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Birch

Run

Birch Run

RM1

RM2

Parking area and boat ramp

01480399

Figure 1. Bathymetric map of Chambers Lake, Chester County, Pennsylvania, September 2014.

HIBERNIA DAM

WAGONTOWN ROAD

75°50'50"

51'

51'30"

51'20"

51'10"

75°51'40"

75°51'50"

51'40"

51'30"

51'20"

51'10"

75°51'

40°02'20"

02'10"

02'

40°01'50"

40°02'10"

02'

01'50"

40°01'40"

EXPLANATION

01480399

RM1

Shaded relief—Shows depth to bottom of lake at time of bathymetric survey, in feet below water 

surface. Mean water surface during period was 579.2 feet above North American Vertical 

Datum 1988 (NAVD 88), normal pool elevation

Water surface (shoreline)—Shows approximate elevation of water surface, September 8–12, 2014. 

Mean water-surface elevation during period was 579.2 feet above NAVD 88, from PAMAP lidar 

(PAMAP, 2008)

Bathymetric index contour—Shows elevation of the lake bottom. Contour interval 10 feet. 

Elevations referenced to NAVD 88 

Intermediate bathymetric contour—Shows elevation of the lake bottom. Contour interval 2 feet. 

Elevations referenced to NAVD 88. Contours tested 2.02 feet vertical accuracy at 95-percent 

confidence level

Riser—Shows approximate location of concrete riser near dam. Elevation 583.6 feet above NAVD 88

U.S. Geological Survey reference mark and identifier

U.S. Geological Survey gaging station and identifier

570

572

0 45.8 

Base from U.S. Geological Survey National Hydrography Dataset (NHD) and Pennsylvania Department of Transportation (2015)

Pennsylvania State Plane South projection, feet, NAD83

100 50 0 100 METERS

0.10 0 0.10 MILE

100 0 100 200 300 400 500 600 700 800 900 1000 FEET Manuscript approved for publication September 14, 2015

MAGNETIC NORTH

APPROXIMATE MEAN

DECLINATION, 2015

TRUE NORTH

12°

U.S. Department of the Interior

U.S. Geological Survey

Prepared in cooperation with the

Chester County Water Resources Authority and the County of Chester

Scientific Investigations Map 3346

Bathymetry and Capacity of Chambers Lake, Chester County, Pennsylvania

By

Matthew C. Gyves

2015

Figure 2. Stage-reservoir capacity relation for Chambers Lake, Chester County, Pennsylvania, from original survey in 1991 before construction of Hibernia Dam and from 

bathymetric survey conducted in September 2014. [Capacity at elevations above 579.2 feet NAVD 88 generated from lidar. Water-surface elevation (stage) relative to the 

North American Vertical datum of 1988 (NAVD 88)]

530

540

550

560

570

580

590

600

0 250 500 750 1,000 1,250 1,500 1,750 2,000

Water-surface elevation, in feet above NAVD 88

Reservoir storage capacity, in acre-feet

Normal pool, elevation 579.2 feet NAVD 88

Auxillary spillway, elevation 586.6 feet NAVD 88

EXPLANATION

Original survey 

Bathymetric survey conducted September 2014

Capacity determined using lidar (PAMAP, 2008)

Table 1. Stage-reservoir storage capacity relation and surface area at selected watersurface elevations, Chambers Lake, Chester County, Pennsylvania, September 2014.

[NAVD 88, North American Vertical Datum of 1988; NGVD 29, National Geodetic Vertical Datum of 1929]

Elevation

(Stage; feet above 

NAVD 88)

Elevation

(Stage; feet above 

NGVD 29)

Reservoir capacity

(acre-feet)

Surface area

(acres)

536.0 536.8 0.0 0.0

538.0 538.8 0.1 0.1

540.0 540.8 0.4 0.2

542.0 542.8 1.1 0.5

544.0 544.8 2.5 1.1

546.0 546.8 6.0 2.4

548.0 548.8 12.4 4.2

550.0 550.8 22.7 6.2

552.0 552.8 37.6 8.8

554.0 554.8 58.4 12.3

556.0 556.8 87.3 16.8

558.0 558.8 125.7 21.6

560.0 560.8 173.0 25.5

562.0 562.8 227.8 29.7

564.0 564.8 292.3 34.6

566.0 566.8 366.3 39.5

568.0 568.8 450.6 44.8

570.0 570.8 546.7 51.6

572.0 572.8 656.6 58.2

574.0 574.8 778.6 63.5

576.0 576.8 910.6 69.3

578.0 578.8 1,063.0 87.0

1

579.2 580.0 1,175.4 95.7

580.0 580.8 1,252.4 97.0

582.0 582.8 1,451.3 102.3

584.0 584.8 1,666.5 111.9

586.0 586.8 1,899.2 120.9

1

Normal pool elevation.

INTRODUCTION

Chambers Lake is a manmade reservoir on Birch Run, a tributary to West Branch 

Brandywine Creek in Chester County, Pennsylvania. The lake was created in 1994 after 

the completion of Multi-Purpose Dam PA-436F (Hibernia Dam), which was built under 

the Watershed Protection & Flood Control Prevention Act (U.S. Soil Conservation 

Service, 1991). Hibernia dam is 1,700 feet upstream from the confluence of Birch Run 

with West Branch Brandywine Creek. The primary objectives for Hibernia Dam were to 

provide (1) flood control, (2) a supplemental source of water supply for the greater City 

of Coatesville public water system, and (3) recreational opportunities. The drainage basin 

of Chambers Lake encompasses approximately 4.5 square miles, and the lake covers a 

surface area of about 95 acres at normal pool, which is at an elevation of 579.2 feet above 

the North American Vertical Datum of 1988 (NAVD 88) [580.0 feet above the National 

Geodetic Vertical Datum of 1929 (NGVD 29)]. The crest of the auxiliary spillway of the 

dam is 586.6 feet above NAVD 88. The elevation of the auxiliary spillway is important to 

this investigation because this elevation defines the flood storage capacity of Chambers 

Lake. Water levels exceeding this elevation are routed through the auxiliary spillway and 

flow through adjoining woodland to Birch Run.

The U.S. Geological Survey (USGS), in cooperation with Chester County Water 

Resources Authority (CCWRA) and the County of Chester, surveyed the bathymetry and 

selected above-water features of Chambers Lake in September 2014. The purpose of the 

survey was to develop an accurate representation of the surface of the bottom of Chambers Lake and to determine the stage area and reservoir-storage capacity relation as of 

September 2014. CCWRA is responsible for operation of the dam and water-supply 

reservoir. Since construction, CCWRA has used a stage–storage capacity relation 

developed from the original survey conducted in the 1990s to estimate the volume of 

water available for water supply and the available flood storage. The bathymetric 

mapping effort was initiated due to interest in potential changes in current (2014) storage 

capacity when compared to the stage–storage capacity relation developed during design. 

The generated bathymetric surface may serve as a baseline to which temporal changes in 

storage capacity, owing to sedimentation and other factors, can be compared. In addition, 

these data will improve the overall accuracy of the stage–storage capacity table that 

CCWRA uses for reservoir and flood management operations.

This report describes the methods used to create a bathymetric map of Chambers 

Lake for the computation of reservoir storage capacity as of September 2014. The 

product is a bathymetric map (fig. 1) and a table (table 1) showing the storage capacity of 

the reservoir at 2-foot increments from minimum usable elevation up to full capacity at 

the crest of the auxiliary spillway.

METHODS

Bathymetry was measured relative to the water surface and an established gage 

datum. The water-surface elevation at the time of the bathymetric survey was monitored 

by real-time continuous-record water-level gaging station (gage) 01480399, Chambers 

Lake near Wagontown, PA, which is operated by the USGS. The gage has a recording 

interval of 15 minutes and is attached to the riser, which is just upstream from the dam 

(fig. 1). The riser is a concrete structure serving as the conduit for water flowing out of 

Chambers Lake into Birch Run. Gage datum was established using static Global 

Positioning System (GPS) techniques (Rydlund and Densmore, 2012) over a single 

control point, Reference Mark 1 (RM1), which is near the boat ramp on the southern side 

of the lake (fig. 1). RM1 is a thick shanked nail with a stainless steel washer stamped 

“USGS survey marker.” A total of 11.5 hours of static GPS observations were made at 

RM1 over 2 days. Three separate occupations were processed using the National 

Geodetic Survey’s Online Positioning Software (OPUS), and a time-weighted average 

elevation of 581.23 feet above NAVD 88 was computed. The estimated uncertainty of 

these static observations was 0.07 feet, and all requirements were met for a Level I 

survey (Rydlund and Densmore, 2012). Peak to peak errors ranged from 0.013 to 

0.028 meters or 0.04 to 0.09 feet. Peak to peak errors are an estimate of uncertainty for 

GPS observations and are based on the minimum and maximum elevations determined 

for a point during post-processing. Differential levels were then run from this reference 

mark to the water surface near the boat ramp, and a backup reference mark (RM2) was 

established along Wagontown Road (fig. 1). A surveying instrument called a total station 

was used to determine the elevation of the riser and the water surface near the dam. Gage 

readings throughout data collection (September 8–12, 2014) ranged from 580.08 to 

579.98 feet, gage datum (NGVD 29), whereas average surveyed water-surface elevations 

ranged from 579.23 to 579.13 feet above NAVD 88. A mean water-surface elevation of 

579.2 feet above NAVD 88 was used for this survey. The adjustment from NGVD 29 to 

NAVD 88 is -0.85 feet, as computed by the National Geodetic Survey’s online vertical 

datum transformation utility Vertcon v. 2.1 (National Geodetic Survey, 2003).

Bathymetric data (water depths and positions) were collected September 8–12, 2014, 

using a variety of methods. The use of commercial hydrographic software 

HydrosurveyorTM (Xylem, Inc., 2013) allowed pre-planned transect lines to be developed 

and followed during the survey. Most of the water-depth measurements were made using 

a Sontek M9 5-beam Acoustic Doppler Current Profiler (ADCP) tethered alongside a 

14-foot Jon boat. An ADCP emits sound pulses that are reflected off the lake bottom and 

received by a transducer. The water-surface elevation assigned during data collection was 

0.00 feet for all surveys. Elevation relative to NAVD 88 was computed during 

post-processing. Bathymetric data were collected with the ADCP along transect lines 

spaced approximately 50 feet apart, which is roughly 1-percent of the longitudinal length 

of the lake (Wilson and Richards, 2006). In order for an ADCP to accurately measure 

depths, the speed of sound must be computed from measurements of water temperature 

(Mueller and others, 2013). The shallow depths and low salinity typically encountered in 

freshwater lakes are not major factors affecting sound speed (U.S. Army Corps of 

Engineers, 2002). For Chambers Lake, effects of water temperature stratification are 

considered minimal because of the time of year this survey was completed. Therefore, the 

standard correction for sound speed was used. To assess depth measurement errors caused 

by incorrect water temperature and speed of sound, all soundings were processed again 

using a fixed water temperature 10 degrees lower than actually measured during the 

bathymetric survey. In the deepest part of the lake, a difference of 0.5 feet (1-percent of 

total depth) was noted. 

Position data were collected using a differentially corrected Global Positioning 

System (DGPS) mounted directly above the ADCP. The positional accuracy of the DGPS 

data is less than 1 meter (Hemisphere GNNS, Inc., 2013). In some areas of the lake, 

especially in areas of heavy aquatic growth, Real-Time Network (RTN) and Real-Time 

Kinematic (RTK) GPS techniques were required to define the lake bottom. These 

methods were also used to define selected above-water features, including the dam breast 

and auxiliary spillway. RTK observations were post-processed using the computed OPUS 

static positions previously discussed, and objective points were adjusted accordingly. 

RTN surveys use real-time corrections broadcast over the Internet. Approximately 

151,000 data points were collected during the 2014 survey. All points were loaded into 

ArcScene [Environmental Systems Research Institute, Inc. (ESRI) 2014a] and obviously 

erroneous data were removed from the dataset before any additional processing. 

For land-surface elevations above the water surface (579.2 feet above NAVD 88, 

normal-pool elevation), Light Detection and Ranging (lidar) data, collected as part of the 

PAMAP program and included in the National Elevation Dataset were used. The Pennsylvania Map Program (PAMAP) is a multi-agency effort and part of the U.S. Geological 

Survey National Map Program, administered by the Pennsylvania Department of Conservation and Natural Resources, Bureau of Topographic and Geologic Survey that enabled 

the collection of a statewide set of high-resolution lidar elevation data and digital 

orthophotographs. The vertical accuracy of this dataset is 18.5-centimeter root mean 

square error (RMSE; PAMAP Program, 2008). The lidar data were also used to define the 

extent of this analysis by creating contours within ArcGIS of the shoreline at the time of 

the survey (579.2 feet above NAVD 88), along with the elevation of the auxiliary 

spillway (586.6 feet above NAVD 88). Selected above-water features surveyed using 

GPS were compared with the lidar elevations where feasible. Differences between these 

two datasets are less than 0.10 foot for the selected features.

Geographic information system (GIS) software produced a three-dimensional 

surface of the reservoir-bottom elevations from the bathymetric data and ground survey. 

A 1.6-foot x 1.6-foot grid was interpolated using the “topo to raster” technique (ESRI, 

2014b) and snapped to the lidar raster, which assured cell alignment between the two 

datasets. Computed elevations of the bathymetric surface ranged from 533.4 to 579.2 feet 

above NAVD 88. The bathymetric surface and lidar surface were merged to create a 

surface model of the lake from the minimum usable elevation up to the auxiliary 

spillway. A table was then produced from the three-dimensional surface (table 1) using 

the surface-volume toolset in ArcGIS (ESRI, 2014). Table 1 lists surface area and water 

volumes of reservoir capacity at selected elevations. The bathymetric surface was 

contoured using GIS software and smoothed to produce 2-foot contours that were 

cartographically edited to create the bathymetric map (fig. 1).

QUALITY ASSURANCE

Accuracy of the bathymetric surface and contours is a function of the survey data 

accuracy, density of the survey data (transect interval and data-collection frequency), and 

the processing steps that occur during creation of the bathymetric surface and contours. 

As previously discussed, the water-surface elevation was measured by real-time 

continuous-record gage 01480399 to ensure depth soundings from the water surface 

would provide an accurate elevation of the lake bottom. Survey ADCP data accuracy also 

is dependent on factors such as vessel draft, platform stability, vessel velocity, and 

subsurface material density (Wilson and Richards, 2006). To reduce these errors, the draft 

(depth of ADCP in water column) was measured daily, as was the water temperature. The 

temperature measured by the ADCP is read and compared with an independent simultaneous temperature measurement made adjacent to the ADCP (Mueller and others, 2013). 

Calibrating the internal magnetic compass of instruments with an internal compass is 

encouraged prior to all ADCP measurements but is mandatory when using GPS as the 

navigation reference (Mueller and others, 2013). The compass was calibrated daily to 

provide accurate headings or after any changes in deployment or setup. Vessel speed was 

kept at less than 5 feet per second to assure adequate point spacing. 

To assess the quality of the 2014 bathymetric surface and contours, qualityassurance data were collected using transect lines that were spaced at 5 times the original 

 survey spacing (approximately 250 feet apart) and oriented at an oblique angle to the

 survey transects. Approximately 14,250 quality-assurance data points were collected

 during the 2014 survey. Data from these transects were used as an independent dataset

 allowing for computation of the accuracy of the bathymetric surface and contour map

 (Wilson and Richards, 2006). For this analysis, quality-assurance points are considered

 coincidental if they are within 0.33 foot of either the bathymetric surface or a contour.

The accuracy of the bathymetric surface and contours was calculated using the 

quality-assurance dataset and is expressed in terms of the RMSE (Wilson and Richards, 

2006), which is a statistical measure of the differences between measured data predicted 

by a model and the values actually observed. The computed RMSE of the bathymetric 

surface was 0.80 foot (1.57 feet at the 95-percent confidence interval or 2-sigma) using 

the 14,254 quality-assurance data points, meaning that 95 percent of all points on the 

surface are within 1.57 feet of the true elevation. The computed RMSE of the bathymetric 

contours was 1.03 feet (2.02 feet at the 95-percent confidence interval) using 524 

quality-assurance data points.

Bathymetric contours are less accurate than the bathymetric surface because of 

cartographic interpretation of the contours for map display. Analysis indicates the greatest 

error between the bathymetric surface and quality-assurance transects occurred in shallow 

areas, which are rockier and more erratic than deep areas. 

RESULTS

Lake water-surface elevation ranged from 579.23 to 579.13 feet above NAVD 88 

during data collection. Lake depth generally increases from west to east toward the dam 

where the lowest point of the lake bottom was 533.4 feet above NAVD 88. The lowest 

points are in a linear, trench-like feature leading to the riser. The banks and old stream 

channel of Birch Run, as well as other small tributaries, are well defined throughout the 

reservoir, especially near the dam.

 Results of the bathymetric survey indicate that at the normal pool elevation of 

579.2 feet above NAVD 88 the lake covers a surface area of 95.7 acres and holds about 

1,175 acre-feet of freshwater (table 1). Reservoir storage capacity at normal pool, as 

determined by the current survey, is about 4 percent less than the original storage capacity 

estimated at the time of construction (fig. 2, table 1). The difference in computed storage 

capacity between the current and original surveys is attributed to a combination of the 

differences in accuracy between the current and original surveys and possibly 

sedimentation, although no previous information on sediment accumulation in this 

watershed is available. The difference in accuracy between the current and original 

surveys is considered the main cause of the apparent loss in storage capacity. The original 

survey is likely less accurate because of its lower resolution, and the resulting 

stage–storage capacity relation would reflect the less accurate survey. With improvements 

in technology, a dense dataset has been used to create the new bathymetric surface that 

was used to develop the stage–storage capacity relation presented in this report. If the 

difference in storage were all the result of sediment accumulation, the sediment 

accumulation rate would be 2.22 acre-feet per year over the last 23 years (1991–2014) or 

0.023 foot per year. Although it is possible the reservoir may have lost storage capacity 

between 1994 and 2014 owing to sedimentation, the loss was probably not as high as that 

computed. Also, the recently created bathymetric map of the reservoir still clearly 

identifies the location and banks of the old stream channel, indicating that the reservoir 

probably has not experienced a substantial amount of sedimentation. A sediment transport 

study and (or) sediment cores may help in quantifying the degree to which the reservoir 

has actually filled in since 1994. Regardless of the cause, the current survey provides 

detailed documentation to assess changes in storage in the future. 

SUMMARY

The U.S. Geological Survey, in cooperation with Chester County Water Resources 

Authority and the County of Chester, conducted a bathymetric survey of Chambers Lake 

from September 8 to September 12, 2014. Chambers Lake is a manmade reservoir that 

was created in 1994 when Hibernia Dam was built on Birch Run, a tributary to West 

Branch Brandywine Creek. The survey was conducted to develop an accurate representation of the surface of the bottom of Chambers Lake. The products developed include a 

map illustrating the submerged surface of the lake bottom using 2-foot contours and a 

table for calculating the capacity of the reservoir at different water-surface elevations. 

Bathymetric data were collected using a differential global positioning system, an 

acoustic doppler current profiler, and commercially available hydrographic software. The 

data were exported into a geographic information system for mapping and calculation of 

reservoir storage volume. At a water-surface elevation of 579.2 feet above North American Vertical Datum of 1988 (580.0 feet above National Geodetic Vertical Datum of 1929), 

reservoir storage capacity for the current survey was about 1,175 acre-feet, 4 percent less 

than the original survey, which was completed around the time the dam was built in the 

early 1990s. The loss of storage is attributed to differences in accuracy and methods 

between the current (2014) and the original surveys, and possibly sedimentation of 

the lake. 

ACKNOWLEDGMENTS

The author would like to thank U.S Geological Survey colleagues for their generous 

contributions to this bathymetric survey. David Galeone, Mason Manis, Robert Meyer, 

Leif Olson, and Kirk White helped with data collection and surveying. Scott Hoffman 

provided his geographic information system expertise during technical review. Drew Reif 

and Lisa Senior provided helpful suggestions for improving the manuscript. Katharine 

Kolb and Tom Ruby provided thorough reviews of the manuscript and map. The staff 

of Hibernia County Park provided support for access to the lake and storage of 

required equipment.

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(Version 2.00): San Diego, Calif., Xylem, Inc., 138 p.

Any use of trade, product, or firm names in this publication is for descriptive purposes only and does not 

imply endorsement by the U.S. Government

This map is not to be used for navigational purposes.

If this map was printed on an electronic plotter directly from digital files, dimensional calibration may vary 

between electronic plotters and between X and Y directions on the same plotter, and paper may change 

size due to atmospheric conditions; therefore, scale and proportions may not be true on plots of this map.

For sale by U.S. Geological Survey, Information Services, Box 25286, Federal Center, Denver, CO 80225, 

1–888–ASK–USGS

Digital files available at http://dx.doi.org/10.3133/sim3346

Suggested citation: Gyves, M.C., 2015, Bathymetry and capacity of Chambers Lake, Chester County, 

Pennsylvania: U.S. Geological Survey Scientific Investigations Map 3346, http://dx.doi.org/10.3133/sim3346.

ISSN 2329-132X (online)

http://dx.doi.org/10.3133/sim3346