+-----------------------------------+------+---------------------------+
| ![](media/image1.                 |      | !                         |
| png){width="3.5590277777777777in" |      | [](media/image2.jpeg){wid |
| height="0.6201388888888889in"}    |      | th="0.7076388888888889in" |
|                                   |      | height                    |
|                                   |      | ="0.48680555555555555in"} |
|                                   |      |                           |
|                                   |      | *Agricultural Research    |
|                                   |      | Service*                  |
+-----------------------------------+------+---------------------------+
| **National Sedimentation          |      |                           |
| Laboratory**                      |      |                           |
|                                   |      |                           |
| **Channel and Watershed Processes |      |                           |
| Research Unit**                   |      |                           |
|                                   |      |                           |
| **Oxford, Mississippi 38655**     |      |                           |
|                                   |      |                           |
| **Acoustic Imaging of Sediment    |      |                           |
| Impounded by a**                  |      |                           |
|                                   |      |                           |
| **USDA-NRCS Flood Control Dam,    |      |                           |
| Oklahoma**                        |      |                           |
+-----------------------------------+------+---------------------------+
| ![](media/image3.                 |      |                           |
| jpeg){width="5.924409448818897in" |      |                           |
| height="4.0244                    |      |                           |
| 09448818898in"}![](media/image4.j |      |                           |
| peg){width="2.5681102362204724in" |      |                           |
| height="1.28346                   |      |                           |
| 45669291338in"}![](media/image5.j |      |                           |
| peg){width="1.6791338582677164in" |      |                           |
| height="1.01889                   |      |                           |
| 76377952756in"}![](media/image6.j |      |                           |
| peg){width="1.9751968503937007in" |      |                           |
| height="1.5374015748031495in"}    |      |                           |
+-----------------------------------+------+---------------------------+
| ##### []{.mark}                   |      |                           |
|                                   |      |                           |
| ##### By John A. Dunbar, Pe       |      |                           |
| ter M. Allen, and Sean J. Bennett |      |                           |
+-----------------------------------+------+---------------------------+
| **Research Report No. 22**        | **S  |                           |
|                                   | epte |                           |
|                                   | mber |                           |
|                                   | 20   |                           |
|                                   | 01** |                           |
+-----------------------------------+------+---------------------------+

#  Executive Summary

Since 1948, the USDA-NRCS has constructed nearly 11,000 upstream flood
control dams in 2000 watersheds in 47 states. Over two-thirds of these
dams have a design life of 50 years. Because of population growth, land
use changes, and time since construction, sediment pools are filling,
some structural components have deteriorated, safety regulations are
stricter, and the hazard classification has changed for some dams.
Before any rehabilitation strategy can be designed and implemented, the
sediment impounded by these dams must be assessed in terms of the
structure's efficiency to regulate floodwaters and the potential hazard
the sediment may pose if reintroduced into the environment. This report
represents the completion of a demonstration project designed to
evaluate the application of acoustic technology for the purpose of
imaging the sediment impounded by a flood control dam.

One field site was chosen for this project. Sugar Creek #12 is located
near Hinton, OK, and it is a relatively small lake with a mud bottom and
fairly shallow water depths. Previous studies have shown that excessive
sedimentation rates have significantly decreased storage capacity.
Moreover, historic land use of cultivated fields of cotton and peanuts
suggests that agrichemicals may be present in the lake sediments.

In May 2001, a subsurface sediment survey was conducted in the reservoir
pool at Sugar Creek #12 using an acoustic profiling system. The system
can comprise up to five acoustic transducers with operating frequencies
of 200, 24, 24, 12, and 3.5 kHz, a receiving hydrophone, and a signal
processor that controls the acoustic profiling, data collection and
processing, and navigational systems. This portable system was deployed
from two Johnboats. Because of water depth limitations and equipment
difficulties, only the 200 kHz transducer was used during the survey.

All collected data were post-processed to amplify the acoustic signals
at depth and to remove reverberations or multiple sound waves due to the
shallow water depth. The acoustic survey successfully identified
numerous stratigraphic horizons within the subsurface. These
stratigraphic horizons agree extremely well with sediment core data
previously collected. By combining the acoustic and sediment core data,
the distribution of sediment thickness, hence sediment volume, is
mapped. The total sediment thickness deduced using the acoustic system
agrees very well with the total sediment recovered in the core. Further
analysis of the data is not possible because of the limitation of using
only the 200 kHz transducer.

This pilot project successfully demonstrated the application of acoustic
technology for conducting fast, cost-effective sedimentation surveys
within flood control reservoirs. Improvements to the existing system
have been identified that will ultimately enable its application in all
reservoirs regardless of size, water depth, and composition and
thickness of deposited sediment.

**Table of Contents**

Executive Summary [2](#executive-summary)

1\. Introduction [8](#introduction)

1.1 Federal Program for Flood Control
[8](#federal-program-for-flood-control)

1.2 Current Status of Small Watershed Program
[9](#current-status-of-small-watershed-program)

1.3 Problem Statement [9](#problem-statement)

1.4 Previous Work [9](#previous-work)

1.5 Focus of Current Report [10](#focus-of-current-report)

2\. Field Site [11](#field-site)

2.1 Sugar Creek #12 [11](#sugar-creek-12)

3\. Sediment Coring [14](#sediment-coring)

4\. Acoustic Survey System [17](#acoustic-survey-system)

4.1 Acoustic Profiling System [17](#acoustic-profiling-system)

4.2 Survey Procedure [21](#survey-procedure)

4.3 Digital Processing of Collected Acoustic Data
[21](#digital-processing-of-collected-acoustic-data)

4.4 Interpreting the Processed Data
[26](#interpreting-the-processed-data)

4.4 Mapping Volumetrics [46](#mapping-volumetrics)

5\. Discussion [51](#discussion)

6\. Conclusions [52](#conclusions)

7\. References [54](#references)

**List of Figures**

Figure 2-1. Photograph of Sugar Creek #12 looking directly south showing
earthen embankment on left, spillway channel in far distance, and
reservoir (November 1999). [12](#__RefHeading___Toc524314198)

Figure 2-2. Photograph of Sugar Creek #12 looking toward the southwest
showing the reservoir and the main tributary on right (November 1999).
[12](#__RefHeading___Toc524314199)

Figure 2-3. Base map of Sugar Creek #12 constructed from a hand-held
global positioning system receiver with differential corrections
applied. Shown are the outline of the lake, the centerline of the
earthen embankment, the primary spillway drain, and the cement dam
marker. All positions are in UTM coordinates.
[13](#__RefHeading___Toc524314200)

Figure 3-1. Base map of Sugar Creek #12 showing locations of all cores
(numbered 1-10). Arrows show flow direction of major tributaries
entering the reservoir. All positions are in UTM coordinates.
[15](#__RefHeading___Toc524314201)

Figure 3-2. Stratigraphic logs of cores obtained at Sugar Creek #12 (see
Figure 3-1 for exact location). cl---clay, st---silt, s---sand, and
gr---gravel. [16](#__RefHeading___Toc524314202)

Figure 4-1. Photograph of Sugar Creek #12 showing the survey vessels
(May 2001). [19](#__RefHeading___Toc524314203)

Figure 4-2. Photograph of Sugar Creek #12 showing the survey vessels,
GPS antennae, and transducer mast and transducer pod (May 2001).
[19](#__RefHeading___Toc524314204)

Figure 4-3. Photograph of acoustic profiling system (May 2001).
[20](#__RefHeading___Toc524314205)

Figure 4-4. Photograph of multifrequency transducer pod (May 2001).
[20](#__RefHeading___Toc524314206)

Figure 4-5. Map of Sugar Creek #12 acoustic survey. Positions of
acoustic profiles Line 9 through Line 15 are shown and line length is
given in meters. Circles with crosses indicate the locations of 10 cores
collected by Bennett and Cooper (2001). Coordinates are given in UTM.
[23](#__RefHeading___Toc524314207)

Figure 4-6. Unprocessed field record of 200 kHz acoustic data collected
along Line 9. See Figure 4-5 for line position. The water column is
clear at a depth of 0.5 m on the south end of the line, increasing to
0.75 m on the north end. [24](#__RefHeading___Toc524314208)

Figure 4-7. Field record of 200 kHz acoustic data collected along Line 9
after digital processing. See Figure 4-5 for line position.
[25](#__RefHeading___Toc524314209)

Figure 4-8. Processed Line 9 with interpretation. See Figure 4-5 for
line position. The position of Core 7 from Bennett and Cooper (2001) is
projected onto the line from a distance of 19 m.
[28](#__RefHeading___Toc524314210)

Figure 4-9. Processed Line 10 with interpretation. See Figure 4-5 for
line position. The position of Core 10 from Bennett and Cooper (2001) is
shown. [29](#__RefHeading___Toc524314211)

Figure 4-10. Processed Line 11 with interpretation. See Figure 4-5 for
line position. [30](#__RefHeading___Toc524314212)

Figure 4-11. Processed Line 12 with interpretation. See Figure 4-5 for
line position. [31](#__RefHeading___Toc524314213)

Figure 4-12. Unprocessed (left) and processed and interpreted (on right)
Line 12. See Figure 4-5 for line position.
[32](#__RefHeading___Toc524314214)

Figure 4-13. Processed Line 12 with interpretation. See Figure 4-5 for
line position. [33](#__RefHeading___Toc524314215)

Figure 4-14. Processed Line 15 with interpretation. See Figure 4-5 for
line position. Location of Core 7 projected onto the core from a
distance of 19 m. [34](#__RefHeading___Toc524314216)

Figure 4-15. Composite profile formed from the south end of Line 11 and
the north end of Line 9. See Figure 4-5 for line positions. Location of
Core 7 projected onto the line from a distance of 19 m. The intersection
between the two lines is shown in red.
[35](#__RefHeading___Toc524314217)

Figure 4-16. Composite profile formed from the south end of Line 9 and
the east end of Line 14. See Figure 4-5 for line positions. The
intersection between the two lines is shown in red.
[36](#__RefHeading___Toc524314218)

Figure 4-17. Composite profile formed from the south end of Line 9 and
the east end of Line 15. See Figure 4-5 for line positions. Location of
Core 7 projected onto the line from a distance of 19 m. The intersection
between the two lines is shown in red.
[37](#__RefHeading___Toc524314219)

Figure 4-18. Composite profile formed from the south end of Line 10 and
the west end of Line 11. See Figure 4-5 for line positions. The
intersection between the two lines is shown in red.
[38](#__RefHeading___Toc524314220)

Figure 4-19. Composite profile formed from the south end of Line 10 and
the east end of Line 14. See Figure 4-5 for line positions. The
intersection between the two lines is shown in red.
[39](#__RefHeading___Toc524314221)

Figure 4-20. Composite profile formed from the south end of Line 10 and
the east end of Line 15. See Figure 4-5 for line positions. Location of
Core 7 projected onto the line from a distance of 19 m. The intersection
between the two lines is shown in red.
[40](#__RefHeading___Toc524314222)

Figure 4-21. Composite profile formed from the east end of Line 11 and
line 12. See Figure 4-5 for line positions. The intersection between the
two lines is shown in red. [41](#__RefHeading___Toc524314223)

Figure 4-22. Composite profile formed from the west end of Line 11 and
the north end of Line 13. See Figure 4-5 for line positions. The
intersection between the two lines is shown in red.
[42](#__RefHeading___Toc524314224)

Figure 4-23. Composite profile formed from the west end of Line 11 and
the west end of Line 14. See Figure 4-5 for line positions. The
intersection between the two lines is shown in red.
[43](#__RefHeading___Toc524314225)

Figure 4-24. Composite profile formed from the east end of Line 11 and
the north end of Line 15. See Figure 4-5 for line positions. Location of
Core 7 projected onto the line from a distance of 19 m. The intersection
between the two lines is shown in red.
[44](#__RefHeading___Toc524314226)

Figure 4-25. Stratigraphic columns and radioactive ^137^Cs emissions
(becquerels per gram; Bq/g) for Cores 4, 7, and 9 taken at Sugar Creek
#12 (Bennett and Cooper, 2001). For the stratigraphic logs, grain size
and lithologic descriptions are based on observational criteria. The
peaks in the distributions of ^137^Cs coincide with the 1964 datum, and
some samples near the top and bottom of each core had zero emissions.
[45](#__RefHeading___Toc524314227)

Figure 4-26. Contour map of water depth in Sugar Creek #12 during the
acoustic survey. All positions are in UTM coordinates.
[47](#__RefHeading___Toc524314228)

Figure 4-27. Contour map of base of sediments in Sugar Creek #12. All
positions are in UTM coordinates. [48](#__RefHeading___Toc524314229)

Figure 4-28. Contour map of the sediment thickness in Sugar Creek #12
derived from the processed and interpreted acoustic data. All positions
are in UTM coordinates. [49](#__RefHeading___Toc524314230)

**List of Tables**

Table 2-1. Changes in land use within the watershed of Sugar Creek #12
(percentages based on 2,016 acres; values are estimates). Information
provided by the USDA-NRCS field office in Hinton, OK.
[11](#table-2-1.-changes-in-land-use-within-the-watershed-of-sugar-creek-12-percentages-based-on-2016-acres-values-are-estimates.-information-provided-by-the-usda-nrcs-field-office-in-hinton-ok.)

Table 4-1. Comparison of thickness of impounded (post-construction)
sediment determined by Bennett and Cooper (2001) from sediment core data
and those determined herein using acoustic technology.
[50](#table-4-1.-comparison-of-thickness-of-impounded-post-construction-sediment-determined-by-bennett-and-cooper-2001-from-sediment-core-data-and-those-determined-herein-using-acoustic-technology.)

**Acknowledgments**

We thank L. Caldwell and G. Miller, USDA-NCRS, Stillwater, OK for
assisting and cooperating in the reservoir surveys and for reviewing the
report. B. Elder, USDA-NRCS, Hinton, OK provided logistical assistance
at the Sugar Creek #12. R. Wells and D. Wren assisted in all previous
sediment coring activities.

Author contact information:

+---+------------------------+--------------------+--------------------+
|   | John A. Dunbar         | Peter M. Allen     | Sean J. Bennett    |
|   |                        |                    |                    |
|   | Department of Geology  | Department of      | USDA-ARS           |
|   |                        | Geology            |                    |
|   | Baylor University      |                    | National           |
|   |                        | Baylor University  | Sedimentation      |
|   | P.O. Box 97354         |                    |                    |
|   |                        | P.O. Box 97354     | Laboratory         |
|   | Waco, TX 76798-7354    |                    |                    |
|   |                        | Waco, TX           | P.O. Box 1157      |
|   |                        | 76798-7354         |                    |
|   |                        |                    | Oxford, MS 38655   |
+---+------------------------+--------------------+--------------------+

# 1. Introduction

# 

## **1.1 Federal Program for Flood Control**

In response to devastating floods of the 1930's and 1940's, Congress
enacted legislation for the construction of flood control dams on small
tributary streams. The Flood Control Act of 1944 (PL-534) authorized 11
projects in the United States. Since 1948, more than 3,400 flood control
dams have been constructed in the 320 subwatershed projects covering
more than 35 million acres in 12 states (Caldwell, 1999).

In 1954, Congress enacted the Watershed Protection and Flood Preventaion
Act (PL-566), commonly referred to as the Small Watershed Program
(Caldwell, 1999). Since that time, more than 6,300 flood control dams
have been constructed in 47 states as well as Puerto Rico and the
Pacific Rim, covering over 109 million acres.

The Pilot Watershed Program provided the transition between PL-534 and
PL-566 (Caldwell, 1999). More than 400 flood control dams were
constructed in 62 projects in 33 states, covering almost 3 million
acres. In addition, the RC&D Program has provided technical and
financial assistance to local sponsors for the planning, designing, and
construction of more than 200 flood control dams since the 1960's.

In total, the U.S. Department of Agriculture, Natural Resources
Conservation Service (USDA-NRCS) and its cooperators have constructed
over 10,943 flood control dams in 47 states. More than \$8.5 billion
(1997 dollars) of federal funds and over \$6.0 billion of local funds
have been invested in these projects since 1948. This \$14.5 billion
infrastructure provides over \$1 billion in benefits annually.

The primary purposes for these structures were to prevent flooding and
to protect watersheds. Other dams were built or have evolved into
structures for water management, municipal and industrial water supply,
recreation, and the improvement of fish and wildlife, water quality, and
water conservation. Local sponsors were to provide leadership in the
program and secure land rights and easements for construction. The
USDA-NRCS was to provide technical assistance and cost-sharing for the
construction of these dams.

Flood control dams typically consist of an earthen embankment 6 to 20-m
high with a principal spillway made of concrete pipe 0.3 to 1.8-m wide
(Caldwell, 1999). Because the dams were built on small streams in the
upper reaches of watersheds, upstream drainage areas range from 1.6 to
16 km^2^. The majority of these dams were planned and designed for a
50-year service life. The inlet pipe of the principal spillway is placed
at an elevation that would provide water retention for the design storm
and storage for sediment accumulation. Each reservoir also has an
emergency or auxiliary spillway for safe conveyance of water around the
embankment when runoff rates exceed storage capacity.

## **1.2 Current Status of Small Watershed Program**

At present, more than half of the dams constructed are older than 34
years and more than 1,800 will reach their 50-year design life within
the next 10 years (Caldwell, 2000). A rapid survey conducted in April
1999 revealed more than 2,200 dams in need of immediate rehabilitation
at an estimated cost of more than \$540 million. The primary issues of
dam rehabilitation are: replacement of deteriorating components, change
in hazard classification, reservoir sedimentation, failure to meet dam
safety regulations, failure to meet resource needs of the watershed,
inadequate land and water rights, inadequate community benefits, and the
potential transfer of responsibility. Common approaches to address
rehabilitation typically involve dredging the reservoir to remove
accumulated sediment, raising the dam to increase storage capacity, and
removing or decommissioning the dam.

Rehabilitation of aging watershed flood control dams is critical to
Oklahoma. Since 1948 more than 2,100 watershed flood control dams have
been constructed including 1,140 in the Washita River Basin, which was
one of the original 11 watershed projects authorized by PL-534. Many of
these dams are in critical need of rehabilitation (Caldwell, 2000).

## **1.3 Problem Statement**

Before any rehabilitation strategy can be designed and implemented, the
sediment impounded by these dams must be assessed in terms of the
structure's efficiency to regulate floodwaters and the potential hazard
the sediment may pose if reintroduced into the environment.

For a given lake within an embankment flood control structure, the
USDA-NRCS needs to determine (1) the volume of sediment deposited, (2)
the rates of sedimentation, (3) the quality of sediment with respect to
agrichemicals (related to agricultural practices) and other
contaminants, and (4) the spatial distribution of the sediment quality.
To this end, demonstration projects were designed to evaluate
technologies, methodologies, and protocols for the cost-effective
characterization of sediment.

## **1.4 Previous Work**

Bennett and Cooper (2001) completed a study designed to evaluate
technologies, methodologies, and protocols for the cost-effective
characterization of sediment impounded within flood control reservoirs.
Three field sites were examined. Sugar Creek #12 and Sugar Creek #14 are
located near Hinton, OK, and historic land use of cultivated fields of
cotton and peanuts at Sugar Creek #12 suggests that agrichemicals may be
present in the lake sediments. Sergeant Major #4 is located near
Cheyenne, OK, and it has become the sole water supply for the town of
Cheyenne.

Seismic profiles were successfully obtained in each of the three
reservoirs in Oklahoma. However, the very shallow water depths at Sugar
Creek #12 and Sugar Creek #14 caused unwanted noise in the seismic
signal, and the processed data were virtually impossible to interpret.
The seismic profiles at Sergeant Major #4 showed a number of distinct
interpreted seismic reflectors in the subsurface.

Ten continuous, undisturbed cores of lake sediment were successfully
obtained at Sugar Creek #12. These cores were composed of sand, silt,
and clay, but most of the deposited sediment was silt and clay in nearly
equal proportions. Four continuous, undisturbed cores of lake sediment
were successfully obtained at Sergeant Major #4. These cores were
composed of poorly sorted gravel, sand, silt, and clay. Select
seismographs showed modest correlation to the stratigraphic boundaries
observed in the sediment cores

The analysis of sediment quality included 50 different pesticides,
herbicides, PCBs, heavy metals, elements, and other contaminants. A
total of 57 sediment samples obtained from these reservoirs were
analyzed. Results from testing these sediments showed very good overall
sediment quality. Residual breakdown products of DDT and methyl
parathion were found in low concentrations in all three reservoirs but
such concentrations pose no health concern.

By using radioactive Cesium (CS-137) emissions as a dating technique,
relatively high rates of sedimentation were deduced at Sugar Creek #12,
presumably related to a basin-wide historic conversion of forested areas
to cropland and knickpoint erosion and channel degradation above the
reservoir. The historic conversion of cropland to native seed grasses
within the watershed of Sergeant Major #4 has resulted in relatively low
rates of sedimentation.

## **1.5 Focus of Current Report**

Since the subsurface imaging of the sediment using geophysical
techniques employed by Bennett and Cooper (2001) was not entirely
successful, an alternate technique was sought. The goal of the present
report was to evaluate the applicability of multifrequency acoustic
profiling for determining the amount and distribution of sediment
impounded within a flood control reservoir. To achieve this end, it was
necessary to image the water bottom and the base of reservoir fill
sediments with as much clarity as possible. A secondary requirement was
the ability to image internal stratigraphy within the sediment column as
an aid to mapping sediment quality parameters within the sediment fill.
Both capabilities would support efforts to rehabilitate aging flood
control reservoirs.

# 2. Field Site

## **2.1 Sugar Creek #12**

Sugar Creek #12 is located near Hinton, OK, and it is a relatively small
lake (19 acres) with a mud bottom and fairly shallow water depths (0.6
to 2 m; Figures 2-1, 2-2, and 2-3). Dam construction was completed on
April 6, 1964. This structure has an upstream drainage area of 2,016
acres. The main stream supplying the lake is considered unstable due to
the presence of actively migrating knickpoints, and excessive
sedimentation rates have significantly decreased storage capacity. No
boat ramp is available, and access for small vessels is difficult but
tolerable.

Historic land use data for the watershed of Sugar Creek #12 are not very
extensive. In the mid-1960's near the time of dam construction, the
watershed was primarily covered with trees and pastureland (Table 2-1;
data provided by the USDA-ARS field office in Hinton, OK). Between the
mid-1960's and the mid-1980's, apparently all forested areas were
converted to cropland that included peanuts, cotton, and small grains.
Since the mid-1980's, approximately 40% of the cultivated land has been
converted to pastureland with no change in the amount of grassland and
tree-lined drains. Cultivated fields of cotton and peanuts suggests that
agrichemicals may be present in the lake sediments.

#### **Table 2-1. Changes in land use within the watershed of Sugar Creek #12 (percentages based on 2,016 acres; values are estimates). Information provided by the USDA-NRCS field office in Hinton, OK.** 

+----------------------------------+-----------+-----------+-----------+
|                                  | Time      |           |           |
|                                  | Interval  |           |           |
+----------------------------------+-----------+-----------+-----------+
| Land Use                         | m         | m         | Present   |
|                                  | id-1960's | id-1980's |           |
+----------------------------------+-----------+-----------+-----------+
| Trees                            | 55        | 0         | 0         |
+----------------------------------+-----------+-----------+-----------+
| Improved Pastureland: Bermuda,   | 10        | 27        | 50        |
| Plains                           |           |           |           |
|                                  |           |           |           |
| Bluestem, and Lovegrass          |           |           |           |
+----------------------------------+-----------+-----------+-----------+
| Cropland: Peanuts, Cotton, and   | 25        | 65        | 41        |
| Small                            |           |           |           |
|                                  |           |           |           |
| grains                           |           |           |           |
+----------------------------------+-----------+-----------+-----------+
| Native Grasses and Tree-Lined    | 10        | 8         | 9         |
| Drains                           |           |           |           |
+----------------------------------+-----------+-----------+-----------+

  -----------------------------------------------------------------------
  ![](media/image7.jpeg){width="4.995833333333334in"
  height="3.3944444444444444in"}

  []{#__RefHeading___Toc524314198 .anchor}Figure 2-1. Photograph of Sugar
  Creek #12 looking directly south showing earthen embankment on left,
  spillway channel in far distance, and reservoir (November 1999).
  -----------------------------------------------------------------------

  -----------------------------------------------------------------------
  ![](media/image8.jpeg){width="4.995833333333334in"
  height="3.3944444444444444in"}

  []{#__RefHeading___Toc524314199 .anchor}Figure 2-2. Photograph of Sugar
  Creek #12 looking toward the southwest showing the reservoir and the
  main tributary on right (November 1999).
  -----------------------------------------------------------------------

  -----------------------------------------------------------------------
  ![](media/image9.wmf){width="5.753472222222222in"
  height="7.802777777777778in"}

  []{#__RefHeading___Toc524314200 .anchor}Figure 2-3. Base map of Sugar
  Creek #12 constructed from a hand-held global positioning system
  receiver with differential corrections applied. Shown are the outline
  of the lake, the centerline of the earthen embankment, the primary
  spillway drain, and the cement dam marker. All positions are in UTM
  coordinates.
  -----------------------------------------------------------------------

# 3. Sediment Coring

Vibracoring is a common approach for obtaining undisturbed cores of
unconsolidated sediment in saturated or nearly saturated conditions
(Lanesky et al., 1979; Smith, 1984). Vibracoring works on the principle
of transferring a high-frequency vibration to a thin-walled core pipe
held in a vertical position on the sediment bed. The vibrating pipe
causes the liquefaction or fluidization of sediment only at the
core-sediment interface, thereby allowing the pipe to penetrate the
sediment with little resistance and without disrupting sediment
stratification.

A commercially available vibracoring system was used by Bennett and
Cooper (2001) to obtain sediment cores. This system uses a 1-HP motor
that drives a pair of weights (masses) eccentrically mounted on two
shafts and housed within a water-tight aluminum chamber. When in
operation, the masses rotate in opposite directions causing the chamber
to vibrate at frequencies ranging from 6000 to 8000 RPM depending upon
the sediment substrate. The chamber (driver) is connected to the top of
an aluminum irrigation pipe 1.5-mm thick, 76-mm wide, and over 3-m long
and cabled to a 4.2-m high aluminum tripod fitted with a
battery-operated winch. Since the driver is sealed, the entire system
can be immersed in water. A simple check valve placed into the flange
connecting the core pipe to the driver induces internal suction during
core extraction. The tripod is mounted to a raft that can be easily
carried and assembled on site, towed with a small boat, and anchored
into position.

Once the core was driven into the sediment, the vibrating motion was
stopped and the winch lifted the core to the water surface. When
successful, the core typically had a hard sediment bottom that acted as
a seal. If excessive sand or gravel was present at the bottom of the
core, the entire contents of the pipe would be lost during lifting. The
position of the raft was recorded with a hand-held GPS receiver whose
data were differentially corrected using available base station
information. The core was transferred to the boat and transported to
shore. Each core was opened on site by cutting the aluminum pipe
length-wise on both sides with a circular saw, and the top half of the
pipe was carefully lifted from the sediment.

Ten continuous, undisturbed cores were obtained by Bennett and Cooper
(2001) at Sugar Creek #12 and their positions are shown in Figure 3-1.
These cores ranged in length from 1.3 to 3.1 m and were extracted from
water depths ranging from 0.5 to 3 m. Stratigraphic columns of all cores
are shown in Figure 3-2. In general, the cores are composed of sand,
silt, and clay. Very thick accumulations, up to 2.4 m, of silt and clay
are common (see Cores 1, 2, 7, and 10, Figure 3-2). Many of these thick
silt and clay units have thin-bedded sand units (ca. 5 to 20 mm) within
them (see Cores 4, 9, and 10, Figure 3-2). Layers rich in organic
material such as vegetation are also common. Virtually no gravel is
observed.

  -----------------------------------------------------------------------
  ![](media/image10.wmf){width="5.760416666666667in"
  height="7.550694444444445in"}

  []{#__RefHeading___Toc524314201 .anchor}Figure 3-1. Base map of Sugar
  Creek #12 showing locations of all cores (numbered 1-10). Arrows show
  flow direction of major tributaries entering the reservoir. All
  positions are in UTM coordinates.
  -----------------------------------------------------------------------

  -----------------------------------------------------------------------
  ![](media/image11.wmf){width="6.0in" height="5.581944444444445in"}

  []{#__RefHeading___Toc524314202 .anchor}Figure 3-2. Stratigraphic logs
  of cores obtained at Sugar Creek #12 (see Figure 3-1 for exact
  location). cl---clay, st---silt, s---sand, and gr---gravel.
  -----------------------------------------------------------------------

# 4. Acoustic Survey System

## **4.1 Acoustic Profiling System**

The acoustic profiling system used herein was developed in collaboration
between Baylor University and Specialty Devices, Inc. of Plano, TX (SDI;
Dunbar, et al., 1999; Figure 4-1 to 4-4). The system was originally
intended to be used in sediment surveys of large water supply
reservoirs, but the commercialized version has been used to survey
lakes, harbors, and rivers as well. The prototype electronics module
includes one computer that controls the acoustic profiling, another that
controls navigation, a built-in computer monitor, and a differential GPS
navigation system. All of these components are contained in one,
suitcase-sized water-resistant box. The prototype module weighs 15 kg.
In the commercialized version, both subsurface profiling and navigation
operations are controlled by a single, faster computer, resulting in an
electronics module that is smaller and lighter. Power for the
electronics and acoustic source is supplied by a 12 volt marine battery.
Depending on the number and type of acoustic transducers used, the sound
source may weigh between 25 and 75 kg. Hence, even though the system was
designed for large reservoir surveys, deployment in small floodwater
retention reservoirs is logistically practical.

The system images the bottom and sub-bottom sediments with up to five
widely separated acoustic frequencies at a time. For large reservoirs,
with water depths of 5 to 50 m and sediment fill thickness of 1 to 10 m,
acoustic transducers with central frequencies of 200, 24, 24, 12, and
3.5 kHz are used. During acquisition the system collects traces using
each transducer independently in rapid succession in round-robin
fashion. The high-frequency signals provide a sharp image of low-density
fluid mud at the water bottom, whereas the low-frequency signals
penetrate many meters of sediment to image the base of sediment fill,
even in areas of high sediment accumulation. The limitation of the 12
and 3.5 kHz transducers is that they require a minimum of 3 to 5 m of
water depth to produce usable records while adding significantly to the
weight of the sound source (50 kg).

As is typical of mature floodwater reservoirs, the water depth in most
of Sugar Creek #12 was less than 1 m deep during the survey. Hence for
the Sugar Creek #12 survey, the 12 and 3.5 kHz transducers were removed
from the source pod. The resulting source pod, which includes the 200,
48 and 24 kHz transducers and frame, weighs 25 kg (Figures 4.2 and 4.4).
The 24 and 48 kHz transducers require 1 to 2 m of water depth to produce
usable records. During the survey, an extra control box that had been
added to the system as an experiment was erroneously omitted. Without
this extra control box, the 24 and 48 kHz would not work. Because most
of the lake is less than 0.6 m deep, it is unlikely that the 24 and 48
kHz data would have been usable, even if it had been collected. Hence,
the Sugar Creek #12 test was conducted with the 200 kHz transducer
alone.

In surveys of water supply reservoirs with boat ramps and significant
water depth, the profiling system is deployed from a 24-ft pontoon boat.
As is typical of floodwater retention reservoirs, boat access to Sugar
Creek #12 is limited to those that can be hand carried to the shore. A
pair of 12-ft Johnboats joined together with an aluminum frame (Figures
4-1 and 4-2) provides a stable platform from which two or three people
can work in water depths as little as 6 inches. The boats are powered
with a 4 HP outboard motor or an electric trolling motor for low-speed
profiling. The sound source is deployed on a mast between the two boats
that holds the transducers at a constant depth below the surface and in
a fixed position relative to the GPS antenna (Figure 4-2). Control over
the transducer location in some fashion similar to this is required to
achieve precision water depth information and sub-meter horizontal
positioning accuracy.

## 

  -----------------------------------------------------------------------
  ![](media/image12.jpeg){width="5.527777777777778in"
  height="3.402083333333333in"}

  []{#__RefHeading___Toc524314203 .anchor}Figure 4-1. Photograph of Sugar
  Creek #12 showing the survey vessels (May 2001).
  -----------------------------------------------------------------------

  -----------------------------------------------------------------------
  ![](media/image13.wmf){width="5.159722222222222in"
  height="3.3986111111111112in"}

  []{#__RefHeading___Toc524314204 .anchor}Figure 4-2. Photograph of Sugar
  Creek #12 showing the survey vessels, GPS antennae, and transducer mast
  and transducer pod (May 2001).
  -----------------------------------------------------------------------

## 

  -----------------------------------------------------------------------
  ![](media/image14.jpeg){width="2.9270833333333335in"
  height="3.3993055555555554in"}

  []{#__RefHeading___Toc524314205 .anchor}Figure 4-3. Photograph of
  acoustic profiling system (May 2001).
  -----------------------------------------------------------------------

  -----------------------------------------------------------------------
  ![](media/image15.wmf){width="5.879861111111111in"
  height="3.402083333333333in"}

  []{#__RefHeading___Toc524314206 .anchor}Figure 4-4. Photograph of
  multifrequency transducer pod (May 2001).
  -----------------------------------------------------------------------

## **4.2 Survey Procedure**

Conventional sediment surveys are conducted by collecting data along a
series of parallel profiles at a set spacing that provides adequate
spatial coverage, plus a number of tie lines to insure consistency in
interpretation between profiles. During the survey, the pre-planned
lines and the current boat location are displayed on the system monitor
as the boat is navigated. DGPS corrections are received from U.S. Coast
Guard beacons so that the location of the boat can be determined with
sufficient accuracy to guide it down the line in real-time. For the
Sugar Creek #12 survey, a strong correction signal was received from a
station at Sallisaw, OK, which broadcasts at 299 kHz and 200 BPS.
However for purposes of the survey, acoustic profiles were collected in
different orientations with the goal of sampling the range of sediment
thickness and water depths in the lake rather than to maximize the
spatial coverage (Figure 4-5).

## **4.3 Digital Processing of Collected Acoustic Data**

Figure 4-6 shows an unprocessed field record of the 200 kHz acoustic
data collected along Line 9. Below the water bottom, the record is
dominated by the first and second water bottom multiples. These events
correspond to sound pulses trapped in the water layer and multiple
reflected energy between the water bottom and the water surface. These
reflectors are not associated with sediment layers within the
subsurface. The deeper parts of the record (Figure 4-6) are dominated by
scattered returns from the lake sediments from depths exceeding 5 m. The
base of the sediment is not recognizable from these raw, unprocessed
data.

The main difference between conventional bathymetric surveying and
subsurface profiling is that subsurface profiling involves more
extensive digital processing and interpretation of the collected data.
The goal of post-survey processing is to correct the recordings for wave
propagation effects that interfere with the subsurface image. Two
corrections were applied to the Sugar Creek #12 data. The first, called
spherical divergence, scales the traces by a factor that increases with
time, such that the normal decay in amplitude of the signal with travel
distance is removed. In relatively deep water, this is normally the only
correction that is needed. However in shallow water typical of flood
control reservoirs like Sugar Creek #12, reverberation within the water
layer tends to mask the true subsurface returns. The reverberations are
produced as signal pulses are reflected between the water surface and
the water bottom. The second correction, called predictive
deconvolution, is a standard tool used to remove such multiples. It
works by filtering out components of the trace that are predictable,
based upon earlier parts of the trace. The repeated arrivals of pulses
trapped in the water layer fall into this category and are effectively
removed by this processing technique (Figure 4-7). To facilitate routine
application of this process to the subsurface data, a custom
implementation is used that reads the binary field records produced by
the SDI system, performs the predictive deconvolution, and writes a
processed file in the same format.

For the example shown in Figure 4-7, predictive deconvolution with a
prediction distance of 50 microseconds (10 times the dominate wave
period) was applied to remove the water bottom multiples. In the
processed record, the water bottom is more distinct, the multiples are
largely removed, and a gradational base of sediment is observable as
compared to the unprocessed record of Figure 4-6. All data collected
were processed in a similar fashion.

  -----------------------------------------------------------------------
  ![](media/image16.png){width="5.177777777777778in"
  height="6.542361111111111in"}

  []{#__RefHeading___Toc524314207 .anchor}Figure 4-5. Map of Sugar Creek
  #12 acoustic survey. Positions of acoustic profiles Line 9 through Line
  15 are shown and line length is given in meters. Circles with crosses
  indicate the locations of 10 cores collected by Bennett and Cooper
  (2001). Coordinates are given in UTM.
  -----------------------------------------------------------------------

  -----------------------------------------------------------------------
  ![](media/image17.png){width="5.999305555555556in"
  height="5.888194444444444in"}

  []{#__RefHeading___Toc524314208 .anchor}Figure 4-6. Unprocessed field
  record of 200 kHz acoustic data collected along Line 9. See Figure 4-5
  for line position. The water column is clear at a depth of 0.5 m on the
  south end of the line, increasing to 0.75 m on the north end.
  -----------------------------------------------------------------------

  -----------------------------------------------------------------------
  ![](media/image18.png){width="5.996527777777778in"
  height="6.345138888888889in"}

  []{#__RefHeading___Toc524314209 .anchor}Figure 4-7. Field record of 200
  kHz acoustic data collected along Line 9 after digital processing. See
  Figure 4-5 for line position.
  -----------------------------------------------------------------------

##  

## **4.4 Interpreting the Processed Data** 

Once the profiles are in an interpretable form, the task is to identify
the stratigraphic surfaces of interest and to trace them along each
profile. This is accomplished using a custom interpretation program
"Depthpic" that reads and displays the SDI binary files. The user traces
the water bottom and subsurface horizons by drawing on the displayed
acoustic data using the computer mouse. The depth and horizontal
position of each interpreted point is exported to a file that can be
read by a mapping program. For the Sugar Creek #12 survey, a velocity of
1470 m/s is used to represent the average velocity of both water and
sediment, which is a typical velocity for fresh water. It may
overestimate the velocity of the clay-rich sediments by as much as 3%
and it may underestimate the speed in the sand-rich sediments by as much
as 2%.

The interpretation of the acoustic data began with Line 9, which crosses
the deepest part of the sediment pool (Figure 4-8). The water bottom is
clear and traceable on this and all other profiles (shown as a blue
line, Figures 4-9 to 4-14). Below the bottom, three distinct acoustic
facies (a package or layer of sediment) can be defined, based upon the
scatter intensity level. Approximately the first meter of sediment below
the bottom on all the profiles is acoustically transparent. The
transparent acoustic facies is associated with shallow fine-grained
sediment. In places the transparent facies contains darker streaks that
thicken towards the flanks of the basin, such as near the north end of
Line 9 (near the 148 m end Figure 4-8). Where one of these streaks was
cored (Figure 4-9), it is associated with a coarse-grained layer within
the fine-grained sediments. These darker streaks are interpreted as
coarse-grained wedges shed from the flanks of the basin during prolonged
low stands. However, no attempt was made to map these small packages.

At depths greater than about 1 m below the current lake bottom, all the
records show a rapid increase in the scatter return level, causing the
displays to turn from light gray to speckled-black. This zone is called
the intermediate-scatter intensity facies. On Line 9 (between the blue
and green lines, Figure 4-8), the scatter intensity within this facies
decreases towards the center of the basin, as if the source of the
scatter is depositionally controlled within the lake environment.
However, the onset of the intensity increase does not correlate with a
recognized textural change within the cores.

Below the intermediate-scatter facies is an interval of high-scatter
intensity. The scatter intensity within this facies does not decrease
toward the center of the basin as does the overlying
intermediate-scatter intensity facies. Hence, in the center of the basin
on Line 9 (between the orange and green lines, Figure 4-8) and Line 15
(Figure 4-14), the distinction between the intermediate- and
high-scatter intensity facies is clear. On the flanks of the basin, the
difference between these two facies is subtle. The interface between the
intermediate- and high-intensity scatter facies correlates with the
interface between fine-grained and coarse-grained sediments in Core 7 on
Line 9 (Figure 4-8) and Line 15 (Figure 4-14) and Core 10 on Line 10
(Figure 4-9). This interface also correlates with the base of
post-impoundment sediment interpreted from ^137^Cs analysis of Cores 4,
7, and 9 (Figure 4-25). Therefore, the acoustically transparent and
intermediate-scatter facies correspond to the post-impoundment sediment
fill.

On all lines, the high intensity scatter facies exhibits a gradational
base, in which the scatter amplitude decays over an interval of about
0.5 m. The onset of the decay maps as an irregular surface that is
consistent from line to line (see composite Figures 4-15 to 4-24). The
surface reaches a maximum depth of 5.5 m below the water surface on Line
9 (Figure 4-8 and 4-15), at a point along the trend of the main inlet to
the lake. This surface is interpreted as the base of pre-impoundment
sediments, which likely takes the form of sand-rich alluvial sediments
and soils.

  -----------------------------------------------------------------------
  ![](media/image19.jpeg){width="5.99375in" height="6.190277777777778in"}

  []{#__RefHeading___Toc524314210 .anchor}Figure 4-8. Processed Line 9
  with interpretation. See Figure 4-5 for line position. The position of
  Core 7 from Bennett and Cooper (2001) is projected onto the line from a
  distance of 19 m.
  -----------------------------------------------------------------------

  -----------------------------------------------------------------------
  ![](media/image20.png){width="6.0in" height="5.715277777777778in"}

  []{#__RefHeading___Toc524314211 .anchor}Figure 4-9. Processed Line 10
  with interpretation. See Figure 4-5 for line position. The position of
  Core 10 from Bennett and Cooper (2001) is shown.
  -----------------------------------------------------------------------

  -----------------------------------------------------------------------
  ![](media/image21.png){width="5.997916666666667in" height="5.7875in"}

  []{#__RefHeading___Toc524314212 .anchor}Figure 4-10. Processed Line 11
  with interpretation. See Figure 4-5 for line position.
  -----------------------------------------------------------------------

  -----------------------------------------------------------------------
  ![](media/image22.png){width="5.99375in" height="4.704861111111111in"}

  []{#__RefHeading___Toc524314213 .anchor}Figure 4-11. Processed Line 12
  with interpretation. See Figure 4-5 for line position.
  -----------------------------------------------------------------------

  -----------------------------------------------------------------------
  ![](media/image23.png){width="5.990277777777778in"
  height="3.8152777777777778in"}

  []{#__RefHeading___Toc524314214 .anchor}Figure 4-12. Unprocessed (left)
  and processed and interpreted (on right) Line 12. See Figure 4-5 for
  line position.
  -----------------------------------------------------------------------

  -----------------------------------------------------------------------
  ![](media/image24.png){width="5.996527777777778in"
  height="5.045138888888889in"}

  []{#__RefHeading___Toc524314215 .anchor}Figure 4-13. Processed Line 12
  with interpretation. See Figure 4-5 for line position.
  -----------------------------------------------------------------------

  -----------------------------------------------------------------------
  ![](media/image25.png){width="5.996527777777778in"
  height="5.214583333333334in"}

  []{#__RefHeading___Toc524314216 .anchor}Figure 4-14. Processed Line 15
  with interpretation. See Figure 4-5 for line position. Location of Core
  7 projected onto the core from a distance of 19 m.
  -----------------------------------------------------------------------

  -----------------------------------------------------------------------
  ![](media/image26.jpeg){width="6.061805555555556in" height="6.1875in"}

  []{#__RefHeading___Toc524314217 .anchor}Figure 4-15. Composite profile
  formed from the south end of Line 11 and the north end of Line 9. See
  Figure 4-5 for line positions. Location of Core 7 projected onto the
  line from a distance of 19 m. The intersection between the two lines is
  shown in red.
  -----------------------------------------------------------------------

  -----------------------------------------------------------------------
  ![](media/image27.jpeg){width="5.061111111111111in"
  height="5.310416666666667in"}

  []{#__RefHeading___Toc524314218 .anchor}Figure 4-16. Composite profile
  formed from the south end of Line 9 and the east end of Line 14. See
  Figure 4-5 for line positions. The intersection between the two lines
  is shown in red.
  -----------------------------------------------------------------------

  -----------------------------------------------------------------------
  ![](media/image28.png){width="5.996527777777778in"
  height="5.436111111111111in"}

  []{#__RefHeading___Toc524314219 .anchor}Figure 4-17. Composite profile
  formed from the south end of Line 9 and the east end of Line 15. See
  Figure 4-5 for line positions. Location of Core 7 projected onto the
  line from a distance of 19 m. The intersection between the two lines is
  shown in red.
  -----------------------------------------------------------------------

  -----------------------------------------------------------------------
  ![](media/image29.png){width="5.999305555555556in"
  height="4.621527777777778in"}

  []{#__RefHeading___Toc524314220 .anchor}Figure 4-18. Composite profile
  formed from the south end of Line 10 and the west end of Line 11. See
  Figure 4-5 for line positions. The intersection between the two lines
  is shown in red.
  -----------------------------------------------------------------------

  -----------------------------------------------------------------------
  ![](media/image30.png){width="5.993055555555555in"
  height="4.5472222222222225in"}

  []{#__RefHeading___Toc524314221 .anchor}Figure 4-19. Composite profile
  formed from the south end of Line 10 and the east end of Line 14. See
  Figure 4-5 for line positions. The intersection between the two lines
  is shown in red.
  -----------------------------------------------------------------------

  -----------------------------------------------------------------------
  ![](media/image31.png){width="5.993055555555555in"
  height="4.061111111111111in"}

  []{#__RefHeading___Toc524314222 .anchor}Figure 4-20. Composite profile
  formed from the south end of Line 10 and the east end of Line 15. See
  Figure 4-5 for line positions. Location of Core 7 projected onto the
  line from a distance of 19 m. The intersection between the two lines is
  shown in red.
  -----------------------------------------------------------------------

  -----------------------------------------------------------------------
  ![](media/image32.png){width="5.99375in" height="4.256944444444445in"}

  []{#__RefHeading___Toc524314223 .anchor}Figure 4-21. Composite profile
  formed from the east end of Line 11 and line 12. See Figure 4-5 for
  line positions. The intersection between the two lines is shown in red.
  -----------------------------------------------------------------------

  -----------------------------------------------------------------------
  ![](media/image33.png){width="5.993055555555555in" height="4.46875in"}

  []{#__RefHeading___Toc524314224 .anchor}Figure 4-22. Composite profile
  formed from the west end of Line 11 and the north end of Line 13. See
  Figure 4-5 for line positions. The intersection between the two lines
  is shown in red.
  -----------------------------------------------------------------------

  -----------------------------------------------------------------------
  ![](media/image34.png){width="5.9944444444444445in"
  height="4.768055555555556in"}

  []{#__RefHeading___Toc524314225 .anchor}Figure 4-23. Composite profile
  formed from the west end of Line 11 and the west end of Line 14. See
  Figure 4-5 for line positions. The intersection between the two lines
  is shown in red.
  -----------------------------------------------------------------------

  -----------------------------------------------------------------------
  ![](media/image35.png){width="5.995138888888889in"
  height="3.936111111111111in"}

  []{#__RefHeading___Toc524314226 .anchor}Figure 4-24. Composite profile
  formed from the east end of Line 11 and the north end of Line 15. See
  Figure 4-5 for line positions. Location of Core 7 projected onto the
  line from a distance of 19 m. The intersection between the two lines is
  shown in red.
  -----------------------------------------------------------------------

## 

  -----------------------------------------------------------------------
  ![](media/image36.wmf){width="5.990972222222222in"
  height="3.9819444444444443in"}

  []{#__RefHeading___Toc524314227 .anchor}Figure 4-25. Stratigraphic
  columns and radioactive ^137^Cs emissions (becquerels per gram; Bq/g)
  for Cores 4, 7, and 9 taken at Sugar Creek #12 (Bennett and Cooper,
  2001). For the stratigraphic logs, grain size and lithologic
  descriptions are based on observational criteria. The peaks in the
  distributions of ^137^Cs coincide with the 1964 datum, and some samples
  near the top and bottom of each core had zero emissions.
  -----------------------------------------------------------------------

##  

## **4.4 Mapping Volumetrics**

The acoustic survey of Sugar Creek #12 was intended as a demonstration
of the system rather than as a detailed volumetric determination of
impounded sediment. A program of more closely spaced profiles covering
the complete lake would be required to produce accurate water and
sediment volume estimates. However, contour maps of water depth (Figure
4-26), depth to the base of sediments (Figure 4-27), and thickness of
sediment (Figure 4-28) were constructed to demonstrate how such analysis
could be performed with the data the system produces. To generate the
water and sediment depth maps, the interpreted depths and horizontal
positions for each profile were exported from Depthpic to an ASCII file
of x, y, z values. These were read by Surfer™, gridded using a minimum
curvature procedure, and contoured. The contour maps generated by
Surfer™ were then exported to a drafting program to make the final
figures. The sediment thickness map (Figure 4-28) was generated in the
same way, except that the sediment isopach thickness (the difference
between the depth to the base of sediment and the water depth) was
exported directly from Depthpic.

The resulting maps are likely to be most accurate in the northern part
of the lake, where the greatest concentration of acoustic profiles lies
and least accurate in the extreme southern part of the lake, which were
not surveyed. The sediment thickness map indicates a maximum sediment
thickness located along the axis of the main inlet in the northwest
corner of the lake. In comparison to the data collected by Bennett and
Cooper (2001), there is excellent agreement between acoustically
determined sediment thickness and the thickness observed in Cores 2, 3,
6, 7, and 10 (Table 4-1).

Since the survey was restricted to the flooded pool, not all of the
sediment deposited was taken into account. According to Larry Caldwell
(USDA-NRCS, personal communication), much sediment, especially the
coarse-grained size fractions, gets deposited within the tributary arms
entering the reservoir. These sediments were not surveyed here, yet
their contribution to the total volume of deposited sediment, hence
reservoir storage capacity, can be significant.

  -----------------------------------------------------------------------
  ![](media/image37.png){width="5.73125in" height="7.311111111111111in"}

  []{#__RefHeading___Toc524314228 .anchor}Figure 4-26. Contour map of
  water depth in Sugar Creek #12 during the acoustic survey. All
  positions are in UTM coordinates.
  -----------------------------------------------------------------------

  -----------------------------------------------------------------------
  ![](media/image38.jpeg){width="5.995138888888889in"
  height="7.567361111111111in"}

  []{#__RefHeading___Toc524314229 .anchor}Figure 4-27. Contour map of
  base of sediments in Sugar Creek #12. All positions are in UTM
  coordinates.
  -----------------------------------------------------------------------

  -----------------------------------------------------------------------
  ![](media/image39.jpeg){width="5.995138888888889in"
  height="7.567361111111111in"}

  []{#__RefHeading___Toc524314230 .anchor}Figure 4-28. Contour map of the
  sediment thickness in Sugar Creek #12 derived from the processed and
  interpreted acoustic data. All positions are in UTM coordinates.
  -----------------------------------------------------------------------

#  

#### **Table 4-1. Comparison of thickness of impounded (post-construction) sediment determined by Bennett and Cooper (2001) from sediment core data and those determined herein using acoustic technology.**

####  

+-----------------------+-----------------------+-----------------------+
| Core                  | Thickness of          |                       |
|                       | Impounded             |                       |
|                       | (Post-Construction)   |                       |
|                       |                       |                       |
|                       | Sediment (m)          |                       |
+-----------------------+-----------------------+-----------------------+
| Number                | Bennett and Cooper    | Present Study         |
|                       | (2001)                |                       |
+-----------------------+-----------------------+-----------------------+
| 1                     | 1.98                  | Outside range of data |
+-----------------------+-----------------------+-----------------------+
| 2                     | 2.44                  | 2.0                   |
+-----------------------+-----------------------+-----------------------+
| 3                     | 1.14                  | 1.2                   |
+-----------------------+-----------------------+-----------------------+
| 4                     | 1.93                  | Outside range of data |
+-----------------------+-----------------------+-----------------------+
| 5                     | 1.93                  | Outside range of data |
+-----------------------+-----------------------+-----------------------+
| 6                     | 1.04                  | 0.7                   |
+-----------------------+-----------------------+-----------------------+
| 7                     | 2.03                  | 2.1                   |
+-----------------------+-----------------------+-----------------------+
| 8                     | 1.45                  | Outside range of data |
+-----------------------+-----------------------+-----------------------+
| 9                     | 1.09                  | Outside range of data |
+-----------------------+-----------------------+-----------------------+
| 10                    | 1.47                  | 1.5                   |
+-----------------------+-----------------------+-----------------------+

# 5. Discussion

The SDI acoustic profiling system in its current configuration produced
interpretable images of the water bottom and the base of sediment fill,
satisfying the primary goal of the survey. However, there were
limitations in the survey as it was conducted with the current system.
First, the spatial coverage of the lake was limited to areas with more
than 0.25 m of water to accommodate the dimensions of the current
transducer pod and the draft of the boats. To produce accurate surveys
of this and similar lakes, it would be necessary to measure both water
depth and sediment thickness in as little as a few centimeters of water.
The ideal system and survey vessel (or amphibious vehicle) would work
and provide acoustic coverage from zero water depth at the lakeshore,
continuously out to water depths of several meters.

The second limitation was uncertainty in tracing the base of sediment
fill. Because of the gradational character of the 200 kHz acoustic
response of the basal surface in Sugar Creek #12, the basal surface can
only be traced with an accuracy of ±0.25 m with 200 kHz data alone. If
the basal surface were consistently picked wrong within this level of
uncertainty, the associated total sediment volume could be in error by
25% or more. A possible solution to this and the water depth limitation
would be to add two new frequencies to the system which bracket the
existing 200 kHz transducer. An additional 100 kHz transducer would be
operable in essentially zero water depth and would provide a sharper
image of the basal surface. An additional 400 kHz transducer would image
the water bottom in only a few centimeters of water. Finally, to operate
the system from the shore through water only a few centimeters deep it
would be necessary to switch from using boats to a small amphibious
vehicle.

The acoustic images of the sediment fill in Sugar Creek #12 contained
acoustic-stratigraphic features that correlated well with a thin
coarse-grained layers observed in previously collected cores. Hence, the
secondary objective of imaging stratigraphic surfaces within the
sediment fill was also achieved with the current system. There were also
acoustic-stratigraphic features in the data that did not correlate to
observed textural changes in the cores. The most unusual aspects of the
Sugar Creek #12 profiles is the intermediate- and high-scatter acoustic
facies and the gradational nature of the basal surface. These features
have not been observed in other small reservoirs.

# 6. Conclusions

Since 1948, the USDA-NRCS has constructed over 10,000 upstream flood
control dams in 2000 watersheds in 47 states, most with a design life of
50 years. The watershed projects, which represent a \$14 billion
infrastructure, have provided flood control, municipal water supply,
recreation, and wildlife habitat enhancement. Because of population
growth and land use changes through time, sediment pools are filling,
some structural components have deteriorated, safety regulations are
stricter, and the hazard classification for some dams has changed.

Before any rehabilitation strategy can be designed and implemented, the
sediment impounded by these dams must be assessed in terms of the
structure's efficiency to regulate floodwaters and the potential hazard
the sediment may pose if reintroduced into the environment. To this end,
a demonstration project was designed to evaluate the application of
acoustic technology to determine (1) the thickness of sediment impounded
within a flood control reservoir and (2) the spatial distribution and
characteristics of the sediments within the pool.

One field site was chosen for this demonstration project. Sugar Creek
#12 is located near Hinton, OK, and was constructed in 1964. It is a
relatively small lake with a mud bottom and fairly shallow water depths.
The main stream supplying the lake is considered unstable due to the
presence of actively migrating knickpoints, and excessive sedimentation
rates have significantly decreased storage capacity. Moreover, historic
land use of cultivated fields of cotton and peanuts suggests that
agrichemicals may be present in the lake sediments.

In May 2001, an acoustic survey of the reservoir sediments was conducted
using an acoustic subsurface profiling system. The system can comprise
up to five acoustic transducers with operating frequencies of 200, 24,
24, 12, and 3.5 kHz, a receiving hydrophone, and a signal processor that
controls the acoustic profiling, data collection and processing, and
navigational systems. This portable system was deployed from two
Johnboats. Because of water depth limitations and omitted equipment,
only the 200 kHz transducer was used during the survey.

All collected data were post-processed to amplify the acoustic signals
at depth (spherical divergence) and to remove reverberations or multiple
sound waves due to the shallow water depth (predictive deconvolution).
Once processed, the acoustic data can be interpreted and subsurface
stratigraphic horizons can be identified.

The acoustic survey successfully identified numerous stratigraphic
horizons within the subsurface. These stratigraphic horizons agree
extremely well with sediment core data previously collected. By
combining the acoustic and sediment core data, the distribution of
sediment thickness, hence sediment volume, is mapped. The thickness of
the impounded sediment deduced using the acoustic system agrees well
sediment core data previously recovered. Further analysis of the data is
not possible because of the limitation of using only the 200 kHz
transducer.

This pilot project successfully demonstrated the application of acoustic
technology for conducting fast, cost-effective sedimentation surveys
within flood control reservoirs. Improvements to the existing system
have been identified that will ultimately enable its application in all
reservoirs regardless of size, water depth, and composition and
thickness of deposited sediment.

# 7. References

Bennett, S.J., and C.M. Cooper, 2001, Characterizing the sediment
impounded by USDA-NRCS flood control dams, Oklahoma. A final report
prepared for the USDA-NRCS, Stillwater, OK. USDA-ARS National
Sedimentation Laboratory Research Report No. 20, 135pp.

Caldwell, L.W., 1999, Rehabilitating our nation's aging small watershed
projects. Presented at the Soil and Water Conservation Annual
Conference, Aug. 8-11, Biloxi, MS.

Caldwell, L.W., 2000, Good for another 100 years: The Rehabilitation of
Sergeant Major Creek Watershed. Presented at the Association of State
Dam Safety Officials, September 28-30, 2000, Providence, RI.

Dunbar, J.A., P.M. Allen, and P.D. Higley, 1999, Multifrequency acoustic
profiling for water reservoir sedimentation studies. Journal of
Sedimentary Research, 69, 521-527.

Lanesky, D.E., B.W. Logan, R.G. Brown, and A.C. Hine, 1979, A new
approach to portable vibracoring underwater and on land. Journal of
Sedimentary Petrology, 49, 654-657.

Smith, D.G., 1984, Vibracoring fluvial and deltaic sediments: Tips on
improving penetration and recovery. Journal of Sedimentary Petrology,
54, 660-663.

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