U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2019–5023

Prepared in cooperation with the Alabama Power Company

Erosion Monitoring Along Selected Bank Locations of the 

Coosa River in Alabama Using Terrestrial Light Detection 

and Ranging (T–Lidar) Technology, 2014–17
Cover. Logan Martin Dam site LM–102 on the Coosa River near Vincent, Alabama, as viewed from 

upstream mid-channel during the survey on October 30, 2015. Inset: Difference between surveyed 

surfaces at Logan Martin Dam site LM–102 on the Coosa River near Vincent, Alabama, for the 

period October 16, 2014, through July 18, 2017.

Back cover. H. Neely Henry Dam site NH–109 on the Coosa River near Gadsden, Alabama, 

as viewed from downstream mid-channel during the survey on June 23, 2015. Inset: Difference 

between surveyed surfaces at Neely Henry Dam site NH–108 on the Coosa River near Gadsden, 

Alabama, for the period January 30, 2015, through July 19, 2017. 

Photographs by Kathryn G. Lee, U.S. Geological Survey. 
Erosion Monitoring Along Selected Bank 

Locations of the Coosa River in Alabama 

Using Terrestrial Light Detection and 

Ranging (T–Lidar) Technology, 2014–17

By Richard J. Huizinga and Daniel M. Wagner

Prepared in cooperation with the Alabama Power Company

Scientific Investigations Report 2019–5023

U.S. Department of the Interior

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

DAVID BERNHARDT, Acting Secretary

U.S. Geological Survey

James F. Reilly II, Director

U.S. Geological Survey, Reston, Virginia: 2019

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Suggested citation:

Huizinga, R.J., and Wagner, D.M., 2019, Erosion monitoring along selected bank locations of the Coosa River in Alabama using terrestrial light detection and ranging (T–lidar) technology, 2014–17: U.S. Geological Survey Scientific 

Investigations Report 2019–5023, 28 p., https://doi.org/10.3133/sir20195023.

ISSN 2328-0328 (online)
iii

Acknowledgments

The authors would like to express their appreciation to our former U.S. Geological Survey colleagues, Kathryn Lee and William Moody, who were instrumental in starting the project and 

collected data for the first 2 years of the study described herein. Additionally, U.S. Geological 

Survey field technician Andrew Vanover was very helpful in subsequent data collection efforts.

The authors also appreciate the direct assistance of Keith Chandler from the Alabama Power 

Company for hourly flow data from the dams on the Coosa River.
iv

Contents

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

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

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

Purpose and Scope ..............................................................................................................................3

Description of Study Area ...................................................................................................................3

Description of Flow Conditions...........................................................................................................3

Data Collection Methods..............................................................................................................................3

Tripod-Mounted Terrestrial Light Detection and Ranging ...........................................................10

Boat-Mounted Terrestrial Light Detection and Ranging..............................................................10

Survey Data Processing ....................................................................................................................10

Survey Data Quality Assurance and Accuracy .............................................................................12

Boresight Calibration Test........................................................................................................12

Error Estimation..........................................................................................................................12

Erosion Monitoring using Terrestrial Light Detection and Ranging Surveys.....................................13

H Neely Henry Dam, Sites NH–104 and NH–108 ...........................................................................13

Site NH–104.................................................................................................................................15

Site NH–108.................................................................................................................................15

Logan Martin Dam, Sites LM–102 and LM–108 .............................................................................15

Site LM–102.................................................................................................................................15

Site LM–108.................................................................................................................................18

Walter Bouldin Dam, Sites WB–101 and WB–106.........................................................................18

Site WB–101................................................................................................................................22

Site WB–106................................................................................................................................26

General Findings and Implications ..................................................................................................26

Summary and Conclusions.........................................................................................................................27

References Cited..........................................................................................................................................28

Figures

1. Map showing location of the Coosa River Basin and associated dams in Alabama........2

2. Map showing location of survey sites NH–104 and NH–108 downstream from H

Neely Henry Dam near Gadsden, Alabama..............................................................................4

3. Map showing location of survey sites LM–102 and LM–108 downstream from

Logan Martin Dam near Vincent, Alabama ..............................................................................5

4. Map showing location of survey site WB–106 immediately downstream from

Walter Bouldin Dam near Wetumpka, Alabama......................................................................6

5. Map showing location of survey site WB–101 3.8 kilometers downstream from

Walter Bouldin Dam near Wetumpka, Alabama......................................................................7

6. Graphs showing monthly mean flows for H Neely Henry, Logan Martin, and Walter

Bouldin Dams on the Coosa River in Alabama during October 2014 to September

2017 .................................................................................................................................................8

7. Photographs showing the Teledyne-Optech ILRIS High Density Enhanced Range

laser scanner mounted on a tripod with the pan/tilt base, a survey boat, and the

FARO Focus3D X 130 laser scanner used in this study.............................................................9
v

8. Conceptual rendition of stream bank data collection using the boat-mounted light

detection and ranging system..................................................................................................11

9. Graphs showing daily mean flow on the Coosa River downstream from H Neely

Henry Dam near Gadsden, Alabama, for October 1, 2014, to September 30, 2017, by

water year, with survey dates indicated.................................................................................14

10. Surveyed banks and incremental differences between surveys at H Neely Henry

Dam site NH–104 on the Coosa River near Gadsden, Alabama, for January 30, 2015,

through July 19, 2017..................................................................................................................16

11. Surveyed banks and incremental differences between surveys at H Neely Henry

Dam site NH–108 on the Coosa River near Gadsden, Alabama, for January 30, 2015,

through July 19, 2017..................................................................................................................17

12. Graphs showing daily mean flow on the Coosa River downstream from Logan

Martin Dam near Vincent, Alabama, for October 1, 2014, to September 30, 2017, by

water year, with survey dates indicated.................................................................................19

13. Surveyed banks and incremental differences between surveys at Logan Martin

Dam site LM–102 on the Coosa River near Vincent, Alabama, for October 16, 2014,

through July 18, 2017..................................................................................................................20

14. Surveyed banks and incremental differences between surveys at Logan Martin

Dam site LM–108 on the Coosa River near Vincent, Alabama, for October 16, 2014,

through July 18, 2017..................................................................................................................21

15. Map showing surveyed points from a narrow band of data near the water line at

Logan Martin Dam site LM–108 on the Coosa River near Vincent, Alabama, for

October 16, 2014, through July 18, 2017 ..................................................................................22

16. Graphs showing daily mean flow on the Coosa River downstream from Walter

Bouldin Dam near Wetumpka, Alabama, for October 1, 2014, to September 30, 2017,

by water year, with survey dates indicated ...........................................................................23

17. Surveyed banks and incremental differences between surveys at Walter Bouldin

Dam site WB–101 on the Coosa River near Wetumpka, Alabama, for November 20,

2014, through July 20, 2017........................................................................................................24

18. Surveyed banks and incremental differences between surveys at Walter Bouldin

Dam site WB–106 on the Coosa River near Wetumpka, Alabama, for November 20,

2014, through July 20, 2017........................................................................................................25

Tables

1. Minimum and maximum horizontal and vertical errors from boat-mounted

terrestrial light detection and ranging surveys at selected bank locations

downstream from H Neely Henry and Walter Bouldin Dams on the Coosa River in

Alabama, 2014–17 .......................................................................................................................13

2. Horizontal and vertical alignment errors relative to the reference scan on June 18,

2015, from tripod-mounted terrestrial light detection and ranging surveys at

selected bank locations downstream from Logan Martin Dam on the Coosa River in

Alabama, 2014–17 .......................................................................................................................13

3. Total net and normalized erosion for selected intervals at selected bank locations

of the Coosa River in Alabama from terrestrial light detection and ranging

technology ...................................................................................................................................18
vi

Conversion Factors

U.S. customary units to International System of Units

Multiply By To obtain

Length

meter (m) 3.281 foot (ft) 

meter (m) 1.094 yard (yd) 

kilometer (km) 0.6214 mile (mi)

Volume

cubic meter (m3) 1.308 cubic yard (yd3) 

Flow rate

cubic meter per second (m3/s) 35.31 cubic foot per second (ft3/s)

Datum

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

(NAVD 88).

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

Supplemental Information

In this report, the words “left” and “right” generally refer to directions that would be reported 

by an observer facing downstream.

Normalized erosion is given in cubic meters per square meter (m3/m2).
vii

Abbreviations

° degree

ER Enhanced Range

FOV field of view

GNSS Global Navigation Satellite System

HD High Density

IMU inertial measurement unit

INS inertial navigation system

M3C2 Multiscale Model-to-Model Cloud Comparison

MC–lidar motion-compensated light detection and ranging

MMS Mobile Mapping Suite

OPUS online positioning user service

POS-MV Position and Orientation Solution for Marine Vessels

PPK postprocessed kinematic (a type of differential correction for navigation with GNSS)

ROI region of interest

SBET smoothed best estimate of trajectory

TIN triangulated irregular network

T–lidar terrestrial light detection and ranging

Erosion Monitoring Along Selected Bank Locations of the 

Coosa River in Alabama Using Terrestrial Light Detection 

and Ranging (T–Lidar) Technology, 2014–17

By Richard J. Huizinga and Daniel M. Wagner

Abstract

The Alabama Power Company operates a series of 

dams on the Coosa River in east central Alabama. Seven 

dams impound the river to form six reservoirs: Weiss Lake, 

H Neely Henry Lake, Logan Martin Lake, Lay Lake, Lake 

Mitchell, and Lake Jordan. Streamflow below these reservoirs 

is primarily controlled by power generation at the dams, and 

there is ongoing concern about the stability of selected stream 

banks downstream from the dams. During relicensing in the 

early 2000s, the Alabama Power Company and stakeholders 

identified particular areas of concern to monitor and document 

the extent of erosion. The U.S. Geological Survey, in cooperation with the Alabama Power Company, conducted a 3-year 

monitoring program, from 2014 to 2017, of the geomorphic 

conditions of six selected reaches along the Coosa River. The 

six reaches included two downstream from H Neely Henry 

Dam near Gadsden, two downstream from Logan Martin 

Dam near Vincent, and two downstream from Walter Bouldin 

Dam near Wetumpka, Alabama. The geomorphic monitoring was conducted using boat- and tripod-mounted terrestrial 

light detection and ranging technology. Site LM–108, an 

island in the Coosa River downstream from Logan Martin 

Dam, exhibited the greatest amount of normalized erosion, 

2.05 cubic meters per square meter of area, likely because 

this site experiences head-on flow from the river. Bank retreat 

at the upstream end of the island (LM–108) was estimated at 

2.9 meters for the study period. The remaining five reaches 

were exposed to shear flow from the river; the greatest amount 

of normalized erosion, 0.467 cubic meter per square meter of 

area, was exhibited by site WB–106 on the right bank downstream from Walter Bouldin Dam. Results of the comparisons 

of terrestrial light detection and ranging scans indicated that 

intervals between scans that exhibited the greatest amounts of 

erosion generally corresponded to periods of above-median 

flow, and that intervals between scans that exhibited the least 

amounts of erosion, or deposition, generally corresponded 

to periods of below-median flow. Relatively smaller surface 

areas could be surveyed at some sites because inundation 

or dense vegetation obscured parts of the banks, suggesting 

that, in future investigations, it may be preferable to conduct 

scans during periods of leaf-off and low flow to avoid bias 

introduced by parts of the banks of interest being inundated or 

obscured by vegetation.

Introduction

The Alabama Power Company operates a series of dams 

on the Coosa River (fig. 1) in east-central Alabama. Seven 

dams impound the river to form six reservoirs: Weiss Lake, 

H Neely Henry Lake, Logan Martin Lake, Lay Lake, Lake 

Mitchell, and Lake Jordan. Two dams are associated with Lake 

Jordan: Jordan Dam, which is on the Coosa River, and Walter 

Bouldin Dam, which is on a diversion channel from Lake Jordan to the Coosa River downstream from Jordan Dam. These 

seven dams provide power generation, flood control, recreation, economic opportunity, and fish and wildlife habitats to 

the region.

Discharges below these reservoirs are primarily controlled by power generation at the dams, and there has been an 

ongoing concern about the stability of selected stream banks 

downstream from the dams (Kimbrow and Lee, 2013). As part 

of Federal Energy Regulatory Commission relicensure of the 

Coosa River project in the early 2000s, the Alabama Power 

Company and various stakeholders identified particular areas 

of concern and wanted to take steps to monitor and document the extent of erosion. The U.S. Geological Survey, in 

cooperation with the Alabama Power Company, conducted a 

monitoring program of the geomorphic conditions of selected 

reaches along the Coosa River downstream from H Neely 

Henry Dam near Gadsden, Logan Martin Dam near Vincent, 

and Walter Bouldin Dam near Wetumpka, Alabama. Boat- and 

tripod-mounted terrestrial light detection and ranging (T–lidar) 

technology was used to determine the condition of the bank 

at each study area. The results of this investigation serve as a 

valuable tool for the Alabama Power Company in evaluating 

any effects on the stream channel geomorphology.

T–lidar technology has proven to be well suited for erosion and mass-failure studies where conventional surveying 
2 Erosion Monitoring Along Bank Locations of the Coosa River Using Terrestrial Light Detection and Ranging Technology

Base from US Geological Survey digital data, 1995, 1:2,000,000

Universal Transverse Mercator projection, zone 16 North

Horizontal coordinate information referenced to the North American Datum of 1983 (NAD 83) 0 10 20 30 40 50 60 70 MILES

0 25 50 75 100 KILOMETERS

89° 88° 87° 86° 85°

35°

34°

33°

32°

31°

EXPLANATION

Upper Coosa Basin

Middle Coosa Basin

Lower Coosa Basin

Weiss Dam

H Neely Henry Dam

Logan Martin Dam

Lay Dam

Mitchell Dam

Jordan Dam

Walter Bouldin Dam

Vincent

Birmingham

Gadsden

ALABAMA

Wetumpka

Montgomery

Weiss Lake

H Neely Henry Lake

Lay Lake

Lake Mitchell

Logan Martin Lake

Lake Jordon

Coosa River

Figure 1. Location of the Coosa River Basin and associated dams in Alabama.
Data Collection Methods 3

techniques may be dangerous and inadequate in supplying 

the necessary topographic detail for erosion-based analysis 

(Collins and others, 2007; Stock and others, 2011). T–lidar 

technology was used to document and quantify any changes in 

stream bank morphology during a 3-year period. Two surveys 

were conducted annually (generally in the summer and fall) 

for 3 years to determine channel geometry at specific bank 

locations above the water line. A comparison of the T–lidar 

datasets allow the U.S. Geological Survey and Alabama Power 

Company to quantify the approximate volume of bank material eroded from a given site.

Purpose and Scope

The purpose of this report is to document the results of 

periodic stream bank surveys completed from 2014 to 2017 at 

six locations downstream from three dams on the Coosa River 

in Alabama using T–lidar. Equipment and methods used and 

results obtained are described. The results obtained from the 

stream bank surveys document the conditions at the time of 

the surveys, and differences between surveys can be used to 

determine rates of erosion, which are correlated to streamflow 

conditions between surveys.

Description of Study Area

The study area included six survey sites on the Coosa 

River, consisting of two specific reach locations downstream 

from three selected dams: H Neely Henry Dam (fig. 2), Logan 

Martin Dam (fig. 3), and Walter Bouldin Dam (figs. 4–5). 

The location and length of these reaches was determined by 

the Alabama Power Company and stakeholders. The naming 

convention illustrated in figures 2–5 corresponds to Alabama 

Power Company’s existing monitoring program. There are two 

survey sites downstream from H Neely Henry Dam: NH–104, 

a long reach on the right bank (fig. 2), and NH–108, a short 

reach on the left bank farther downstream (fig. 2). Downstream from Logan Martin Dam, site LM–102 on the right 

bank (fig. 3) was the subject of the previous study (Kimbrow 

and Lee, 2013); site LM–108 is the upstream end of an island 

near the right bank (fig. 3). Downstream from Walter Bouldin 

Dam, site WB–106 is on the right bank near the dam (fig. 4), 

whereas site WB–101 is on the left bank about 3.8 kilometers 

downstream from the dam (fig. 5).

Description of Flow Conditions

Hourly flows from H Neely Henry, Logan Martin, 

and Walter Bouldin Dams that represent flow through the 

generators and floodgates but do not include seepage flows 

were obtained from the Alabama Power Company (Keith E. 

Chandler, Alabama Power Company, written commun., 2018). 

Monthly mean flows were computed from the hourly flows for 

October 1, 2014, to September 30, 2017, and were generally 

lowest from May to November and highest from December to 

April, although flow conditions were highly variable during 

the study period (fig. 6). Alabama’s proximity to the Gulf 

of Mexico results in increased precipitation during the late 

autumn, winter, and early spring when cold, dry continental air 

masses are forced southward by the polar jet stream and meet 

warm, moist maritime air originating over the gulf (Evans, 

1999). Monthly flow conditions for H Neely Henry, Logan 

Martin, and Walter Bouldin Dams are described separately.

Hourly flow through H Neely Henry Dam generators and 

floodgates during October 1, 2014, to September 30, 2017, 

ranged from 0 cubic meters per second (m3/s) on several days 

to 2,640 m3/s at 4:00 a.m. on December 26, 2015. The median 

hourly flow during the period was 232 m3/s. Monthly mean 

flow through H Neely Henry Dam ranged from 47.6 m3/s 

during the month of November 2016 to 808 m3/s during the 

month of December 2015 (fig. 6A). The median monthly flow 

during October 1, 2014, to September 30, 2017, was 169 m3/s 

(fig. 6A).

Hourly flow through Logan Martin Dam generators and 

floodgates during October 1, 2014, to September 30, 2017, 

ranged from 0 m3/s on several days to 2,120 m3/s at 9:00 a.m. 

on December 28, 2015. The median hourly flow during the 

period was 171 m3/s. Monthly mean flow through Logan Martin Dam ranged from 59.5 m3

/s during the month of November 

2016 to 953 m3/s during the month of January 2016 (fig. 6B). 

The median monthly flow during October 1, 2014, to September 30, 2017, was 193 m3

/s (fig. 6B).

Walter Bouldin Dam is on a diversion channel from 

Jordan Lake that flows into the Coosa River downstream 

from Jordan Dam. Because of this, flow characteristics of 

Walter Bouldin Dam differ from those of H Neely Henry and 

Logan Martin Dams. Flow from Jordan Lake is preferentially 

released through Jordan Dam for habitat maintenance on the 

Coosa River; therefore, it is not uncommon to have substantial periods of no flow from Walter Bouldin Dam. Hourly 

flow through Walter Bouldin Dam generators and floodgates 

during October 1, 2014, to September 30, 2017, ranged from 

0 m3/s on several days to 822 m3/s at 12:00 p.m. on April 8, 

2017. The median hourly flow during the period was 0 m3/s. 

Monthly mean flow through Walter Bouldin Dam ranged from 

1.70 m3/s during the month of November 2016 to 656 m3/s 

during the month of January 2016 (fig. 6C). The median 

monthly flow during October 1, 2014, to September 30, 2017, 

was 170 m3/s (fig. 6C).

Data Collection Methods

Bank condition and stability at each site was determined 

using either a tripod- or boat-mounted T–lidar system. For all 

the surveys completed in this investigation, the primary instrument used was a Teledyne-Optech ILRIS High Density (HD) 

Enhanced Range (ER) laser scanner (Teledyne-Optech, 2012; 

figs. 7A, 7B); this is the same type of scanner that was used in 
4 Erosion Monitoring Along Bank Locations of the Coosa River Using Terrestrial Light Detection and Ranging Technology

86°03'20" 86°03'00" 86°02'40" 86°02'20"

33°47'00"

33°46'40"

33°46'20"

33°46'00"

33°45'40"

0 500 1,000 1,500 2,000 FEET

Base from National Agriculture Imagery Program, 2015 0 100 200 300 400 500 600 METERS

Universal Transverse Mercator projection, zone 16 North

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

Gadsden

Map area

NH–108

NH–104

H NEELY HENRY DAM

ALABAMA

Approximate location of

temporary benchmark near

Hart’s Ferry boat ramp 

Figure 2. Location of survey sites NH–104 and NH–108 downstream from H Neely Henry Dam near Gadsden, Alabama.
Data Collection Methods 5

86°20'40" 86°20'20" 86°20'00"

33°25'40"

33°25'20"

33°25'00"

0 250 500 750 1,000 FEET

Base from National Agriculture Imagery Program, 2015 0 100 200 300 METERS

Universal Transverse Mercator projection, zone 16 North

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

Map area

Vincent

LM–102

LM–108

LOGAN MARTIN DAM

ALABAMA

Figure 3. Location of survey sites LM–102 and LM–108 downstream from Logan Martin Dam near Vincent, 

Alabama.
6 Erosion Monitoring Along Bank Locations of the Coosa River Using Terrestrial Light Detection and Ranging Technology

86°17' 86°16'40" 86°16'20"

32°35'

32°34'40"

32°34'20"

0 250 500 750 1,000 FEET

Base from National Agriculture Imagery Program, 2015 0 100 200 300 METERS

Universal Transverse Mercator projection, zone 16 North

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

Map area Wetumpka

WB–106

WALTER BOULDIN DAM

ALABAMA

Figure 4. Location of survey site WB–106 immediately downstream from Walter Bouldin Dam near Wetumpka, Alabama.
Data Collection Methods 7

86°16'20" 86°16'00" 86°15'40"

32°33'20"

32°33'00"

32°32'40"

0 250 500 750 1,000 FEET

0 100 200 300 METERS Base from National Agriculture Imagery Program, 2015

Universal Transverse Mercator projection, zone 16 North

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

Map area Wetumpka

WB–101

ALABAMA

Figure 5. Location of survey site WB–101 3.8 kilometers downstream from Walter Bouldin Dam near Wetumpka, 

Alabama.
8 Erosion Monitoring Along Bank Locations of the Coosa River Using Terrestrial Light Detection and Ranging Technology

Fall 2014 survey

November 20, 2014

Summer 2015 survey

June 19, 2015

Fall 2015 survey

January 26, 2016

Summer 2016 survey

July 11, 2016

Fall 2016 survey

November 2, 2016

Summer 2017 survey

July 20, 2017

Fall 2014 survey

October 16, 2014

Summer 2015 survey

June 18, 2015

Fall 2015 survey

October 30, 2015

Summer 2016 survey

June 14, 2016

Fall 2016 survey

November 1, 2016

Summer 2017 survey

July 18, 2017

Fall 2014 survey

January 30, 2015

Summer 2015 survey

June 23, 2015

Fall 2015 survey

December 10, 2015

Summer 2016 survey

July 6, 2016

Fall 2016 survey

October 31, 2016

Summer 2017 survey

July 19, 2017

Date

Monthly mean flow, in cubic meters per second

0

900800700600500400300200100

0

900800700600500400300200100

1,000

10/2014

11/2014

1/2015

2/2015

3/2015

5/2015

12/2014

4/2015

9/2015

6/2015

7/2015

8/2015

1/2016

12/2015

3/2016

4/2016

5/2016

6/2016

2/2016

8/2016

7/2016

10/2016

11/2016

12/2016

9/2016

2/2017

3/2017

4/2017

5/2017

6/2017

7/2017

8/2017

1/2017

9/2017

11/2015

10/2015

0

700600500400300200100

A. H NEELY HENRY DAMB. LOGAN MARTIN DAMC. WALTER BOULDIN DAM

Median monthly mean flow, 

169 cubic meters per second

Median monthly mean flow, 

193 cubic meters per second

Median monthly mean flow, 

170 cubic meters per second

Figure 6.

Monthly mean flows for H Neely Henry, Logan Martin, and Walter Bouldin Dams on the Coosa River in Alabama during October 2014 to 

September 2017.
Data Collection Methods 9

B

A

C

Teledyne-Optech ILRIS High Density 

Enhanced Range laser scanner on tripod

Teledyne-Optech ILRIS High Density 

Enhanced Range laser scanner on boat

FARO Focus3D X 130

laser scanner on tripod

Figure 7. The Teledyne-Optech ILRIS High Density Enhanced Range laser scanner mounted on A, a tripod with the pan/tilt 

base; B, a survey boat; and C, the FARO Focus3D X 130 laser scanner used in this study.
10 Erosion Monitoring Along Bank Locations of the Coosa River Using Terrestrial Light Detection and Ranging Technology

a previous study at Logan Martin Dam, described in Kimbrow 

and Lee (2013). As described in the previous study (Kimbrow and Lee, 2013), T–lidar uses laser pulses that are sent 

from the instrument and reflected off objects within its field 

of view (FOV). It records the vertical and horizontal angle 

of each laser pulse relative to the instrument. The instrument 

calculates the distance of each returned laser pulse based on 

its round-trip time of travel and velocity. Although the primary T–lidar instrument is the same in both systems (boat- or 

tripod-mounted), the setup and data collection methods are 

somewhat different for each. The tripod-mounted T–lidar system was used to survey downstream from Logan Martin Dam, 

whereas the boat-mounted T–lidar system was used in surveys 

downstream from H Neely Henry and Walter Bouldin Dams.

Tripod-Mounted Terrestrial Light Detection and 

Ranging

The current study used a tripod-mounted system to 

survey the two sites downstream from Logan Martin Dam 

(LM–102 and LM–108; fig. 4). The ILRIS instrument was 

equipped with a pan/tilt base, allowing the scanner’s standard 

40 x 40 degree (°) FOV to be rotated 360° and also tilted 

vertically at any tripod setup point, if necessary. Topographic 

data were obtained by panning the T–lidar unit about 60° in 

discrete steps at a single tripod setup point on a gravel bar 

upstream from the surveyed reach to obtain enough data. Reference spheres were placed at known (relative) target points in 

the FOV of the lidar unit to assist in aligning each scan with 

prior scans. Data generally were collected from only one tripod setup point during each survey, and the region of interest 

(ROI) in the FOV was limited to the bank and island. The ROI 

would be broken into overlapping files any time the pan/tilt 

base was used to rotate the scanner to cover the total ROI.

In several of the surveys at Logan Martin, additional 

detail was collected for the island (site LM–108) using a 

FARO Focus3D X 130 laser scanner. The FARO scanner is substantially smaller than the ILRIS HD ER (fig. 7C) with a more 

limited range; however, it can rapidly collect data in an about 

130-meter (m) sphere around the unit. The smaller size and 

rapid data collection make the FARO scanner useful for “filling in” data gaps for limited survey areas. Topographical data 

were collected using the FARO scanner to supplement data 

gathered using the ILRIS HD ER. These supplemental data 

on the upstream face and top of the island were obtained by 

allowing the FARO unit to rotate 360° at two different tripod 

setups, one upstream from and one on top of the island. Reference spheres placed at various positions in the FOV of both 

T–lidar units were used to assist in aligning the scans from the 

same survey. The reference spheres on the bank target points 

(within the larger FOV and ROI of the ILRIS scanner) were 

used to align each scan with scans from previous surveys.

Boat-Mounted Terrestrial Light Detection and 

Ranging

The boat-mounted T–lidar system (hereinafter referred 

to as the “motion-compensated lidar” or “MC–lidar”) was 

used in surveys at the sites downstream from H Neely Henry 

and Walter Bouldin Dams. The MC–lidar system consists of 

the T–lidar unit, an inertial navigation system (INS), and a 

data-collection and data-processing computer. The T–lidar 

unit is the same Teledyne-Optech ILRIS HD ER unit used 

for tripod-mounted surveys at Logan Martin Dam but is 

instead mounted to the roof of a boat without the pan/tilt 

base (fig. 7B). The INS that was used is the Applanix Position and Orientation Solution for Marine Vessels (POS-MV) 

WaveMaster system, which consists of two Global Navigation 

Satellite System (GNSS) receivers, an inertial motion unit 

(IMU), and a controller/processor. The INS provides position 

in three-dimensional space and measures the heave, pitch, roll, 

and heading of the vessel (and, thereby, the T–lidar unit) to 

accurately position the data received by the T–lidar unit. Position data from the INS were displayed in real time during the 

survey and logged for additional processing after the survey. 

A Topcon GR5 or Trimble model R8 GNSS base receiver was 

set on a local benchmark near each site to provide the postprocessed kinematic (PPK) differential corrections to the INS 

for the navigation and tide solution after the survey. During 

surveys of sites downstream from H Neely Henry Dam, a 

temporary benchmark near the Hart’s Ferry Boat Ramp (fig. 2) 

was occupied, for which high-accuracy National Spatial 

Reference System (NSRS) coordinates were determined using 

the National Geodetic Survey online positioning user service 

(OPUS; K.G. Lee, U.S. Geological Survey, written commun., 2016). During surveys of sites downstream from Walter 

Bouldin Dam, National Geodetic Survey benchmark PID 

CN3663, was occupied (see https://www.ngs.noaa.gov/cgi-bin/

ds_mark.prl?PidBox=CN3363).

For an MC–lidar survey, the ROI is limited to a single 

vertical line in the FOV of the instrument, and data are essentially collected in a “fan” along that line as the boat moves 

(fig. 8). Topographic data were obtained along a longitudinal 

transect line along the bank of interest in multiple passes with 

different aspect angles and speeds to capture data from multiple directions in an effort to maximize the coverage.

Survey Data Processing

An initial processing step required for the MC–lidar data 

was to process the navigation information collected by the INS 

from the MC–lidar surveys using the POS-Pac Mobile Mapping Suite (MMS) software (Applanix Corporation, 2009). 

POS-Pac MMS provides tools to identify and compensate for 

sensor and environmental errors and computes an optimally 

blended navigation solution from the GNSS and IMU raw 

data. The blended navigation solution (called a “smoothed 

best estimate of trajectory” or “SBET” file) generated by 
Data Collection Methods 11

Survey transect line

Vertical line along which the

“fan” of light detection 

and ranging data points

are collected as the

boat moves

Direction of boat

movement parallel

 to bank

Figure 8. Conceptual rendition of stream bank data collection using the boat-mounted light detection and ranging system.

postprocessing the navigation data was applied to the survey at 

a given site to properly position the accumulated lidar data in 

three-dimensional space.

The data from the T–lidar and INS components (when 

used) were parsed, processed, and integrated into cohesive 

datasets for visualization and cleanup. The ILRIS T–lidar 

data from the tripod-mounted surveys were parsed in the 

Teledyne-Optech Parser executable (Teledyne-Optech, 2012) 

to process the raw data into multiple XYZ datasets with signal 

return intensity, one for each pivot step at the tripod setup. 

For MC–lidar surveys, the parsing step included combining 

the raw T–lidar data with the necessary offset and orientation 

parameters contained in a boresight calibration file (explained 

in the “Survey Data Quality Assurance and Accuracy” section below) and georeferencing the data using the navigation 

and position solution data from the SBET file from POS-Pac 

MMS. The MC–lidar data were output to multiple XYZ datasets with intensity, one for each survey transect line pass. The 

FARO data (when used) were processed in the FARO Scene 

software (FARO Technologies, Inc., 2016), which allows multiple FARO scan files to be aligned using the reference targets 

and common topographic features between the scan files and 

output to multiple XYZ datasets with intensity, one for each 

scanner setup location.

The various XYZ files for a given survey were combined into a single topographic dataset and visualized in the 

PolyWorks IM-Align and IM-Survey software packages, 

which create a surface model of the data for a given survey 

(Innovmetric, 2012). The data were referenced and aligned 

with prior surveys using coordinates for the various target 

reference spheres in the surveyed area. These target reference 

spheres also were used to improve the alignment of the various 

MC–lidar surveys with prior surveys; although the MC–lidar 

surveys are georeferenced in three-dimensional space through 

the SBET file, minor differences in the location of these target 

spheres were observed between surveys, which are the result 

of subtle variations in vessel setup, atmospheric conditions 

during the survey, and error associated with using a motioncompensation system.

After alignment, the T–lidar point clouds were further 

processed to remove as much vegetation as possible. The 

final dataset for each survey location and date consisted of 

essentially bare earth topography. The processed and cleaned 

data were output to a space-delimited file XYZ dataset with 

intensity, one for each survey at each site, and are available as 

a U.S. Geological Survey data release (Huizinga and Wagner, 

2019).

The various final T–lidar XYZ point clouds for a given 

site were compared to one another using the Multiscale 

Model-to-Model Cloud Comparison (M3C2) plugin in the 

CloudCompare software (CloudCompare, 2018; Lague and 

others, 2013). The M3C2 plugin computes signed and robust 

distances directly between two point clouds at core points 

subsampled from the first cloud. The M3C2 distance was 

computed along a horizontal axis that would provide the most 

meaningful result (into the face of the bank). A variety of 

parameters can be chosen by the user, such as a subsample 

distance for core points, which is the distance at which the 

full-density point cloud is subsampled to improve speed of 

computation in the comparison; a normal scale, which is the 

diameter of the spherical neighborhood extracted around 

each core point to compute a local normal and used to orient 

a cylinder inside which equivalent points are searched for in 

the second cloud; a projection scale, which is the diameter of 

the cylinder used to search for equivalent points in the second 

point cloud; and a maximum depth, which is the height of the 

cylinder used to search for equivalent points in the second 

point cloud. The values for these parameters were determined 

empirically for each survey site to optimize the view of the 

comparison cloud while minimizing computation time. A point 

cloud representing the output of the M3C2 plugin was saved 

as an XYZ file in American Standard Code for Information 
12 Erosion Monitoring Along Bank Locations of the Coosa River Using Terrestrial Light Detection and Ranging Technology

Interchange (referred to as “ASCII”) format, with additional 

attributes generated by the tool. These data files also are 

included with metadata in Huizinga and Wagner (2019).

Volume gain or loss between scans was computed using 

the 2.5D Volume tool in the CloudCompare software (CloudCompare, 2018). The tool creates a gridded (raster) surface of 

each point cloud and computes the difference in volume along 

a user-selected axis, generally chosen to provide the most 

meaningful result (into the face of the bank), using a cell size 

that was similar to the core point subsample distance used in 

the M3C2 plugin. Each cell was assigned the average value of 

points within the cell, and the values of empty cells generally were interpolated from surrounding cells. However, two 

survey areas (Walter Bouldin sites WB–101 and WB–106) had 

a substantial percentage of empty cells due to dense vegetation 

obscuring the bank during the surveys. Interpolation of empty 

cells in these areas resulted in unrealistic volume computations; therefore, the empty cells were left empty for these two 

sites.

Survey Data Quality Assurance and Accuracy

Survey methods used to obtain tripod-mounted T–lidar 

data were similar to those described in Kimbrow and Lee 

(2013). A surveying methodology was used with the intent of 

one-sided coverage of features in the ROI. These data were 

supplemented with additional scans from the smaller FARO 

scanner to fill in small missing areas when feasible.

For the MC–lidar system, the principal quality-assurance 

measures were a boresight calibration test used to determine 

the positional and angular offsets of the MC–lidar unit and 

assessment of the INS in real time during the survey to ensure 

quality of the acquired data. Data acquired by the MC–lidar 

system were nominally viewable in real time during the latter 

two surveys, but a surveying methodology was used in all 

the MC–lidar surveys with the intent of one-sided coverage 

(from the water) of features in the ROI. Multiple passes using 

different aspect angles were made along the surveyed reach to 

reduce any “shadows” behind smaller objects resulting from a 

single pass.

Boresight Calibration Test

A boresight calibration test is used to check for subtle 

variations in the orientation of the T–lidar unit with respect to 

the INS and real-world coordinates (Teledyne-Optech, 2012). 

In a boresight calibration test, the angular offsets to roll, pitch, 

and yaw caused by the alignment of the T–lidar unit and the 

INS on the survey vessel were determined for each scan direction (port or starboard) of the T–lidar unit on each boat.

For a boresight calibration test, all instrumentation (T–

lidar, IMU, and GNSS antennae) must first be surveyed, and 

their relative positions (lever arms) must be resolved with 

respect to the origin point of the IMU. Determination of the 

angular offsets involves surveying at least three targets with 

traditional methods in real-world, earth-centered, earth-fixed 

coordinates and then scanning those same targets using the 

MC–lidar system (which has been mounted on the boat) 

while the boat is held stationary but collecting INS data. The 

Teledyne-Optech MatchView executable (Teledyne-Optech, 

2012) is then used to derive the angular differences necessary 

to align the T–lidar points to their real-world coordinates. The 

output boresight calibration file contains the identified and 

quantified lever arms and angular offsets.

The offsets obtained from a boresight test are assumed 

to be essentially constant for a given boat and directional 

configuration (Teledyne-Optech, 2012), provided the T–lidar 

is mounted in the same location and configuration each time. 

Alignment brackets were used on both survey boats in this 

study to ensure consistent re-location of the T–lidar each 

time it was used for the MC–lidar system. The lever arm and 

angular offsets determined in the boresight calibration test are 

applied when processing the data collected from a given MC–

lidar survey.

Error Estimation

The errors associated with the collection of topographic 

data can be classified as systematic or random. Systematic 

errors are those that can be measured or modeled through 

calibration (Byrnes and others, 2002). Random errors are 

a result of the limitations of the measuring device and an 

inability to perfectly model the systematic errors. Therefore, 

the overall accuracy of a point cloud dataset collected using 

T–lidar is limited by three factors: laser error, alignment error, 

and georeferencing error (Collins and others, 2009). Laser 

error is inherent to all data acquired by the laser scanner and 

is 0.008 m for the Teledyne-Optech ILRIS HD ER scanner 

as stated by the manufacturer (Teledyne-Optech, 2012) and 

0.002 m for the FARO Focus3D X 130 scanner as stated by the 

manufacturer (FARO Technologies, Inc., 2014).

Alignment and georeferencing errors are generally synonymous in the MC–lidar surveys. The errors reported for the 

MC–lidar surveys (table 1) are related to the positional accuracy of the INS when collecting the topographic data and are 

based on the minimum and maximum observed peak-to-peak 

root mean square errors. As discussed in the “Survey Data 

Processing” section above, although the MC–lidar data are 

georeferenced in three-dimensional space through the SBET 

file, minor differences in the location of these target spheres 

were observed between surveys, which likely are the result 

of subtle variations in vessel setup, atmospheric conditions 

during the survey, and error associated with using a motioncompensation system (table 1). These differences in alignment 

were minimized using the target reference spheres in the MC–

lidar surveys.

The horizontal and vertical alignment errors for each 

of the tripod-mounted T–lidar surveys at Logan Martin Dam 

(relative to the reference scan on June 18, 2015) were determined based on the difference between the easting, northing, 

and elevation values of virtual reference points at the centers 
Erosion Monitoring using Terrestrial Light Detection and Ranging Surveys 13

Table 1. Minimum and maximum horizontal and vertical errors 

from boat-mounted terrestrial light detection and ranging surveys 

at selected bank locations downstream from H Neely Henry and 

Walter Bouldin Dams on the Coosa River in Alabama, 2014–17.

[RMSE, root mean square error; m, meter]

Survey date

Horizontal RMSE Vertical RMSE

Mimimum

(m)

Maximum

(m)

Mimimum

(m)

Maximum

(m)

H Neely Henry Dam

1/30/2015 0.004 0.013 0.008 0.038

6/23/2015 0.010 0.022 0.038 0.047

12/10/2015 0.005 0.011 0.007 0.014

7/6/2016 0.004 0.009 0.006 0.013

10/31/2016 0.019 0.025 0.049 0.055

7/19/2017 0.014 0.019 0.039 0.046

Walter Bouldin Dam

11/20/2014 0.005 0.014 0.008 0.029

6/19/2015 0.006 0.024 0.008 0.021

1/26/2016 0.012 0.018 0.028 0.030

7/11/2016 0.018 0.034 0.063 0.070

11/2/2016 0.016 0.021 0.032 0.038

7/20/2017 0.011 0.020 0.034 0.042

of the reference spheres on the bank of site LM–102 and the 

easting, northing, and elevation values of the sphere center 

points in the June 18, 2015 survey (table 2). The real-world 

coordinates for the sphere center points were determined using 

GNSS on June 18, 2015, at the site; hence, there is no alignment error for that survey.

All the Logan Martin Dam surveys were then approximately georeferenced to real-world coordinates using GNSS 

coordinates obtained for two of the reference spheres on the 

bank at site LM–102 for the reference scan on June 18, 2015. 

A minimum of three targets are necessary for full georeferencing to fully account for three-dimensional position and orientation. However, approximate position and orientation of the 

points could be obtained using the two targets, and additional 

orientation verification was afforded by the water-surface 

elevation, which was assumed to be level between the island 

and bank for the reference scan. The error between the GNSS 

coordinates and the virtual reference points at the center of 

the two reference spheres was determined to be 0.011 m in the 

horizontal and 0.040 m in the vertical, and can be considered 

the overall georeferencing error for the Logan Martin surveys. 

However, the small horizontal and vertical alignment errors 

relative to the reference scan on June 18, 2015, indicate that 

the surveys are closely aligned with each other and the magnitude of the alignment errors is small compared to the georeferencing error (table 2).

Table 2. Horizontal and vertical alignment errors relative to the 

reference scan on June 18, 2015, from tripod-mounted terrestrial 

light detection and ranging surveys at selected bank locations 

downstream from Logan Martin Dam on the Coosa River in 

Alabama, 2014–17.

[m, meter]

Survey date Horizontal error

(m)

Vertical error

(m)

10/16/2014 0.0050 0.0001

6/18/2015 a

0 a0

10/30/2015 0.0055 0.0031

6/14/2016 0.0058 0.0021

11/1/2016 0.0069 0.0001

7/18/2017 0.0041 0.0000

a

The survey of June 18, 2015, was used as the “reference” survey to which 

all other surveys were aligned. This survey was used to approximately georeference all the Logan Martin surveys using Global Navigation Satellite System 

(GNSS) coordinates for two of the three reference spheres and the surveyed 

water-surface elevation as a verification. The overall horizontal error of the 

georeferencing (the difference between the GNSS coordinates and the virtual 

coordinates of the targets) was 0.011 meter, and the overall vertical error was 

0.040 meter.

Erosion Monitoring using Terrestrial 

Light Detection and Ranging Surveys

The site-specific results for each dam site are discussed 

in the following sections, from upstream to downstream. All 

elevation data were referenced to the North American Vertical 

Datum of 1988 (NAVD 88).

In the following sections, erosion (or deposition) values 

are reported in terms of a “normalized” value. The normalized 

erosion (or deposition) is computed as the total net erosion (or 

deposition) between the scan surfaces for a given time interval, divided by the surface area common to both surfaces, and 

reported in cubic meters per square meter. This normalized 

value is intended to aid in the comparability of the values for 

the vastly different areal extents of the sites.

H Neely Henry Dam, Sites NH–104 and NH–108

Daily mean flow through H Neely Henry Dam generators and floodgates (not including seepage) during October 1, 

2014, through September 30, 2017, was computed from hourly 

flows provided by the Alabama Power Company. Daily mean 

flow ranged from 0 to 2,140 m3/s, and the median daily mean 

flow was 140 m3/s (fig. 9).
14 Erosion Monitoring Along Bank Locations of the Coosa River Using Terrestrial Light Detection and Ranging Technology

Fall 2016 survey

October 31, 2016

Summer 2017 survey

July 19, 2017

Fall 2015 survey

December 10, 2015

Summer 2016 survey

July 6, 2016

Median daily mean flow, 

140 cubic meters per second

Fall 2014 survey

January 30, 2015

Summer 2015 survey

June 23, 2015

Median daily mean flow, 

140 cubic meters per second

Date

Daily mean flow, in cubic meters per second

1,600

0

10/1 10/16 11/16 12/16 11/1 12/1 1/16 1/1 3/16 3/1 4/16 4/1 5/16 5/1 6/16 6/1 7/16 7/1 8/16 8/1 9/16 9/1 10/1 2/16 2/1

800600400200

2,2002,0001,8001,4001,2001,000

1,600

0

800600400200

2,2002,0001,8001,4001,2001,0001,600

0

800600400200

2,2002,0001,8001,4001,2001,000

10/1 10/16 11/16 12/16 11/1 12/1 1/16 1/1 3/16 3/1 4/16 4/1 5/16 5/1 6/16 6/1 7/16 7/1 8/16 8/1 9/16 9/1 10/1 2/16 2/110/1 10/16 11/16 12/16 11/1 12/1 1/16 1/1 3/16 3/1 4/16 4/1 5/16 5/1 6/16 6/1 7/16 7/1 8/16 8/1 9/16 9/1 10/1 2/16 2/1

2014 20152015 20162016 2017

Median daily mean flow, 

140 cubic meters per second

Figure 9. Daily mean flow on the Coosa River downstream from H Neely Henry Dam near Gadsden, Alabama, for October 1, 2014, to September 30, 2017, by water year, with survey dates indicated.
Erosion Monitoring using Terrestrial Light Detection and Ranging Surveys 15

Site NH–104

Comparison of the fall 2014 (January 2015) and summer 

2017 (July 2017) T–lidar scans (fig. 10) of site NH–104 indicated a normalized erosion of 0.273 cubic meters per square 

meter (m3/m2) (table 3). The largest differences between the 

scans occurred at bank failures apparent near the upstream and 

downstream ends of the bank, where greater than 0.5 m of erosion was indicated (fig. 10G).

Net erosion was observed during four of the five intervals 

between T–lidar scans, with the greatest amount, 0.154 m3/m2, 

occurring between the summer 2015 and fall 2015 (June and 

December 2015) scans (table 3). About 0.5 m of erosion was 

indicated near the upstream end of the bank at the location 

of a bank failure and corresponding deposit at the toe of the 

bank (fig. 10C). Although daily mean flows through H Neely 

Henry Dam during the June to December 2015 interval were 

not of the highest magnitude experienced during the study, 

above-median and generally increasing daily mean flow 

occurred from October 1, 2015, until the day of the scan on 

December 10, 2015 (fig. 9). The maximum daily mean flow 

during the summer to fall 2015 interval, 1,000 m3/s, occurred 

on December 3, 2015, just 1 week before the scan on December 10, and daily mean flows exceeded 730 m3

/s from December 2 to 10 (fig. 9).

Net deposition of 0.013 m3/m2 occurred between the 

summer 2016 (July 2016) and fall 2016 (October 2016) scans 

(table 3). Relatively minor, somewhat uniform deposition of 

less than 0.2 m between surveys was observed along the bank 

(fig. 10E). Daily mean flows during the July to October 2016 

period were below the median of 140 m3/s (fig. 9).

Site NH–108

Comparison of the fall 2014 (January 2015) and summer 

2017 (July 2017) T–lidar scans of site NH–108 indicated net 

erosion of 0.165 m3/m2 during the study (table 3). The largest 

differences between the scans occurred at bank failures apparent near the upstream end of and near the center of the top of 

the bank, where greater than 0.5 m of change was indicated 

(fig. 11G).

Net erosion was observed during three of the five 

intervals between T–lidar scans, with the greatest amount of 

normalized erosion, 0.098 m3/m2, occurring between the fall 

2015 (December 2016) and summer 2016 (July 2016) scans 

(table 3). Greater than 0.5 m of change was indicated at two 

areas of bank failure, one near the top of the upstream end of 

the bank (with a corresponding deposit at the toe of the bank) 

and the other near the center of the top of the bank (fig. 11D). 

Daily mean flows through H Neely Henry Dam during the fall 

2015 to summer 2016 interval included those of the greatest magnitude experienced during the study. A long duration 

of above-median flow occurred from the fall 2015 scan on 

December 10 through the end of April 2016, followed by 

a period of near- to below-median flow from May 1, 2016, 

through the date of the summer 2016 scan on July 6 (fig. 9).

Net deposition was observed during two of five intervals, 

summer 2015 to fall 2015 and summer 2016 to fall 2016. Similar amounts of normalized deposition, 0.029 and 0.031 m3

/m2, 

respectively, were observed during the two intervals, and 

relatively minor, uniform change of less than about 0.2 m was 

observed along the bank (table 3; fig. 11E). Daily mean flows 

during the summer to fall 2015 period were generally below 

the median of 140 m3/s from the date of the summer 2015 scan 

on June 23 through October and were above-median from 

November through the date of the fall 2015 scan on December 10. Daily mean flows during the summer to fall 2016 

period were below the median of 140 m3/s (fig. 9).

Logan Martin Dam, Sites LM–102 and LM–108

Daily mean flow through Logan Martin Dam generators and floodgates (not including seepage) during October 1, 

2014, through September 30, 2017, was computed from hourly 

flows provided by the Alabama Power Company. Daily mean 

flow ranged from 24.1 to 2,120 m3/s, and the median was 

158 m3/s (fig. 12).

Flow through the Logan Martin Dam generators and 

floodgates was halted the evening before each of the scans at 

the Logan Martin sites to ensure the low-lying island was not 

inundated. Therefore, only flow from seepage through the dam 

occurred during each scan, which resulted in relatively similar 

water-surface elevations in all of the scans.

Site LM–102

Comparison of the fall 2014 (October 2014) and summer 2017 (July 2017) T–lidar scans (fig. 13) of site LM–102 

indicated normalized erosion of 0.419 m3/m2 during the study 

(table 3). The difference between the scans exceeded 0.5 m 

along much of the vertical part of the bank (fig. 13G).

Net erosion was observed during all five intervals 

between T–lidar scans, with the greatest amount of normalized erosion, 0.161 m3

/m2, occurring between the fall 2015 

(October 2015) and summer 2016 (June 2016) scans (table 3). 

A large area of greater than 0.5 m of change was indicated 

near the upstream end of the bank (fig. 13D). During nearly 

all of the interval between the fall 2015 and summer 2016 

scans, daily mean flows through Logan Martin Dam exceeded 

the median of 158 m3/s, and the two greatest magnitude daily 

mean flows experienced during the study, 2,120 m3/s on 

December 28, 2015, and 1,740 m3/s on February 26, 2016, 

also occurred during the period (fig. 12).

The least amount of normalized erosion between T–lidar 

scans, 0.019 m3/m2, occurred between the summer 2015 (June 

2015) and fall 2015 (October 2015) scans (table 3). Relatively 

minor, uniform change of less than 0.1 m was observed along 

the bank (fig. 13C). Daily mean flows during the summer to 

fall 2015 interval were below the median of 158 m3/s most of 

the time (fig. 12).
16 Erosion Monitoring Along Bank Locations of the Coosa River Using Terrestrial Light Detection and Ranging Technology

A. Bank on January 30, 2015,

 colored by signal

 return intensity

B. January 30, 2015, to

 June 23, 2015

C. June 23, 2015, to

 December 10, 2015

D. December 10, 2015, to

 July 6, 2016

E. July 6, 2016, to

 October 31, 2016

F. October 31, 2016, to

 July 19, 2017

G. January 30, 2015, to

 July 19, 2017

H. Bank on July 19, 2017,

 colored by signal

 return intensity

FLOW

Orientation

N

E

Z

0 10 20 FEET

0 10 20 METERS

> 0.5

0.4

0.3

0.2

0.1

0

−0.1

−0.2

−0.3

−0.4

< −0.5

No comparison

Deposition

Erosion

Distance between surveyed 

surfaces, in meters

EXPLANATION

Figure 10. Surveyed banks and incremental differences between surveys at H Neely Henry Dam site NH–104 on the Coosa River near Gadsden, Alabama, for January 30, 

2015, through July 19, 2017. A, bank on January 30, 2015, colored by signal return intensity; B, January 30, 2015, to June 23, 2015; C, June 23, 2015, to December 10, 2015; D, 

December 10, 2015, to July 6, 2016; E, July 6, 2016, to October 31, 2016; F, October 31, 2016, to July 19, 2017; G, January 30, 2015, to July 19, 2017; and H, bank on July 19, 2017, 

colored by signal return intensity.
Erosion Monitoring using Terrestrial Light Detection and Ranging Surveys 17

A. Bank on January 30, 2015,

 colored by signal

 return intensity

B. January 30, 2015, to

 June 23, 2015

C. June 23, 2015, to

 December 10, 2015

D. December 10, 2015, to

 July 6, 2016

E. July 6, 2016, to

 October 31, 2016

F. October 31, 2016, to

 July 19, 2017

G. January 30, 2015, to

 July 19, 2017

H. Bank on July 19, 2017,

 colored by signal

 return intensity

FLOW

Orientation

N

E

Z

0 10

0 5 15 METERS

5 15 FEET

10

> 0.5

0.4

0.3

0.2

0.1

0

−0.1

−0.2

−0.3

−0.4

< −0.5

No comparison

Deposition

Erosion

Distance between surveyed 

surfaces, in meters

EXPLANATION

Figure 11. Surveyed banks and incremental differences between surveys at H Neely Henry Dam site NH–108 on the Coosa River near Gadsden, Alabama, for January 30, 

2015, through July 19, 2017. A, bank on January 30, 2015, colored by signal return intensity; B, January 30, 2015, to June 23, 2015; C, June 23, 2015, to December 10, 2015; D, 

December 10, 2015, to July 6, 2016; E, July 6, 2016, to October 31, 2016; F, October 31, 2016, to July 19, 2017; G, January 30, 2015, to July 19, 2017; and H, bank on July 19, 2017, 

colored by signal return intensity.
18 Erosion Monitoring Along Bank Locations of the Coosa River Using Terrestrial Light Detection and Ranging Technology

Table 3. Total net and normalized erosion for selected intervals at selected bank locations of the Coosa River in Alabama from 

terrestrial light detection and ranging technology.

[Negative values indicate deposition]

Survey site

Selected interval

Fall 2014 to 

summer 2015

Summer 2015 to 

fall 2015a

Fall 2015 to 

summer 2016a

Summer 2016 to 

fall 2016

Fall 2016 to 

summer 2017

Fall 2014 to 

summer 2017

Total net erosion volume, in cubic meters

NH–104 8.85 113 54.3 −13.6 101 256

NH–108 13.6 −9.33 32.7 −13.8 38.0 65.4

LM–102 34.4 7.36 50.7 6.95 42.4 159

LM–108b 1.14 7.27 12.7 −1.66 10.2 23.1

WB–101 27.7 −7.01 74.6 −146 76.1 77.4

WB–106 232 −268 −127 1,170 235 1,310

Normalized erosionc

, in cubic meters per square meter

NH–104 0.009 0.154 0.074 −0.013 0.106 0.273

NH–108 0.032 −0.029 0.098 −0.031 0.086 0.165

LM–102 0.090 0.019 0.161 0.022 0.109 0.419

LM–108b 0.099 0.573 0.692 −0.100 0.572 2.05

WB–101 0.068 −0.025 0.226 −0.196 0.199 0.331

WB–106 0.084 −0.121 −0.066 0.457 0.083 0.467

a

The “summer 2015 to fall 2015” and “fall 2015 to summer 2016” intervals likely are biased by the relatively smaller bank area that could be surveyed during 

the fall 2015 survey.

b

Site LM–108 is an island, and the surveyed area is the part that experiences head-on flow, as compared with the shear flow experienced by all the other sites.

c

The normalized erosion is computed as the total net erosion for the interval divided by the surface area common to both survey areas.

Site LM–108

Comparison of the fall 2014 (October 2014) and summer 

2017 (July 2017) T–lidar scans of site LM–108, an island in 

the Coosa River, indicated normalized erosion of 2.05 m3/m2

during the study (table 3).This is the largest amount of normalized erosion of all the surveyed sites, likely because the surveyed area experiences head-on flow from the river, compared 

with the other sites experiencing predominantly shear flow. 

The difference between the scans exceeded 1.0 m on much of 

the upstream end and right (west) side of the island (fig. 14G). 

Bank retreat at the upstream end of the island (using a narrow 

band of data near the water line common in all the scans) during the study is estimated to be 2.9 m (fig. 15).

Net erosion was observed during four of the five intervals 

between T–lidar scans, with the greatest amount of normalized erosion, 0.692 m3

/m2, occurring between the fall 2015 

(October 2015) and summer 2016 (June 2016) scans (table 3). 

Greater than 0.5 m of change was indicated near the upstream 

end of the island and along the right (west) side of the island 

(fig. 14D). During the interval between the fall 2015 and 

summer 2016 scans, nearly all daily mean flows exceeded 

the median of 158 m3/s, and the two greatest magnitude daily 

mean flows through Logan Martin Dam that were experienced 

during the study, 2,120 m3/s on December 28, 2015, and 

1,740 m3/s on February 26, 2016, also occurred during the 

period (fig. 12).

Normalized deposition of 0.100 m3/m2 occurred between 

the summer 2016 (June 2016) and fall 2016 (November 2016) 

scans (table 3). Relatively minor and uniform change of less 

than about 0.2 m was observed on the surveyed part of the 

island, although a few areas at the upstream end and along 

the right (west) side of the island experienced about 0.5 m of 

erosion (fig. 14E). Daily mean flows during the summer to fall 

2016 interval were below the median of 158 m3/s (fig. 12).

Walter Bouldin Dam, Sites WB–101 and WB–106

Daily mean flow through Walter Bouldin Dam generators and floodgates (not including seepage) during October 1, 

2014, through September 30, 2017, was computed from hourly 

flows provided by the Alabama Power Company. Daily mean 

flow ranged from 0 to 809 m3/s, and the median was 114 m3/s 

(fig. 16). As explained in the “Description of Flow Conditions” section above, flow from Jordan Lake is preferentially 

released through Jordan Dam for habitat maintenance on the 

Coosa River; therefore, it is not uncommon to have substantial 

periods of no flow from Walter Bouldin Dam.
Erosion Monitoring using Terrestrial Light Detection and Ranging Surveys 19

Fall 2016 survey

November 1, 2016

Summer 2017 survey

July 18, 2017

Fall 2015 survey

October 30, 2015

Summer 2016 survey

June 14, 2016

Median daily mean flow, 

158 cubic meters per second

Fall 2014 survey

October 16, 2014

Summer 2015 survey

June 18, 2015

Median daily mean flow, 

158 cubic meters per second

Date

Daily mean flow, in cubic meters per second

1,600

0

10/1 10/16 11/16 12/16 11/1 12/1 1/16 1/1 3/16 3/1 4/16 4/1 5/16 5/1 6/16 6/1 7/16 7/1 8/16 8/1 9/16 9/1 10/1 2/16 2/1

800600400200

2,2002,0001,8001,4001,2001,000

1,600

0

800600400200

2,2002,0001,8001,4001,2001,0001,600

0

800600400200

2,2002,0001,8001,4001,2001,000

10/1 10/16 11/16 12/16 11/1 12/1 1/16 1/1 3/16 3/1 4/16 4/1 5/16 5/1 6/16 6/1 7/16 7/1 8/16 8/1 9/16 9/1 10/1 2/16 2/110/1 10/16 11/16 12/16 11/1 12/1 1/16 1/1 3/16 3/1 4/16 4/1 5/16 5/1 6/16 6/1 7/16 7/1 8/16 8/1 9/16 9/1 10/1 2/16 2/1

2014 20152015 20162016 2017

Median daily mean flow, 

158 cubic meters per second

Figure 12. Daily mean flow on the Coosa River downstream from Logan Martin Dam near Vincent, Alabama, for October 1, 2014, to September 30, 2017, by water year, with survey dates indicated.
20 Erosion Monitoring Along Bank Locations of the Coosa River Using Terrestrial Light Detection and Ranging Technology

A. Bank on October 16, 2014,

 colored by signal

 return intensity

B. October 16, 2014, to

 June 18, 2015

C. June 18, 2015, to

 October 30, 2015

D. October 30, 2015, to

 June 14, 2016

E. June 14, 2016, to

 November 1, 2016

F. November 1, 2016, to

 July 18, 2017

G. October 16, 2014, to

 July 18, 2017

H. Bank on July 18, 2017,

 colored by signal

 return intensity

FLOW

Orientation

E N

Z

0 10 FEET

0 5 10 METERS

> 0.5

0.4

0.3

0.2

0.1

0

−0.1

−0.2

−0.3

−0.4

< −0.5

No comparison

Deposition

Erosion

Distance between surveyed 

surfaces, in meters

EXPLANATION

Figure 13. Surveyed banks and incremental differences between surveys at Logan Martin Dam site LM–102 on the Coosa River near Vincent, Alabama, for October 16, 

2014, through July 18, 2017. A, bank on October 16, 2014, colored by signal return intensity; B, October 16, 2014, to June 18, 2015; C, June 18, 2015, to October 30, 2015; D, 

October 30, 2015, to June 14, 2016; E, June 14, 2016, to November 1, 2016; F, November 1, 2016, to July 18, 2017; G, October 16, 2014, to July 18, 2017; and H, bank on July 18, 

2017, colored by signal return intensity.
Erosion Monitoring using Terrestrial Light Detection and Ranging Surveys 21

A. Island on October 16, 2014,

 colored by signal

 return intensity

B. October 16, 2014, to

 June 18, 2015

C. June 18, 2015, to

 October 30, 2015

D. October 30, 2015, to

 June 14, 2016

E. June 14, 2016, to

 November 1, 2016

F. November 1, 2016, to

 July 18, 2017

G. October 16, 2014, to

 July 18, 2017

H. Island on July 18, 2017,

 colored by signal

 return intensity

FLOW

Orientation

N

E

Z

0 3 FEET

0 3 METERS

> 0.1

0.8

0.6

0.4

0.2

0

−0.2

−0.4

−0.6

−0.8

< −1.0

No comparison

Deposition

Erosion

Distance between surveyed 

surfaces, in meters

EXPLANATION

Figure 14. Surveyed banks and incremental differences between surveys at Logan Martin Dam site LM–108 on the Coosa River near Vincent, Alabama, for October 16, 

2014, through July 18, 2017. A, island on October 16, 2014, colored by signal return intensity; B, October 16, 2014, to June 18, 2015; C, June 18, 2015, to October 30, 2015; D, 

October 30, 2015, to June 14, 2016; E, June 14, 2016, to November 1, 2016; F, November 1, 2016, to July 18, 2017; G, October 16, 2014, to July 18, 2017; and H, island on July 18, 

2017, colored by signal return intensity.
22 Erosion Monitoring Along Bank Locations of the Coosa River Using Terrestrial Light Detection and Ranging Technology

Universal Transverse Mercator projection, zone 16 North

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

0 5 10 15 20 FEET

0 1 2 3 4 5 METERS

86°20'28"

86°20'27.8"

86°20'27.6"

86°20'27.4"

33°25'9.4" 33°25'9.6" 33°25'9.8"

EXPLANATION

October 16, 2014

June 18, 2015

October 30, 2015

June 14, 2016

November 1, 2016

July 18, 2017

Survey date

2.9 meters

FLOW

N

Figure 15. Surveyed points from a narrow band of data near the water line at Logan Martin Dam site LM–108 on the Coosa 

River near Vincent, Alabama, for October 16, 2014, through July 18, 2017.

Site WB–101

Comparison of the fall 2014 (November 2014) and summer 2017 (July 2017) T–lidar scans of site WB–101 indicated 

normalized erosion 0.331 m3/m2 during the study (table 3). 

The difference between the scans exceeded 0.5 m along much 

of the bank (fig. 17G).

Net erosion was observed during three of the five intervals between T–lidar scans, with the greatest amount of normalized erosion, 0.226 m3

/m2, occurring between the fall 2015 

(January 2016) and summer 2016 (July 2016) scans (table 3). 

Greater than 0.2 m of change was indicated for much of the 

bank, with some locations exceeding 0.5 m (fig. 17D). During 

the interval between the fall 2015 and summer 2016 scans, 

an extended period of above-median daily mean flows lasted 

through mid-April, 2016, with occasional above-median flows 

occurring from mid-April through mid-May 2016. From midMay 2016 until the summer 2016 scan on July 11, 2016, daily 

mean flows were well below the median of 114 m3/s (fig. 16). 

The maximum daily mean flow through Walter Bouldin 

Dam of 809 m3/s, occurred on April 7, 2017. Furthermore, 

during the fall 2016 to summer 2017 interval, daily mean 

flows exceeded 700 m3/s four times: April 4–8, June 6–8, 

June 23–25, and July 1, 2017 (fig. 16).
Erosion Monitoring using Terrestrial Light Detection and Ranging Surveys 23

Fall 2016 survey

November 2, 2016

Summer 2017 survey

July 20, 2017

Fall 2015 survey

January 26, 2016

Summer 2016 survey

Jul y 11, 2016

Median daily mean flow, 

114 cubic meters per second

Fall 2014 survey

November 20, 2014

Summer 2015 survey

June 19, 2015

Median daily mean flow, 

114 cubic meters per second

Date

Daily mean flow, in cubic meters per second

800

0

10/1 10/16 11/16 12/16 11/1 12/1 1/16 1/1 3/16 3/1 4/16 4/1 5/16 5/1 6/16 6/1 7/16 7/1 8/16 8/1 9/16 9/1 10/1 2/16 2/1

900700600500400300200100

800

0

900700600500400300200100800

0

900700600500400300200100

10/1 10/16 11/16 12/16 11/1 12/1 1/16 1/1 3/16 3/1 4/16 4/1 5/16 5/1 6/16 6/1 7/16 7/1 8/16 8/1 9/16 9/1 10/1 2/16 2/110/1 10/16 11/16 12/16 11/1 12/1 1/16 1/1 3/16 3/1 4/16 4/1 5/16 5/1 6/16 6/1 7/16 7/1 8/16 8/1 9/16 9/1 10/1 2/16 2/1

2014 20152015 20162016 2017

Median daily mean flow, 

114 cubic meters per second

Figure 16. Daily mean flow on the Coosa River downstream from Walter Bouldin Dam near Wetumpka, Alabama, for October 1, 2014, to September 30, 2017, by water year, with survey dates indicated.
24 Erosion Monitoring Along Bank Locations of the Coosa River Using Terrestrial Light Detection and Ranging Technology

A. Bank on November 20, 2014,

 colored by signal

 return intensity

B. November 20, 2014, to

 June 19, 2015

C. June 19, 2015, to

 January 26, 2016

D. January 26, 2016, to

 July 11, 2016

E. July 11, 2016, to

 November 2, 2016

F. November 2, 2016, to

 July 20, 2017

G. November 20, 2014, to

 July 20, 2017

H. Bank on July 20, 2017,

 colored by signal

 return intensity

FLOW

Orientation

N

E

Z

0 10 20 FEET

0 10 20 METERS

> 0.5

0.4

0.3

0.2

0.1

0

−0.1

−0.2

−0.3

−0.4

< −0.5

No comparison

Deposition

Erosion

Distance between surveyed 

surfaces, in meters

EXPLANATION

Figure 17. Surveyed banks and incremental differences between surveys at Walter Bouldin Dam site WB–101 on the Coosa River near Wetumpka, Alabama, for 

November 20, 2014, through July 20, 2017. A, bank on November 20, 2014, colored by signal return intensity; B, November 20, 2014, to June 19, 2015; C, June 19, 2015, to 

January 26, 2016; D, January 26, 2016, to July 11, 2016; E, July 11, 2016, to November 2, 2016; F, November 2, 2016, to July 20, 2017; G, November 20, 2014, to July 20, 2017; 

and H, bank on July 20, 2017, colored by signal return intensity.
Erosion Monitoring using Terrestrial Light Detection and Ranging Surveys 25

A. Bank on November 20, 2014,

 colored by signal

 return intensity

B. November 20, 2014, to

 June 19, 2015

D. January 26, 2015, to

 July 11, 2016

C. June 19, 2015, to

 January 26, 2016

F. November 2, 2016, to

 July 20, 2017

E. July 11, 2016, to

 November 2, 2016

G. November 20, 2014, to

 July 20, 2017 H. Bank on July 20, 2017,

 colored by signal

 return intensity

FLOW

Orientation

N

E

Z

0 10 20 FEET

0 10 20 METERS

> 0.1

0.8

0.6

0.4

0.2

0

−0.2

−0.4

−0.6

−0.8

< −1.0

Distance between surveyed 

surfaces, in meters

EXPLANATION

No comparison

Deposition

Erosion

Figure 18. Surveyed banks and incremental differences between surveys at Walter Bouldin Dam site WB–106 on the Coosa River near Wetumpka, Alabama, for 

November 20, 2014, through July 20, 2017. A, bank on November 20, 2014, colored by signal return intensity; B, November 20, 2014, to June 19, 2015; C, June 19, 2015, to 

January 26, 2016; D, January 26, 2016, to July 11, 2016; E, July 11, 2016, to November 2, 2016; F, November 2, 2016, to July 20, 2017; G, November 20, 2014, to July 20, 2017; 

and H, bank on July 20, 2017, colored by signal return intensity.
26 Erosion Monitoring Along Bank Locations of the Coosa River Using Terrestrial Light Detection and Ranging Technology

Net deposition was observed between the summer and 

fall 2015 (June 2015 and January 2016) scans and between the 

summer and fall 2016 (July and November 2016) scans, with 

the greatest amount of normalized deposition, 0.196 m3/m2, 

occurring between the summer and fall 2016 scans (table 3). 

Relatively uniform change of about 0–0.2 m was observed for 

much of the bank during that interval (fig. 17E). Daily mean 

flows during the summer to fall 2016 period were below the 

median of 114 m3/s (fig. 16).

Site WB–106

Comparison of the fall 2014 (November 2014) and summer 2017 (July 2017) T–lidar scans of site WB–106 indicated 

normalized erosion 0.467 m3/m2 during the study (table 3). 

The difference between the scans exceeded 1.0 m along much 

of the upstream half of the bank and within a distance of about 

20 m from the waterline (fig. 18G).

Net erosion was observed during three of the five 

intervals between T–lidar scans, with the greatest amount of 

normalized erosion, 0.457 m3/m2, occurring between the summer 2016 (July 2016) and fall 2016 (November 2016) scans 

(table 3). Although there are no “hot-spots” of erosion during 

this period, comparison of the scans indicated that the greatest amount of change occurred near the upstream end of the 

bank (fig. 18E). During the interval between the summer and 

fall 2016 scans, daily mean flows were below the median of 

114 m3/s (fig. 16), which is anomalous. Assessment of erosion 

during this interval was likely biased by abundant vegetation present during the summer 2016 scan, which obscured 

the bank and resulted in a smaller surface area that could be 

surveyed compared with the fall 2016 scan.

Similar amounts of erosion were observed during the 

intervals between the fall 2014 to summer 2015 and fall 2016 

to summer 2017 scans; normalized erosion was 0.084 and 

0.083 m, respectively (table 3). Although erosion seems to be 

mostly minor and distributed somewhat uniformly throughout the bank in both intervals, in the comparison of the fall 

2016 to summer 2017 scans, greater than 0.6 m of change 

was observed at several locations on the bank within about 

20 m of the waterline (fig. 18F). Daily mean flows through 

Walter Bouldin Dam during the fall 2016 to summer 2017 

interval were below the median of 114 m3/s during the month 

of November 2016 and were mostly above the median for the 

remainder of the interval (fig. 16). The maximum daily mean 

flow experienced during the study, 809 m3/s, occurred on 

April 7, 2017, during the fall 2016 to summer 2017 interval, 

and daily mean flows exceeded 700 m3/s four times during the 

interval: April 4–8, June 6–8, June 23–25, and July 1, 2017 

(fig. 16).

Net deposition was observed between the summer and 

fall 2015 (June 2015 and January 2016) scans and between 

the fall 2015 and summer 2016 (January and July 2016) 

scans, with the greatest amount of normalized deposition, 

0.121 m3/m2, occurring between the summer and fall 2015 

scans (table 3). Relatively minor, uniform change of less than 

about 0.2 m was observed between the scans, although one 

area in the middle of the bank about 20 m from the waterline 

experienced greater than 0.6 m of erosion (fig. 18C). Daily 

mean flows during the summer to fall 2015 interval were 

mostly below the median of 114 m3/s from June through October 2015 and above the median and generally increasing from 

November to January 26, 2016, the date of the fall 2015 scan 

(fig. 16). In fact, daily mean flows exceeded 700 m3/s three 

times immediately before the fall 2015 scan: December 3–6, 

2015; December 27, 2015, to January 9, 2016; and January 22–26, 2016.

General Findings and Implications

Results from T–lidar scan comparisons indicate that 

intervals between scans that exhibited the greatest amounts 

of normalized erosion generally corresponded to periods of 

above-median flow, and intervals between scans that exhibited 

the least amounts of erosion—or deposition—corresponded to 

periods of below-median flow. Of the five intervals between 

scans, the three that exhibited the greatest amounts of normalized erosion corresponded to periods of above-median flow 

through the dams (table 3; figs. 6, 9, 12, 16). With the exception of site WB–106, erosion was observed at all six sites 

during the three “Fall to Summer” intervals, and, with the 

additional exception of site NH–104, the greatest amounts of 

erosion occurred during either the fall 2015 to summer 2016 

or fall 2016 to summer 2017 interval. However, the interval 

that experienced the greatest daily mean flows, fall 2015 to 

summer 2016, did not correspond to the greatest amounts of 

erosion at all sites. Site WB–106 was surveyed on January 26, 

2016, in the middle of an extended period of very high flow 

through Walter Bouldin Dam that lasted from mid-December 

2015 to mid-April 2016 (fig. 16). In mid-May 2016, flows 

through the dam abruptly went to zero or near-zero until the 

date of the next survey on July 11, 2016 (fig. 16). The shift 

from high- to low-flow was not as drastic at H Neely Henry 

or Logan Martin Dams (figs. 9, 12), and was the result of a 

drought on the Coosa River that necessitated all flow into 

Jordan Lake being diverted through Jordan Dam for habitat 

preservation. The abrupt shift from relatively high flows to 

essentially zero flow at Walter Bouldin Dam may explain why 

deposition occurred at site WB–106 during the fall 2015 to 

summer 2016 interval, as material sloughed from the banks 

due to excess pore pressure but was not carried away by 

higher flows, whereas erosion occurred at all other sites for 

this interval.

Intervals between scans that exhibited the least amounts 

of normalized erosion generally corresponded to periods 

of below-median flow through the dams (table 3; figs. 6, 9, 

12, 16). With the exception of sites NH–104 and WB–106, 

the summer 2015 to fall 2015 or summer 2016 to fall 2016 

intervals exhibited the least amounts of normalized erosion or 

minor amounts of deposition. Mid-June through mid-October 

2015 was a period of generally below-median flow through the 
Summary and Conclusions 27

dams, with few daily mean flows exceeding 275 m3/s (figs. 9, 

12, 16). After November 1, 2015, flows through all three dams 

increased to above-median values through January 2016, with 

the largest flows experienced during the study occurring at 

all three dams in late December 2015 (figs. 9, 12, 16). Site 

NH–104 was surveyed on December 10, 2015, 1 week after 

a relatively sharp rise in daily mean flow from 265 m3/s on 

November 30 to 1,000 m3/s on December 3. This may explain 

the large amount of net erosion observed for site NH–104 

relative to the other sites during the summer 2015 to fall 2015 

interval. Sites WB–101 and WB–106 experienced minor to 

moderate normalized deposition during the same interval, 

while sites LM–102 and LM–108 experienced minor normalized erosion. Furthermore, the dates that the T–lidar scans 

were conducted likely account for the variation between sites. 

The fall 2015 scans of sites WB–101 and WB–106 were conducted on January 26, 2016, after a sustained period of abovemedian flows and 3 weeks after daily mean flows had peaked 

at greater than 800 m3/s on January 5; conversely, scans of 

sites LM–102 and LM–108 were conducted on October 30, 

2015, 1 month after daily mean flows through Logan Martin 

Dam had increased slightly after about 3 months of mostly 

below-median flow.

The total surface area available to be surveyed during a 

given survey had an effect on the comparison results. During 

the summer 2016 to fall 2016 interval, an anomalously large 

amount of normalized erosion was observed at site WB–106, 

while four of the five other sites experienced minor to moderate deposition, and site LM–102 experienced a minor amount 

of erosion (table 3). The amount of erosion observed during 

the summer 2016 to fall 2016 interval—and consequently for 

the duration of the study—at site WB–106 may be biased high 

because of the relatively smaller surface area that could be 

surveyed on the date of the summer 2016 scan (July 11, 2016) 

resulting from dense vegetation obscuring the upper banks 

(fig. 18E). Furthermore, the fall 2015 surveys at the H Neely 

Henry and Walter Bouldin Dam sites were affected by abovemedian flows (figs. 9, 16), which caused the lower part of the 

surveyed bank to be inundated, limiting the area that could be 

surveyed and used for comparison. This reduction in area may 

have skewed the comparison results, creating more apparent 

deposition (or less erosion) during the summer 2015 to fall 

2015 interval and more apparent erosion during the fall 2015 

to spring 2016 interval. While none are currently planned, 

future surveys could benefit from deliberate attempts to survey 

during leaf-off and low-flow conditions to minimize the effects 

of vegetation and inundation.

During the study, site LM–108, the island in the middle 

of the Coosa River downstream from Logan Martin Dam, 

exhibited the largest normalized erosion of all six sites 

(table 3; figs. 14, 15). The normalized erosion during the study 

period, 2.05 m3/m2, was more than four times that of the site 

with the next greatest amount (site WB–106, 0.467 m3/m2; 

table 3), and likely is because LM–108 experiences head-on 

flow as compared with predominantly shear flow at the other 

sites. The overall retreat of the bank at the upstream end of the 

island near the water line is estimated at 2.9 m (fig. 15). Most 

of this retreat seems to have occurred during the fall 2015 to 

summer 2016 interval (fig. 15; table 3), during the period of 

the largest flows at this site (fig. 13).

Summary and Conclusions

The Alabama Power Company operates a series of dams 

on the Coosa River in east central Alabama. Seven dams 

impound the river to form six reservoirs: Weiss Lake, Neely 

Henry Lake, Logan Martin Lake, Lay Lake, Lake Mitchell, 

and Lake Jordan. Streamflow below these reservoirs primarily is controlled by power generation at the dams, and there is 

ongoing concern about the stability of selected stream banks 

downstream from the dams. As part of the Federal Energy 

Regulatory Commission relicensure of the Coosa River project 

in the early 2000s, the Alabama Power Company and various 

stakeholders identified particular areas of concern to monitor and document the extent of erosion. From 2014 to 2017, 

the U.S. Geological Survey, in cooperation with the Alabama 

Power Company, conducted a monitoring program of the 

geomorphic conditions of six selected reaches along the Coosa 

River downstream from H Neely Henry Dam near Gadsden, 

Logan Martin Dam near Vincent, and Walter Bouldin Dam 

near Wetumpka, Alabama, using boat- and tripod-mounted terrestrial light detection and ranging (T–lidar) technology. The 

results of the investigation served to help the Alabama Power 

Company evaluate effects on the stream channel geomorphology. This report documents the results of the periodic stream 

bank surveys, equipment and methods used and differences 

between surveys, which were used to compute volumes of 

material eroded or deposited. Erosion and deposition were 

then correlated to streamflow conditions between surveys.

Results of the comparisons of T–lidar scans indicated that 

intervals between scans that exhibited the greatest amounts of 

erosion generally corresponded to periods of above-median 

flow, and that intervals between scans that exhibited the least 

amounts of erosion, or deposition, generally corresponded to 

periods of below-median flow. During the summer 2016 to fall 

2016 interval, an anomalously large amount of erosion was 

observed at site WB–106 downstream from Walter Bouldin 

Dam near Wetumpka, Alabama. The amounts of erosion 

observed during the interval, and consequently for the duration of the study, at site WB–106 may be biased high because 

of the relatively smaller surface area that could be surveyed 

on the date of the summer 2016 scan (July 11, 2016) resulting from dense vegetation obscuring the upper banks during 

the survey. Apparent deposition or additional erosion may 

also have been caused by inundation during one of the survey 

intervals. This suggests that, in future investigations using T–

lidar technology, it may be preferable to conduct scans during 

periods of leaf-off and low flow to avoid bias introduced by 

parts of the banks of interest being inundated or obscured by 

vegetation.
28 Erosion Monitoring Along Bank Locations of the Coosa River Using Terrestrial Light Detection and Ranging Technology

During the study, site LM–108, an island in the middle of 

the Coosa River downstream from Logan Martin Dam, exhibited normalized erosion of 2.05 cubic meters per square meter 

of area, the greatest amount of all six sites, likely because this 

site experiences head-on flow from the river. Bank retreat at 

the upstream end of the island near the waterline was estimated at 2.9 meters. The remaining five reaches were exposed 

to shear flow from the river, with the greatest amount of 

normalize erosion, 0.467 cubic meter per square meter of area, 

being exhibited by site WB–106, on the right bank downstream from Walter Bouldin Dam.

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For more information about this publication, contact:

Director, USGS Central Midwest Water Science Center 

1400 Independence Road

Rolla, MO 65401

573–308–3667

For additional information, visit: https://www.usgs.gov/centers/cmwater

Publishing support provided by the 

Rolla Publishing Service Center

Huizinga and Wagner—Erosion Monitoring Along Bank Locations of the Coosa River Using Terrestrial Light Detection and Ranging Technology—SIR 2019–5023

ISSN 2328-0328 (online)

https://doi.org/10.3133/sir20195023