084070 -75.201857 4659130.235 483304.739

CHAMB Cannonsville 1178.949 42.117752 -75.276912 4662887.302 477109.085

DRYBK Cannonsville 1169.004 42.131994 -75.299097 4664475.169 475280.736

TURNER Cannonsville 1237.191 42.070400 -75.364244 4657655.694 469867.390

NeversinkHARN Neversink 1492.500 41.825295 -74.637255 4630442.860 530123.737

Neversink2 Neversink 1437.310 41.873361 -74.650864 4635774.670 528971.895

ARENA Pepacton 1315.399 42.109523 -74.741883 4661968.766 521339.923

EDIC Pepacton 1325.375 42.074256 -74.901567 4658025.497 508142.529

POND Pepacton 1805.666 42.095323 -74.816583 4660376.188 515167.460

RC1 Rondout 858.570 41.799529 -74.430826 4627675.105 547285.398

RC4 Rondout 842.950 41.846000 -74.514803 4632791.805 540279.653

STIC Schoharie 1140.490 42.356059 -74.443907 4689460.012 545796.700
Methods 9

Figure 4. Survey boat and 

global navigation satellite 

system (GNSS) rover receiver 

used for the study of the West 

of Hudson reservoirs in

New York State.

GNSS rover receiver

Sound Speed

Echo sounders determine depth by transmitting a pulse 

of sound into the water and measuring the amount of time it 

takes for an echo to return. In order to calculate the depth, 

the speed of sound must be known. Sound speed varies with 

temperature, pressure, and salinity; because reservoirs are 

often stratified by temperature, the speed of sound typically 

varies with depth. The sound speed of the echo-sounder 

control box was set to a value that was representative of the 

middle to upper layers of the reservoir, and profiles of sound 

speed over depth were measured for use in post-processing 

1,276.8

1,277.0

1,277.2

1,277.4

July 13 July 14 July 15 July 16 July 17

Water surface elevation, in feet above NAVD 88

EXPLANATION

Observed

2-hour moving-average

Water surface elevation

Figure 5. Example of observed 5-minute interval and 2-hour 

moving-average water surface elevation, Pepacton Reservoir, 

New York State, July 2015.

using the hydrographic software. Sound speed profiles were 

measured using an Applied Microsystems Smart SV Sensor 

(AML Oceanographic, 2010) at least once per day, and more 

often when data were collected in different areas during the 

same day (for example, shallow inlet bays and deep areas near 

dams). Sound speed was recorded at 5-ft increments over the 

depth at the location of measurement; below the thermocline 

in deep water, where the sound speed was stable, the measurement interval was sometimes increased to 10 ft. The maximum 

depth for which a sound speed was measured was 155 ft at 

Neversink Reservoir. Water temperature at the reservoir surface was also noted two to three times per day as a QA check.

Depth-Measurement Checks

Echo sounder depth measurements were regularly 

checked by performing bar checks, a process in which a bar or 

plate is suspended at a known depth below the echo sounder, 

and the depth measured from the echo return off the bar is then 

compared to the known depth of the bar. A 3-ft by 4-ft perforated aluminum plate (fig. 6) was lowered into the reservoir 

below the echo sounder to specified depths, typically at 5-ft 

intervals, to verify live echo sounder readings. Live readings 

were typically within 0.2 ft of expected values. Variation from 

expected values can be caused by variable draft, drift of the 

boat relative to the bar as a result of wind, wave action, variation of the speed of sound with depth, or a combination of 

effects. Bar checks were performed three times a day (before 

data collection, at noon, and after data collection) when conditions permitted. The bar check conducted before data collection commenced was used to help set the echo sounder control 

box for the day, but subsequent bar checks were used as verification only. Windy conditions made conducting bar checks of 

deeper depths impractical on a fairly regular basis, especially 

at depths greater than 20 ft, as even slight winds would cause 
10 Bathymetry of Ashokan, Cannonsville, Neversink, Pepacton, Rondout, and Schoharie Reservoirs, New York, 2013–15

Figure 6. Bar check plate used 

during surveys of the West of Hudson 

reservoirs in New York State. 

the boat to drift so that the echo sounder transducer was no 

longer directly above the bar check plate. Bar checks were 

typically carried as deep as it was possible to get a readable 

return in the available depth; they typically went to 30 to 40 ft. 

The maximum depth of a bar check was 70 ft at Cannonsville, 

Neversink, and Rondout Reservoirs. 

Data Integration (HYPACK)

Live echo sounder readings and RTK–GPS position data 

were integrated in the field using HYPACK. Latency tests 

showed that the echo sounder depth measurement for a point 

was received 1.8 seconds before the RTK–GPS position measurement; without correction, this latency would result in an 

inaccurate position being applied to each depth measurement. 

Data collected in 2013 were corrected for this latency using 

a single, constant time offset. Beginning in 2014, data were 

corrected for the latency by using the ZDA synchronization 

function in HYPACK, which synchronized the computer clock 

with the RTK–GPS clock as data were collected.

Additional Sources of Depth and Elevation Data

Four additional types of depth or elevation data were 

used in conjunction with the echo sounder depth measurements: manual RTK–GPS point measurements, acoustic 

Doppler current profiler (ADCP) point measurements, edge of 

water points digitized from aerial orthophotographs, and lidar 

points (table 4). Elevations were measured using the RTK–

GPS rover on a 6.65 or 7.38 ft pole at selected points in the 

West Basin of Ashokan Reservoir, which were above the water 

surface during the 2013 survey but were below the water surface at the time of 2009 lidar data collection, and in areas shallow enough for wading near the inlet of Schoharie Reservoir 

along the channel of Schoharie Creek. The average vertical 

precision for the manual RTK–GPS points measured at Ashokan Reservoir was 0.31 ft. Depths were measured with the 

0.5-megahertz vertical beam of a Sontek RiverSurveyor M9 

ADCP (Sontek, 2016) deployed from a remote control boat in 

small bays at Cannonsville Reservoir that were inaccessible 

by manned boat and in the areas too deep to wade in the inlet 

of Schoharie Creek. Position data for the ADCP depths were 

obtained using a separate RTK–GPS system supplied by the 

ADCP manufacturer (Sontek, 2016), and vertical control was 

established using water surface elevations provided by the 

DEP. The minimum depth measureable with an M9 is 0.66 ft, 

with a resolution of 0.003 ft and a manufacturer-stated accuracy of 1 percent. Shoreline points were digitized along the 

edge of water in aerial orthophotographs to help fill in shallow 

areas inaccessible by boat. The aerial orthophotographs used 

were collected from 2006 to 2013 (table 4) by the National 

Agriculture Imagery Program (NAIP, U.S. Department of 

Agriculture, 2016) and New York State Digital Orthoimagery 

Program (NYSDOP, New York State, 2016a); an elevation was 

assigned to water edge points based on the average water level 

on the date the aerial photo was taken. Lidar data were used 

to supplement collected data in areas above the water surface 

elevation at the time of the surveys and to allow calculation 

of capacity above spillway elevations. The lidar data were 

collected from March through June 2009, by Sanborn Map 

Company, Inc., on behalf of DEP (New York City Department of Environmental Protection, 2009). The lidar data were 

downloaded in tiled form from New York Orthos Online 
Methods 11

(New York State, 2016b) and converted from a 6.56-ft raster 

grid to points. The stated vertical accuracy of the lidar dataset 

is 0.305 ft (Terry Spies, New York City Department of Environmental Protection, oral commun., 2016).

Data Processing

Data processing included editing of echo sounder depth 

data, assembly of data into a geographic information system 

(GIS) database, bathymetric map editing, creation of contours, 

and generation of elevation-area-capacity tables.

Echo Sounder Data Processing

Echo sounder data were processed in HYPACK before 

output for use in a GIS. Processing in HYPACK included 

application of sound-speed corrections, application of water 

surface elevation data for calculation of point elevations from 

measured depths, and screening for errors and spikes in the 

data. 

All of the reservoirs except Rondout were moderately to 

strongly stratified at the time of field surveys, with the largest 

range in sound speed observed at Pepacton Reservoir (table 7). 

Stratification was stable at Neversink, Pepacton, and Schoharie Reservoirs but varied with time at Ashokan, Cannonsville, 

and Rondout Reservoirs (fig. 7). Corrections for sound-speed 

variation over depth were applied to all reservoirs except 

Rondout, where substantial stratification was not present, and 

measured speed of sound was never more than 0.6 percent 

different from the value used by the echo sounder. Observed 

sound-speed profiles (dots in fig. 7) were grouped by date 

and averaged into representative profiles (solid lines in fig. 7) 

for application to observed depths. The median correction 

to observed depths ranged from 0.04 ft in the West Basin of 

Ashokan to 0.38 ft in Pepacton; the maximum speed of sound 

correction was almost 4 ft (Pepacton Reservoir; table 7). 

Measured depths were converted to elevations in 

HYPACK by subtracting the depth, corrected for the speed of 

sound, from processed water surface elevations. After conversion to elevation, each transect was screened for spikes and 

measurement errors. Spikes and errors can occur in the echo 

sounder data in the digitization process (the process by which 

the echo sounder determines a depth value from the analog 

echo signal received by the transducer). For example, a strong 

return from objects in the water column such as debris, fish, or 

vegetation can be digitized as the measured depth, or the second acoustic return can be digitized instead of the first. In shallow water, sound can be reflected off the water surface as well 

as the reservoir bottom; the second return would travel from 

echo sounder to reservoir bottom, to water surface, to reservoir 

bottom, and back to the echo sounder before being digitized; 

the recorded value is then approximately twice as deep as the 

actual value. An example of an edited echo sounder transect 

is shown in figure 8, with red points marking the removed 

spikes. After processing and editing, position and elevation 

data were exported from HYPACK to a comma-delimited text 

file for import to a GIS. From 184,000 to 550,000 main echo 

sounder points per reservoir were used (table 8).

Geographic Information System Database 

Creation and Linear Enforcement Editing 

The edited bathymetry points were combined in a GIS 

with ADCP point measurements, the manual RTK–GPS point 

measurements, points digitized from aerial orthophotographs 

(table 8), and lidar points for creation of a triangulated irregular network (TIN). All data were projected into a common 

horizontal datum (NAD 83) and vertical datum (NAVD 88). 

The TINs were created by connecting each point with its two 

nearest neighbors; for single-beam echo sounder data collected in transects, this creates a three-dimensional array of 

thin triangles. Because the nearest neighbors are connected 

Table 7. Sound-speed corrections by depth applied to the West of Hudson reservoirs surveyed in New York State. 

[Locations of reservoirs shown in figure 1. --, not used]

Reservoir

Average difference between Sound-speed correction

shallowest and deepest 

measured sound speed

(percent)

deepest measured sound speed 

and echo sounder value

(percent)

Applied Median

(feet)

Maximum

(feet)

Standard 

deviation

(feet)

Ashokan (East Basin) 1.7 0.7 Yes 0.13 0.78 0.14

Ashokan (West Basin) 1.3 1.0 Yes 0.04 3.40 0.42

Cannonsville 3.2 1.5 Yes 0.17 2.06 0.22

Neversink 3.5 1.2 Yes 0.25 2.19 0.42

Pepacton 4.2 2.0 Yes 0.38 3.93 0.73

Rondout 0.6 0.2 No -- -- --

Schoharie 2.2 1.4 Yes 0.05 1.72 0.28
12 Bathymetry of Ashokan, Cannonsville, Neversink, Pepacton, Rondout, and Schoharie Reservoirs, New York, 2013–15

Ashokan Cannonsville Neversink

Pepacton Rondout Schoharie

EXPLANATION

Sept. 9 to 12, 2013

Sept. 23 to 26, 2013

Nov. 6 to 7, 2013

Nov. 14 to 15, 2013

May 14 to 20, 2014

May 27 to 28, 2014

June 7 to 11, 2014

Sept. 2 to 12, 2014

May 4 to 6, 2015

May 18 to 19, 2015

July 6 to 16, 2015

April 28, 2014

May 12 to 13, 2014

May 12, 2015

May 13, 2015

May 14 to 15, 2015

Sound speed, in feet per second

Depth, in feet

0

0

50

100

150

50

100

150

4,700 4,750 4,800 4,850 4,900 4,700 4,750 4,800 4,850 4,900 4,700 4,750 4,800 4,850 4,900

Figure 7. Sound-speed profiles, measured points, and processing averages (lines) for each West of Hudson reservoir surveyed 

in New York State. Dots represent individual observations; lines represent averaged profiles. Profiles are color coded by date with 

oranges being the earliest measurements and purples and pinks being the latest measurements. Ashokan East Basin (green) and 

Ashokan West Basin (orange) Reservoirs are shown combined. Averaged profiles from Rondout Reservoir were not applied to data 

during processing. Locations of reservoirs shown in figure 1.

in the GIS without reference to linear geomorphic features, 

often the TIN surface does not accurately reflect features such 

as channels and steep slopes (fig. 9). These linear features 

were enforced by manually adding breaklines to the raw TIN 

surfaces, creating edited TIN surfaces (fig. 10). The breaklines were hand drawn along features observed in the survey 

data—for example, to connect the deepest observations in old 

channels and to connect points along lines running parallel 

to the reservoir shore or along slopes. Most breaklines were 

added based solely on observations in the surveyed data. 

Topographic maps created before reservoir construction were 

also used to draw breaklines in some locations. In areas that 

had highly nonlinear features, breaklines were added and the 

resulting points were adjusted horizontally to produce smooth 

transitions in the edited TIN surface, or points were added 

directly to the TIN surface at interpolated elevations to allow 

formation of triangles that better conformed to a realistic 

bathymetric surface. Points were also added to the edited TIN 

along spillways to allow mapped contours at spillway elevations (depth of zero ft) to close. 
Accuracy Assessment 13

725

750

775

800

Elevation, in feet

Point removed in editing

Point kept

EXPLANATION

Figure 8. Profile of an echo sounder point screening and 

editing example from Rondout Reservoir, New York State.

Table 8. Number of data points used per West of Hudson 

reservoir in New York State after data editing, classified by data 

source.

[Locations of reservoirs shown in figure 1. ADCP, acoustic Doppler current 

profiler; RTK-GPS, real-time kinematic global positioning system; --, not 

used]

Reservoir

Echo sounder

ADCP 

points

Manual 

RTK-GPS 

survey 

points

Aerial 

orthophotograph edge 

of water 

points

Main 

points

Quality 

assurance 

points

Ashokan 

(East Basin)

490,764 57,641 -- -- 6,404

Ashokan 

(West Basin)

258,911 36,153 -- 41 7,699

Cannonsville 550,270 76,522 3,787 -- 813

Neversink 198,062 28,246 -- -- 1,469

Pepacton 464,231 69,479 -- --

Rondout 296,375 23,673 -- -- 202

Schoharie 183,560 26,450 4,127 295 307

Contour Creation and Elevation-Area-Capacity 

Table Computations

Bathymetic contours were created at 2-ft intervals to 

match existing above-water contours (which were calculated 

by DEP from 2009 lidar data). The TIN surface for each 

reservoir was converted to a 6.56-ft cell-size raster using 

the TIN-to-Raster natural neighbor interpolation tool in the 

ArcGIS (Esri, Inc., 2016). The raster was then smoothed using 

a low-pass filter, and contours were created at 2-ft elevation 

increments that correspond to even-foot depth-below-spillway 

increments; an example low-pass filtered raster and contours 

are shown in figure 11. 

Elevation-area-capacity tables were calculated at 

0.1-meter intervals using the 3-dimensional analyst surfacevolume tool in ArcMap (Esri Inc., 2016) and were expanded 

using linear interpolation to 0.01-ft increments. Tabular 

values of surface area and volume are presented for NAVD 88 

elevations, BWS reservoir datum elevations, and depth below 

spillway (see tables in the “Results of Surveys” section).

Accuracy Assessment

The accuracy of the bathymetric data was evaluated using 

a QA dataset collected along transects oriented at oblique 

angles to the main echo sounder transects, as described by 

Wilson and Richards (2006). About 23,000 to 76,000 QA 

points were collected at each reservoir (table 8). The points 

from the QA dataset were spatially intersected with the main 

echo sounder data points, the TIN and raster surfaces, and the 

mapped contours. The elevations from the QA points were 

then compared with the matching elevations from the points, 

surfaces, and contours for each reservoir (fig. 12). 

The National Standard for Spatial Data Accuracy 

(NSSDA), published by the Federal Geographic Data Committee (FGDC; 1998), defines a standard for assessing map 

accuracy based on the root mean square error (RMSE) of the 

data, calculated with the following equations:

RMSE

Z Z

n z

i

n

data check i i

= ( ) − ∑ =1

2

(1)

where RMSE

is the vertical coordinate of the 

ith check point in the dataset,

is the number of points being 

checked. 

Assuming the errors are normally distributed, the vertical 

accuracy of the map product can be calculated at the 95-percent accuracy level based on the RMSE:

where 

(2)

n

z is the vertical root mean square 

error,

is the vertical coordinate of 

the ith check point in the QA 

dataset,

Zdatai

Zchecki

i is an integer from 1 to n, and

A R z z = 1 960 . * MSE

Az is the fundamental vertical 

accuracy calculated at the 

95-percent confidence level.
14 Bathymetry of Ashokan, Cannonsville, Neversink, Pepacton, Rondout, and Schoharie Reservoirs, New York, 2013–15

74°14'50" 74°14'40" 74°14'30" 74°14'20" 74°14'10" 74°14'0"

41°57'30"

41°57'20"

41°57'10"

0 0.1 0.2 MILES

0 0.1 0.2 KILOMETERS

EXPLANATION

656

414

Elevation, in feet

Figure 9. An example of a 

raw triangulated irregular 

network in the West Basin 

of Ashokan Reservoir in 

New York State. Location of 

reservoir is shown in figure 1.

74°14'50" 74°14'40" 74°14'30" 74°14'20" 74°14'10" 74°14'0"

41°57'30"

41°57'20"

41°57'10"

0 0.1 0.2 MILES

0 0.1 0.2 KILOMETERS

EXPLANATION

656

414

Elevation, in feet

Breakline

Figure 10. An example of 

breakline additions and edited 

triangulated irregular network 

in the West Basin of Ashokan 

Reservoir in New York State.

Location of reservoir is shown 

in figure 1.
Accuracy Assessment 15

74°14'50" 74°14'40" 74°14'30" 74°14'20" 74°14'10" 74°14'0"

41°57'30"

41°57'20"

41°57'10"

0 0.1 0.2 MILES

0 0.1 0.2 KILOMETERS

EXPLANATION

656

414

Elevation, in feet

Contour line, 2-foot

interval 

Figure 11. Example low-pass 

filtered raster and contours 

in the West Basin of Ashokan 

Reservoir in New York State. 

Location of reservoir is shown 

in figure 1.

Main echosounder points Raw TIN surface Edited TIN surface Contours 1,448 840 2,402 1,159 1,835 851 1,298 57,640 36,153 76,522 28,246 69,479 23,673 26,450 57,640 36,153 76,522 28,246 69,479 23,673 26,450 8,866 5,804 21,168 9,221 22,337

5,9395,935

Error, in feet

0.1

10.0

23,673

EXPLANATION

Number of values

Interquartile

range

90th percentile

50th percentile

(median)

25th percentile

75th percentile

10th percentile

Ashokan (East Basin)

Ashokan (West Basin)

Cannonsville

Neversink

Pepacton

Rondout

Schoharie

Reservoir 

Figure 12. Accuracy assessment of survey data—elevation error calculated by comparing quality assurance points to 

main echo sounder points, triangulated irregular network (TIN) surfaces, and contours by reservoir in New York State.
16 Bathymetry of Ashokan, Cannonsville, Neversink, Pepacton, Rondout, and Schoharie Reservoirs, New York, 2013–15

Because it is not possible to separate the effects of many 

different factors on each measured point in the dataset, this 

accuracy assessment includes the cumulative effects of many 

potential sources of errors or inaccuracies, including those 

associated with the measurements of depth, horizontal position, and water surface elevation, as well as those arising from 

the motion of the boat, including pitch, roll, or heave. 

As might be expected, the accuracy of the measured 

points was higher than that of the TIN surfaces and contours 

(fig. 12). The linear-enforcement editing process provided a 

moderate improvement in the accuracy of the bathymetric 

surfaces (fig. 12). The accuracy of the mapped surfaces (and 

therefore also the resulting contours) was highest close to the 

measured echo sounder points (median error of about 0.2 ft) 

and lowest between transects farthest from the measured echo 

sounder points (median error of about 1 ft; fig. 13).

Because the capacity tables represent a spatial average of 

the depth measurements, the accuracy of the capacity tables 

can be assessed by calculating confidence intervals around the 

mean of the depth measurement error of the TIN surfaces from 

which capacity values were calculated, as in Helsel and Hirsch 

(2002). A symmetric confidence interval around the mean 

error can be calculated by

x t s n x t s n n n − ≤ ≤ + ( ) α α − ( ) − μ / , / , / / 2 1

2

2 1

2 i i (3)

where x is the sample mean error,

t is the Student’s t value,

α is (1 – confidence interval),

n is the number of observations,

s2 is the sample variance, and

μ is the population mean error.

In this case, a 95-percent confidence interval was calculated, 

and equation 3 becomes 

x s − ≤ 1 96 1 n x ≤ + 96 s n 2 2 . / i i μ . / (4)

Survey Data Accuracy—Echo Sounder Points

The QA points were spatially joined to the nearest main 

echo sounder point occurring within a 3-ft radius, resulting 

in 840 to 2,402 paired points per reservoir and 9,833 points 

total (table 9). The elevation of the main point was subtracted 937 2,746 7,720 13,147 16,200 11,485 9,079 16,856 1,107

Main echosounder points Raw TIN surface Edited TIN surface Contours 2,521 7,310 2,521 7,310 22,960 41,172 58,576 48,899 41,839 88,778 6,107 2,521 7,310 22,960 41,172 58,576 48,899 41,839 88,778 6,107

0.1

1.0

10.0

Error, in feet

23,673

EXPLANATION

Number of values

Interquartile

range

90th percentile

50th percentile

(median)

25th percentile

75th percentile

10th percentile

Distance from main echosounder

point, in feet

0 to 1

1 to 3

3 to 10

10 to 25

25 to 50

50 to 75

75 to 100

100 to 200

200 to 300

Figure 13. Accuracy assessment of survey data—elevation error calculated by comparing quality assurance points 

to main echo sounder points, triangulated irregular network (TIN) surfaces, and contours, by distance from main echo 

sounder point in the West of Hudson reservoirs in New York State.
Accuracy Assessment 17

Table 9. Accuracy of point elevations for quality assurance 

echo sounder points compared to main echo sounder points for 

the West of Hudson reservoirs, New York State. 

[Locations of reservoirs shown in figure 1. n, number of points—each quality assurance point was compared to the nearest main point within 3 feet; 

RMSEz, vertical root mean square error; accuracyz, National Standard 

for Spatial Data Accuracy fundamental vertical accuracy calculated at the 

95-percent confidence level; WOH, West of Hudson]

Reservoir n

Median 

signed 

error

(feet)

Median 

absolute 

error

(feet)

RSMEz

(feet)

Accuracyz

,

95-percent 

confidence 

level

(feet)

Ashokan 

(East Basin)

1,448 -0.06 0.19 0.79 1.55

Ashokan 

(West Basin)

840 -0.05 0.25 0.75 1.48

Cannonsville 2,402 -0.02 0.22 1.29 2.53

Neversink 1,159 -0.07 0.31 0.78 1.53

Pepacton 1,835 0.07 0.32 0.94 1.84

Rondout 851 -0.01 0.27 0.74 1.44

Schoharie 1,298 -0.02 0.20 1.55 3.04

All WOH 

reservoirs

9,833 -0.02 0.24 1.07 2.10

from the elevation of the QA point, and descriptive statistics 

were calculated on the signed error and the absolute value of 

the error. A map of the point-to-point comparison errors for 

Schoharie Reservoir is shown as an example in figure 14; the 

largest errors tend to occur near steep features in the reservoir. 

The median signed error between QA point elevation and 

main point elevation (which addresses potential bias between 

datasets) ranged from 0.07 ft at Pepacton Reservoir to -0.07 ft 

at Neversink Reservoir and was -0.02 ft overall. The median 

absolute error (which assesses reproducibility of the data or an 

average vertical distance between the main points and the QA 

points) was 0.24 ft overall and ranged from 0.19 ft at the East 

Basin of Ashokan Reservoir to 0.32 ft at Pepacton Reservoir 

(table 9). The NSSDA accuracy of the point measurements at 

95-percent confidence level was 2.10 ft for all points combined and ranged from 1.44 ft at Rondout Reservoir to 3.04 ft 

at Schoharie Reservoir (table 9).

Survey Product Accuracy—Bathymetric 

Surfaces, Contours, and Capacity Tables

The QA points were spatially joined to the raw and edited 

TINS, the elevations were compared, and descriptive statistics 

were calculated (table 10; a map of the point-to-TIN comparison errors for Schoharie Reservoir is shown as an example in 

42°21'

42°22'

42°23'

-74°27' -74°26'

0 0.25 0.5 MILES

0 0.25 0.5 KILOMETERS

≤0.1

>0.1 to 0.2

>0.2 to 0.5

>0.5 to 1

>1 to 2

>2 to 5

>5 to 10

>10 to 15

>15 to 20

>20 to 40

EXPLANATION

Error, in feet

Figure 14. Quality assurance echo sounder points 

compared to main echo sounder points, Schoharie 

Reservoir, New York State. Location of reservoir is shown 

in figure 1.
18 Bathymetry of Ashokan, Cannonsville, Neversink, Pepacton, Rondout, and Schoharie Reservoirs, New York, 2013–15

Table 10. Accuracy of triangulated irregular network (TIN) elevations for quality assurance echo sounder points compared to edited 

and raw TIN surfaces for the West of Hudson reservoirs, New York State. 

[Locations of reservoirs shown in figure 1. n, number of points—each quality assurance point was compared to the corresponding elevation of the edited and 

raw TINs; TIN, triangulated irregular network; RMSEz, vertical root mean square error; accuracyz, National Standard for Spatial Data Accuracy fundamental 

vertical accuracy calculated at the 95-percent confidence level; WOH, West of Hudson]

Reservoir n

Edited TIN Raw TIN Improvement from editing

Mean 

signed 

error

(feet)

Median 

absolute 

error

(feet)

RSMEz

(feet)

Accuracyz

(feet)

Mean 

signed 

error

(feet)

Median 

absolute 

error

(feet)

RSMEz

(feet)

Accuracyz

(feet)

Mean 

signed 

error

(feet)

Median 

absolute 

error

(feet)

RMSEz

(feet)

Accuracyz

(feet)

Ashokan 

(East Basin)

57,641 -0.26 0.59 2.00 3.92 -0.60 0.63 2.40 4.70 0.34 0.04 0.4 0.78

Ashokan 

(West Basin)

36,153 0.15 0.73 2.28 4.48 -0.48 0.91 3.48 6.82 0.63 0.18 1.2 2.34

Cannonsville 76,522 0.02 0.43 2.21 4.33 -1.32 0.87 4.02 7.89 1.34 0.44 1.81 3.56

Neversink 28,246 0.00 0.75 2.17 4.26 -0.86 0.86 4.18 8.19 0.86 0.11 2.01 3.93

Pepacton 69,479 -0.01 0.79 3.59 7.04 -1.29 1.12 4.96 9.72 1.28 0.33 1.37 2.68

Rondout 23,673 0.13 0.73 1.98 3.88 -0.37 0.78 2.46 4.83 0.50 0.05 0.48 0.95

Schoharie 26,450 -0.15 0.38 1.71 3.36 -0.52 0.48 2.77 5.43 0.37 0.10 1.06 2.07

All WOH 

reservoirs

318,164 -0.03 0.59 2.50 4.91 -0.91 0.82 3.78 7.42 0.87 0.23 1.28 2.51

figure 15). The median absolute error for the edited TINs was 

0.59 ft overall and ranged from 0.38 ft at Schoharie Reservoir 

to 0.79 ft at Pepacton Reservoir. The NSSDA accuracy of the 

edited TINs was 4.91 ft and ranged from 3.36 ft at Schoharie 

Reservoir to 7.04 ft at Pepacton Reservoir. The linear-enforcement editing process improved the NSSDA accuracy by 2.51 ft 

overall, with a minimum improvement of 0.78 ft at the East 

Basin of Ashokan Reservoir and a maximum improvement of 

3.93 ft at Neversink Reservoir. The mean signed error for raw 

TINs was -0.91 ft overall and was negative for all reservoirs, 

indicating that the raw TIN surface elevations were on average higher than the elevations of the QA points. The linearenforcement editing process reduced the mean signed error for 

the TINs to -0.03 ft overall, with a minimum improvement of 

0.34 ft at the East Basin of Ashokan Reservoir and a maximum 

improvement of 1.34 ft at Cannonsville Reservoir. The comparison of QA points and low-pass filtered rasters was almost 

identical to that for the edited TINs (table 11). 

The QA points were spatially joined to the nearest 

mapped contour occurring within 3 ft of each QA point, the 

elevations were compared and descriptive statistics were 

calculated (table 12; a map of the point-to-contour comparison errors for Schoharie Reservoir is shown as an example 

in figure 16). The median absolute error for the contours 

was 1.19 ft overall and ranged from 0.90 ft at the East Basin 

of Ashokan Reservoir to 1.52 ft at Pepacton Reservoir. The 

NSSDA accuracy was 6.80 ft overall and ranged from 4.52 ft 

at the East Basin of Ashokan Reservoir to 9.05 ft at Pepacton 

Reservoir. The decrease in accuracy from the surfaces to the 

contours is because contours are closely spaced in steep areas; 

as a result of this close spacing, steep areas are oversampled 

in the assessment of contours as compared to the assessment 

of surfaces. In steep areas, small errors in horizontal-position 

measurement can create large vertical errors, and even small 

distances between a QA point and its paired contour can result 

in relatively large elevation errors. Bathymetric contours were 

mapped at a 2-ft interval to emulate existing topographic 

maps, but the user should be aware that the 95-percent confidence level accuracy of these contours is much larger than the 

mapped contour interval at all of the WOH reservoirs.

The accuracy of the capacity at the spillway elevation 

for each reservoir was assessed using the comparison of the 

QA points to the edited TINs because capacity was calculated 

using the TIN surfaces. The volume of a reservoir represents 

the spatial integration of depth over area; therefore, the accuracy of the calculated capacity can be represented by putting 

confidence intervals on the signed mean depth error. This 

assessment, however, does not include any potential bias in 

measurement of water surface elevation. A more conservative 

estimate of the accuracy of the capacity can be calculated by 

putting confidence intervals on the mean absolute depth error. 

Using the mean signed error, the 95-percent confidence interval calculated using equation 4 for all WOH reservoirs was 

0.6 percent or less of total capacity at spillway elevation; using 

the mean absolute error, the 95-percent confidence interval for 

all WOH reservoirs was 3.0 percent or less of total capacity at 

spillway elevation (table 13). 
Accuracy Assessment 19

-74°27' -74°26'

≤0.1

>0.1 to 0.2

>0.2 to 0.5

>0.5 to 1

>1 to 2

>2 to 5

>5 to 10

>10 to 15

>15 to 20

>20 to 40

EXPLANATION

Error, in feet

A B

42°21'

42°22'

42°23'

-74°27' -74°26'

0 0.25 0.5 MILES

0 0.25 0.5 KILOMETERS

Figure 15. Quality assurance echo sounder points compared to A, raw and B, edited triangular irregular networks 

(TINs), Schoharie Reservoir in New York State. Location of reservoir is shown in figure 1.
20 Bathymetry of Ashokan, Cannonsville, Neversink, Pepacton, Rondout, and Schoharie Reservoirs, New York, 2013–15

Table 11. Accuracy of raster elevations for quality assurance 

echo sounder points compared to raster surfaces for West of 

Hudson reservoirs, New York State. 

[Locations of reservoirs shown in figure 1. n, number of points—each 

quality assurance point was compared to the corresponding elevation of the 

low-pass filtered rasters; RMSEz, vertical root mean square error; accuracyz, 

National Standard for Spatial Data Accuracy fundamental vertical accuracy 

calculated at the 95-percent confidence level; WOH, West of Hudson]

Reservoir n

Median 

absolute 

error

(feet)

RSMEz

(feet)

Accuracyz

,

95-percent 

confidence 

level

(feet)

Ashokan

(East Basin)

57,641 0.59 1.99 3.90

Ashokan

(West Basin)

36,153 0.73 2.27 4.45

Cannonsville 76,522 0.45 2.19 4.30

Neversink 28,246 0.74 2.16 4.24

Pepacton 69,479 0.79 3.55 6.96

Rondout 23,673 0.72 1.97 3.86

Schoharie 26,450 0.39 1.74 3.41

All WOH reservoirs 318,164 0.60 2.48 4.87

Table 12. Accuracy of contour elevations for quality assurance 

echo sounder points compared to contours for West of Hudson 

reservoirs, New York State. 

[Locations of reservoirs shown in figure 1. n, number of points—each quality assurance point was compared to the elevation of the nearest contour 

within 3 feet; RMSEz, vertical root mean square error; accuracyz, National 

Standard for Spatial Data Accuracy fundamental vertical accuracy calculated 

at the 95-percent confidence level; WOH, West of Hudson]

Reservoir n

Median 

absolute 

error

(feet)

RSMEz

(feet)

Accuracyz

,

95-percent 

confidence 

level

(feet)

Ashokan

(East Basin)

8,866 0.90 2.31 4.52

Ashokan

(West Basin)

5,804 1.25 3.37 6.60

Cannonsville 21,168 1.10 3.03 5.94

Neversink 9,221 1.16 2.95 5.79

Pepacton 22,345 1.52 4.62 9.05

Rondout 5,939 1.07 2.63 5.15

Schoharie 5,935 1.10 2.91 5.70

All WOH reservoirs 79,278 1.19 3.47 6.80

42°21'

42°22'

42°23'

-74°27' -74°26'

0 0.25 0.5 MILES

0 0.25 0.5 KILOMETERS

≤0.1

>0.1 to 0.2

>0.2 to 0.5

>0.5 to 1

>1 to 2

>2 to 5

>5 to 10

>10 to 15

>15 to 20

>20 to 40

EXPLANATION

Error, in feet

Figure 16. Quality assurance echo sounder points compared to 

contours for Schoharie Reservoir in New York State. Location of 

reservoir is shown in figure 1.
Results of Surveys 21

Table 13. Accuracy of reservoir capacity at spillway elevations for the West of Hudson reservoirs, New York State. 

[Locations of reservoirs shown in figure 1. n, number of points—each quality assurance point was compared to the corresponding elevation of the edited 

triangulated irregular networks (TINs); CI, 95-percent confidence interval]

Reservoir

TIN surface elevation Capacity at spillway elevation

n

Mean 

signed 

error

(feet)

Mean 

absolute 

error

(feet)

Variance 

of error

(feet2

)

CI,

mean 

signed 

error

(feet)

CI,

mean 

absolute 

error

(feet)

CI, 

mean signed 

error

(billion gallons)

CI,

 mean absolute error

(billion gallons)

CI, 

mean signed 

error

(percent of 

total capacity)

CI,

mean absolute 

error

(percent of 

total capacity)

Ashokan

(East Basin)

57,641 -0.258 1.18 3.94 ±0.281 ±1.21 ±0.46 ±2.00 ±0.59 ±2.5

Ashokan

(West Basin)

36,153 0.151 1.36 5.20 ±0.174 ±1.38 ±0.18 ±1.39 ±0.37 ±3.0

Cannonsville 76,522 0.020 1.11 4.87 ±0.036 ±1.12 ±0.06 ±1.73 ±0.06 ±1.8

Neversink 28,246 0.003 1.35 4.73 ±0.029 ±1.37 ±0.01 ±0.68 ±0.04 ±1.9

Pepacton 69,479 -0.011 1.82 12.90 ±0.037 ±1.85 ±0.07 ±3.40 ±0.05 ±2.3

Rondout 23,673 0.125 1.21 3.91 ±0.151 ±1.24 ±0.10 ±0.85 ±0.20 ±1.6

Schoharie 26,450 -0.146 0.89 2.91 ±0.166 ±0.91 ±0.06 ±0.33 ±0.31 ±1.7

Results of Surveys

Echo sounder points, TINs, raster surfaces, contours, elevation-area-capacity tables, and associated metadata are available for download as digital data online (Nystrom 2018a–f) 

at https://dx.doi.org/10.5066/F7P26W7P (Ashokan Reservoir), https://dx.doi.org/10.5066/F7WM1BJK (Cannonsville 

Reservoir), https://dx.doi.org/10.5066/F71C1V1W (Neversink 

Reservoir), https://dx.doi.org/10.5066/F7DJ5CSM (Pepacton 

Reservoir), https://dx.doi.org/10.5066/F7542KR6 (Rondout 

Reservoir), and https://dx.doi.org/10.5066/F7J964HB (Schoharie Reservoir). Elevation-area-capacity tables at 10-ft increments of depth for each reservoir are in tables 14–20. 

Effect of Linear Enforcement on Capacity 

Estimation

To assess the effect that linear enforcement of the TINs 

had on estimation of the WOH reservoir capacities, the capacities of the raw TINs were calculated and compared to those 

calculated from the linearly enforced (or edited) TINs (table 

21). The calculated capacity of the raw TIN was less than the 

calculated capacity of the linearly enforced TIN for all of the 

WOH reservoirs, with a difference totaling more than 5 Ggal 

(1.1 percent) of the combined total capacity at spillway elevations. The effect of linear enforcement on total volume was 

smallest at the Schoharie Reservoir (about 0.1 Ggal) and largest at Pepacton Reservoir (about 2.2 Ggal). The relative effect 

of linear enforcement on volume was smallest at Rondout 

Reservoir (about 0.6 percent) and largest at Pepacton Reservoir (about 1.5 percent).

Change in Reservoir Capacity Over Time

Comparison of newly calculated reservoir capacities 

to previously published as-built capacities (U.S. Geological 

Survey, 2016a–f) shows a decrease in the total capacity of all 

six WOH reservoirs over time (table 22). The total calculated 

storage capacity at spillway elevations of the WOH reservoirs 

decreased by 11.5 Ggal, or 2.3 percent. The largest changes 

in total reservoir capacity were in Ashokan Reservoir, which 

decreased about 4.8 Ggal (about 2.6 Ggal in the West Basin 

and about 2.2 Ggal in the East Basin) and Cannonsville Reservoir, which decreased by about 2.6 Ggal. The largest percent 

change in total capacity was at Schoharie Reservoir, which 

decreased by about 8.6 percent. The change in total capacity at 

spillway elevation was greater than the 95-percent confidence 

interval calculated using the mean signed error at all reservoirs 

(table 13). The change in total capacity was greater than the 

more conservative confidence interval calculated using mean 

absolute error at Ashokan Reservoir (both basins), Cannonsville Reservoir, and Schoharie Reservoir. The useable capacity 

(the volume between the spillway elevation and the minimum 

operating level required to deliver full flow for drinking 

water supply) of the WOH reservoirs decreased by 7.9 Ggal 

(1.7 percent). The largest decreases in useable capacity were at 

Ashokan Reservoir, which decreased about 3.1 Ggal, and Cannonsville Reservoir, which decreased by about 2.3 Ggal; the 

largest percent decrease in useable capacity was at Schoharie 

Reservoir, which decreased by about 5 percent. The available 

capacity (the volume between the spillway elevation and the 

lowest intake or sill elevation used for drinking water supply) 

of the WOH reservoirs decreased by 10.0 Ggal (2.1 percent). 

Dead storage (the volume below the lowest intake or sill 

elevation) decreased by 1.5 Ggal (9.0 percent).
22 Bathymetry of Ashokan, Cannonsville, Neversink, Pepacton, Rondout, and Schoharie Reservoirs, New York, 2013–15

Table 14. Reservoir area and capacity at specified elevations for Ashokan Reservoir, East Basin, New York State.

[Location of reservoir shown in figure 1. Expanded elevation-area-capacity table is available for download at https://dx.doi.org/10.5066/F7P26W7P. NAVD 88, 

North American Vertical Datum of 1988; BWS, New York City Department of Environmental Protection Bureau of Water Supply; total capacity is total volume 

at spillway elevation (including dead storage); dead storage is the volume below minimum intake height or sill elevation for drinking water supply; useable 

capacity is the volume between the spillway elevation and the minimum operating level required to deliver full flow for drinking water supply; available capacity is the volume between the spillway elevation and the lowest intake or sill elevation used for drinking water supply]

Elevation

(feet above 

NAVD 88)

Elevation

(feet above BWS 

reservoir datum)

Depth below 

spillway

(feet)

Area

(square miles)

Total capacity

(billion gallons)

Useable capacity

(billion gallons)

Available capacity

(billion gallons)

585.68 587.00 0 7.94 78.526 74.339 78.526

575.68 577.00 10 7.31 62.589 58.402 62.589

565.68 567.00 20 6.36 48.345 44.158 48.345

555.68 557.00 30 5.64 35.790 31.603 35.790

545.68 547.00 40 4.81 24.893 20.706 24.893

535.68 537.00 50 4.11 15.602 11.415 15.602

525.68 527.00 60 2.91 8.061 3.874 8.061

515.68 517.00 70 2.07 2.790 0.000 2.790

505.68 507.00 80 0.60 0.286 0.000 0.286

Table 15. Reservoir area and capacity at specified elevations for Ashokan Reservoir, West Basin, New York State.

[Location of reservoir shown in figure 1. Expanded elevation-area-capacity table is available for download at https://dx.doi.org/10.5066/F7P26W7P. NAVD 88, 

North American Vertical Datum of 1988; BWS, New York City Department of Environmental Protection Bureau of Water Supply; total capacity is total volume 

at spillway elevation (including dead storage); dead storage is the volume below minimum intake height or sill elevation for drinking water supply; useable 

capacity is the volume between the spillway elevation and the minimum operating level required to deliver full flow for drinking water supply; available capacity is the volume between the spillway elevation and the lowest intake or sill elevation used for drinking water supply]

Elevation

(feet above 

NAVD 88)

Elevation

(feet above BWS 

reservoir datum)

Depth below 

spillway

(feet)

Area

(square miles)

Total capacity

(billion gallons)

Useable capacity

(billion gallons)

Available capacity

(billion gallons)

588.68 590.00 0 4.81 46.816 41.475 45.101

578.68 580.00 10 4.26 37.353 32.012 35.638

568.68 570.00 20 3.69 29.004 23.663 27.289

558.68 560.00 30 3.14 21.906 16.565 20.191

548.68 550.00 40 2.49 16.041 10.700 14.326

538.68 540.00 50 1.96 11.414 6.073 9.699

528.68 530.00 60 1.43 7.860 2.518 6.145

518.68 520.00 70 1.05 5.341 0.000 3.626

508.68 510.00 80 0.75 3.477 0.000 1.762

498.68 500.00 90 0.52 2.161 0.000 0.446

488.68 490.00 100 0.38 1.251 0.000 0.000

478.68 480.00 110 0.23 0.596 0.000 0.000

468.68 470.00 120 0.10 0.263 0.000 0.000

458.68 460.00 130 0.04 0.127 0.000 0.000

448.68 450.00 140 0.02 0.061 0.000 0.000

438.68 440.00 150 0.01 0.027 0.000 0.000

428.68 430.00 160 0.01 0.010 0.000 0.000
Results of Surveys 23

Table 16. Reservoir area and capacity at specified elevations for Cannonsville Reservoir, New York State.

[Location of reservoir shown in figure 1. Expanded elevation-area-capacity table is available for download at https://dx.doi.org/10.5066/F7WM1BJK. 

NAVD 88, North American Vertical Datum of 1988; BWS, New York City Department of Environmental Protection Bureau of Water Supply; total capacity is 

total volume at spillway elevation (including dead storage); dead storage is the volume below minimum intake height or sill elevation for drinking water supply; 

useable capacity is the volume between the spillway elevation and the minimum operating level required to deliver full flow for drinking water supply; available capacity is the volume between the spillway elevation and the lowest intake or sill elevation used for drinking water supply]

Elevation

(feet above 

NAVD 88)

Elevation

(feet above BWS 

reservoir datum)

Depth below 

spillway

(feet)

Area

(square miles)

Total capacity

(billion gallons)

Useable capacity

(billion gallons)

Available capacity

(billion gallons)

1,149.58 1,150.00 0 7.37 96.004 93.448 94.379

1,139.58 1,140.00 10 6.68 81.427 78.871 79.802

1,129.58 1,130.00 20 6.16 68.046 65.490 66.421

1,119.58 1,120.00 30 5.66 55.718 53.162 54.093

1,109.58 1,110.00 40 5.09 44.497 41.941 42.872

1,099.58 1,100.00 50 4.47 34.508 31.952 32.883

1,089.58 1,090.00 60 3.77 25.878 23.322 24.253

1,079.58 1,080.00 70 3.13 18.702 16.146 17.077

1,069.58 1,070.00 80 2.48 12.859 10.303 11.234

1,059.58 1,060.00 90 1.87 8.365 5.808 6.739

1,049.58 1,050.00 100 1.36 5.062 2.506 3.437

1,039.58 1,040.00 110 1.05 2.556 0.000 0.931

1,029.58 1,030.00 120 0.57 0.952 0.000 0.000

1,019.58 1,020.00 130 0.19 0.159 0.000 0.000

Table 17. Reservoir area and capacity at specified elevations for Neversink Reservoir, New York State.

[Location of reservoir shown in figure 1. Expanded elevation-area-capacity table is available for download at https://dx.doi.org/10.5066/F71C1V1W. NAVD 88, 

North American Vertical Datum of 1988; BWS, New York City Department of Environmental Protection Bureau of Water Supply; total capacity is total volume 

at spillway elevation (including dead storage); dead storage is the volume below minimum intake height or sill elevation for drinking water supply; useable 

capacity is the volume between the spillway elevation and the minimum operating level required to deliver full flow for drinking water supply; available capacity is the volume between the spillway elevation and the lowest intake or sill elevation used for drinking water supply]

Elevation

(feet above 

NAVD 88)

Elevation

(feet above BWS 

reservoir datum)

Depth below 

spillway

(feet)

Area

(square miles)

Total capacity

(billion gallons)

Useable capacity

(billion gallons)

Available capacity

(billion gallons)

1,439.21 1,440.00 0 2.38 36.647 34.692 35.163

1,429.21 1,430.00 10 2.20 31.871 29.916 30.387

1,419.21 1,420.00 20 2.02 27.478 25.523 25.994

1,409.21 1,410.00 30 1.85 23.455 21.500 21.971

1,399.21 1,400.00 40 1.67 19.771 17.816 18.287

1,389.21 1,390.00 50 1.50 16.465 14.510 14.981

1,379.21 1,380.00 60 1.34 13.506 11.551 12.022

1,369.21 1,370.00 70 1.19 10.868 8.913 9.384

1,359.21 1,360.00 80 1.04 8.543 6.588 7.059

1,349.21 1,350.00 90 0.91 6.513 4.558 5.029

1,339.21 1,340.00 100 0.79 4.734 2.779 3.250

1,329.21 1,330.00 110 0.65 3.224 1.269 1.739

1,319.21 1,320.00 120 0.49 2.055 0.100 0.571

1,309.21 1,310.00 130 0.37 1.153 0.000 0.000

1,299.21 1,300.00 140 0.25 0.505 0.000 0.000

1,289.21 1,290.00 150 0.12 0.130 0.000 0.000
24 Bathymetry of Ashokan, Cannonsville, Neversink, Pepacton, Rondout, and Schoharie Reservoirs, New York, 2013–15

Table 18. Reservoir area and capacity at specified elevations for Pepacton Reservoir, New York State.

[Location of reservoir shown in figure 1. Expanded elevation-area-capacity table is available for download at https://dx.doi.org/10.5066/F7DJ5CSM. NAVD 88, 

North American Vertical Datum of 1988; BWS, New York City Department of Environmental Protection Bureau of Water Supply; total capacity is total volume 

at spillway elevation (including dead storage); dead storage is the volume below minimum intake height or sill elevation for drinking water supply; useable 

capacity is the volume between the spillway elevation and the minimum operating level required to deliver full flow for drinking water supply; available capacity is the volume between the spillway elevation and the lowest intake or sill elevation used for drinking water supply]

Elevation

(feet above 

NAVD 88)

Elevation

(feet above BWS 

reservoir datum)

Depth below 

spillway

(feet)

Area

(square miles)

Total capacity

(billion gallons)

Useable capacity

(billion gallons)

Available capacity

(billion gallons)

1,278.81 1,280.00 0 8.82 148.690 139.320 142.372

1,268.81 1,270.00 10 8.25 130.890 121.520 124.572

1,258.81 1,260.00 20 7.68 114.270 104.900 107.952

1,248.81 1,250.00 30 7.00 98.946 89.576 92.628

1,238.81 1,240.00 40 6.36 85.047 75.677 78.729

1,228.81 1,230.00 50 5.72 72.468 63.098 66.150

1,218.81 1,220.00 60 5.19 61.089 51.719 54.771

1,208.81 1,210.00 70 4.74 50.766 41.396 44.448

1,198.81 1,200.00 80 4.31 41.312 31.942 34.994

1,188.81 1,190.00 90 3.88 32.778 23.408 26.460

1,178.81 1,180.00 100 3.39 25.179 15.809 18.861

1,168.81 1,170.00 110 2.88 18.643 9.273 12.325

1,158.81 1,160.00 120 2.42 13.098 3.728 6.780

1,148.81 1,150.00 130 1.96 8.532 0.000 2.214

1,138.81 1,140.00 140 1.53 4.904 0.000 0.000

1,128.81 1,130.00 150 1.07 2.165 0.000 0.000

1,118.81 1,120.00 160 0.50 0.515 0.000 0.000

1,108.81 1,110.00 170 0.05 0.028 0.000 0.000

Table 19. Reservoir area and capacity at specified elevations for Rondout Reservoir, New York State.

[Location of reservoir shown in figure 1. Expanded elevation-area-capacity table is available for download at https://dx.doi.org/10.5066/F7542KR6. NAVD 88, 

North American Vertical Datum of 1988; BWS, New York City Department of Environmental Protection Bureau of Water Supply; total capacity is total volume 

at spillway elevation (including dead storage); dead storage is the volume below minimum intake height or sill elevation for drinking water supply; useable 

capacity is the volume between the spillway elevation and the minimum operating level required to deliver full flow for drinking water supply; available capacity is the volume between the spillway elevation and the lowest intake or sill elevation used for drinking water supply]

Elevation

(feet above 

NAVD 88)

Elevation

(feet above BWS 

reservoir datum)

Depth below 

spillway

(feet)

Area

(square miles)

Total capacity

(billion gallons)

Useable capacity

(billion gallons)

Available capacity

(billion gallons)

838.88 840.00 0 3.27 51.770 49.060 49.480

828.88 830.00 10 3.03 45.221 42.511 42.931

818.88 820.00 20 2.83 39.115 36.405 36.825

808.88 810.00 30 2.60 33.442 30.732 31.152

798.88 800.00 40 2.38 28.261 25.551 25.971

788.88 790.00 50 2.23 23.457 20.747 21.167

778.88 780.00 60 2.05 18.991 16.281 16.701

768.88 770.00 70 1.82 14.938 12.228 12.648

758.88 760.00 80 1.55 11.432 8.722 9.142

748.88 750.00 90 1.30 8.450 5.740 6.160

738.88 740.00 100 1.10 5.947 3.236 3.657

728.88 730.00 110 0.88 3.873 1.163 1.583

718.88 720.00 120 0.64 2.290 0.000 0.000

708.88 710.00 130 0.43 1.188 0.000 0.000

698.88 700.00 140 0.25 0.489 0.000 0.000

688.88 690.00 150 0.10 0.137 0.000 0.000

678.88 680.00 160 0.02 0.018 0.000 0.000
Results of Surveys 25

Table 20. Reservoir area and capacity at specified elevations for Schoharie Reservoir, New York State.

[Location of reservoir shown in figure 1. Expanded elevation-area-capacity table is available for download at https://dx.doi.org/10.5066/F7J964HB. NAVD 88, 

North American Vertical Datum of 1988; BWS, New York City Department of Environmental Protection Bureau of Water Supply; total capacity is total volume 

at spillway elevation (including dead storage); dead storage is the volume below minimum intake height or sill elevation for drinking water supply; useable 

capacity is the volume between the spillway elevation and the minimum operating level required to deliver full flow for drinking water supply; available capacity is the volume between the spillway elevation and the lowest intake or sill elevation used for drinking water supply]

Elevation

(feet above 

NAVD 88)

Elevation

(feet above BWS 

reservoir datum)

Depth below 

spillway1

(feet)

Area

(square miles)

Total capacity

(billion gallons)

Useable capacity

(billion gallons)

Available capacity

(billion gallons)

1,128.63 1,129.73 0 1.76 19.599 16.601 18.240

1,118.63 1,119.73 10 1.56 16.155 13.157 14.796

1,108.63 1,109.73 20 1.43 13.049 10.051 11.690

1,098.63 1,099.73 30 1.31 10.189 7.191 8.830

1,088.63 1,089.73 40 1.17 7.604 4.606 6.245

1,078.63 1,079.73 50 0.94 5.361 2.363 4.002

1,068.63 1,069.73 60 0.72 3.653 0.655 2.294

1,058.63 1,059.73 70 0.57 2.306 0.000 0.947

1,048.63 1,049.73 80 0.37 1.338 0.000 0.000

1,038.63 1,039.73 90 0.23 0.726 0.000 0.000

1,028.63 1,029.73 100 0.12 0.373 0.000 0.000

1,018.63 1,019.73 110 0.08 0.167 0.000 0.000

1,008.63 1,009.73 120 0.03 0.049 0.000 0.000

1

After spillway reconstruction, completed 2015.

Table 21. Effect of linear enforcement on calculated capacity at spillway elevations in the West of Hudson reservoirs in New York 

State.

[Location of reservoir shown in figure 1. Rows in italics present duplicative information and are not included in calculation of West of Hudson reservoirs total. 

TIN, triangulated irregular network]

Reservoir

Capacity at spillway, linearly 

enforced TIN

(billion gallons)

Capacity at spillway,

unedited TIN, 

(billion gallons)

Difference

(billion 

gallons)

Difference

(percent)

Ashokan (East Basin) 78.526 78.086 -0.440 -0.6

Ashokan (West Basin) 46.816 46.149 -0.667 -1.4

Ashokan (Total) 125.342 124.235 -1.107 -0.9

Cannonsville 96.004 94.935 -1.069 -1.1

Neversink 36.647 36.326 -0.321 -0.9

Pepacton 148.690 146.530 -2.160 -1.5

Rondout 51.770 51.454 -0.316 -0.6

Schoharie1 19.599 19.467 -0.132 -0.7

Total 478.052 472.947 -5.105 -1.1

1

After spillway reconstruction, completed 2015.
26 Bathymetry of Ashokan, Cannonsville, Neversink, Pepacton, Rondout, and Schoharie Reservoirs, New York, 2013–15 Table 22. Summary of change in reservoir capacity since construction in the West of Hudson reservoirs in New York State. [Location of reservoir shown in figure 1. Rows in italics present duplicative information and are not included in calculation of West of Hudson reservoirs total. Total capacity is total volume at spillway eleva- tion (including dead storage); useable capacity is the volume between the spillway elevation and the minimum operating level required to deliver full flow for drinking water supply; available capacity is the volume between the spillway elevation and the lowest intake or sill elevation used for drinking water supply; dead storage is the volume below minimum intake height or sill elevation for drinking water supply; green shaded cells, change in total capacity at spillway elevation exceeds the 95-percent confidence interval computed using both the mean signed error and the mean absolute error (table 13); blue shaded cells, change in total capacity at spillway elevation exceeds the 95-percent confidence interval computed using the mean signed error but not the mean absolute error (table 13); --, not applicable] Reservoir As built1 (billions of gallons) At time of survey (billions of gallons) Change (billions of gallons) Change (percent) Total ca- pacity at spillway Useable capacity Available capacity Dead storage Total ca- pacity at spillway Useable capacity Available capacity Dead storage Total ca- pacity at spillway Useable capacity Available capacity Dead storage Total ca- pacity at spillway Useable capacity Available capacity Dead storage Ashokan (East Basin) 80.678 75.683 80.678 0.000 78.526 74.339 78.526 0.000 -2.152 -1.344 -2.152 0.000 -2.7 -1.8 -2.7 -- Ashokan (West Basin) 49.417 43.199 47.180 2.237 46.816 41.475 45.101 1.715 -2.601 -1.724 -2.079 -0.522 -5.3 -4.0 -4.4 -23.3 Ashokan (Total) 130.095 118.882 127.858 2.237 125.342 115.814 123.627 1.715 -4.753 -3.068 -4.231 -0.522 -3.7 -2.6 -3.3 -23.3 Cannonsville 98.618 95.706 96.726 1.892 96.004 93.448 94.379 1.625 -2.614 -2.258 -2.347 -0.267 -2.7 -2.4 -2.4 -14.1 Neversink 37.146 34.941 35.466 1.680 36.647 34.692 35.163 1.484 -0.499 -0.249 -0.303 -0.196 -1.3 -0.7 -0.9 -11.7 Pepacton 149.799 140.190 143.701 6.098 148.690 139.320 142.372 6.318 -1.109 -0.870 -1.329 0.220 -0.7 -0.6 -0.9 3.6 Rondout 52.435 49.617 50.048 2.387 51.770 49.060 49.480 2.290 -0.665 -0.557 -0.568 -0.097 -1.3 -1.1 -1.1 -4.1 Schoharie (before spillway re- construction in 2015) 21.551 17.582 19.583 1.968 19.698 16.700 18.339 1.359 -1.853 -0.882 -1.244 -0.609 -8.6 -5.0 -6.4 -30.9 Schoharie (after spillway recon- struction in 2015) 21.454 17.485 19.486 1.968 19.599 16.601 18.240 1.359 -1.855 -0.884 -1.246 -0.609 -8.6 -5.1 -6.4 -30.9 Total 489.644 456.918 473.382 16.262 478.151 449.034 463.360 14.791 -11.493 -7.884 -10.022 -1.471 -2.3 -1.7 -2.1 -9.0

1From published U.S. Geological Survey annual summaries (U.S. Geological Survey, 2016a–f).
References Cited 27

Summary

Bathymetric surveys of the six West of Hudson (WOH) 

reservoirs that supply water to New York City—Ashokan, 

Cannonsville, Neversink, Pepacton, Rondout, and Schoharie—

were completed by the U.S. Geological Survey, in cooperation 

with the New York City Department of Environmental Protection, from 2013 to 2015 to provide updated and more accurate 

elevation-area-capacity tables and bathymetric maps. Depths 

were measured using a single-beam echo sounder, horizontal 

positions were measured using a real-time kinematic global 

positioning system, and reservoir-bottom elevations were 

referenced to observed water surface elevations. Planned 

transects were spaced to achieve a ratio of transect spacing 

to reservoir length of 1 percent or less and were aligned to be 

perpendicular to the long axis of the reservoir. A second quality assurance set of echo sounder data was collected at oblique 

angles to the main transects for elevation-accuracy assessment. 

Data were integrated and processed using HYPACK, including corrections for speed of sound, before being imported to a 

geographic information system. Surfaces were created using 

triangulated irregular networks (TINs) and were edited to 

more accurately represent geomorphic features; without this 

editing for linear enforcement, the total capacity of the WOH 

reservoirs would have been underestimated by about 5 Ggal, 

or 1.1 percent. Elevation-area-capacity tables were calculated 

at 0.01-foot (ft) intervals from the edited TINs, and contours 

were mapped at 2-ft intervals from a raster conversion of the 

edited TINs.

Quality assurance data points were compared with the 

main data points, mapped surfaces, and contours and showed 

that for the combined results of the six reservoir surveys 

the directly measured points have better accuracy (2.10 ft at 

the 95-percent confidence level as defined by the National 

Standard for Spatial Data Accuracy [NSSDA]) than mapped 

surfaces (4.91 ft for edited TINs) or mapped contours (6.80 ft). 

Linear enforcement of the TIN surfaces improved accuracy 

by 2.51 ft overall. Users should be aware that the 95-percent 

confidence level accuracy of the mapped contours is larger 

than the contour interval (that is, greater than 2 ft) at all of the 

WOH reservoirs. The 95-percent confidence interval calculated for total capacity at spillway elevations was 0.6 percent 

or less when calculated using the mean signed error of the 

TIN surfaces and 3.0 percent or less when calculated using the 

mean absolute error of the TIN surfaces. 

The results of the surveys show that the total capacity 

of the WOH reservoirs has decreased 11.5 Ggal (2.3 percent) 

since construction. The largest changes in capacity occurred 

at Cannonsville and Ashokan Reservoirs; the largest percent 

change in capacity occurred at Schoharie Reservoir. The useable capacity of the WOH reservoirs decreased by 7.9 Ggal 

(1.7 percent). Digital data products, including echo sounder 

points, TIN and raster surfaces, contour maps, and elevation-area-capacity tables are available for download online 

at https://dx.doi.org/10.5066/F7P26W7P (Ashokan Reservoir), https://dx.doi.org/10.5066/F7WM1BJK (Cannonsville 

Reservoir), https://dx.doi.org/10.5066/F71C1V1W (Neversink 

Reservoir), https://dx.doi.org/10.5066/F7DJ5CSM (Pepacton 

Reservoir), https://dx.doi.org/10.5066/F7542KR6 (Rondout 

Reservoir), and https://dx.doi.org/10.5066/F7J964HB (Schoharie Reservoir).

References Cited

AML Oceanographic, 2010, Smart SV user 

manual (ver. 2.1, January 13, 2010): AML 

Oceanographic, 22 p., accessed October 5, 2016, at 

https://amloceanographic.app.boxenterprise.net/

web_links/3328063/shared/a1qjym370915odho0683.

Esri, Inc., 2016, ArcGIS: Esri, Inc., software release, accessed 

October 5, 2016, at http://www.esri.com/software/arcgis/.

Federal Geographic Data Committee, 1998, National standard 

for spatial data accuracy, part 3 of Geospatial positioning 

accuracy standards: Federal Geographic Data Committee, 

no. FGDC-STD-007.3, p. 3-1 to 3-25, accessed October 24, 

2016, at https://www.fgdc.gov/standards/projects/accuracy/

part3/chapter3.

Helsel, D.R., and Hirsch, R.M., 2002, Statistical methods in 

water resources: U.S. Geological Survey Techniques of 

Water Resources Investigations, book 4, chap. A3, 522 p. 

HYPACK, Inc., 2016, HYPACK—Hydrographic survey and 

processing software: HYPACK, Inc., software release, 

accessed October 5, 2016, at http://www.hypack.com/new/

Sales/Products/HYPACK/tabid/56/Default.aspx.

New York City Department of Environmental Protection, 

2009, West of Hudson lidar metadata: New York State web 

page, accessed October 5, 2016, at https://gis.ny.gov/

elevation/metadata/2009-West-of-Hudson-LiDAR.xml.

New York City Department of Environmental Protection, 

2016a, New York City drinking water supply and quality 

report: New York City Department of Environmental Protection, 17 p., accessed December 13, 2016, at 

http://www.nyc.gov/html/dep/pdf/wsstate15.pdf.

New York City Department of Environmental Protection, 

2016b, Ashokan: New York City Department of Environmental Protection web page, accessed August 15, 2016, at 

http://www.nyc.gov/html/dep/html/watershed_protection/

ashokan.shtml.

New York City Department of Environmental Protection, 

2016c, Cannonsville: New York City Department of Environmental Protection web page, accessed August 15, 2016, 

at http://www.nyc.gov/html/dep/html/watershed_protection/

cannonsville.shtml.
28 Bathymetry of Ashokan, Cannonsville, Neversink, Pepacton, Rondout, and Schoharie Reservoirs, New York, 2013–15

New York City Department of Environmental Protection, 

2016d, Neversink: New York City Department of Environmental Protection web page, accessed August 15, 2016, at 

http://www.nyc.gov/html/dep/html/watershed_protection/

neversink.shtml.

New York City Department of Environmental Protection, 

2016e, Pepacton: New York City Department of Environmental Protection web page, accessed August 15, 2016, at 

http://www.nyc.gov/html/dep/html/watershed_protection/

pepacton.shtml.

New York City Department of Environmental Protection, 

2016f, Rondout: New York City Department of Environmental Protection web page, accessed August 15, 2016, at 

http://www.nyc.gov/html/dep/html/watershed_protection/

rondout.shtml.

New York City Department of Environmental Protection, 

2016g, Schoharie: New York City Department of Environmental Protection web page, accessed August 15, 2016, at 

http://www.nyc.gov/html/dep/html/watershed_protection/

schoharie.shtml.

New York State, 2016a, New York State high resolution 

digital orthoimagery 2000–2014: New York State web page, 

accessed October 5, 2016, at https://gis.ny.gov/gateway/mg/

nysdop_descrip.htm.

New York State, 2016b, New York State orthos online: New 

York State web mapping service, accessed October 5, 2016, 

at http://www.orthos.dhses.ny.gov/.

Nystrom, E.A., 2018a, Geospatial bathymetry dataset and 

elevation-area-capacity table for Ashokan Reservoir, 

2013 to 2014: U.S. Geological Survey data release, 

https://dx.doi.org/10.5066/F7P26W7P.

Nystrom, E.A., 2018b, Geospatial bathymetry dataset and 

elevation-area-capacity table for Cannonsville Reservoir, 2015: U.S. Geological Survey data release, 

https://dx.doi.org/10.5066/F7WM1BJK.

Nystrom, E.A., 2018c, Geospatial bathymetry dataset and 

elevation-area-capacity table for Neversink Reservoir, 

2013 to 2014: U.S. Geological Survey data release, 

https://dx.doi.org/10.5066/F71C1V1W.

Nystrom, E.A., 2018d, Geospatial bathymetry dataset 

and elevation-area-capacity table for Pepacton Reservoir, 2015: U.S. Geological Survey data release, 

https://dx.doi.org/10.5066/F7DJ5CSM.

Nystrom, E.A., 2018e, Geospatial bathymetry dataset and 

elevation-area-capacity table for Rondout Reservoir, 

2013 to 2014: U.S. Geological Survey data release, 

https://dx.doi.org/10.5066/F7542KR6.

Nystrom, E.A., 2018f, Geospatial bathymetry dataset 

and elevation-area-capacity table for Schoharie Reservoir, 2015: U.S. Geological Survey data release, 

https://dx.doi.org/10.5066/F7J964HB.

SonTek, 2016, Riversurveyor M9: SonTek web page, accessed 

October 5, 2016, at http://www.sontek.com/

productsdetail.php?RiverSurveyor-S5-M9-14.

Syqwest, Inc., 2008, Bathy-500MF multi-frequency survey 

echo sounder: Syqwest, Inc. web page, accessed August 30, 

2016, at http://www.syqwestinc.com/media/bathy-500mf/

bathy500mf-manual.pdf.

Trimble, 2016, Trimble R8 GNSS Receiver User Guide: 

Trimble web page, accessed December 19, 2016, at 

http://trl.trimble.com/docushare/dsweb/Get/

Document-666215/R8-R6-5800_v400A_UserGuide.pdf.

U.S. Department of Agriculture, 2016, NAIP Imagery: U.S. 

Department of Agriculture web page, accessed October 5, 

2016, at https://www.fsa.usda.gov/programs-and-services/

aerial-photography/imagery-programs/naip-imagery/.

U.S. Geological Survey, 2016a, Water-year summary for 

site 01363400 Ashokan Reservoir at Ashokan, NY: USGS 

National Water Information System web page, accessed 

August 15, 2016, at http://waterdata.usgs.gov/nwis/

wys_rpt?dv_ts_ids=105128&wys_water_yr=2015&site_

no=01363400.

U.S. Geological Survey, 2016b, Water-year summary for

site 01424997 Cannonsville Reservoir near

Stilesville, NY: USGS National Water Information System 

web page, accessed August 15, 2016, at 

http://waterdata.usgs.gov/nwis/wys_rpt?dv_ts_

ids=105328&wys_water_yr=2015&site_no=01424997.

U.S. Geological Survey, 2016c, Water-year summary for site 

01435900 Neversink Reservoir near Neversink, NY: USGS 

National Water Information System web page, accessed 

August 15, 2016, at http://waterdata.usgs.gov/nwis/

wys_rpt?dv_ts_ids=105407&wys_water_yr=2015&site_

no=01435900.

U.S. Geological Survey, 2016d, Water-year summary for site 

01416900 Pepacton Reservoir near Downsville, NY: USGS 

National Water Information System web page, accessed 

August 15, 2016, at http://waterdata.usgs.gov/nwis/

wys_rpt?dv_ts_ids=105290&wys_water_yr=2015&site_

no=01416900.

U.S. Geological Survey, 2016e, Water-year summary for site 

01366400 Rondout Reservoir at Lackawack, NY: USGS 

National Water Information System web page, accessed 

August 15, 2016, at http://waterdata.usgs.gov/nwis/

wys_rpt?dv_ts_ids=105138&wys_water_yr=2015&site_

no=01366400.
References Cited 29

U.S. Geological Survey, 2016f, Water-year summary for Scho-

harie Reservoir near Grand Gorge, NY: USGS National 

Water Information System web page, accessed August 15, 

2016, at http://waterdata.usgs.gov/nwis/wys_rpt?dv_ts_

ids=105034&wys_water_yr=2015&site_no=01350100.

Wilson, G.L., and Richards, J.M., 2006, Procedural documen-

tation and accuracy assessment of bathymetric maps and 

area/capacity tables for small reservoirs: U.S. Geological 

Survey Scientific Investigations Report 2006–5208, 24 p. 

plus oversize figs. [Also available at http://pubs.usgs.gov/

sir/2006/5208/.]

For more information about this report, contact:

Director, New York Water Science Center

U.S. Geological Survey

425 Jordan Road

Troy, NY 12180–8349

dc_ny@usgs.gov

(518) 285–5602

or visit our website at

https://ny.water.usgs.gov

Publishing support provided by the Pembroke, Menlo 

Park, and West Trenton Publishing Service Centers
Nystrom—Bathymetry of Ashokan, Cannonsville, Neversink, Pepacton, Rondout, and Schoharie Reservoirs, New York, 2013–15—SIR 2017–5064

ISSN 2328-0328 (online)

https://doi.org/10.3133/sir20175064