Prepared in cooperation with the New Jersey Department of Environmental Protection

Bathymetry of Morris Lake (Newton Reservoir), 

New Jersey, 2018

Scientific Investigations Report 2020–5010

U.S. Department of the Interior

U.S. Geological Survey
Cover. Morris Lake, New Jersey, viewed from survey boat. Photograph by Elizabeth Nystrom, 

U.S. Geological Survey.
Bathymetry of Morris Lake (Newton 

Reservoir), New Jersey, 2018

By Elizabeth A. Nystrom and Jerilyn V. Collenburg

Prepared in cooperation with the 

New Jersey Department of Environmental Protection

Scientific Investigations Report 2020–5010

U.S. Department of the Interior

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

DAVID BERNHARDT, Secretary

U.S. Geological Survey

James F. Reilly II, Director

U.S. Geological Survey, Reston, Virginia: 2020

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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., and Collenburg, J.V., 2020, Bathymetry of Morris Lake (Newton Reservoir), New Jersey, 2018: 

U.S. Geological Survey Scientific Investigations Report 2020–5010, 14 p., https://doi.org/10.3133/sir20205010.

Associated data for this publication:

Nystrom, E.A., and Collenburg, J.V., 2020, Geospatial bathymetry dataset and elevation-area-capacity table for Morris 

Lake (Newton Reservoir), New Jersey: U.S. Geological Survey data release, https://doi.org/10.5066/P977GO3J.

ISSN 2328-0328 (online)
iii

Acknowledgments

The authors would especially like to thank Jack Smalley, operator of the filtration plant at 

Morris Lake, for his assistance and hospitality during our time on the lake. The authors would 

like to acknowledge the assistance provided by several colleagues at the U.S. Geological Survey 

(USGS) New Jersey Water Science Center: Karl M. Braun, for operating the boat and other supporting field work; Jason C. Shvanda for supporting field and office work; and Thomas P. Suro for 

technical assistance.

v

Contents

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

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

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

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

Description of Study Area ...................................................................................................................1

Bathymetric Survey and Processing Methods .........................................................................................2

Vertical Control and Water Surface Elevation .................................................................................2

Sound Velocity .......................................................................................................................................3

Multibeam Echosounder .....................................................................................................................3

Quality Assurance Dataset: Single-Beam Echosounder ...............................................................5

Bathymetric Map Creation and Results .....................................................................................................6

Results of Survey ..................................................................................................................................6

Accuracy Assessment .........................................................................................................................9

Summary........................................................................................................................................................13

References Cited..........................................................................................................................................13

Figures

1. Map showing location of Morris Lake (Newton Reservoir) in New Jersey .......................2

2. Photograph of survey boat and global navigation satellite system rover receiver 

used for the bathymetric survey of Morris Lake (Newton Reservoir), New Jersey ..........3

3. Graph showing sound velocity profiles, including measured values and 

processing average for Morris Lake (Newton Reservoir), New Jersey .............................4

4. Photograph of multibeam echosounder ...................................................................................4

5. Photograph of single-beam echosounder ................................................................................5

6. Map showing interpolated areas and mapped bathymetric depths and depth 

contours of Morris Lake (Newton Reservoir), New Jersey ...................................................7

7. Map showing bathymetric elevations and elevation contours of Morris Lake 

(Newton Reservoir), New Jersey, and elevations of surrounding area ..............................8

8. Map showing quality assurance echosounder points compared to mapped 

elevation and slope of bathymetric surface, Morris Lake (Newton Reservoir), 

New Jersey ..................................................................................................................................10

9. Graph showing results of comparison of quality assurance points and mapped 

surface by depth and slope .......................................................................................................11

10. Illustration of echosounder beam geometry and potential cause of errors on 

steep slopes .................................................................................................................................12
vi

Tables

1. Results of bar check, April 23, 2018, Morris Lake (Newton Reservoir), New Jersey ........6

2. Reservoir area and capacity at specified depths for Morris Lake (Newton 

Reservoir), New Jersey ...............................................................................................................9

3. Reservoir area and capacity at specified elevations for Morris Lake (Newton 

Reservoir), New Jersey ...............................................................................................................9

4. Accuracy of point elevations of single-beam echosounder quality assurance 

points compared to mapped multibeam echosounder raster surface for Morris 

Lake (Newton Reservoir), New Jersey, bathymetric survey ...............................................12

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

acre 4,047 square meter (m2)

acre 0.004047 square kilometer (km2)

square mile (mi2) 2.590 square kilometer (km2)

Volume

gallon (gal) 3.785 liter (L)

gallon (gal) 0.003785 cubic meter (m3)

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

acre-foot (acre-ft) 1,233 cubic meter (m3)

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.
vii

Abbreviations

FGDC Federal Geographic Data Committee

GIS geographic information system

GNSS global navigation satellite system

INS inertial navigation system

kHz kilohertz

lidar light detection and ranging

POS MVTM Position Orientation Solution for Marine Vessels

RTK real-time kinematic

RMSE root mean square error

USGS U.S. Geological Survey

VRS virtual reference station network

Bathymetry of Morris Lake (Newton Reservoir), 

New Jersey, 2018

By Elizabeth A. Nystrom and Jerilyn V. Collenburg

Abstract

Morris Lake, also known as Newton Reservoir, has been 

the source of drinking water for the Town of Newton, New 

Jersey, since the early 1900s. Although Morris Lake has been 

used as a source of drinking water for many years, its capacity 

was previously uncertain. In April 2018, the U.S. Geological 

Survey and the New Jersey Department of Environmental 

Protection conducted a bathymetric survey of Morris Lake 

using a multibeam echosounder to map the reservoir. The 

points measured with the multibeam echosounder were 

combined with light detection and ranging data above the 

water surface and processed to create a 3.3-foot (1 meter) 

raster grid of the bathymetric surface, bathymetric contours at 

2-foot intervals of depth and elevation, and an elevation-areacapacity table.

The results of the bathymetric survey show that Morris 

Lake has a maximum depth of just over 119 feet with an 

average depth of 42 feet. Like the surrounding topography, 

parts of the reservoir are extremely steep. The capacity of the 

reservoir at full spillway level is 1,980 million gallons, with 

a corresponding surface area of 145 acres. The accuracy of 

the mapped multibeam echosounder bathymetric data was 

evaluated using a quality assurance dataset collected with a 

single-beam echosounder; 9,386 quality assurance points were 

spatially joined with the mapped raster surface to compute 

measurement errors. The calculated median point error for 

Morris Lake was 0.23 foot, the median absolute error was 

0.35 foot, and the 95-percent accuracy was 2.68 feet. The 

largest errors occurred in the steepest areas of the reservoir 

and in unmeasured areas. Geospatial files of the bathymetry 

data, including the mapped bathymetric surface, contours, 

and capacity tables, quality assurance points, and associated 

metadata are available for download as part of an accompanying U.S. Geological Survey data release.

Introduction

Morris Lake in Sparta Township, New Jersey, has been 

the source of drinking water for the Town of Newton since 

the early 1900s. Although Morris Lake has been used as a 

source of drinking water for many years, the depths of the 

reservoir and storage capacity were previously uncertain. In 

2018, the U.S. Geological Survey (USGS) and the New Jersey 

Department of Environmental Protection conducted a bathymetric survey of Morris Lake to create a map of the bathymetric surface, to produce bathymetric contours, and to compute 

an elevation-area-capacity table.

Purpose and Scope

The purpose of this report is to document the results 

of the bathymetric survey of Morris Lake completed in 

April 2018 using a multibeam echosounder. Equipment and 

methods of data collection and processing are described and 

results, including data accuracy assessment, are presented.

Description of Study Area

Morris Lake, also known as the Newton Reservoir, is 

located in Sparta Township in the Sparta Mountains in Sussex 

County, New Jersey (fig. 1). According to historical documents (Dickinson, 1899), Morris Lake was originally a deep, 

natural lake that covered approximately 130 acres and was 

fed mainly by natural springs with a drainage area of about 

1.25 square miles (mi2). In the late 1700s, mill owners in the 

village of Sparta erected a several-foot-high dam across the 

lake’s outlet. The dam increased the depth and storage of the 

lake, allowing the village to continue to draw water during 

dry conditions. Then in the mid-1800s, another dam was 

built approximately 0.25 mile below the lake, which formed 

a pond between the lake and Pine Swamp Brook (not shown 

on fig. 1). Eventually the pond and the lake were united when 

the pond was raised to the level of the first dam located at 

the original outlet of Morris Lake. Through damming a portion of Pine Swamp Brook, an artificial channel and smaller 

artificial lake were created below Morris Lake, which is now 

known as Glen Lake (fig. 1). The drainage area of these two 

lakes combined was increased to about 3.80 mi2. Gates were 

then constructed in the dams so that they could be opened and 

closed to supply water to the mills in the village (Dickinson, 

1899). From the late 1800s to the present (2019), Morris Lake 

has been supplying water to the Town of Newton, located 

about 7 miles from the lake.
2 Bathymetry of Morris Lake (Newton Reservoir), New Jersey, 2018

VILLAGE

OF SPARTA 

Morris Lake

Base from U.S. Geological Survey digital data

The National Map, USGS Topo

Web Mercator Auxiliary Sphere

World Geodetic System of 1984

74°39' 74°38' 74°37' 74°36'

41°03'

41°02'

NEW

JERSEY

Newton Study

area

0 0.5 1 KILOMETER

0 0.5 1 MILE

Figure 1. Location of Morris Lake (Newton Reservoir) in New Jersey.

Bathymetric Survey and Processing 

Methods

A bathymetric survey was conducted in April 2018 using 

a multibeam echosounder from a small moving boat (fig. 2). 

Ancillary data measured and used in processing the echosounder data included water surface elevation (for vertical 

position data) and sound velocity profiles at three locations 

in the lake. A quality assurance dataset was collected using 

a single-beam echosounder for comparison with the multibeam echosounder dataset. Vertical coordinate information 

is referenced to the North American Vertical Datum of 1988 

(NAVD 88), transformed by GEOID09 (conterminous United 

States) to vertical datum. Horizontal coordinate information is 

referenced to the North American Datum of 1983 (NAD 83).

Vertical Control and Water Surface Elevation

Vertical control was established using global navigation 

satellite system (GNSS) surveys to determine the elevation 

of the spillway and establish a reference point from which to 

measure the water surface elevation. GNSS surveys were done 

utilizing a virtual reference station (VRS) network with highly 

precise GNSS reference stations and a survey-grade Trimble® 

R10 rover/receiver. The continuously operating VRS provided base stations for the survey, and once set up over an 

objective point, the VRS network corrected for ionospheric 

and other atmospheric conditions in the satellite signals to 

increase the accuracy of the GNSS at the survey location. 

Continuous real-time kinematic (RTK) and differential corrections to the GNSS horizontal and vertical positions were 

made using the fixed-base station VRS network operated by 
Bathymetric Survey and Processing Methods 3

Figure 2. Survey boat and global navigation satellite system (GNSS) rover receiver used for the 

bathymetric survey of Morris Lake (Newton Reservoir), New Jersey. Photograph by Elizabeth 

Nystrom, U.S. Geological Survey. 

KeyNetGPS, Inc. (2019). The survey followed the approach 

and methods of a Level II quality survey as described by 

Rydlund and Densmore (2012), including blunder checks, 

redundancy checks, and vertical order 2 benchmark checks 

before and after surveying objective points at the lake. The 

left and right edges of the spillway were surveyed; the average 

elevation of the spillway observations was 938.39 feet (ft) 

above NAVD 88. A reference point was also surveyed for use 

to relate the water surface to elevation above NAVD 88.

A time series of water surface elevation, measured using 

pressure transducers, was used to convert mapped bathymetric 

depths to elevations. An unvented pressure transducer was 

installed in the reservoir near the spillway; a second pressure transducer installed above the water surface was used to 

correct the underwater time series for changes in barometric 

pressure. Measured pressures were converted to depths by calculating water density using the water temperature measured 

by the pressure transducer. The depth time series was then 

converted to elevations using measurements from the reference point (two on April 23 and two on April 24; before and 

after daily echosounder data collection). During the survey, 

the water surface elevation was essentially constant, approximately 0.10 to 0.15 ft above the spillway elevation.

Sound Velocity

Echosounders determine depth by transmitting a pulse of 

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

for an echo to return; to accurately calculate a depth, the sound 

velocity must be known. Sound velocity varies with temperature, pressure, and salinity; reservoirs are often stratified by 

temperature, so the sound velocity usually varies with depth. 

Additionally, sound velocity profiles can vary by location 

because surface water in shallow areas may warm differently 

than deep areas. To account for the change of sound velocity 

over depth and area, profiles were measured using an Applied 

Microsystems Smart SV Sensor (AML Oceanographic, 2010). 

Five sound velocity profiles were measured during the survey, 

one on April 23 and four on April 24 (fig. 3). Sound velocity 

profiles were measured in the deepest part of the reservoir on 

April 23 at 15:55 and on April 24 at 09:15 and 15:50 to record 

a full profile for processing; sound velocity profiles were also 

taken in shallower locations around the reservoir—on April 24 

at 15:45 (near the north end of the reservoir) and on April 24 

at 16:05 (near the south end of the reservoir)—to verify consistency of the profiles throughout the reservoir. Sound velocity was recorded at 5-ft increments from the surface to the 

deepest depth at the location of measurement (20 to 115 ft). 

When the profiles were plotted and examined, it was determined that a single average profile could reasonably be used 

for the entire survey (fig. 3); sound speed was most variable in 

the upper 30 ft of the reservoir and at the water surface.

Multibeam Echosounder

A multibeam echosounder is an instrument that uses 

sound to measure water depths at many locations simultaneously along a particular swath. Multibeam echosounders 

are manufactured in many configurations, but they often 

use two phased-array transducers to shape acoustic transmit 

and receive beams and slice the acoustic returns into hundreds of individual depth measurements along each swath. 

To accurately map the locations of the depth measurements 

in space, multibeam echosounders are used with an inertial 
4 Bathymetry of Morris Lake (Newton Reservoir), New Jersey, 2018

4,675 4,700 4,725 4,750 4,775

0

30

60

90

120

Sound velocity, in feet per second 

Depth, in feet 

4/23/2018 at 15:55

(surface to 105 feet)

4/24/2018 at 09:15

(surface to 110 feet)

4/24/2018 at 15:45

(surface to 25 feet)

4/24/2018 at 15:50

(surface to 115 feet)

4/24/2018 at 16:05

(surface to 20 feet)

Average sound velocity,

4/23 to 4/24/2018 

EXPLANATION

Figure 3. Sound velocity profiles, including measured values 

(points) and processing average (line) for Morris Lake (Newton 

Reservoir), New Jersey. Dates are in month/day/year format, and 

times are in 24-hour format.

navigation system (INS) to measure heave, pitch, roll, 

heading, and position. More information about multibeam 

echosounders and examples of their use for surveying rivers 

and lakes is described in Huizinga and Heimann (2018) and 

Huizinga (2016).

Bathymetric data were collected with a multibeam echosounder on April 24, 2018. The multibeam echosounder used 

for this study (fig. 4) was a Teledyne Odom Hydrographic 

MB2 (Teledyne Odom Hydrographic, 2019) with integrated 

Applanix Position Orientation Solution for Marine Vessels 

(POS MVTM) Wavemaster II INS (Applanix Corporation, 

2017) and a Teledyne Reson SVP–70 sound velocity sensor 

(Teledyne RESON, 2019). The MB2 has up to 256 adjustablefrequency beams—from 200 to 460 kilohertz (kHz)—with 

up to a 140-degree swath width and configurable beam width 

(nominal beam width 1.8 degrees).

For the survey of Morris Lake, the MB2 was generally 

operated at 460 kHz with 256 beams and 140-degree swath 

width. In some areas of the reservoir, changes to the configuration of the MB2 were made because of field conditions; for 

example, in areas of excessive aquatic plant growth, the frequency of the MB2 was lowered to 200 kHz to obtain a stronger reflection from the bottom of the reservoir. The minimum 

depth measurable with the MB2 was approximately 2 ft. The 

position data from the Wavemaster II INS was supplemented 

with RTK GNSS position data from a Trimble R10 GNSS 

receiver and the VRS; this GNSS receiver was positioned 

directly above the echosounder transducer. Additionally, the 

NMEA 0183 ZDA string output by this GNSS receiver was 

used to time synchronize the INS and MB2 echosounder data. 

The MB2 echosounder data were displayed and recorded using 

Teledyne PDS version 4.1.5.3 (Teledyne, 2019) software. 

PDS creates a raster grid of raw measured depths in real time, 

which was used by the boat driver to navigate for the most 

complete coverage of the bathymetric surface possible.

The INS installed in the multibeam echosounder measures pitch, roll, heading, and heave to compute the correct 

location in three-dimensional space of the points measured by 

the MB2. To verify the performance of these measurements 

and to calibrate the alignment of these sensors, a patch test 

was performed during the morning of April 24. A patch test 

consists of a series of movements recorded with a multibeam 

echosounder over a bathymetric surface: two passes of data 

are collected traveling in opposite directions over a flat surface 

to calibrate the roll correction; two passes are collected traveling in opposite directions over a slope to calibrate the pitch 

correction; and two passes are collected traveling in the same 

direction along offset paths to calibrate the heading correction. 

A patch test was conducted at Morris Lake over the flat surfaces in the deepest portion of the lake and over the adjacent 

steep slope along the northwestern edge of the lake. The computed pitch correction was 0.03 degree, the roll correction was 

Figure 4. Multibeam echosounder. Photograph by Elizabeth 

Nystrom, U.S. Geological Survey. 
Bathymetric Survey and Processing Methods 5

–0.05 degree, and the heading correction was –3.09 degrees.

Because the POS Wavemaster II INS is permanently installed

inside the MB2 transducer enclosure, the pitch, roll, and heading corrections are generally consistent over time.

The multibeam echosounder data were processed using 

the same software used to collect the data, Teledyne PDS 

version 4.1.5.3 (Teledyne, 2019). Multibeam echosounder processing included correction for changes in sound velocity over 

depth, conversion from depth to elevation above NAVD 88, 

and editing to remove erroneous points or spikes. The five 

measured sound velocity profiles were averaged to form a 

single sound velocity profile for Morris Lake. During multibeam echosounder data collection, sound velocity was also 

measured near the surface with the SVP–70; PDS was used to 

combine the time series of measurements of sound velocity at 

the surface with the average sound velocity profile over depth 

to form a time series of sound velocity profiles. Data from 

adjacent MB2 measurement swaths were generally spaced to 

overlap at the edges by 10 to 25 percent; these overlapping 

areas were used as an additional quality assurance check to 

verify reproducibility of point measurements after pitch, roll, 

heading, and sound velocity profile corrections.

Depths measured by the MB2 were converted to elevations above NAVD 88 using the water surface elevation as a 

reference. A moving average of the pressure transducer water 

surface elevation time series (recorded at 15-minute intervals) was computed using a 2-hour (9 observation) centered 

window. Depths were then subtracted from the water surface 

elevation time series to compute bathymetric elevations.

After correction for heading, pitch, roll, sound velocity, and conversion to elevation, multibeam echosounder 

point data were edited to remove erroneous data and spikes. 

Point editing in PDS uses filters and manual editing; filters 

use metadata about each return and surrounding measured 

points to identify spikes and points of poor quality, which 

are then reviewed and removed. Manual editing was largely 

used to remove points recorded above the reservoir bottom 

when the acoustic signal was reflected off aquatic plants. 

The MB2 recorded 476,515 swaths (each a single observation in time with up to 256 point observations), for a total of 

121,987,840 possible points recorded. Of the possible points, 

58.6 percent were rejected by filters and manual editing, 

including 48.7 percent that were rejected by the echosounder’s 

quality filter, many in areas of dense aquatic plant growth, 

resulting in a total of 50,466,514 valid point observations 

after editing.

Quality Assurance Dataset: Single-Beam 

Echosounder

Bathymetric data were collected with a single-beam 

echosounder on April 23, 2018, for use as a quality-assurance 

check of the mapped multibeam echosounder data. The 

single-beam echosounder used for this study was a SyQwest 

Bathy–500 MF (fig. 5), a survey-grade echosounder 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). A 

200-kHz narrow-beam transducer (3 degrees at 3 decibels)

was used; the minimum measurable depth with this configuration was approximately 3 ft. Position data were measured using the Trimble R10 GNSS receiver with VRS RTK

corrections; the GNSS receiver was mounted directly above

the single-beam transducer during data collection. Pitch and

roll were not recorded or used in processing the single-beam

echosounder data, but the transducer was leveled on the boat

using a bubble level attached to the transducer mount; errors in

alignment of the transducer or changes in tilt of the boat while

under way can therefore contribute to errors in measurement

of depth with the single-beam echosounder.

Live echosounder readings and RTK–GNSS position data 

were integrated in the field using the hydrographic software 

HYPACK® (HYPACK, Inc., 2019), which used the NMEA 

0183 ZDA message in the GNSS data string to time synchronize position and depth data. Single-beam echosounder data 

were collected along predetermined lines, spaced approximately 350 ft apart at a 45-degree angle to the main axis of the 

reservoir; the goal of the spacing was to record data along 10 

or more lines from edge to edge of the reservoir. The configuration of these quality assurance lines followed procedures 

similar to those used by Wilson and Richards (2006).

Single-beam echosounder depth measurement was 

checked by performing a bar check, a process in which a bar 

or plate is suspended at a known depth below the echosounder 

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 was lowered into the reservoir below the 

single-beam echosounder to specified depths at 5-ft intervals 

from 5 ft to 25 ft to verify live echosounder readings. The bar 

check was performed at the start of data collection on April 23 

(table 1).

Figure 5. Single-beam echosounder. Photograph by Elizabeth 

Nystrom, U.S. Geological Survey. 
6 Bathymetry of Morris Lake (Newton Reservoir), New Jersey, 2018

Table 1. Results of bar check, April 23, 2018, Morris Lake (Newton Reservoir), New Jersey.

[Location of reservoir shown in figure 1]

Depth of bar, in feet Raw recorded depth, in feet Sound speed correction, in feet Final corrected depth, in feet

5 4.7 0.05 4.75

10 9.9 0.10 10.00

15 14.6 0.12 14.72

20 19.9 0.13 20.03

25 24.9 0.13 25.03

Single-beam echosounder data were processed using 

HYPACK; processing included correction for changes in 

sound velocity over depth, conversion from depth to elevation 

above NAVD 88, and manual editing to remove erroneous 

points or spikes. The same averaged sound velocity profile 

that was used to process the multibeam echosounder data was 

used to process the single-beam data; however, there was no 

time series of sound velocity at the surface. Depths measured 

by the single-beam echosounder were converted to elevations 

above NAVD 88 by using the same method as that for the 

multibeam echosounder, using the water surface elevation as a 

reference. After processing the single-beam echosounder data, 

9,386 point observations remained.

Bathymetric Map Creation and Results

The processed multibeam echosounder points were used 

to create a raster grid bathymetric surface, bathymetric contours, and an elevation-area-capacity table. The raster grid and 

contours were created in PDS, and the elevation-area-capacity 

table was created in a geographic information system (GIS) 

using ArcMap (Esri, Inc., 2019).

The Grid Model Editor in PDS was used to create a 

3.3-ft (1 meter) raster grid of the bathymetric surface using 

the average elevation of the edited points within a raster cell; 

the mean count of measured points within a cell was 95. 

Complete ensonification of the bathymetric surface was not 

possible, especially in shallow areas where navigation of the 

boat was limited to protect the multibeam echosounder from 

damage and areas with excessive aquatic plants. Light detection and ranging (lidar) data (OCM Partners, 2019) with root 

mean square error (RMSE) of 0.61 ft for the area surrounding 

the reservoir above the water surface elevation was used to 

supplement measured multibeam echosounder points to allow 

interpolation of shallow cells near the edge of the reservoir; 

lidar elevation values above the water surface were extracted 

from the 5-ft cell-size raster and were added as point values to 

the multibeam data. The area between the lidar and multibeam 

data was interpolated using the interpolate circular method in 

the grid editor of PDS. Additional point values were added 

manually to a shallow area on the east side of the lake to represent a group of large rocks identified from satellite imagery 

and field observations. About 11 percent of Morris Lake was 

not directly measured using the multibeam echosounder; 

mapped cells that contained no point observations (fig. 6) were 

interpolated using the interpolate circular method in PDS to 

produce a complete raster grid of Morris Lake.

Bathymetric contours were created at 2-ft intervals of 

depth and elevation above NAVD 88 from the 3.3-ft raster 

using the Grid Model Editor in PDS. A smoothing window of 4 (medium) was used and contours less than 32.8 ft 

(10 meters) long were removed. Elevation-area-capacity tables 

were calculated from the mapped raster surface at 0.1-ft intervals of depth and elevation using the three-dimensional analyst 

surface-volume tool in ArcMap (Esri, Inc., 2019).

Results of Survey

The results of the bathymetric survey (figs. 6 and 7) show 

that the deepest part of Morris Lake is just over 119 ft (maximum mapped depth 119.34 ft); the average depth is 42 ft. 

Tabular values of surface area and volume at 10-ft intervals of 

depth below the spillway and elevation above NAVD 88 are 

shown in tables 2 and 3, respectively; the full elevation-areacapacity tables at 0.1-ft increments of depth and elevation 

are available online in a USGS data release (Nystrom and 

Collenburg, 2020). Steep, rocky outcrops to the northwest of 

the reservoir continue underwater, and slopes of more than 

80 degrees are present in some areas of the reservoir; other 

areas of the reservoir are quite flat with slopes of less than 

10 degrees. At full capacity (water surface elevation equal 

to the elevation of the top of the spillway), the capacity of 

the reservoir is 1,980 million gallons and the surface area is 

145 acres (table 2). The useable capacity of the reservoir, or 

the volume above the minimum operating level for drinking 

water supply, is less than the full capacity of the reservoir. GIS 

files of the bathymetry data including the mapped bathymetric 

surface, contours and capacity tables, quality assurance points, 

and associated metadata are available for download as digital 

data in Nystrom and Collenburg (2020). These digital data are 

presented in State Plane coordinates referenced horizontally to 

NAD 83 and vertically to NAVD 88.
Bathymetric Map Creation and Results 7

0

10

20

50 60

100

90

110

10

20

30

40

70

80

New Jersey State Plane coordinate system

North American Datum of 1983

74°36'30" 74°36'

41°03'

41°02'30"

0 0.1 0.2 MILE

0 0.1 0.2 KILOMETER

EXPLANATION

Morris Lake boundary—Depth contour 0 feet deep

Interpolated (unmeasured) area

Depth below spillway elevation, in feet

119.3

0

Depth contour—Contour interval 10 feet

60

10

Figure 6. Interpolated areas and mapped bathymetric depths and depth contours of Morris Lake (Newton Reservoir), New Jersey.
8 Bathymetry of Morris Lake (Newton Reservoir), New Jersey, 2018

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1070

1060

1050

1040

1020

1000

950

1040

1000

980

970

960

990

950

1070

1050

970

960

950

940

950

1070

1060

960

950

1090

970

1030

940

1040

860

1130

1140

1110

1070

960

1030

960

940

1130

1090

1090

1070

1080

1070

1060

1030

1020

1010

1020

970

970

970 950

950

930

980

Base from New Jersey Highlands Council lidar data, 2006 and 2007

New Jersey State Plane coordinate system

North American Datum of 1983

0 0.1 0.2 MILE

0 0.1 0.2 KILOMETER

74°36'30" 74°36'

41°03'

41°02'30"

10 Depth contour—Contour interval 10 feet

Morris Lake boundary—Depth contour 0 feet deep

Elevation, in feet above North American Vertical Datum of 1988 

1,150

819

EXPLANATION

985

938.39 (spillway elevation)

Figure 7. Mapped bathymetric elevations and elevation contours of Morris Lake (Newton Reservoir), New Jersey, and elevations of 

surrounding area.
Bathymetric Map Creation and Results 9

Table 2. Reservoir area and capacity at specified depths for Morris Lake (Newton Reservoir), New Jersey.

[Location of reservoir shown in figure 1. Expanded elevation-area-capacity table is available in Nystrom and Collenburg (2020); areas shown below are rounded 

to three significant figures. NAVD 88, North American Vertical Datum of 1988]

Elevation, 

in feet above NAVD 88

Depth below spillway, 

in feet

Capacity, 

in million gallons

Area, 

in square miles

Area, 

in acres

938.39 0.00 1,980 0.226 145

928.39 10.00 1,561 0.175 112

918.39 20.00 1,231 0.135 86.4

908.39 30.00 985.6 0.109 70.0

898.39 40.00 765.5 0.102 65.1

888.39 50.00 563.5 0.0909 58.2

878.39 60.00 392.1 0.0725 46.4

868.39 70.00 261.8 0.0526 33.6

858.39 80.00 167.5 0.0393 25.1

848.39 90.00 95.52 0.0297 19.0

838.39 100.00 43.58 0.0201 12.9

828.39 110.00 11.55 0.0105 6.75

Table 3. Reservoir area and capacity at specified elevations for Morris Lake (Newton Reservoir), New Jersey.

[Location of reservoir shown in figure 1. Expanded elevation-area-capacity table is available in Nystrom and Collenburg (2020); areas shown below are rounded 

to three significant figures. NAVD 88, North American Vertical Datum of 1988]

Elevation, 

in feet above NAVD 88

Depth below spillway, 

in feet

Capacity, 

in million gallons

Area, 

in square miles

Area, 

in acres

940.00 –1.61 2,058 0.236 151

930.00 8.39 1,621 0.181 116

920.00 18.39 1,278 0.145 92.5

910.00 28.39 1,023 0.111 70.9

900.00 38.39 799.9 0.103 65.9

890.00 48.39 594.4 0.0931 59.6

880.00 58.39 417.0 0.0757 48.4

870.00 68.39 280.0 0.0558 35.7

860.00 78.39 180.9 0.0410 26.2

850.00 88.39 105.8 0.0313 20.0

840.00 98.39 50.59 0.0216 13.8

830.00 108.39 15.35 0.0121 7.75

820.00 118.39 0.03013 0.000858 0.549

Accuracy Assessment

The accuracy of the mapped multibeam echosounder 

bathymetric data was evaluated using a quality assurance 

dataset collected with a single-beam echosounder, similar to 

methods described by Wilson and Richards (2006). A total of 

9,386 quality assurance points was spatially joined with the 

mapped raster surface in a GIS and the measured elevations 

were compared (figs. 8 and 9) and descriptive statistics were 

calculated (table 4).

The National Standard for Spatial Data Accuracy, published by the Federal Geographic Data Committee (FGDC; 

1998), defines a standard for assessing map accuracy based 

on the RMSE of the data. Assuming the errors are normally 

distributed, the vertical accuracy of the map product can be 

calculated at the 95-percent accuracy level as 1.96 times the 

RMSE. 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 
10 Bathymetry of Morris Lake (Newton Reservoir), New Jersey, 2018

74°36'30" 74°36'

41°03'

41°02'30"

0 0.1 0.2 MILE

0 0.1 0.2 KILOMETER

New Jersey State Plane coordinate system

North American Datum of 1983

EXPLANATION

Slope, in degrees

83

42

0

Error, in feet [>, greater than]

Quality assurance points

−3.3 to −2

>−2 to −1

>−1 to −0.5

>−0.5 to 0

>0 to 0.5

>0.5 to 1

>1 to 2

>2 to 5

>5 to 10

>10 to 12.3 Morris Lake boundary—

Depth contour 0 feet deep

(Newton Reservoir), New Jersey.

Figure 8. Quality assurance echosounder points compared to mapped elevation and slope of bathymetric surface, Morris Lake 
Bathymetric Map Creation and Results 11

0

25

50

75

100

125

0 5 10

Error (elevation of quality assurance point

minus mapped elevation), in feet 

Depth, in feet

20

40

60

Slope of reservoir bottom, in degrees

Quality assurance points

Compared to measured multibeam depth

Compared to interpolated depth

EXPLANATION

80

0

Figure 9. Results of comparison of quality assurance points and 

mapped surface by depth and slope.

those associated with the measurements of depth, position, 

attitude of the boat (pitch, roll, heading, and heave), sound 

velocity, time synchronization errors, and other sources of 

measurement error.

Using the quality assurance dataset, errors were calculated by subtracting the multibeam echosounder mapped 

raster elevation from the measured single-beam echosounder 

point elevation. The median computed error was 0.23 ft, the 

median absolute error (the median of the absolute values of 

the computed errors) was 0.35 ft, and the 95-percent accuracy 

(computed from the RMSE of the errors) was 2.68 ft (table 4). 

Generally, the quality assurance elevations measured with 

the single-beam echosounder were about the same or slightly 

above (shallower than) the elevation measured with the multibeam echosounder (noted as positive errors in figs. 8 and 9).

The quality assurance points were categorized by 

location to determine the effects of interpolation and slope, 

and accuracy statistics were recomputed by category. The 

95-percent accuracy of interpolated areas (2.14 ft) tends to

average slightly better than the overall accuracy (2.71 ft;

table 4) because most interpolated areas were shallow and

fairly flat, and neighboring measured values provided close

estimates of unmeasured areas. However, the largest negative

errors (single-beam echosounder elevations slightly below

[deeper than] multibeam echosounder elevations) were in

the interpolated areas near the edges of the reservoir (fig. 9)

and illustrate that interpolation using the lidar data was not

accurate in all locations, likely as a result of the interpolation method. The accuracy statistics were also categorized

by the slope of the mapped surface; in flat areas (slope 0 to

10 degrees) the 95-percent accuracy was much better (0.73 ft)

than in extremely steep areas (slope 70 to 80 degrees) where

the 95-percent accuracy was 11.67 ft. Large errors can easily

occur in steep areas because even small errors in time synchronization, measurement of position and attitude of the boat,

or position of the measured point within the mapped cell can

result in large errors in measured depth. However, some of the

calculated error in extremely steep areas may also result from

the echosounder beam geometry and the incidence angle of

the echosounder on the reservoir bottom. To measure depth,

echosounders form acoustic beams that have some angular

width; the single-beam echosounder used has a nominal width

of 3 degrees (SyQwest, Inc., 2008) and the multibeam echosounder has nominal beam widths of 1.8 degrees (Teledyne

Odom Hydrographic, 2019); some sound, though less than in

the main portion of the beam, is also formed at angles away

from the center of the beam (referred to as “side lobes”).

In sloped areas, the acoustic beam will strike the bottom of

the reservoir at an angle; since some width is inherent in the

beam, part of the beam will strike the bottom (the leading

edge of the beam) before other parts (the trailing edge of the

beam; fig. 10). Depending on when the returned echo is loud

enough to be digitized by the echosounder as the measured

depth, this can result in a depth reading shallower, sometimes

by several feet, than the depth directly under the center of the

echosounder beam. Wider beam width, steeper slopes, and
12 Bathymetry of Morris Lake (Newton Reservoir), New Jersey, 2018

leading edge of 

misaligned beam 

misalignmnet beam with 3-degree Single-beam echosounder

Single-beam echosounder beam

Multibeam echosounder beam Multibeam

echosounder

swath

Depth at center of beam

Depth at trailing edge of beam

Depth at leading edge of beam 

Trailing edge

Range at leading edge 

Depth at 

Table 4. Accuracy of point elevations of single-beam echosounder quality assurance points compared to mapped multibeam 

echosounder raster surface for Morris Lake (Newton Reservoir), New Jersey, bathymetric survey.

[Location of reservoir shown in figure 1. n, number of points—each quality assurance point was compared to the corresponding elevation of mapped raster; 

RMSEz, vertical root mean square error; Accuracyz, National Standard for Spatial Data Accuracy fundamental vertical accuracy calculated at the 95-percent 

confidence level]

Area n

Median error, 

in feet

Median absolute error, 

in feet

RMSEz, 

in feet

Accuracyz, 95-percent 

confidence level, in feet

Morris Lake 9,386 0.23 0.35 1.37 2.68

Measured areas 8,870 0.26 0.35 1.38 2.71

Interpolated areas 516 –0.31 0.42 1.09 2.14

Slope 0 to 10 degrees 2,621 0.09 0.23 0.37 0.73

Slope 10 to 20 degrees 2,639 0.16 0.29 0.56 1.09

Slope 20 to 30 degrees 1,394 0.22 0.33 0.59 1.15

Slope 30 to 40 degrees 1,013 0.51 0.75 1.32 2.58

Slope 40 to 50 degrees 665 0.90 0.99 1.65 3.24

Slope 50 to 60 degrees 724 1.30 1.30 2.53 4.95

Slope 60 to 70 degrees 265 2.56 2.56 4.52 8.85

Slope 70 to 80 degrees 65 3.99 3.99 5.95 11.67

Figure 10. Echosounder beam geometry and potential cause of errors on steep slopes.
References Cited 13

deeper depths will all increase this shallow bias. To obtain the 

best return in the field from steep slopes, multibeam echosounder survey track lines are usually oriented parallel to the 

slope so that one edge of the swath (or fan) has beams hitting 

the slope more perpendicularly (fig. 10). In addition to the 

narrower beam width, this beam orientation relative to the 

slope can significantly reduce the shallow bias measured with 

the multibeam echosounder because there is less difference 

between when the leading edge and trailing edge of the beam 

strike the bottom. Furthermore, the real-time orientation of the 

single-beam is not measured as it is with the multibeam (with 

the INS), which may have introduced additional directional 

angle bias to the single-beam data, and would be exacerbated 

in high-slope areas (indicated with dashed lines in fig. 10). A 

shallow bias of the single-beam echosounder in steep areas 

can be seen by examining the sign of the errors and comparing 

the median error and the median absolute error. In flat areas 

(0 to 10 degrees slope), the median error was small (0.09 ft) 

and the median absolute error was larger (0.23 ft); however, 

in steep areas (slope 70 to 80 degrees), they were the same 

(both were 3.99 ft; table 4). Furthermore, the magnitude of the 

average signed error and average absolute error were the same 

(and not randomly distributed on either side of zero), which 

indicates that these errors likely at least partially reflect a shallow bias due to beam geometry.

Summary

A bathymetric survey of Morris Lake (Newton Reservoir) 

was conducted in April 2018 using a multibeam echosounder 

from a small moving boat. A quality assurance dataset was 

collected with a single-beam echosounder for comparison 

to the multibeam echosounder dataset. A Teledyne Odom 

MB2 multibeam echosounder with integrated inertial navigation system and real-time sound velocity measurement at the 

transducer head was used to collect multibeam data. A patch 

test was performed to calibrate and verify the performance of 

the inertial navigation system. Sound velocity profiles were 

measured to correct echosounder data for stratification with 

depth. The multibeam data were processed to include corrections for sound velocity, conversion of depth to elevation 

using a time series of water surface elevation, and to remove 

erroneous points. Following multibeam data processing and 

editing, 50,466,514 point observations remained for use in 

creation of a 3.3-foot (1 meter) raster grid. Light detection and 

ranging (lidar) data above the water surface elevation were 

used to supplement measured multibeam data. Bathymetric 

contours at 2-foot intervals of elevation and depth and an 

elevation-area-capacity table were computed from the raster 

grid. The bathymetric data and results are available as a USGS 

data release.

The results of the bathymetric survey indicate that the 

deepest part of Morris Lake is just over 119 feet and the average depth is 42 feet. Steep, rocky outcrops along the northwestern edge of the reservoir continue underwater, and slopes 

of more than 80 degrees are present in some areas of the reservoir; other areas of the reservoir are quite flat with slopes of 

less than 10 degrees. The capacity of the reservoir at full spillway level is 1,980 million gallons, and the reservoir has a surface area of 145 acres at the spillway elevation. The accuracy 

of the raster grid mapped with the multibeam echosounder 

was evaluated using a quality assurance dataset collected with 

a single-beam echosounder; 9,386 quality assurance points 

were spatially joined with the mapped raster surface in a 

geographic information system and the measured elevations 

were compared. The median computed error was 0.23 foot, 

the median absolute error was 0.35 foot, and the 95-percent 

accuracy was 2.68 feet. Generally, the quality assurance 

elevations measured with the single-beam echosounder were 

about the same or slightly greater than the elevation measured 

with the multibeam echosounder. The accuracy in interpolated 

areas and measured areas was similar, but the interpolation 

using the lidar data was not accurate in all locations. The 

95-percent accuracy in flat areas (0.73 foot) was much better 

than the accuracy in extremely steep areas (11.67 feet). Large 

errors can easily occur in steep areas because of small errors 

in measurement of position and attitude, but some of the large 

calculated errors in steep areas likely result from the beam 

geometry of the single-beam echosounder.

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

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operation guide, rev. 17: Richmond Hill, Ontario, Canada, 

PUBS–MAN–004291, 293 p.

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v. The Town of Newton et al., Reports of Cases Decided in 

the Court of Chancery of the State of New Jersey: Vol. XII: 

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Esri, Inc., 2019, ArcGIS Desktop: Esri, Inc., software release, 

accessed February 20, 2019, at https://www.esri.com/en-us/

arcgis/products/arcgis-desktop/overview.
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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, 

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surveys of rivers and lakes using a multibeam echosounder 

mapping system: U.S. Geological Survey Fact Sheet 

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KeyNet GPS website, accessed February 20, 2019, at 

http://www.keynetgps.com/.

Nystrom, E.A., and Collenburg, J.V., 2020, Geospatial 

bathymetry dataset and elevation-area-capacity table 

for Morris Lake (Newton Reservoir), New Jersey: U.S. 

Geological Survey data release, https://doi.org/10.5066/

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OCM Partners, 2019, 2006 FEMA New Jersey flood 

mitigation lidar—Highlands area: National Oceanic 

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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://www.usgs.gov/centers/ny-water

Publishing support provided by the 

Pembroke and Madison Publishing Service Centers
Nystrom and Collenburg—Bathymetry of Morris Lake (Newton Reservoir), New Jersey, 2018—Scientific Investigations Report 2020–5010

ISSN 2328-0328 (online)

https://doi.org/10.3133/sir20205010