THICKNESS AND VOLUME OF 

SEDIMENT IN PELICAN LAKE, 

SOUTH DAKOTA, JUNE 1994

By STEVEN K. SANDO

U.S. GEOLOGICAL SURVEY 

Water-Resources Investigations Report 96-4247

Prepared In cooperation with the

PELICAN LAKE WATER PROJECT DISTRICT

Rapid City, South Dakota 

1996
U.S. DEPARTMENT OF THE INTERIOR 

BRUCE BABBITT, Secretary

U.S. GEOLOGICAL SURVEY 

Gordon P. Eaton, Director

The use of firm, trade, or brand names in this report is for identification purposes 

only and does not constitute endorsement by the U.S. Geological Survey.

For addtional information write to:

District Chief 

U.S. Geological Survey 

1608 Mt. View Rd. 

Rapid City, SD 57702

Copies of this report can be purchased 

from:

U.S. Geological Survey 

Information Services 

Box 25286

Denver Federal Center 

Denver, CO 80225-0046
CONTENTS

Abstract.....................................................................................................................................................^ 1

Introduction ..............................................................................................................................................^ 1

Description of Pelican Lake area........................................................................................................................................... 3

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

Determination of horizontal position........................................................................................................................... 3

Determination of water depth and sediment thickness................................................................................................ 4

Data interpretation and analysis .................................................................................................................................. 6

Verification and effectiveness of seismic system................................................................................................................... 6

Water depth and sediment thickness...................................................................................................................................... 8

Summary...............................................................^ 16

References............................................................................................................................................................................. 16

ILLUSTRATIONS

1. Map showing location of Pelican Lake and U.S. Coast and Geodetic Survey disks near

Watertown in northeastern South Dakota................................................................................................................... 2

2. Map showing planned locations of transects for sediment survey of Pelican Lake................................................... 4

3. Map showing planned locations of transects and actual locations where water-depth records were collected.......... 5

4. Map showing planned locations of transects and actual locations where seismic records of sediment

thickness and probing-depth records were collected.................................................................................................. 6

5. Example seismic record and corresponding interpreted profile.................................................................................. 7

6. Example seismic record and corresponding interpreted profile showing interference in sub-sediment record......... 9

7. Map showing water depth in Pelican Lake, June 1994............................................................................................... 10

8. Map showing thickness of Holocene lake sediment in Pelican Lake, June 1994....................................................... 11

9. Map showing locations and depth of penetration where manual probing was performed......................................... 12

10. Map showing distribution of coarser grained and fine-grained surficial sediment in Pelican Lake........................... 13

11. Graphs showing interpreted cross-sectional profiles for selected transects across Pelican Lake, June 1994............. 14

TABLE

1. Elevation/area/capacity information for Pelican Lake................................................................................................ 10

Contents III
CONVERSION FACTORS AND VERTICAL DATUM

Multiply

acre

acre

acre-foot

acre-foot

foot

foot per second

inch

mile

square mile

square mile

yard

By

4,047

0.4047

1,233

1,613.333

0.3048

0.3048

25.4

1.609

259.0

2.590

0.9144

To obtain

square meter

hectare

cubic meter

cubic yard

meter

meter per second

millimeter

kilometer

hectare

square kilometer

meter

Sea level: In this report, "sea level" refers to the National Geodetic Vertical Datum of 1929 (NGVD 

of 1929) a geodetic datum derived from a general adjustment of the first-order level nets of both 

the United States and Canada, formerly called Sea Level Datum of 1929.

IV Contents
Thickness and Volume of Sediment in Pelican Lake, 

South Dakota, June 1994

BySTEVENK. SANDO

ABSTRACT

A survey to determine the amount and 

distribution of fine-grained Holocene lake sediment in Pelican Lake, South Dakota, was made 

during June 1994. A high-frequency, continuous 

seismic-reflection system was used to estimate 

thickness of sediment, and a global-positioning 

system was used to monitor horizontal and vertical 

position while traversing 27 northwest-southeast 

transects and one southwest-northeast transect of 

the lake. Standard electronic fathometers were 

used to measure water depth. A geographic information system was then used to generate plots of 

water depth and lake-sediment thickness, and to 

calculate lake sediment and water volumes, using 

point inputs of location, water depth, and sediment 

thickness. The water-surface elevation of Pelican 

Lake during the survey was 1,710.6 feet above sea 

level. The volume of water in Pelican Lake was 

calculated to be about 19,600 acre-feet, and the 

average depth was calculated to be 7.0 feet. The 

volume of lake sediment beneath Pelican Lake 

was estimated to be 41 million cubic yards. The 

maximum sediment thickness evident in the seismic record for the western half of the lake was 

about 23 feet, and the volume-weighted mean 

sediment thickness beneath the western half of the 

lake was about 9 feet.

INTRODUCTION

Pelican Lake is a natural lake with partial artificial regulation in Codington County, South Dakota 

(fig. 1). It serves as an important recreational resource

to numerous adjacent cabin owners as well as to the 

nearby city of Watertown. Pelican Lake is hypereutrophic; in recent years, algal blooms and declining 

fish populations have limited the recreational opportunities provided by the lake.

Pelican Lake was listed as a priority water body 

by the South Dakota Nonpoint Source Task Force for 

improvement of water quality. As a result, a Lake 

Assessment Project was initiated in August 1993 to 

determine the trophic status of the lake and develop 

specific restoration alternatives (Tony Hagen, Pelican 

Lake Water Project District, oral commun., 1995). 

Information about the amount and distribution of lake 

sediment was required as part of the Lake Assessment 

Project. Organic-rich sediments often serve as nutrient 

sources in shallow prairie lake systems (Keeney, 1973; 

Allan and others, 1980, Kenney, 1985), and restoration 

alternatives need to address possibilities for dealing 

with problems associated with sediment accumulation.

The U.S. Geological Survey, in cooperation with 

the Pelican Lake Water Project District, performed a 

sediment survey of Pelican Lake during June 1994. 

The primary objective of the survey was to determine 

the thickness and volume of fine-grained Holocene 

lake sediment deposited on top of the glacial drift that 

formed the original lake bed. A secondary objective of 

the survey was to determine the depth and volume of 

water in Pelican Lake. The purpose of this report is to 

present the results of the sediment survey of Pelican 

Lake.

Information about the amount and distribution of 

sediment in Pelican Lake was needed to develop and 

evaluate lake-management strategies, especially as 

related to sediment-dredging operations. Most adverse 

impacts from sedimentation, such as loss of capacity 

and aquatic life habitat degradation, are due primarily 

to inputs of fine-grained sediment (defined for this 

report as silt-sized or smaller sediment particles).

Introduction 1
97°15'

50'45" -

44°50'15" -

U.S. Coast and Geodetic 

A Survey Disk "Rauville"

U.S. Coast and 

Geodetic Survey 

Disk"APStaA2

50'30" -

R.54W.

T. 118N.

T. 117N.

T. 116N.

R. 53 W.

Base from U.S. Geological Survey planimetric map, 

1:100,000,1985

GtL^ ENLARGED 

AREA

R. 52 W. 

3 4 MILES

4 KILOMETERS

Figure 1 . Location of Pelican Lake and U.S. Coast and Geodetic Survey disks near Watertown in northeastern 

South Dakota.

2 Thickness and Volume of Sediment in Pelican Lake, South Dakota, June 1994
Thus, the focus of the survey was to determine the 

amount and distribution of fine-grained sediment in the 

lake. In the shallow, nearshore areas of the lake, bed 

materials generally were predominantly coarser 

grained sediments (defined for this report as sand-sized 

or larger sediment particles). Although some of this 

coarser grained material is undoubtedly of Holocene 

origin, the predominantly coarser grained sediments 

were not included in the lake-sediment thickness and 

volume as determined in this survey.

DESCRIPTION OF PELICAN LAKE AREA

Pelican Lake was formed by glacial processes, 

probably the melting of a remnant ice block, in a zone 

of glacial stagnation on the boundary between endmoraine till and outwash deposits (Steece, 1957). The 

composition of bed material of the lake shortly following its formation probably consisted of till with overlying outwash at some places. Because of the uncertainty 

concerning the specific formation processes and 

because of the water covering the sediments, the extent 

and thickness of outwash in the original lake bed is 

uncertain. Drill logs of wells located around the margin of the lake show variable outwash thicknesses, 

ranguig from 0 to about 38 feet, and show some locations where outwash immediately underlies the soil. 

Since the formation of Pelican Lake during glacial 

times, post-glacial sediment of Holocene age has been 

accumulating in the lake, reducing its original volume.

The natural drainage area of Pelican Lake is 

20.4 square miles. The lake receives surface flow from 

numerous minor ephemeral channels surrounding the 

lake. Pelican Lake is hydraulically connected to the 

Big Sioux aquifer (Hansen, 1989); typically the aquifer 

discharges to the lake and, at times, can contribute substantially to the lake. The natural outlet of Pelican 

Lake consists of a short channel connecting the lake to 

the Big Sioux River (fig. 1). This channel could also 

serve as an inlet for water moving from the Big Sioux 

River into Pelican Lake during periods of high flow in 

the Big Sioux River. In the 1930's, a low-head control 

structure on the Big Sioux River and an associated artificial channel were constructed to provide partial regulation of the water level of the lake. The control 

structure was modified in the 1980's and the current 

(June 1994) elevation of the top of the control structure 

is 1,710.2 feet (Ken Madison, South Dakota Department of Environment and Natural Resources, oral commun., 1994); the control structure serves to maintain

the minimum elevation of Pelican Lake within about 

1 foot of this elevation. During periods of high flow, 

water from the Big Sioux River is diverted into Pelican 

Lake through the artificial channel, and this can raise 

the water-surface elevation of the lake to levels it 

probably would not reach naturally.

Mean annual precipitation (1961-90) at the 

Watertown airport, located about 2.5 miles north of 

Pelican Lake (fig. 1) is 22.23 inches (U.S. Department 

of Commerce, 1994). Mean annual free-water surface 

evaporation for the Pelican Lake area is about 

41 inches (Farnsworth and others, 1982). Although 

long-term systematic records of lake stage are not 

available for Pelican Lake, water-level fluctuations 

prior to the construction of the control structure 

probably were large due to variable surface-water 

inflow and ground-water discharge, and because 

annual evaporation generally exceeds annual precipitation. Pelican Lake was known to have been completely 

dry during the 1930's prior to the construction of the 

control structure.

METHODS

The general approach for the survey was to 

traverse 27 approximately evenly spaced northwestsoutheast transects and one southwest-northeast longitudinal transect (fig. 2) by boat while simultaneously 

and continuously operating: (1) a standard water depth 

fathometer; (2) a seismic system to determine the 

thickness of fine-grained sediment; and (3) a global 

positioning system (GPS) to determine the horizontal 

position of the seismic and water depth measurements.

Determination of Horizontal Position

While operating the seismic system and 

fathometer, the horizontal position of the boat was continuously monitored using GPS. Accurate GPS positioning requires collection and post-processing of data 

that have been simultaneously transmitted by at least 4 

NAVSTAR (NAVigation Satellite Time And Ranging) 

satellites and recorded by at least 2 receivers. During 

the survey, one receiver and antenna were located at a 

U.S. Coast and Geodetic Survey topographic station 

disk (denoted "AP Sta A2"; fig. 1) of known latitude 

and longitude, which served as a stationary reference 

base station. A second receiver was located on the boat 

with the antenna positioned next to the seismic

Methods
19 20 21

23 24 OR 26 27

16

17

18.

14

0.5 1 MILES

0 0.5 1 KILOMETERS

EXPLANATION

PLANNED TRANSECTS-Number 

indicates transect identification

Base from U.S. Geological Survey 

1:24,000, Watertown West, 1969 

and Pelican Lake, 1969

Figure 2. Planned locations of transects for sediment survey of Pelican Lake.

transducer and served as a continuously operated roving receiver. Data from the two receivers were postprocessed using differential-correction techniques to 

give horizontal positions for the roving receiver. The 

GPS horizontal positions were tied to the seismic and 

water-depth records by marking the seismic thermal 

chart and the fathometer chart about every minute and 

recording an associated GPS clock time.

The accuracy and precision of the GPS measurements can be determined by positioning the roving 

GPS antenna at a standard surveying disk of known latitude and longitude located an appropriate distance 

from the base-station disk. However, appropriately 

located surveying disks of adequate horizontal-position accuracy were not present near Pelican Lake. To 

determine the accuracy of the horizontal positioning 

for this survey, the location of a Coast and Geodetic 

Survey standard disk (denoted "Rauville"; fig. 1) that 

had been disturbed and removed was estimated based 

on detailed measurements from reference marks. The 

estimated location of the disk probably was within 3 

feet of the location of the original disk. The accuracy 

of the GPS measurements was checked by locating the 

roving receiver and antenna at the estimated location of 

the Rauville disk for about one minute, generally at the 

end of each day of data collection.

Comparison of GPS positions determined when 

occupying the estimated location of the Coast and 

Geodetic Survey "Rauville" disk with the known coordinates for that disk indicated an average error of 

3.5 feet. The errors ranged from 0.2 to 5.8 feet, with a 

standard deviation of 1.7 feet.

Determination of Water Depth and 

Sediment Thickness

A standard electronic strip-chart water-depth 

fathometer was used to determine water depth. 

Accuracy of the water-depth record was determined by 

comparing with a second concurrently-operated digital 

water depth fathometer and also by comparing with 

water depth indicated in the seismic record. The elevation of the lake water surface at the time of the survey 

was estimated by periodically measuring the depth of 

water flowing over the control structure on the Big 

Sioux River and adding it to the known elevation of the 

structure. The accuracy of this elevation estimate is 

probably about plus-or-minus 0.5 foot.

The thickness of fine-grained Holocene lake sediment was determined using a continuous seismicreflection system as described in Placzek and Haeni

Thickness and Volume of Sediment in Pelican Lake, South Dakota, June 1994
(1995). Continuous seismic-reflection systems transmit and receive high-energy acoustic signals through 

the water column and sub-aqueous sediments (Haeni, 

1986). When the signal encounters layers of different 

acoustical impedance (defined as the product of density 

of a medium and the velocity of the sound within the 

medium), part of the signal is reflected back to the surface seismic receiver and part penetrates farther into 

the sediment. The strength of the reflection is dependent on the contrast in acoustic impedance between 

two adjoining layers. The average velocity of sound in 

pure water and saturated sediments (approximately 

5,000 feet per second; Gorin and Haeni, 1988) was 

used in determining the thickness of fine-grained sediment based on the seismic record. The tuned transducer of the seismic system typically was operated at 

7 kilohertz during this survey. Trials were run with the 

transducer operated at 3.5 kilohertz in an attempt to 

improve the seismic record, but little improvement was 

achieved, and all sediment thicknesses were determined using the 7-kilohertz runs. The transducer was 

suspended from a boom extending about 3 feet outward from the starboard gunnel of the boat, submersed 

about 1 foot below the water surface, and towed alongside. The reflection signal from the seismic transducer

was recorded on a thermal chart recorder and a digital 

audio tape recorder. The digital audio tape recorder 

was used to play back the seismic signal for fine-tuning 

and interpretation during data analysis, but nearly all 

sediment-thickness determinations were made from 

the chart recorder output produced in the field. To verify interpretation of the seismic record, manual probing 

and coring were performed sporadically while the seismic record, the fathometer record, and the GPS location record were being collected.

Comparison of the strip-chart fathometer record 

with the simultaneously operated digital fathometer 

generally indicated agreement within 0.3 foot for the 

water-depth measurement. Locations where waterdepth records were collected are shown in figure 3. 

Locations where sediment thickness was determined 

using the seismic system are shown in figure 4.

In parts of the lake where the seismic system was 

not effective, the thickness of fine-grained lake sediment was determined by manual probing. About every 

400 feet along the transects, the boat was anchored and 

a 1/2-inch-diameter steel rod was thrust into the sediment as far as possible, and the depth of penetration 

was measured.

19 20 21 22 23 24

14

15

13

Base from U.S. Geological Survey 

1:24,000, Watertown West, 1969 

and Pelican Lake, 1969

1 MILES

1 KILOMETERS

EXPLANATION

PLANNED TRANSECTS-Number 

indicates transect identification

LOCATION WHERE WATER-DEPTH 

RECORD WAS COLLECTED

Figure 3. Planned locations of transects and actual locations where water-depth records were collected.

Methods
19 20 21 22 23

14

15 16

17

18

13

MILES

Base from U.S. Geological Survey 

1:24,000, Watertown West, 1969 

and Pelican Lake, 1969

1 KILOMETERS

EXPLANATION

PLANNED TRANSECTS-Number 

indicates transect identification

LOCATION WHERE PROBING-DEPTH 

RECORD WAS COLLECTED

LOCATION WHERE SEDIMENTTHICKNESS RECORD WAS 

COLLECTED USING SEISMIC 

REFLECTION

Figure 4. Planned locations of transects and actual locations where seismic records of sediment thickness and probingdepth records were collected.

Data Interpretation and Analysis

Data collected in the field, including water depth, 

sediment thickness, and horizontal position, were 

loaded into the ARC/INFO Geographical Information 

System (GIS) on the U.S. Geological Survey Data 

General computer in Huron, South Dakota, to produce 

lines of equal water depth and fine-grained lakesediment thickness in Pelican Lake. A kriging procedure using a spherical function was used to produce 

lattices of the data. Lines of equal value were first constructed from the lattices, and then manually modified 

in locations where the constructed lines did not accurately represent the original measured data. The mean 

area between adjacent lines was calculated on the GIS, 

and was multiplied by the water-depth interval or sediment-thickness interval between the adjacent lines to 

calculate the volume of water or sediment within each 

interval (Blanton, 1982). Total volumes of water or 

sediment for Pelican Lake were then calculated by 

summing the volumes within each interval. Crosssectional profiles for selected transects were constructed from the plots and then modified to show 

greater detail in some sections by incorporating lakesediment thickness values taken directly from the 

original seismic record.

VERIFICATION AND EFFECTIVENESS OF 

SEISMIC SYSTEM

There were distinct changes in the seismic record 

where qualitative changes in the surficial composition 

of the bed material could be felt by manual probing 

with steel rods and PVC pipes. Typically, a change in 

intensity and/or pattern in the seismic record was associated with a change in composition of the bed 

material. An example of the seismic record and its corresponding interpreted profile are shown in figure 5 to 

illustrate how differences in bed composition are represented in the seismic record. It is evident from figure 5 

that the top of the sediment is barely visible in the 

seismic record at some locations. This is because the 

settings of the seismic system were adjusted to provide 

optimum discernment of sub-sediment surface reflectors. In some locations where the surficial sediments 

were very soft and porous, the reflector off the top of 

the sediment appeared very light in the seismic record.

Manual coring was performed using a pistontype coring unit in an effort to verify the interpretation 

of the seismic record. Although the coring unit is 

designed to allow extraction of sequential cores from a 

single hole and thus permit relatively deep penetration, 

the resistance of the sediments generally did not allow 

penetration of more than 4 or 5 feet below the

Thickness and Volume of Sediment in Pelican Lake, South Dakota, June 1994
10

15

20

25

30

 ^.o. ---^ V; "5 «T"i;trrWinterference produced ' -V?- - ,7, ^^^ftffi'&'g??1. interference produced /_

t|ii|^ ;';-T '£i^!|prby mu|tjPle signals " £ ,' ; ;: '< [ ^": '.£& :^5;^ by multiple signals \|

' '."'' '* ' r*i~"1 * «.'**" » ' "-"«,' ' *«ii v 'j-''"'PC-'>- x'

 ' *-?'" -' "- '". '.'.-':^ff*T\r,, " '

 \ '.-" ';' ii"^^^. positioning marks, ^f^J, ~"

LU

LU 5

n »J

DC 

CO 

£ 15 5

o 20

30

top of sediment

layered lake sediment 

or glacial outwash

glacial drift

Pelican Lake

LOCATION OF SEISMIC 

RECORD PROFILE

Figure 5. Example seismic record and corresponding interpreted profile.

Verification and Effectiveness of Seismic System 7
sediment-water interface. Thus, the coring was of little 

value in verifying the seismic record that typically 

showed the lake sediment/glacial drift interface to be 

about 10 feet or more below the top of the sediment.

A strong, undulating sub-sediment reflector was 

apparent beneath much of the western part of the lake 

and was interpreted to be the interface between the 

fine-grained lake sediment and underlying glacial drift. 

At some locations, several reflectors below the top of 

the sediment were apparent in the seismic record 

(fig. 5). These reflectors could represent: (1) layers of 

coarser grained lake sediment; (2) compacted layers 

that resulted from drying and oxidizing of the sediment 

during periods when the lake was dewatered; or 

(3) layers within the glacial drift (for example, layers 

of outwash on top of glacial till). Where more than one 

reflector was present below the top of the sediment, the 

deepest strong reflector was assumed to be the top of 

the glacial till, and the depth from the top of the sediment to the deepest reflector was used to estimate the 

lake-sediment thickness. This procedural choice has 

the effect of possibly including any glacial outwash or 

coarse-grained lake sediment together with the overlying fine-grained lake sediment in subsequent 

sediment-thickness estimates at locations where the 

geologic composition of the material producing the 

reflectors in the seismic record was uncertain. The 

seismic system produced easily interpretable records 

for about 65 percent of the western half of the lake.

The seismic system was not everywhere effective in distinguishing the interface between finegrained lake sediment and glacial drift, especially in 

the eastern half of Pelican Lake. Deeper reflectors 

were not always apparent in the seismic record 

because, at places, they were obscured by an interference near the top of the sediment. An example of 

seismic record with associated interpreted profile that 

shows such an interference is presented in figure 6. 

Efforts were made during the survey to reduce the 

interference in the seismic record by adjusting the 

transducer frequency, transmitter power, and chart and 

receiver gains, but these procedures were ineffective. 

The ineffectiveness of the seismic system in some areas 

probably was due to the presence of gas from the 

decomposition of organic material in the sediments. 

Accumulated gas within the sediments can act as a 

strong scatterer or reflector of the acoustic energy and 

result in interference patterns (typically multiple 

signals 1 ) that obscure deeper reflectors in the seismic 

record. Observations of gas bubbles released from the

sediments during probing indicated that gas tended to 

be more prevalent in the sediments in the eastern half 

of the lake. Locations where sediment thickness was 

estimated using manual probing are shown in figure 4.

WATER DEPTH AND SEDIMENT 

THICKNESS

Water depth in Pelican Lake is presented in 

figure 7. Elevation/area/capacity data are presented in 

table 1. The mean water surface elevation of Pelican 

Lake was about 1,710.6 feet above sea level during the 

survey. The volume of water in Pelican Lake at the 

time of the survey was calculated to be about 

19,600 acre-feet, and the surface area was 2,809 acres. 

The maximum water depth was 8.8 feet, and the 

average water depth was 7.0 feet.

Thickness of fine-grained lake sediment in the 

bed of the western half of Pelican Lake is presented in 

figure 8. In the western half of Pelican Lake, the maximum fine-grained lake-sediment thickness evident 

from the seismic record was about 23 feet, and the 

volume-weighted mean sediment thickness was about 

9 feet.

Penetration depths for manual probing in the 

eastern half of Pelican Lake are shown in figure 9. 

Manual probing was not very effective because the lake 

sediments typically were sufficiently compacted about 

1 foot below their top so that they resisted penetration. 

Also, instability of the boat, even when anchored, made 

it difficult to force the steel rod directly downward into 

the sediment. As a result, the probing penetration 

depth generally does not represent the total thickness of 

fine-grained lake sediment on top of the glacial drift. 

While probing in some locations, a distinct coarser 

grained layer that generally could not be penetrated 

more than about 1 foot was detected below the finegrained material at the top of the sediment. Whether 

this coarser grained material was coarser lake sediment 

or glacial outwash is unknown. Points where coarser 

grained material was encountered below the finegrained surficial material are indicated with an asterisk 

(*) in figure 9. Because probing penetration probably

Multiple signals can occur in the seismic record when the 

acoustic signal encounters a specific layer that reflects or scatters 

nearly all of the signal and allows little penetration. The signal 

repeatedly reflects back and forth between the specific layer and 

the water surface producing equally spaced bands in the seismic 

record.

8 Thickness and Volume of Sediment in Pelican Lake, South Dakota, June 1994
$3

30

UJ

DC

CC HC 111 ID

20

UJ 

CO

30

top of sediment

fine-grained lake sediment

glacial drift

Pelican Lake

LOCATION OF SEISMIC 

RECORD PROFILE

Figure 6. Example seismic record and corresponding interpreted profile showing interference in sub-sediment record.

Water Depth and Sediment Thickness 9
1 MILES

1 KILOMETERS

EXPLANATION

 e LINE OF EQUAL WATER DEPTHInterval, 2 feet

Base from U.S. Geological Survey 

1:24,000, Watertown West, 1969 

and Pelican Lake, 1969

Figure 7. Water depth in Pelican Lake, June 1994 (water-surface elevation 1,710.6 feet above sea level).

Table 1 . Elevation/area/capacity information for Pelican Lake

Elevation 

(feet above sea level)

1,710.6

1,710.5

1,710.0

1,709.5

1,709.0

1,708.5

1,708.0

1,707.5

1,707.0

1,706.5

1,706.0

1,705.5

1,705.0

1,704.5

1,704.0

1,703.5

1,703.0

1,702.5

1,702.0

1,701.8

Depth below water surface at 

time of survey 

(feet)

0.0

0.1

0.6

1.1

1.6

2.1

2.6

3.1

3.6

4.1

4.6

5.1

5.6

6.1

6.6

7.1

7.6

8.1

8.6

8.8

Lake surface area 

(acres)

2,809

2,806

2,792

2,777

2,763

2,743

2,724

2,701

2,678

2,607

2,535

2,431

2,327

2,039

1,977

1,730

1,386

847

242

0

Lake capacity 

(acre-feet)

19,596

19,315

17,915

16,523

15,138

13,762

12,395

11,039

9,694

8,372

7,087

5,845

4,656

3,564

2,560

1,634

855

296

24

0

10 Thickness and Volume of Sediment in Pelican Lake, South Dakota, June 1994
1 MILES

1 KILOMETERS

15

Base from U.S. Geological Survey 

1:24,000, Watertown West, 1969 

and Pelican Lake, 1969

EXPLANATION

AREA WHERE THE SEISMIC SYSTEM WAS 

LARGELY INEFFECTIVE IN DISTINGUISHING 

THE INTERFACE BETWEEN LAKE SEDIMENT 

AND GLACIAL DRIFT

LINE OF EQUAL SEDIMENT THICKNESSInterval, 2.5 feet

Figure 8. Thickness of sediment in Pelican Lake, June 1994.

Water Depth and Sediment Thickness 11
0.5

0.5

1 MILES

______I

1 KILOMETERS

Base from U.S. Geological Survey 

1:24,000, Watertown West, 1969 

and Pelican Lake, 1969

2.5

EXPLANATION

LOCATION OF MANUAL PROBING AND 

PENETRATION-Number indicates depth 

of penetration, in feet. Asterisk (*) indicates 

location where distinct layer of coarser 

grained material was encountered below 

fine-grained material.

Figure 9. Locations and depth of penetration where manual probing was performed.

12 Thickness and Volume of Sediment in Pelican Lake, South Dakota, June 1994
did not accurately measure the fine-grained lake sediment thickness, the probing measurements were not 

used in calculating the total lake sediment volume. 

Instead, the volume of fine-grained lake sediment 

beneath the eastern half of Pelican Lake was extrapolated on the basis of area using the volume-weighted 

mean sediment thickness determined from the western 

half of the lake using the seismic record. The total

volume of fine-grained lake sediment in the lake was, 

thus, estimated to be about 41 million cubic yards. The 

lateral distribution of coarser material (that is, material 

containing substantial amounts of sand and/or gravel) 

versus fine-grained material occurring at the upper 

surface of the lake sediments is presented in figure 10. 

Interpreted cross-sectional profiles for selected 

transects are presented in figure 11.

1 MILES

1 KILOMETERS

Base from U.S. Geological Survey 

1:24,000, Watertown West, 1969 

and Pelican Lake, 1969

EXPLANATION

FINE-GRAINED SURFICIAL SEDIMENT 

COARSER GRAINED SURFICIAL SEDIMENT

Figure 10. Distribution of coarser grained and fine-grained surficial sediment in Pelican Lake.

Water Depth and Sediment Thickness 13
500 1,000 1,500 2,000

DISTANCE FROM NORTHWEST SHORELINE, IN FEET

2,500 3,000

Figure 11. Interpreted cross-sectional profiles for selected transects across Pelican Lake, June 1994. 

14 Thickness and Volume of Sediment in Pelican Lake, South Dakota, June 1994
D'

10

LLI

III 15

g 20

£ 

DC

5 25

tt 0

IS £ 

I °

g

LU 

CD

LU 

Q

20

1 ''''' x ' ^

water surface

top of sediment

lake sediment

glacial drift

500 1,000 1,500 2,000 2,500 3,000 3,500 4,000 4,500 5,000 5,500 6,000

£'

30

1,000 2,000 3,000 4,000 5,000

DISTANCE FROM NORTHWEST SHORELINE, IN FEET

6,000 7,000

Pelican Lake

LOCATIONS OF INTERPRETED CROSS-SECTIONAL 

PROFILES-Number indicates transect identification

DFigure 11. Interpreted cross-sectional profiles for selected transects across Pelican Lake, June 1994.--Continued

Water Depth and Sediment Thickness 15
SUMMARY REFERENCES

A survey to determine the amount and distribution of fine-grained lake sediment in Pelican Lake, 

South Dakota, was made during June 1994. A highfrequency, continuous seismic-reflection system and 

manual probing were used to estimate thickness of 

sediment, and a global positioning system was used to 

monitor horizontal and vertical position while 

traversing 27 northwest-southeast transects and one 

southwest-northeast longitudinal transect of the lake. 

The seismic system was not everywhere effective in 

distinguishing the interface between fine-grained lake 

sediment and underlying glacial drift, especially in the 

eastern half of Pelican Lake. The ineffectiveness of the 

seismic system in some areas probably was due to the 

presence of gas from the decomposition of organic 

material in the sediments. Standard electronic 

fathometers were used to measure water depth.

A geographic information system was then used 

to generate plots of water depth and fine-grained 

Holocene lake-sediment thickness, and to calculate the 

sediment and water volumes using point inputs of location, water depth, and sediment thickness. The watersurface elevation of Pelican Lake during the survey 

was 1,710.6 feet above sea level. The volume of water 

in Pelican Lake was calculated as about 19,600 acrefeet, and the average depth was 7.0 feet. The volume 

of lake sediment in Pelican Lake was estimated to be 

41 million cubic yards. The maximum sediment thickness evident in the seismic record beneath the western 

half of the lake was about 23 feet, and the volumeweighted sediment thickness in the western half of the 

lake was about 9 feet.

Allan, R.J., Williams, J.S., Joshi, S.R., and Warwick, W.F., 

1980, Historical changes and relationship to internal 

loading of sediment phosphorus forms in hypertrophic 

prairie lakes: Journal of Environmental Quality, v. 9, 

p. 199-206.

Blanton, J.O., III, 1982, Procedures for monitoring reservoir 

sedimentation: Denver, Technical Guideline for 

Bureau of Reclamation, 40 p.

Farnsworth, R.K., Thompson, E.S., and Peck, E.L., 1982, 

Evaporation atlas for the contiguous 48 United States: 

National Oceanic and Atmospheric Administration 

Technical Report NWS 33, 26 p.

Gorin, S.R., and Haeni, P.P., 1988, Use of surface-geophysical methods to assess riverbed scour at bridge piers: 

U.S. Geological Survey Water-Resources Investigations Report 88-4212, 33 p.

Haeni, P.P., 1986, Application of continuous seismic reflection methods to hydrologic studies: Ground Water, 

v. 24, no. 1, p. 23-31.

Hansen, D.S., 1989, Water resources of Codington and Grant 

Counties, South Dakota: U.S. Geological Survey 

Water-Resources Investigations Report 89-4147, 47 p.

Keeney, D.R., 1973, The nitrogen cycle in sediment-water 

systems: Journal of Environmental Quality, v. 2, p. 15- 

29.

Kenney, B.C., 1985, Sediment resuspension and currents in 

Lake Manitoba: Journal of Great Lakes Research, v. 11, 

no. 2, p. 85-86.

Placzek, Gary, and Haeni, P.P., 1995, Surface-geophysical 

techniques used to detect existing and infilled scour 

holes near bridge piers: U.S. Geological Survey WaterResources Investigations Report 95-4009, 44 p.

Steece, F.V., 1957, Geologic map of the Watertown area, 

South Dakota: South Dakota Geological Survey 

Geologic Quadrangle Map, scale 1:62,500.

U.S. Department of Commerce, National Oceanic and 

Atmospheric Administration, Environmental Data 

Service, 1994, Climatological data, South Dakota, 

annual summary 1993: Asheville, N.C., v. 95, no. 13.

16 Thickness and Volume of Sediment in Pelican Lake, South Dakota, June 1994