Applications of LIDAR Data in the McPherson Watershed, Fort Bragg, North Carolina Beth M' Wrege and

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Applications of LIDAR Data in the McPherson
Watershed, Fort Bragg, North Carolina
Beth M. Wrege and Michelle Cienek Water
Resources Program USGS, Raleigh, NC
Applications of LIDAR Data in the McPherson
Watershed, Fort Bragg, North Carolina   Beth M.
Wrege and Michelle Cienek U.S. Geological
Survey Raleigh, N.C.   The U.S. Geological Survey
(USGS) is working with Fort Bragg, N.C., in the
development of a Stormwater Pollution Prevention
Plan and with the development of a
watershed-management plan. This effort will
enable Fort Bragg to develop best management
practices for reducing surface-water pollutants
in the Little and Cape Fear Rivers. Eight
subwatersheds intercept Fort Braggs cantonment
area, including the McPherson watershed. The
cantonment area quarters the majority of the
troops stationed at Fort Bragg and contains the
majority of the Bases industrial activities and
is therefore an area of potential high stormwater
pollution impact. Approximately 603 acres, or 15
percent of the 4,026 acres (6.29 square miles) in
the McPherson watershed, drain the cantonment
area. In order to develop best management
practices and effectively manage their
watersheds, Fort Bragg must have information on
surface elevation, drainage basins,
stormwater-conveyance systems, streamflow, and
current manmade and natural features within the
watersheds. Once relevant data sets are obtained
and compiled in a digital format within a
Geographical Information System, they can provide
a base from which to address watershed-management
questions. To analyze these data efficiently and
accurately, the data need to be translated into a
scale that reflects the detail necessary to
interpret hydrologic conditions within small
watersheds. The highest resolution
continuous-surface elevation data set currently
available for Fort Bragg is the USGS National
Elevation Dataset. However, the resolution of
30-meters of this dataset proves is too coarse
for working with watersheds at this scale.
Existing vector elevation data also were
considered for use within the GIS. The current
highest resolution elevation contours available
for Fort Bragg have a 2-foot contour interval but
lack elevation tags and connectivity. These
digital contours are applicable to engineering
purposes but lack the needed portability for
effective use in a GIS. For this pilot study,
to generate high resolution surface data, Light
Interferometric Distance and Ranging (LIDAR) data
were used. These data, which were collected in
August 1998 by Earthdata, Inc., (1) were
ortho-rectified and tagged at 5-meter intervals.
A LIDAR-based surface-elevation map of the
McPherson watershed was created as a pilot study
for watershed assessment at Fort Bragg. The LIDAR
point data were examined at 10-meter, 5-meter,
1-meter, and 2-foot interval resolutions, and the
5-meter interval was selected for use in the
watershed analysis. Arc/Info (1) software was
used to create a digital elevation model with a
5-meter cell size. The 5-meter data were used to
create elevation contours, flow direction and
flow accumulation grids, subbasin delineation,
and a 3-D surface map. The pilot study
demonstrates one approach to subwatershed data
management. These spatial data can be effectively
used as part of Fort Braggs stormwater-management
plan, or the watershed-management plan. The
advantages obtained from using LIDAR in this
study include a data set with digital elevations
that allows for control of topographic intervals,
control of map units, tagged topography, and
overlay ability. The new elevation data layer can
be combined with existing data sets to better
define watersheds and calculate the effects of
sedimentation and rainfall runoff. Model runs
based on these data can be used to determine and
target high-risk areas susceptible to
surface-water runoff and erosion. In addition,
the LIDAR data can be used to document
topographic change within Fort Bragg. Periodic
surveys using LIDAR data can assist resource
managers in understanding long-term resource
trends and in estimating the effects of
watershed-management efforts, erosion-control
devices, and best management practices. The LIDAR
data also can be used following a hurricane, a
major storm event, or other significant event to
effectively assess the storms impact and to
measure erosion. The McPherson watershed pilot
study demonstrates the feasibility for using
LIDAR data for watershed analysis. (1) The use
of firm, trade, or brand names in this document
is for identification purposes only and does not
constitute endorsement by the U.S. Geological
Survey.
Existing Data GIS and Data Layers
Study Area

The USGS has data in several scales 1250,000,
1100,000, and 124,000 are readily available for
the Fort Bragg Area
Microstation DXF data are available in a readable
format
Applications LIDAR data can be used to delineate
watersheds, create contours, and general resource
management
LIDAR
McPherson Creek Watershed

• LIDAR is an acronym for Light Interferometric
  Distance and Ranging
• LIDAR data is collected by aerial topographic
  surveys that measure elevation using lasers.
• The first LIDAR lasers existed in the 1970s but
  lacked applicability until the development of
  accurate Global Positioning System units,
  powerful and inexpensive computers and public
  availability of LIDAR systems.
• LIDAR is an active sensor that works by pulsing a
  laser pulse at a rate of 2,000 to 5,000 times per
  second. It measures each pulses return time to
  map surface features.
• The vertical precision of LIDAR data is stated
  to be /- 6 inches of reality.
• LIDAR produces a point coverage with elevation
  for each point.

Watershed
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Overlay

• Applications of Advanced LIDAR for DEM
  Applications, Micheal S. Renslow,
  http//www.sbgmaps.com/lidar_apps.htm
• Inertial Measurement and LIDAR Meet Digital
  Ortho Photography A Sensor Fusion Boon for GIS,
  Robert G. Kletzli and John L. Peterson
• http//www.arcdataonline.com/library/userconf/pro
  c98/PROCEED/TO600/PAP597/P597.HTM

Contours
Comparison
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3-D View
Average Difference 1 meter
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