Prepared in cooperation with Alabama Power

Erosion Monitoring along the Coosa River below 

Logan Martin Dam near Vincent, Alabama, 

Using Terrestrial Light Detection and Ranging 

(T-LiDAR) Technology

U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2013–5128
Cover: T-LiDAR instrument collecting data downstream of Logan Martin Dam near Vincent, Alabama.
Erosion Monitoring along the Coosa River 

below Logan Martin Dam near Vincent, 

Alabama, Using Terrestrial Light Detection 

and Ranging (T-LiDAR) Technology 

By Dustin R. Kimbrow and Kathryn G. Lee

Prepared in cooperation with Alabama Power

Scientific Investigations Report 2013–5128

U.S. Department of the Interior

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

SALLY JEWELL, Secretary

U.S. Geological Survey

Suzette M. Kimball, Acting Director

U.S. Geological Survey, Reston, Virginia: 2013

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Suggested citation:

Kimbrow, D.R., and Lee, K.G., 2013, Erosion monitoring along the Coosa River below Logan Martin Dam near Vincent, 

Alabama, using terrestrial light detection and ranging (T-LiDAR) technology: U.S. Geological Survey Scientific 

Investigations Report 2013–5128, 7 p., http://pubs.usgs.gov/sir/2013/5128/.
iii

Contents

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

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

Data Collection Methods..............................................................................................................................1

Data Processing and Accuracy .........................................................................................................3

Georeferencing .....................................................................................................................................4

Geomorphic Assessment..............................................................................................................................4

Electronic Data Format .................................................................................................................................7

Summary..........................................................................................................................................................7

References Cited............................................................................................................................................7

Figures

1. Map showing location of the study area below Logan Martin Dam near

Vincent, Alabama..........................................................................................................................2

2. Photograph of the study area and T-LiDAR instrument downstream of

Logan Martin Dam near Vincent, Alabama ..............................................................................3

3. Three-dimensional map demonstrating how the change in volume between

datasets was computed by comparing each surface model to a plane,

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

4. Error map depicting the geomorphic change along the streambank from

November 2010 to July 2011, downstream of Logan Martin Dam near

Vincent, Alabama..........................................................................................................................6

Tables

1. Alignment errors between virtual reference points used for the November 2010 

and July 2011 datasets for part of the streambank downstream of 

Logan Martin Dam near Vincent, Alabama ..............................................................................3

2. Georeferencing error between global positioning system (GPS) control

points and virtual control points, November 2010 and July 2011,

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

3. Erosion at points along cross sections downstream of Logan Martin

Dam near Vincent, Alabama, from November 2010 to July 2011 ..........................................6
iv

Conversion Factors

SI to Inch/Pound

Multiply By To obtain

Length

centimeter (cm) 0.3937 inch (in.)

millimeter (mm) 0.03937 inch (in.)

meter (m) 3.281 foot (ft) 

kilometer (km) 0.6214 mile (mi)

kilometer (km) 0.5400 mile, nautical (nmi) 

meter (m) 1.094 yard (yd) 

Volume

cubic meter (m3

) 35.31 cubic foot (ft3)

cubic meter (m3

) 1.308 cubic yard (yd3) 

Elevation, as used in this report, refers to the distance above the vertical 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), and projected in Universal Transverse Mercator (UTM).
Erosion Monitoring along the Coosa River below Logan 

Martin Dam near Vincent, Alabama, Using Terrestrial Light 

Detection and Ranging (T-LiDAR) Technology 

By Dustin R. Kimbrow and Kathryn G. Lee

Abstract

Alabama Power operates a series of dams on the Coosa 

River in east central Alabama. These dams form six reservoirs 

that provide power generation, flood control, recreation, economic 

opportunity, and fish and wildlife habitats to the region. The Logan 

Martin Reservoir is located approximately 45 kilometers east 

of Birmingham and borders Saint Clair and Talladega Counties. 

Discharges below the reservoir are controlled by power generation at Logan Martin Dam, and there has been an ongoing concern 

about the stability of the streambanks downstream of the dam. The 

U.S. Geological Survey, in cooperation with Alabama Power conducted a scientific investigation of the geomorphic conditions of 

a 115-meter length of streambank along the Coosa River by using 

tripod-mounted terrestrial light detection and ranging technology. 

Two surveys were conducted before and after the winter flood season of 2010 to determine the extent and magnitude of geomorphic 

change. A comparison of the terrestrial light detection and ranging 

datasets indicated that approximately 40 cubic meters of material 

had been eroded from the upstream section of the study area. The 

terrestrial light detection and ranging data included in this report 

consist of electronic point cloud files containing several million 

georeferenced data points, as well as a surface model measuring 

changes between scans.

Introduction

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

Alabama Power, conducted a scientific investigation of the 

geomorphic conditions of a reach along the Coosa River downstream of Logan Martin Dam near Vincent, Alabama, by using 

tripod-mounted terrestrial light detection and ranging (T-LiDAR) 

technology (fig. 1). The Logan Martin Reservoir is located 

approximately 45 kilometers (km) east of Birmingham, Alabama, 

and borders Saint Clair and Talladega Counties. Discharges below 

the reservoir are controlled by power generation at Logan Martin 

Dam, and the stability of the banks downstream of the dam has 

been an ongoing concern. T-LiDAR technology has proven to be 

well suited for erosion and mass failure studies where conventional surveying techniques may be dangerous, as well as inadequate in supplying the necessary topographic detail for erosionbased analysis (Collins and others, 2007; Stock and others, 2011). 

The primary objective of this investigation was to use T-LiDAR 

technology to document any changes in streambank morphology 

and to quantify the observed changes. Two surveys were conducted before and after the winter flood season of 2010 to determine the extent and magnitude of geomorphic change on the right 

streambank located 0.75 km downstream of the dam. Specific 

details on the methods, data, and results of the geomorphic assessment are included in this report. 

Data Collection Methods

T-LiDAR technology involves the use of laser pulses that 

are sent from the instrument and reflected off objects within its 

Field of View (FOV). The instrument calculates the distance 

of each returned laser pulse based on its velocity, and it also 

records the vertical and horizontal angle of each laser pulse. For 

both surveys completed in this investigation, an Optech ILRIS 

High Density (HD) Enhanced Range (ER) (Optech, 2009) 

laser scanner was mounted on a surveyor’s tripod and set up 

on an island approximately 75 meters (m) from the study area 

(fig. 2). The Optech ILRIS HD ER has a laser repetition rate of 

10 kilohertz with a laser wavelength of 1,535 nanometers, which 

is within the near-infrared (NIR) portion of the electromagnetic 

spectrum. The NIR portion of the electromagnetic spectrum has 

been traditionally used in the LiDAR community for standard 

topographic mapping and change analysis studies (J.J. Danielson, 

U.S. Geological Survey, written commun., 2012). The laser scanner 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, if necessary. The initial point cloud dataset acquired during 

the baseline survey in November 2010 consisted of 8 million data 

points with a point spacing typically less than 10 centimeters (cm). 

The subsequent point cloud dataset acquired after the winter flood 

season in July 2011 consisted of 9 million data points, also with a 

point spacing of less than 10 cm. 
2 Erosion Monitoring along the Coosa River below Logan Martin Dam near Vincent, Alabama

86°20'45" 86°20'30" 86°20'15" 86°20'

33°25'30"

33°25'15"

33°25'

33°24'45"

Study site

Aerial image from Terrain Navigator Pro, 2011

0

0 1,000 2,000 Feet

250 500 Meters

 

Logan Martin Reservoir

LOGAN MARTIN DAM

Vincent

SAINT CLAIR

TALLADEGA

Enlarged

area

JEFFERSON

SHELBY

Birmingham

Figure 1. Location of the study area below Logan Martin Dam near Vincent, Alabama.
Data Collection Methods 3

Figure 2. The study area and T-LiDAR instrument downstream of Logan Martin Dam near 

Vincent, Alabama.

Data Processing and Accuracy

Laser scanning data require several post-processing steps 

in order for useable datasets to be generated. Data were collected from only one setup location during each survey; however, the laser scanner automatically divides the raw data into 

overlapping tasks when the pan/tilt base is used. The degree of 

overlap is specified by the user of the laser scanner. After each 

field survey, the raw data files from each task were imported 

into the Optech Parser software, where scan settings were 

adjusted and the .pif files (Innovmetric, 2012) were created 

from the raw scanner data. The .pif files were then imported 

into Polyworks IMAlign software module (Innovmetric, 

2012) in order to precisely merge each scan file together. The 

IMAlign software module creates a surface model of each .pif 

file and uses best-fit algorithms to precisely match the overlapping surfaces based on common topographic features between 

the scan files. The alignment error in this process ranged from 

0.001 m to 0.01 m for both time series datasets. This error was 

determined by inspecting the color-shaded comparison maps 

and histogram outputs by the IMAlign software module. Once 

proper alignment was achieved, the overlapping .pif files for 

each separate survey were merged into a single file. 

The IMAlign software module can also be used to precisely align datasets that were acquired at different time periods, provided there are stable objects of sufficient size within 

both datasets that can be used as common reference objects 

(for example, a stable rock outcrop). However, in this investigation there were no such objects of sufficient size, so the 

alignment of the two different surveys was completed in the 

Polyworks IMSurvey software module (Innovmetric, 2012) by 

using geodetic reference targets rather than control surfaces. 

Three geodetic reference targets consisting of concrete-filled 

PVC pipes, each with a metal rod slightly extending above the 

top of each pipe and set in concrete 0.5 m below the ground, 

were constructed in the study area prior to the survey. Virtual 

reference points were created using the IMSurvey module in 

both datasets at the top of these metal rods and also at points 

on a boulder that was stable during the time series. However, 

Target 1 was not used as alignment control due to sparse data 

in the November 2010 scan. The alignment errors between 

the November 2010 and July 2011 datasets were determined 

based on the variation in position between the virtual reference 

points (table 1).

Table 1. Alignment errors between virtual reference points 

used for the November 2010 and July 2011 datasets for part of 

the streambank downstream of Logan Martin Dam near Vincent, 

Alabama. 

[RMSE, root mean square error] 

Virtual reference 

point 

Error between time series datasets, in meters 

Easting Northing Elevation RMSE

Target 2 0.001 0.022 0.001 0.013

Target 3 0.016 0.031 0.003 0.02

Boulder 0.014 0.053 0.002 0.032
4 Erosion Monitoring along the Coosa River below Logan Martin Dam near Vincent, Alabama

Georeferencing

The laser scanner collects three-dimensional point 

data with reference to a relative datum, where the 

Cartesian coordinate origin is a reference point located 

on the base of the instrument. The point clouds collected in this study were subsequently transformed to a 

commonly used horizontal and vertical datum to utilize 

these data along with other geographically referenced 

datasets. A real-time kinematic (RTK) global positioning system (GPS) rover unit was leveled over the top of 

the threaded rod extending above each PVC pipe target, 

and three RTK GPS positions were measured at each 

of the three targets. The GPS coordinates were averaged for each target and then imported into IMSurvey 

as GPS control points. The three GPS control points 

were then matched to the three virtually created reference points in the July 2011 point cloud dataset. By 

using this process, both the November 2010 and the 

July 2011 datasets were transformed from the scanner’s relative horizontal datum to the North American 

Datum of 1983 and projected to Universal Transverse 

Mercator Zone 16 North. This process also converted 

the original elevation values in both datasets to the 

North American Vertical Datum of 1988. The georeferencing error was determined based on the difference 

in the easting, northing, and elevation values between 

the known coordinates of the GPS control points and 

the position of the virtual reference points in each point 

cloud (table 2). 

The overall accuracy of both point cloud datasets included in this report 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 as 

stated by the manufacturer (Optech, 2009). The combined point cloud root mean square error (RMSE) from 

all three factors was 0.263 m for the November 2010 

dataset and 0.138 m for the July 2011 dataset.

Geomorphic Assessment

The objective of this investigation was to use 

T-LiDAR technology to document and quantify changes 

in streambank morphology during the winter flood season 

of 2010. The initial baseline survey was completed in 

November 2010 during low-flow conditions, and the second survey was done in July 2011 when the likelihood of 

sustained high flows had diminished. Geomorphic changes 

were quantified at 10 cross sections by measuring the linear difference of points on the streambank between survey 

scans at the top of slope, mid-slope, and bottom of slope. 

The points along the slope that were compared were chosen based on their point on the slope (top, middle, bottom) 

and the exact Universal Transverse Mercator (UTM) 

Northing coordinate between survey scans. The linear differences between cross sections were then computed along 

the UTM Easting axis using the survey measurement tool 

in the IMSurvey module. The UTM Easting axis was used 

as the comparison axis in order to remove bias in point 

selection between cross sections, and it also approximates 

the direction of bank retreat. 

The volume of material eroded from the streambank 

during the time series was also computed. In order to 

determine this volume, a continuous surface model of 

the point data from each scan was created in IMSurvey 

by interpolating between nearby data points, producing a triangulated irregular network (TIN). This process 

used all data points for interpolation, and the maximum 

triangle edge length for the TIN was limited to 1.0 m. 

Volumes were then calculated by creating a vertical plane 

positioned parallel to the surface models and using the 

surface-to-plane volume tool to determine the volume 

of space between each individual surface model and the 

plane (fig. 3). The difference between the two values was 

considered the net change in volume, or net erosion. 

A limitation of comparing time series T-LiDAR 

datasets is the occurrence of data shadows in areas out of 

the line of sight of the laser scanner, particularly when 

the shadow areas are incongruent between datasets. 

Vegetative cover was more prominent in July 2011 than 

in November 2010, causing large data shadows. Accurate 

interpolation across these large data shadows was not 

possible. In order to minimize measurement error, comparisons were limited to the most upstream portion of the 

streambank that exhibited the least amount of vegetation 

in both datasets.

A comparison of the T-LiDAR datasets was used 

to quantify erosion of the streambank during the winter 

flood season of 2010. Linear differences between datasets 

at 3 points on the slope of the streambank (top, middle, 

bottom) were measured along each of 10 cross sections 

(table 3). The volume of eroded material was quantified 

by comparing the volume of space between a user-defined 

plane and a surface model of the data points. This value 

was computed for both datasets, and it was determined 

from these measurements that approximately 40 cubic 

meters of material was removed from the upstream section 

of the streambank during the time series. This calculation 

was limited to the upstream section of the streambank in 

order to minimize errors in the surface model creation 

phase due to vegetation interference. Figure 4 is an error 

map depicting change detection analysis of the streambank. The color spectrum ranges from red to blue, with 

red indicating erosion up to 2 m and blue indicating sedimentation up to 2 m. The color green depicts zero change.
Geomorphic Assessment 5

Table 2. Georeferencing error between global positioning system (GPS) control points and 

virtual reference points, November 2010 and July 2011, downstream of Logan Martin Dam near 

Vincent, Alabama.

[RMSE, root mean square error]

GPS 

control 

point

Error between GPS control points and virtual reference points, in meters 

November 2010 virtual reference point July 2011 virtual reference point

Easting Northing Elevation RMSE Easting Northing Elevation RMSE

1 –0.17 0.252 –0.445 0.311 0.038 0.066 0.031 0.047

2 –0.045 0.105 0.021 0.067 0.044 0.127 0.02 0.078

3 –0.098 –0.092 –0.054 0.084 0.082 0.061 0.051 0.066

No

November 2010 July 2011

5 meters 5 meters

No Ea

El

Figure 3. Three-dimensional map demonstrating how the change in volume between datasets was computed by comparing each 

surface model to a plane, downstream of Logan Martin Dam near Vincent, Alabama.
6 Erosion Monitoring along the Coosa River below Logan Martin Dam near Vincent, Alabama

Table 3. Erosion at points along cross sections downstream of Logan Martin Dam 

near Vincent, Alabama, from November 2010 to July 2011. 

Cross section Erosion from November 2010 to July 2011, in meters

(beginning upstream) Top of slope Mid-slope Bottom of slope

1 0.29 0.17 0.14

2 0.45 0.18 0.43

3 0.22 0.11 0.39

4 0.83 0.10 0.20

5 0.05 0.13 0.22

6 0.61 0.10 0.25

7 1.34 0.20 0.29

8 0.58 0.07 0.19

9 0.55 0.21 0.29

10 0.44 0.27 0.13

2.000

1.000

0

–0.250

–0.500

–0.750

–1,000

–1.250

–1.500

–1.750

–2.000

Ea No

El Meters

Figure 4. Error map depicting the geomorphic change along the streambank from November 2010 to July 2011, 

downstream of Logan Martin Dam near Vincent, Alabama. 
References Cited 7

Electronic Data Format

This report contains time series T-LiDAR point cloud 

datasets in ASCII text format with the extension .xyz. The 

horizontal XY coordinates have been cast in the North 

American Datum of 1983, Univeral Transverse Mercator, 

Zone 16 North coordinate system. The vertical Z values 

have been positioned in the North American Vertical Datum of 1988 vertical reference system. Although the data 

files are compressed (.zip), file sizes are relatively large 

and typically require specialized viewing software. Polyworks software was used for analysis and viewing of these 

data for this study, but many similar software packages 

are available. Three point cloud files are included in this 

report, and each is named according to the date on which 

the data were acquired and the manner in which each point 

is displayed (for example, 20101110_intensity.xyz). These 

data are formatted as text and contain x,y,z coordinates 

along with either intensity or red, green, blue (RGB) color 

values. Metadata are also included for each of the point 

cloud files in .xml format. Also included as a separate file 

is a surface model with colors depicting the quantity of 

change along the streambank (fig. 4). This file type (.pol) 

may only be viewed using Polyworks software. Included 

with the data is a link to the Polyworks IMView software 

(Innovmetric, 2012), which is available for free download. 

Summary

A scientific investigation of geomorphic conditions of 

a 115-meter length of streambank along the Coosa River 

below Logan Martin Dam near Vincent, Alabama, using 

tripod-mounted T-LiDAR technology was conducted to 

assess the extent and magnitude of geomorphic change 

after the winter flood season of 2010. A survey was conducted before and after the flood season, and a comparison 

of the datasets was used to quantify erosion during the 

time series. Approximately 40 cubic meters of material was 

eroded from the upstream section of the streambank, and a 

comparison of cross sections showed upwards of 1 meter 

of bank retreat in some areas. This study demonstrated the 

utlility of T-LiDAR for change detection and geomorphic 

analysis. 

References Cited

Collins, B.D., Kayen, R., Minasian, D., and Reiss, T., 2009, 

Terrestrial lidar datasets of New Orleans, Louisiana, 

levee failures from Hurricane Katrina, August 29, 2005: 

U.S. Geological Survey Data Series 470, 24 p.

Collins, B.D., Kayen, R., Reiss, T., and Sitar, N., 2007, 

Terrestrial LIDAR investigation of the December 2003 and 

January 2007 activations of the Northridge Bluff Landslide, 

Daly City, California: U.S. Geological Survey Open-File 

Report 2007–1079, 32 p., accessed December 17, 2012, at 

http://pubs.usgs.gov/of/2007/1079/. 

Innovmetric, 2012, Parametric Image Format, Polyworks/

IMView software, accessed February 12, 2012, at 

http://www.innovmetric.com/polyworks/3D-scanners/viewer.

aspx?lang=en.

Optech, 2009, ILRIS summary specification sheet, accessed 

February 12, 2012, at http://www.optech.ca/pdf/ILRIS_SpecSheet_110309_Web.pdf. 

Stock, G.M., Bawden, G., Green, J., Hanson, E., Downing, G., Collins, B., Bond, S., and Leslar, M., 2011, High 

resolution three-dimensional imaging and analysis of rock 

falls in Yosemite Valley, California: Geosphere, v. 7, no. 2, 

p. 573–581. 
For further information about this publication contact:

Director

U.S. Geological Survey

Alabama Water Science Center

75 TechnaCenter Drive

Montgomery, AL 36117

Or visit the Alabama Water Science Center Web site at

http://al.water.usgs.gov/

Prepared by the Raleigh Publishing Service Center
Kimbrow and Lee—Erosion Monitoring along the Coosa River below Logan Martin Dam near Vincent, Alabama–Scientific Investigations Report 2013–5128